CAROTENOID-BASED DEWLAP COLOR AS A VISUAL SIGNAL IN SOCIAL 
COMMUNICATION OF BROWN ANOLES (Norops sagrei) 
 
 
 
Except where reference is made to the work of others, the work described in this 
dissertation is my own or was done in collaboration with my advisory committee.  This 
dissertation does not include proprietary or classified information. 
 
 
______________________________________ 
John Edward Steffen 
 
 
 
Certificate of Approval: 
 
 
_______________________                                        _______________________ 
Craig C. Guyer, Co-Chair                                             Geoffrey E. Hill, Co-Chair 
Professor                                                                        Professor 
Biological Sciences                                                       Biological Sciences 
 
 
_______________________                                        _______________________ 
F. Stephen Dobson                                                        George T. Flowers 
Professor                                                                        Interim Dean 
Biological Sciences                                                       Graduate School  
 
CAROTENOID-BASED DEWLAP COLOR AS A VISUAL SIGNAL IN SOCIAL  
 
COMMUNICATION OF BROWN ANOLES (Norops sagrei) 
 
 
John Edward Steffen 
 
 
 
 
A Dissertation 
Submitted to 
the Graduate Faculty of 
Auburn University 
in Partial Fulfillment of the  
Requirements for the 
Degree of  
Doctor of Philosophy 
 
 
 
Auburn, Alabama 
December 17, 2007
 iii
CAROTENOID-BASED DEWLAP COLOR AS A VISUAL SIGNAL IN SOCIAL 
COMMUNICATION OF BROWN ANOLES (Norops sagrei) 
 
 
 
 
 
 
 
 
John Edward Steffen 
 
 
Permission is granted to Auburn University to make copies of the dissertation at its 
discretion, upon request of individuals or institutions and at their expense.  The author 
reserves all publication rights. 
 
 
 
 
__________________________________ 
                                John E. Steffen 
 
__________________________________ 
                                      Date of Graduation 
 iv
VITA 
John Edward Steffen, son of Fred W. Steffen and Marcia A. Haines, was born 
October 7, 1966, in Cleveland, Ohio.  He graduated Brecksville High School in 1985.  He 
attended Ohio University in September 1985, and graduated summa cum laude in May, 
1989, with a B.S. in Zoology.  After being employed as a technician for several ecology 
laboratories, as well as working as a teacher, social worker, and musician in Seattle, WA, 
he entered graduate school at Western Washington University, in Bellingham, WA, on 
September, 1999.  He graduated with a M.S. in Ecology, and then entered Auburn 
University Graduate School in September, 2001 to pursue a Ph.D.  While participating in 
an Organization for Tropical Studies graduate course in Costa Rica, he met fellow 
biologist Lindsay Amsberry.  He married Lindsay Amsberry on August 7, 2004.   
 v
DISSERTATION ABSTRACT  
 
CAROTENOID-BASED DEWLAP COLOR AS A VISUAL SIGNAL IN SOCIAL 
COMMUNICATION OF BROWN ANOLES (Norops sagrei) 
John E. Steffen 
 
Doctor of Philosophy in Science, December 17, 2007 
(M.S. Western Washington University, 2001) 
(B.S. Ohio University, 1989) 
 
172 typed pages 
 
Co-directed by Craig C. Guyer and Geoff E. Hill 
 
Carotenoids have been shown to be important integumentary coloring agents in 
many birds and fishes.  The role of carotenoids as a prominent integumentary coloring 
agent of the dewlap has been noted in many Anoline lizards, but the role of carotenoids 
as a social signal has not been considered. Here, I investigated some proximate causes of 
male and female dewlap color, and found that males and females differed in pterin 
pigment concentrations but not in carotenoid concentrations.  I also found that sexes 
differed in UV as well as long wavelength reflectance, and that carotenoid-based UV 
color correlated positively with body condition.  I then used a visually-based color 
detection model that incorporates knowledge about UV vision to simulate and describe 
the conspicuousness of dewlap colors as conspecific lizards should see it, under different 
 vi
forest light environments.  Two sets of behavior experiments were performed to test 
assumptions about signal spectral variability, signal honesty and signal use.  One set of 
experiments investigated a potential role for UV (a carotenoid-based dewlap color) to be 
used as a visual signal in contests for females.  I quantified natural dewlap coloration, and 
paired males into size-matched dyads that naturally differed in UV reflectance.  Males 
that won male-male contests, and copulated with females, had lower UV reflectance than 
males that lost contests.  I then manipulated the UV component in dewlap colors, and I 
investigated whether the manipulation changed the contest outcome.  While 
manipulations had no effect on contest outcomes, the underlying natural colors still 
correlated with contest success.  A final set of experiments investigated the dual 
contributions of nutritional stress and carotenoid access on male dewlap color.  I found 
that carotenoid availability altered UV and long wavelength reflectance, and that UV 
amplitude decreased with nutritional stress.   
These results summarily suggest that dewlap color is a signal used to 
communicate information about the senders? phenotypic quality to the receiver, and that 
dewlap color (including ultraviolet wavelengths) is highly visible in some light 
environments.  Furthermore ultraviolet aspects of dewlap color among males correlates 
with contest success.  Finally, dewlap color is at least partially influenced by availability 
of carotenoids during adulthood, and can convey information about an individuals? 
health.   
 vii
ACKNOWLEDGEMENTS 
I would like to thank Craig Guyer for his friendship, as well as his immense 
academic and financial support.  Craig Guyer gave me the intellectual freedom to fully 
pursue my interests, a gift which I hope will benefit the scientific community, at least in 
some small but significant way.  I would also like to thank Geoff Hill for allowing me to 
be a contributor to his lab, where my interests in behavioral ecology were able to flourish.  
I would like to thank F. Steven Dobson for allowing me to drop in occasionally 
unannounced and acting as a non-judgemental sounding board while I attempted to 
synthesize many seemingly disparate ideas.  Thanks to Art Appel for agreeing to be my 
outsider reader, and for enthusiastically taking me on as a post-doctoral student ? I look 
forward to this next stage in my intellectual development.  I am grateful to Micky 
Eubanks for his friendship and statistical advice.  I would like to acknowledge my co-
authors Kevin McGraw and Lynn Siefferman for their editorial skills, as well as their 
patience with my writing abilities.  Thanks to Leo Fleishman for providing Norops sagrei 
spectral sensitivity data, and reviewing Chapter 3, and to John Endler for providing 
irradiance data and for answering my questions.  I am grateful to my parents (Marcia and 
Fred Steffen) for the genes (G), my brothers and sister (too numerous to name here) for 
the environment (E), and my stepfather, David Simecek, as well as my mom, for the G x 
E interaction.  Finally, I am most grateful to Lindsay Amsberry for her friendship, her 
sense of humor, and her unwavering emotional and intellectual support.   
 viii
Style manual or journal used:  Copeia journal, published by the American Society for 
Icthyologists and Herpetologists. 
 
Computer software used: Microsoft excel, JMP, SAS, and SPSS statistical packages, 
Etholog v. 2.1 (event recording software), OOibase spectrometry software, and a Spectral 
Processing Program copyright Bob Montgomerie 2002.   
 
 ix
TABLE OF CONTENTS 
LIST OF TABLES............................................................................................................. xi 
LIST OF FIGURES .......................................................................................................... xii 
CHAPTER 1.  INTRODUCTION .......................................................................................1 
CHAPTER 2.  DEWLAP SIZE AND COLORATION IN RELATION TO SEX AND 
PIGMENT CONTENT IN THE BROWN ANOLE, Norops sagrei.................................12 
 Abstract..................................................................................................................12 
 Introduction............................................................................................................13 
 Methods..................................................................................................................16 
 Results....................................................................................................................22 
 Discussion..............................................................................................................27 
 References..............................................................................................................32 
CHAPTER 3.  LIGHT ENVIRONMENT INFLUENCES DEWLAP 
CONSPICUOUSNESS OF MALE AND FEMALE BROWN ANOLES,  
Norops sagrei.....................................................................................................................53 
 Abstract..................................................................................................................53 
Introduction............................................................................................................54 
 Methods..................................................................................................................57 
 Results....................................................................................................................67 
 Discussion..............................................................................................................69  
 x
References..........................................................................................................................74 
CHAPTER 4.  THE ROLE OF CAROTENOID-BASED MALE DEWLAP COLOR AS 
A VISUAL SIGNAL IN CONTESTS FOR FEMALES...................................................86 
 Abstract..................................................................................................................86 
Introduction............................................................................................................86 
Methods..................................................................................................................89 
Results....................................................................................................................93 
Discussion..............................................................................................................93 
 References..............................................................................................................96 
CHAPTER 5.  EFFECTS OF NUTRITIONA STRESS AND CAROTENOID ACCESS 
ON THE DEWLAP COLOR OF MALE BROWN ANOLES, Norops sagrei...............120 
 Abstract................................................................................................................120 
 Introduction..........................................................................................................121 
 Methods................................................................................................................124 
 Results..................................................................................................................129 
 Discussion............................................................................................................130 
 References............................................................................................................135 
 xi
LIST OF TABLES 
Table 2a. Relationship between tri-stimulus scores and PC1 in dewlaps..........................49 
Table 2b. Relationship between tri-stimulus scores and PC2 in dewlaps..........................50 
Table 2c.  Sex differences in color-based PC scores .........................................................51 
Table 2d.  Contribution of pigment concentration to PC-based spectral variation............52 
Table 3a.  Color differences in dewlap conspicuousness by background color                                        
and light habitat..................................................................................................................84 
Table 3b.  Brightness differences in dewlap conspicuousness by background                          
color and light habitat ........................................................................................................84 
Table 3c.  Effect of background color on aspects of dewlap conspicuousness .................85 
Table 4.  Effect of sunscreen on dewlap spectra by dewlap region.................................116 
 
 
 xii
LIST OF FIGURES 
Figure 1 a & b.  Dewlap regions of male Brown Anoles...................................................10 
Figure 1 c.  Dewlap regions of female Brown Anoles.......................................................11 
Figure 2 a & b.  Mean spectral curves of dewlaps by dewlap region................................42 
Figure 2 c-f.  Relationship of PC 1 & PC 2 to spectral wavelength,                                  
by sex and dewlap region...................................................................................................43 
Figure 2 g & h.  Carotenoid and pterin concentrations by sex and dewlap region............44 
Figure 2 i.  Effect of pterin spectral absorption on carotenoid spectral reflectance                                      
in the lateral dewlap region of males .................................................................................45 
Figure 2 j. Frequency histogram of hues from male lateral dewlap region??.. .............46 
Figure 2 k.  Regression of carotenoid concentrations on                                                         
male dewlap area................................................................................................................47 
Figure 2 l. Regression of PC2 against BCI, midline dewlap region                                                 
for male N. sagrei ..............................................................................................................48 
Figure 3 a.  The major light habitats in forests when the sun is not blocked by clouds ....82 
Figure 3 b.  Relative spectral sensitivities of photoreceptor cells in Norops sagrei..........83 
Figure 4 a.  Significant difference in UV brightness and contest outcome of Norops 
sagrei................................................................................................................................118 
Figure 4 b.  Significant difference in contest win percentage by experimental group  
in male Norops sagrei .....................................................................................................119 
 xiii
Figure 5 a.  Average mass lost in high (left) and low (right)                                                      
provision rate treatments..................................................................................................156 
Figure 5 b.  Effect of food deprivation on repeatedly measured                                              
values of UV amplitude in the lateral dewlap region ......................................................157 
Figure 5 c.  Effect of xanthophyll supplementation on repeatedly                                     
measured values of UV chroma for the lateral dewlap region.........................................158 
Figure 5 d.  Effect of xanthophylls supplementation on repeatedly                                       
measured values of red chroma of the midline dewlap region ........................................159 
 1
CHAPTER 1: INTRODUCTION 
Darwin devised the idea of sexual selection to explain traits that seemed to defy  
explanation by natural selection: some traits seemed to aid in the attraction or defense of 
mates, at an apparent cost to survival or fecundity of the individual (Darwin, 1871).  
Ornaments are a well-known class of phenotypic traits that meet the criteria of a sexually 
selected trait.  Ornamental traits are morphological features that are exaggerated and 
presumably physically constrain an individual by limiting its mobility and increasing its 
conspicuousness to predators.  A well-known example is the tail length of male African 
long-tailed widow birds (Andersson, 1982).  The tail is approximately half a meter long, 
and presumably hinders a male?s flight ability, yet the trait is maintained in the 
population, despite its reduction of one?s survival.  Observational data show that 
territories of males with larger tails contained more nests than territories of shorter tailed 
males.  Experimental manipulations of male tail length in territory holders altered female 
nest numbers contained in the territories, whereby males with enlarged tails contained 
more female nests than males with artificially reduced tail lengths.   
Ornaments are often very colorful and further advertise the possessors? presence 
to predators.  Carotenoid-based ornament color has been of interest to biologists because 
it reveals aspects of an individuals? health, and thus acts as an honest visual signal in 
intraspecific communication.  Carotenoids reveal aspects of an individuals health or 
?condition? because a) they cannot be synthesized de novo and must be ingested through 
 2
a dietary source, b) may be limiting in the environment, and c) their expression in the 
integument is influenced by physiological state (Hill, 2002; Lozano, 1994b; Hill, 1992).  
Carotenoid-based color signals have been studied in many birds and fish, especially 
noteworthy are research on house finches (Hill, 2002), goldfinches (McGraw et al., 2001; 
McGraw, 2004; McGraw and Hill, 2001), guppies (Kodric-Brown, 1984; Kodric-Brown, 
1989; Brooks, 1995; Kodric-Brown, 1985), and sticklebacks (Bakker, 1993; Baube, 
1995; Frischknecht, 1993).  Carotenoid color signals have not been studied extensively in 
any reptile. 
Anoles are a group of lizards inhabiting tropical and subtropical habitats, and are 
the most species-rich genus of lizard in the world (Jackman et al., 1999; Nicholson, 
2002).  In many tropical habitats, it is common to see several species co-occurring in 
sympatry, and a great deal of research shows that sympatric species partition the habitat 
according to perch location and light in the habitat.  In fact, Anoles are a model organism 
that helped to define the concept of an ?ecomorph? (Williams, 1983); that is, species of 
different phyletic origin with similar morphological adaptations to similar niches.  In 
addition, in part because there are so many species and they seem to partition available 
habitats in relatively consistent ways, anoles have become a classic example of a group 
undergoing adaptive radiation (Schluter, 2000). 
Anoles possess a mating system that can be described as a resource defense 
polygyny.  Males are highly territorial, and appear to aggregate in and defend areas where 
there are females present, while females appear to aggregate around areas of high food 
availability.  In most species, males and females maintain home ranges, female home 
ranges tend to be smaller than males home ranges, and are encompassed by one or more 
 3
male territories.  Anole species vary widely in sexual size dimorphism, but large body 
size is a major determinant of male courtship success in social contests (Tokarz, 1985). 
Females of most species lay 1 egg every 10 -14 days, and reproductive activity can occur 
seasonally or year round.   
Anoles are also well known because males possess an extendable throat fan 
known as a ?dewlap?.  These dewlaps are extended conspicuously as a social signal to 
advertise one?s presence to males in male-male territorial contests ? which may help 
establish dominance in male-male rivalry interactions, and to females in courtship 
interactions ? and potentially used by females to aid in mate choice decisions.  
Furthermore, females possess a dewlap in some species, which is used in social 
interactions.  Little is known about the communicative role of female dewlaps.   
The dewlaps of male anoles are often colored so that extended dewlaps contrast 
maximally with the surroundings, and dewlaps can contain up to 3 human-visible ?colors? 
in one individual.  Differences in dewlap color among sympatric species have been 
shown to communicate information about species identity (Losos, 1985), and presumably 
serves to reduce courtship between sympatric species (Williams and Rand, 1977).  Recent 
research that tests predictions of dewlap color derived from the species recognition and 
ecomorph convergence hypotheses, has  concluded that much of the dewlap color in 
Caribbean anoles is not adequately explained by  these hypotheses (Nicholson et al., 
2007).   
Many different species of anoles who have had their dewlaps measured with a 
UV-visible spectrometer have been shown to have strong components of UV reflectance 
to the dewlap spectral variation (Fleishman et al., 1993).  These dewlaps have also shown 
 4
that dewlap color (including UV) varies with respect to light environment, and their 
variation in color appears to maximize dewlap detectability in some environments and 
not in others (Fleishman et al., 1997; Leal and Fleishman, 2004).   
Recent analyses of dewlap pigments show xanthophyll carotenoids to be present 
in the dewlap of several caribbean anoles (Macedonia et al., 2000; Steffen and McGraw, 
2007), including the Brown Anole, Norops sagrei (Steffen and McGraw, 2007).  The 
Brown Anole is a successful invader that can occur at extremely high population 
densities.  Brown anoles are seen to occupy a variety of habitats in areas that represent its 
current geographic range, and presumably communicate with conspecifics in a variety of 
habitats and light conditions.  Brown anoles live for 1-2 years.  Adult males tend to be 
larger than adult females.   
In this dissertation, I investigate the role of carotenoid-based dewlap color as a 
social signal in the Brown Anole, and I rely on a few anatomical terms to describe the 
different colored regions of the dewlap in both males and females (males, see Figure 1a 
and b; females, see Figure 1 c).  The lateral dewlap region is the area exposed when the 
dewlap is extended (perceived as red by the human eye).  This region is lateral to the 
midline of the body, which is the plane of dewlap extension.  The midline dewlap region 
is the anterior margin when extended (perceived as white or yellow by human eyes; 
(Conant and Collins, 1998).  Because no anatomically-based nomenclature has been 
offered to describe these regions, I suggest that future authors consider this terminology.   
In this dissertation, I present four chapters that examine different facets of the 
Brown Anole visual signal ecology.  In Chapter Two, I quantify pigments in, and 
measure color of male and female dewlaps, in order to understand how pigments are 
 5
dispersed throughout male and female dewlaps and how the dewlap colors reflect the 
pigment content.  Furthermore, I investigate the potential for dewlap color to act as a 
condition dependent visual signal.  Males and females were found to differ in dewlap 
coloration, as well as in concentrations of the pterin pigment which is responsible for red 
dewlap coloration.  Sexes did not differ in carotenoid concentrations.  In males, UV color 
correlates with body condition, and provides support for dewlap color acting as a 
condition-dependent signal. 
 In Chapter Three, I use an anole-based visual physiology model to predict how 
conspicuous dewlap colors would appear to conspecifics in common light environments, 
as well as against different display backgrounds.  This model takes into account that 
Anoline lizards have tetra chromatic vision (i.e., color vision is the result of four different 
cones, including one that is especially sensitive to ultraviolet radiance).  Dewlap color 
differs between the sexes, and is highly conspicuous in woodland shade, which 
presumably represents pre-invasion light environments, and may also represent the type 
of light available in some suburban environments.   
 In Chapter Four, I perform social experiments in which two males compete for 
access to a female in the lab and I determine if natural dewlap color correlates with 
intrasexual contest dominance and intersexual copulation success.  Based on findings 
from these experiments, I then performed a manipulation of UV dewlap color in one of 
the dyadic males, to determine if an experimental switch in UV reflectance altered 
dominance and copulation success among the two males.  This research partially supports 
a role for the use of UV as a badge of status between males engaged in male-male rivalry. 
 6
 In Chapter Five, I perform a two factor experiment in which I manipulate 
carotenoid access and food provisioning rate, to determine if adult male dewlap color is 
dependent on carotenoid access, as well as nutritional condition.  This research suggests 
that the UV and yellow expression of Brown Anole dewlaps is dependent on carotenoid 
availability, and that UV also can be affected by nutritional stress. 
References 
Bakker, T. C. M., and M. Milinski. 1993. The advantages of being red: sexual selection 
in the stickleback. Marine Behavioral Physiology. 23:287-300. 
Baube, C. L. R., W.J.Rowland, and J.B. Fowler. 1995. The mechanisms of colour-based 
mate choice in female threespine sticklebacks: hue, contrast and configurational 
cues. Behaviour. 132:979-996. 
Brooks, R. and N. Caithness. 1995. Female choice in a feral guppy population: are there 
multiple cues? Animal Behaviour. 50:301-307. 
Conant, R. and J. T. Collins. 1998. A Field Guide to Reptiles and Amphibians of Eastern 
and Central North America. 
Darwin, C. 1871. The Descent of Man, and Selection in Relation to Sex. Murray, 
London. 
Fleishman, L. J., Bowman, M., Saunders, D., Miller, W.E., Rury, M.J. and E.R. Loew. 
1997. The visual ecology of Puerto Rican anoline lizards: habitat light and 
spectral sensitivity. Journal of Comparative Physiology A. 181:446-460. 
Fleishman, L. J., Loew, E.R. and M. Leal. 1993. Ultraviolet vision in lizards. Nature. 
365:397. 
 7
Frischknecht, M. 1993. The breeding coloration of male three-spined sticklebacks 
(Gasterosteus aculeatus) as an indicator of energy investment in vigour. 
Evolutionary Ecology. 7:439-450. 
Hill, G. E. 1992. Proximate basis of variation in carotenoid pigmentation in male house 
finches. Auk. 109:1-12. 
?. 2002. Red bird in a brown bag: the function and evolution of colorful plumage in the 
house finch. Oxford University Press, Inc. 
Jackman, T. R., Larson, A., de Queiroz, K. and Losos, J.B. 1999. Phylogenetic 
relationships and tempo of early diversification in Anolis lizards. Sytematic 
Biology. 48:254-285. 
Kodric-Brown, A. 1985. Female preference and sexual selection for male coloration in 
the guppy (Poecilia reticulata). Behavioral Ecology and Sociobiology. 17:199-
205. 
?. 1989. Dietary carotenoids and male mating success in the guppy: an environmental 
component to female choice. Behavioral Ecology and Sociobiology. 25:393-401. 
Kodric-Brown, A. and J. H. Brown. 1984. Truth in advertising: the kinds of traits favored 
by sexual selection. The American Naturalist. 124:309-323. 
Leal, M. and L. J. Fleishman. 2004. Differences in visual signal design and detectability 
between allopatric populations of Anolis lizards. The American Naturalist. 
163:26-39. 
Losos, J. B. 1985. An experimental demonstration of the species-recognition role of 
Anolis dewlap color. Copeia. 1985:905-910. 
Lozano, G. A. 1994. Carotenoids, parasites, and sexual selection. Oikos,. 70:309-311. 
 8
Macedonia, J. M., James, S., Wittle, L.W., and D.L. Clark. 2000. Skin pigments and 
coloration in the Jamaican radiation of Anolis lizards. Journal of Herpetology. 
34:99-109. 
McGraw, K. J., Hill, G.E., Stradi, R., and R.S. Parker. 2001. The influence of carotenoid 
acquisition and utilization on the maintenance of species-typical plumage 
pigmentation in male American Goldfinches (Carduelis tristis) and Northern 
Cardinals (Cardinalis cardinalis). Physiological and Biochemical Zoology. 
74:943-852. 
McGraw, K. J. and A. J. Gregor. 2004. Carotenoid pigments in male American 
Goldfinches:what is the optimal biochemical strategy for becoming colourful? 
Biological Journal of the Linnaean Society. 83:273-280. 
McGraw, K. J. and G. E. Hill. 2001. Carotenoid access and intraspecific variation in 
plumage pigmentation in male American Goldfinches (Carduelis tristis) and 
Northern Cardinals (Cardinalis cardinalis). Functional Ecology. 15:732-739. 
Nicholson, K. E. 2002. Phylogenetic analysis and a test of the current infrageneric 
classification of Norops (beta-Anolis). Herpetological Monographs. 16:93-120. 
Nicholson, K. E., Harmon, L.J., and J.B. Losos. 2007. Evolution of Anolis lizard dewlap 
diversity. PLOS One. 2:1-12. 
Schluter, D. 2000. The Ecology of Adaptive Radiation. Oxford University Press Inc., 
New York, New York. 
Steffen, J. E. and K. J. McGraw. 2007. Contributions of pterin and carotenoid pigments 
to dewlap coloration in two anole species. Comparative Biochemistry and 
Physiology, Part B. 146:42-46. 
 9
Tokarz, R. R. 1985. Body size as a factor determining dominance in staged agonistic 
encounters between male brown anoles (Anolis sagrei). Animal Behavior. 33:746-
753. 
Williams, E. E. 1983. Ecomorphs, fauna, island size, and diverse endpoints in island 
radiations of Anolis, p. 326-370. In: Lizard Ecology: Studies of a model organism. 
E. R. P. R.B. Huey, and T.W. Schoener (ed.). Harvard University Press, 
Cambridge Mass. 
Williams, E. E. and A. S. Rand. 1977. Species recognition, dewlap function, and faunal 
size. American Zoologist. 17:261-270. 
 10
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 1 a & b.  The dewlap regions of a male Brown anole, Norops sagrei.  ?mid? 
refers to the midline dewlap region (i.e. dewlap edge), and ?lat? refers to the lateral 
dewlap region (i.e. dewlap side, when extended).  Note: in males, the dewlaps? 
midline region appears yellow or white to the human eye, but emits strong UV 
reflectance, and is visible when the dewlap is extended or retracted.  The dewlaps? 
lateral region appears red and/or yellow to the human eye, does not emit UV strongly, 
is relatively inconspicuous when the dewlap is retracted, and is highly visible during 
times when the dewlap is extended only. Drawings by J.E.Steffen 
mid lat mid
lat
 11
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
mid
lat
Figure 1 c.  The dewlap regions of a female Brown anole, Norops sagrei.  ?mid? refers 
to the midline dewlap region (i.e. dewlap edge), and ?lat? refers to the lateral dewlap 
region (i.e. dewlap side, when extended).  Note: in females, the dewlap is reduced to a 
small patch of color on the throat, and which can only extend to a small degree, 
because of an underdeveloped (?feminized?) hyoid apparatus.  In female Norops 
sagrei, there is less pigmented skin in the dewlap region but more scalation, and 
consequently there is less color observable to the human eye.  However, the midline 
dewlap region is white to the human eye, but emits strong UV reflectance.  The lateral 
region of the female dewlap appears light red or white to the human eye (because of 
the overlying scales), and also emits UV strongly.  Drawing by J.E. Steffen. 
 12
CHAPTER 2: DEWLAP SIZE AND COLORATION IN RELATION TO SEX 
AND PIGMENT CONTENT IN THE BROWN ANOLE, Norops sagrei 
Abstract 
 Sexual selection has led to a diversity of colorful displays in animals, and the 
pigments responsible for sexual coloration often belong to several pigment classes.  
These pigment classes differ in important mechanistic and functional ways, and 
understanding the identity and distribution of pigments in male and female integuments 
can lend great insights into their roles as visual signals.  We examined full-spectrum 
color variation as well as pterin and carotenoid pigment concentrations in the sexually 
dichromatic dewlaps of male and female Brown Anoles (Norops sagrei). To the human 
eye, male dewlaps are red and yellow in color, and are large and extendable, whereas 
female dewlaps are light red or pink, and are non-extendable.  UV-VIS reflectance 
spectrometry revealed UV to be a major and variable component of dewlap color in N. 
sagrei.  Female dewlaps had greater UV reflectance than males, but males had greater 
long-wavelength reflectance than females.  Absorbance spectrophotometry identified the 
pterins bound in dewlap tissue as drosopterin, and carotenoids as lutein or zeaxanthin.  
Male dewlaps had greater pterin concentrations, but not carotenoid concentrations, than 
female dewlaps.  Total pterin and carotenoid concentrations significantly increased 
brightness of the lateral dewlap region of males, and high carotenoid concentrations 
significantly increased brightness of midline dewlap regions.  Pterin concentrations 
 13
increased chroma of female dewlaps.  Carotenoid concentrations, but not pterin 
concentrations, correlated significantly and positively with dewlap size in males.  UV 
reflectance from the midline dewlap region in males correlated positively with a body 
condition index.  These results show that sexes differ in the ways that pigment classes 
influence dewlap spectral variation, and we speculate that these differences relate to 
differences in dewlap use as a visual signal. 
Introduction 
Colorful ornaments are a well-known class of conspicuous secondary sex 
characters in animals.  Sexual dichromatism, or difference in color between the sexes, is 
one of the most common ways that ornaments vary.  Sexual dichromatism, especially in 
lizards, is thought to be a visual signal that is used for sex recognition (Cooper and 
Greenberg, 1992; Macedonia et al., 2003; Andersson, 1994), and in most cases males are 
the more colorful sex.  Aspects of color can vary within a sex as well, and have been 
shown to advertise information about phenotypic quality of an individual in a number of 
species (Kodric-Brown and Brown, 1984; Andersson 1994). 
The colors of animal integuments are caused by the interaction of pigment 
molecules with their integumentary structures.  Structural colors refer to those in which 
properties of the integument act alone, or in concert with melanin pigments, to produce 
white, iridescent, blue, and UV colors.  This type of coloration is responsible for feather 
color in many birds (Auber, 1957; Fox, 1976), and for blue scale color in phrynosomatid 
lizards (Morrison, 1995; Morrison et al., 1996).  Many vertebrate colors, however, are 
produced by the interaction of non-melanin pigment molecules with their integument 
structure.  Among several reptiles studied, non-melanin-based pigments are contained in 
 14
specialized integumentary cells called chromatophores.  Xanthophores and erythrophores 
are chromatophores that include red or yellow light-filtering pigments, respectively, and 
these pigments include fat-soluble carotenoids, obtained in the diet, and pteridines, 
produced during purine synthesis (Obika and Bagnara, 1964; McGraw, 2006).  Animals 
that possess sexual colors obtained by both of these pigment types are useful in proximate 
studies of integumentary color because they offer the opportunity to understand how 
different pigment classes interact to produce color.   
Dewlaps are colorful throat patches that are displayed to conspecifics in many 
families of lizards.  In most anoles (Family Polychrotidae), male dewlaps are large, 
extendable, and conspicuously colored compared to those of females.  Pteridines 
(hereafter pterins, the most common pteridine in squamates) have been identified as a 
coloring agent in the dewlaps of male Puerto Rican anoles (e.g. Ortiz and Williams-
Ashman, 1963; Ortiz and Maldanado, 1966).  More recently, carotenoids, pterins and 
melanins have been identified as dewlap coloring agents in males of the ?grahami? series 
of anoles (Macedonia et al., 2000), and it is generally believed that dewlap color in anoles 
is produced by variations in any of these three pigment classes (Macedonia et al., 2000).   
In conjunction with head-bobs and push-ups, dewlaps are displayed to other males 
during territorial contests (Jenssen, 1977; Leal and Rodriguez-Robles, 1997; Leal, 1999; 
McMann, 2000; Paterson and McMann, 2004; Tokarz, 2003; Tokarz et al., 2002), to 
females in courtship interactions (Jenssen 1977; Tokarz 2002; Tokarz et al., 2003) and to 
predators during an attack (Leal and Rodriguez-Robles, 1997; Leal, 1999).  Male dewlap 
color is purported to serve a role in species recognition (Losos, 1985), and may be under 
the influence of sensory drive (Leal and Fleishman, 2002, 2004).  Some speculate a role 
 15
of male dewlap color in mate choice (Greenberg and Noble, 1944; Sigmund, 1983) but 
results of these studies are equivocal.  Females also have colored throat patches in many 
anole species, but they appear to be drab to the human eye, and are small and non-
extendable.  Females of many anoles also perform head bobs and push-ups, but few 
studies (Jenssen et al., 2000) consider the source or function of color in female dewlaps.   
Steffen and McGraw (2007) previously quantified pterin and carotenoid 
concentrations in two Norops lizards [i.e. beta-Anolis, sensu Williams (Williams, 1976 a; 
Williams, 1976 b)] with red and yellow dewlaps.  Although the sample sizes were small, 
the two species, N. sagrei and N. humilis, appeared to differ in the distributions of and 
relationships between carotenoids and pterins in different regions of the dewlap, despite 
the apparent similarities in color pattern.  This led me to ask whether the two pigment 
classes might interact in interesting ways in each of the two species to produce the 
observed colors.  Unfortunately, in this previous study, full-spectrum spectrometry was 
not performed and how pigment types or amounts relate to dewlap color could not be 
determined.  To date, no study exists that directly relates pigment concentrations to 
dewlap spectral reflectance; such relationships have only been conducted in bird feathers 
(Saks et al., 2003; McGraw and Gregory 2004; McGraw et al., 2006). 
I studied pigment and color variation in dewlaps of male and female Brown 
Anoles (Norops sagrei).  Brown Anoles are native to Cuba, the Bahamas, and related 
islands (Schwartz and Henderson, 1991) but are successful invaders of the southeastern 
United States (Lee, 1992; Means, 1990; Lee, 1985; Echternacht et al., 1995), as well as 
Hawaii (McKeown, 1996; Goldberg and Bursey, 2000).  Throughout their range, Brown 
Anoles occupy and display in a wide variety of habitats that range from forests (Paterson, 
 16
2002; McMann and Paterson, 2003) to disturbed environments such as commercial 
buildings and houses (Echternacht et al., 1995).  Here I describe how pigment 
concentrations influence hue, chroma, and brightness in male and female lizards using 
two common methods for summarizing color data: Principal Components Analysis 
(PCA) and Tristimulus Scoring.  I investigate chromatic and achromatic intersexual 
differences in dewlap coloration, including UV, and quantify the extent to which these 
color properties have a pigmentary basis and are condition-dependent. 
Methods 
Adult male and female Brown Anoles were obtained from a pet store (Glades 
Herp, Bushnell, Lee County, Florida), and shipped to Auburn, AL after one day in 
captivity.  Lizards were identified as adult males if they possessed a large (minimum 50 
mm
2
) extendable dewlap, or as adult female if they lacked one.  Lizards were housed in 
screen-topped, 37.90 liter (i.e. 10-gallon), glass terraria, and each individual terrarium 
was partitioned into 4 separate compartments.  Each lizard was placed in a separate 
compartment which contained a perch and a water dish on a sandy substrate.  Lighting 
strips containing full-spectrum fluorescent bulbs (Vitalite T8, 32 watt) were suspended 
30.48 cm (i.e., 12 inches) above each terrarium top.  Natural sunlight also illuminated 
each terrarium through a nearby window.  Lizards were fed crickets and meal worms ad 
libitum, which were dusted with repta-vite (Zoo Med laboratories, San Luis Obispo, CA).  
Dewlap colors and size were quantified 1 day after lizards arrived in Auburn, AL (see 
below for methods).  Lizards were then held in captivity for three weeks for use in 
behavioral experiments.  After these experiments, I measured snout-to-vent length (SVL; 
nearest mm) of male and female lizards and body mass (nearest 0.01 g).  Animals were 
 17
then sacrificed for dewlap removal and pigment quantification.  Estimates of body 
condition index (BCI) were obtained from residuals generated by regressing body mass 
on SVL.  This is a common index of body condition in the herpetological literature 
(Brandt et al., 2003; Whiting et al, 2005; Kotiaho, 1999; Jakob, 1996; LeBas and 
Marshall, 2001) and regressions of mass on SVL for males and females were statistically 
significant (males: R
2
 = 0.789, P < 0.0001, N = 20; females: R
2
 = 0.805, P = 0.0002, N = 
11).    
A digital image was taken of each dewlap (Kodak Easyshare DX4530 camera) so 
that dewlap area could be measured from photos.  For each image, forceps were used to 
attain maximal extension of the dewlap (point at which further extension resulted in a 
change of dewlap shape without an increase in size).  A plastic millimeter ruler was 
placed in each image for scale.  Each lizard had its dewlap extended and photographed 
twice.  Dewlap area of each male lizard was quantified with imaging software (CIAS, 
2000) that converted pixel size to metric size from the ruler increments present in the 
digital photo.  Each digital image of a male was measured twice then averaged, and the 
average of the two images was used as dewlap area (i.e., four measurements per 
individual).  Dewlap area was highly repeatable using this method (R
2
 = 0.953, P < 
0.001, N = 20).  Dewlap area was not calculated for females because small dewlap size in 
this sex prevented reliable dewlap extension. 
We measured dewlap coloration of living male and female lizards using an Ocean 
Optics S2000 spectrometer (range 250-880 nm: Dunedin, Florida), with tungsten-
deuterium light source.  We used a bifurcated fiber-optic cable mounted in a metal probe 
that was placed at an angle of 90? to the plane of any tissue that was measured.  
 18
Following Steffen and McGraw (2007), we considered two regions of the dewlap in both 
males and females.  The lateral dewlap region was the area exposed when a dewlap was 
extended (perceived as red by the human eye).  The midline dewlap region was the 
anterior dewlap margin when extended (perceived as white or yellow by human eyes 
(Conant, 1998). 
In each dewlap region, we took three non-overlapping measurements from males 
and two from females.  We took fewer measurements of females because the dewlap area 
was only large enough to measure two unique locations.  Color data were gathered as 
percent reflectance per wavelength (nm) of light and this output was processed using 
ColoR v. 1.5 software (R. Montgomerie copyright 2002).  We generated a spectral 
reflectance curve for every measurement, and determined mean reflectance curves for the 
two dewlap regions in each individual lizard.  
We described color from PCA. Each reflectance curve comprised 382 data points 
(the reflectance intervals from 320-700nm at 1-nm intervals).  We reduced the curves to 
19 data points per dewlap region per sex by determining the means of each 20-nm 
spectral increment (Cuthill et al., 1999).  We then used SPSS to perform PCA (Grill, 
2000; Macedonia, 2001) on the 20-nm bandwidth means of each dewlap region for each 
sex.  PC coefficients (factor loadings) were used to transform the original variables into 
PC scores that represented how an individual varied in some spectral parameter, relative 
to the principal components derived by all the individuals analyzed together.   
The main limitation to PCA is that the nature of the principal components (i.e., 
the transformation that relates PC scores to the original data) is dependent on the data 
included in the original analysis (Cuthill et al., 1999).  That is, unless we perform a PCA 
 19
that includes data from both dewlap regions for both sexes, we cannot compare sexes or 
dewlap regions from data analyzed for each dewlap region or sex separately.  Thus, to 
overcome this limitation, we performed 6 PCA?s on dewlap color data, to allow for 
different statistical comparisons.  We performed two PCA?s, one on male and female 
lateral dewlap region spectral variation, and a  second PCA on male and female midline 
dewlap region spectral variation, to investigate region-specific sex differences in PC 
scores.  We graph PC coefficients from this analysis in the results section (see below for 
rationale), and we use this analysis as the basis for comparing PC scores by sex within 
dewlap region.  We then performed four separate PCA?s, one on each specific dewlap 
region of each sex, to precisely describe spectral variation in each dewlap region of each 
sex, without the influence of different regions or sexes.  The PC scores generated from 
these analyses were used in multiple regressions (see below) to understand how pterins 
and carotenoids contributed to PC1 and PC2.   
To interpret the spectral significance of the first two PC?s, we followed two 
methods.  In one, outlined in Cuthill et al. (1999), we graphed PC coefficients across each 
20-nm wavelength increment.  Inspection of spectral patterns in this way described 
behavior of known variables in a data set, and can be used to infer biological significance 
of principal components (Cuthill et al. 1999; Cuthill 2000).  If coefficients relating PC1 
to wavelength were positive and of similar magnitude, then they represented variation in 
mean reflectance (Cuthill et al., 1999).  This describes reflectance variation along a 
black-gray-white axis.  If coefficients relating PC2 to wavelength had positive values 
associated with long wavelengths, and negative values associated with medium and short 
wavelengths, then PC2 represented relative contributions of short wavelengths of light to 
 20
medium and high wavelengths of light.  This describes reflectance variation in the UV 
and blue wavelengths relative to variation in the green and red wavelengths.  If a plot of 
PC2 coefficients versus wavelength showed rounded peaks and troughs, then PC2 
represented chromatic variation in addition to reflectance.  If a plot of PC coefficients 
versus wavelength showed multiple adjacent peaks that were all positive or all negative, 
then PC2 would represent hue (associated with the wavelength of each peak) as well as 
brightness and chroma.   
I described color using a second method, referred to as ?tri-stimulus scores?, 
which describe spectral variation along three non-independent axes (hue, chroma, and 
brightness), but are standard ways of describing color in the biological literature (Hill and 
McGraw, 2006).   For these scores, hue, the everyday meaning of color, was defined to 
be the location of the maximum reflectance in a spectral curve. Chroma described the 
relative peak height (saturation) of a spectral curve at a given wavelength or bandwidth.  
Brightness described differences in percent reflectance (i.e. amplitude or overall 
intensity) of a curve.  Areas of a curve that were peaked in shape were assumed to have 
higher chroma (more area under the curve) than areas that were flat, assuming the 
minimum reflectance within the bandwidth was the same.   
Dewlap tissue was removed from lizards as described by Macedonia et al., (2000) 
and Steffen and McGraw (2007).  Concentrations of carotenoid and pterin pigments were 
measured in each tissue region using the methods described in Steffen and McGraw 
(2007).  
Statistical analyses 
Normality was tested using the Shapiro-Wilk test.  Carotenoid and pterin 
 21
concentrations were log-transformed to meet assumptions of parametric statistics 
(normality and homogeneity of variance), but non-transformed data are displayed in the 
figures and tables.  We used a two-way ANOVA to investigate the effects of sex and 
dewlap region on pigment concentrations.  4 separate one-way ANOVA?s were used to 
compare PC?s by sex and dewlap region.  Linear regression was used to investigate the 
relationship of pterin concentration to carotenoid concentration in each sex and dewlap 
region separately.  We used backward step-wise multiple regression in two ways. In one 
set of regression models we assessed the relative contributions of tristimulus scores to 
PC1 and PC2 scores.  In a second set of regression models we assessed the relative 
contributions of pterin and carotenoid pigment concentrations (independent variables) to 
PC1 and PC2 scores (dependent variables).  In all of these regression models, P to 
remove was > 0.1.  We chose this elevated significance level to allow investigation of 
marginally-significant relationships.  When multiple regressions yielded independent 
variables that contributed significantly to the dependent variable, we performed linear 
regressions of each significant independent variable against the dependent variable to 
assess the direction (positive or negative) of the significant relationship.  We also used 
linear regression to assess the effect of dewlap area on pigment concentration and the 
effect of BCI on PC1 and PC2. 
To examine how carotenoids and pterins interact to produce observed reflectance 
spectra we created four groups of males according to the relative concentrations of 
pterins and carotenoids present in the midline dewlap region. The four groups were high 
pterin-high carotenoid, low pterin-high carotenoid, high pterin-low carotenoid, and low 
pterin-low carotenoid, with high and low being relative to mean pterin and carotenoid 
 22
concentrations of all individuals.  We compared the spectral qualities of the four groups 
to determine how the combination of pigments affected the shape of the spectral curve.  
Results 
Reflectance spectra of dewlap regions 
Lateral and midline regions of the dewlap in males and females were spectrally 
distinct (Figure 2 a & b).  Female lateral dewlap regions showed a maximum reflectance 
(~30%) in the orange-red portion of the spectrum (600-700 nm), but there was relatively 
high reflectance across all wavelengths.  Male lateral dewlap regions showed a maximum 
reflectance (~30%) in the red portion of the spectrum (640-700 nm), but the spectral 
curve showed low reflectance at short and medium wavelengths of light (320-500 nm).  
The female midline dewlap region had a maximum reflectance (40%) in the orange-red 
portion of the spectral curve (600-700 nm), but reflected relatively strongly across all 
wavelengths.  Male midline dewlap regions showed a maximum reflectance (45%) in the 
upper middle and long wavelength portion of spectrum (540 -700 nm, which is yellow to 
the human eye), with relatively low reflectance in the mid-wavelengths and a second 
reflectance peak in the UV.  
 PC interpretations of dewlap reflectance spectra by sex and region 
PC1 accounted for 89.7% and 69.4% of the variance in male midline and lateral 
dewlaps, respectively, and for 92.4% and 96.2% of the variance in female midline and 
lateral dewlaps, respectively. Because correlation coefficients of PC1 were consistent in 
magnitude across all wavelengths of light, PC1 represented brightness independent of 
chroma in both dewlap regions of both sexes (Figure 2 c-f).  This interpretation was 
supported by tri-stimulus multiple regression, which showed that total % reflectance in 
 23
UV, blue, green, and red regions all contributed significantly to PC1 variance for both 
sexes and in both dewlap regions (Table 2 a).       
PC2 accounted for 7.1% and 22.6 % of the variance in the male midline and 
lateral dewlap regions respectively, and for 6.4% of the variance in female midline 
dewlap region; there was no significant PC2 for the lateral region of female dewlaps.  
Interpretation of PC2 differed between sexes and dewlap regions. In males, PC2 
represented UV brightness and chroma in the midline region, and long wavelength (red, 
orange, and yellow) brightness and chroma in the lateral region (Figure 2 b).  These 
interpretations were supported by tri-stimulus multiple regression models in which 
chroma in the UV, yellow and red portions of the spectra significantly contributed to PC2 
for male midline regions and in which % reflectance and chroma in the yellow and red 
portions of the spectrum contributed significantly to PC2 for male lateral regions (Table 
2).  In the case of male midline regions, separate linear regressions showed that UV 
contributed positively while yellow and red contributed negatively to PC2 (UV chroma = 
0.159 + 0.03172 PC2, P < 0.0001;  Yellow chroma = 0.09159 - 0.03168 PC2, P = 
0.0104;  Red chroma = 0.43139 - 0.03056 PC2, P = 0.0011).  In the case of male lateral 
regions, separate linear regressions showed that yellow and red chroma contributed 
positively to PC2, while UV chroma and % reflectance contributed negatively to PC2 
(Yellow chroma = 0.89612 + 0.33451 PC2, P = 0.0148; Red chroma = 0.62674 + 
0.07838 PC2, P = 0.0132; UV chroma = 0.09804 - 0.03403 PC2, P = 0.0132).   
In females, PC2 represented presence of UV, blue and green wavelengths that are 
induced by the relative absence of yellow and red pigments in the midline dewlap region.  
PC2 did not explain a significant amount of variation in the lateral dewlap region (Figure 
 24
2 f).  Interpretation of results for the female midline region were corroborated by tri-
stimulus multiple regression analysis in which UV, blue and red chroma explained a 
significant proportion of variation in PC2 (Table 2 b).  Separate linear regressions 
showed that UV and blue chroma contributed positively to PC2, while red chroma 
contributed negatively to PC2 (UV chroma = 0.14501 + 0.0231 PC2, P = 0.0002; Blue 
chroma = 0.24737 + 0.01341 PC2, P = 0.0184; Red chroma = 0.43328 - 0.0319 PC2, P 
<.0001). 
When examined by ANOVA, sexes did not differ in midline brightness (i.e. PC1), 
but did differ in midline UV chroma and brightness (i.e., PC2, Table 3).  Female dewlaps 
had higher PC2 values than those of males.  Sexes differed in lateral dewlap brightness 
(PC1); females had higher PC scores than males (Table 2 c).  Finally, sexes differed in 
long wavelength brightness and chroma (i.e., PC2) in that male dewlaps were brighter 
and more chromatic at yellow-red wavelengths than were those of females (Table 2 c).  
Pigment concentrations & how they relate to dewlap coloration 
Absorbance spectrophometry identified pterins bound in male and female dewlap 
tissues as drosopterins (?
max
 = 490 nm) as drosopterins, and carotenoids as xanthophylls, 
such as lutein and/or zeaxanthin (?
max
 = 455 nm).  Two-way ANOVA revealed that 
carotenoid concentrations did not differ by dewlap region (P
0.3301, 1
 =  0.5677) or sex 
(P
0.0818, 1
 = 0.7758) and there was no significant interaction between region and sex 
(P
0.4132, 1
 = 0.4132, see Figure 2 g).  Pterin concentrations displayed a significant sex-by-
dewlap-region interaction (Figure 2 h; P
6.561, 1
 = 0.0129).  Male lateral dewlap regions 
were significantly more pterin-enriched compared to male midline dewlap regions and 
both regions were more pterin-enriched in males than in females, especially in the lateral 
 25
dewlap region (Figure 2 h).  Dewlap carotenoid concentrations did not correlate with 
pterin concentrations in male lateral or midline dewlap regions (lateral: R
2 
= 0.080, df = 
21, P = 0.200; midline: R
2 
= 0.003, df = 19, P = 0.829), or in female lateral or midline 
dewlap regions (lateral: R
2 
= 0.110, df = 9, P = 0.319; midline: R
2 
= 0.050, df = 11 , P = 
0.484).  
Because sexes and dewlap regions differed in reflectance properties, we examined 
relationships between pigments and spectral principal components separately, according 
to sex and dewlap region.  In males, carotenoids explained 17.9% of the variance in PC1 
for the midline dewlap region (Table 2 d).  This was further supported by a separate, 
marginally-significant, positive, linear regression between carotenoid concentration and 
average total percent reflectance in the male midline dewlap region (R
2
 = 0.179, P = 
0.06).  Pigments did not contribute significantly to variance in UV relative to red chroma 
in the midline dewlap regions for males (Table 2 d).  In the lateral dewlap region of male 
N. sagrei, both pterin and carotenoid concentrations contributed significantly to PC1 
(Table 2 d).  In separate linear regressions, however, increased pterin concentrations 
yielded significant increases in PC1 (R
2
 = 0.213, df = 19, P = 0.03), while increased 
carotenoid concentration did not correlate with PC1 (R
2
 = 0.000, df = 19, P = 0.994).  No 
pigment explained significant variation in PC2 of the lateral dewlap region (Table 2 d). 
In females, neither carotenoid nor pterin concentration explained a significant 
amount of variation in PC1 for either dewlap region (Table 2 d).  Pterin concentration, 
however, explained a significant amount of variation in PC2 of the dewlap midline (Table 
2 d).  Pterin concentration was inversely proportional to PC2 (R
2
 = 0.574, df = 9, P = 
 26
0.007), such that the tissue reflected more short- and medium-wavelength light when 
fewer pterins were present.   
Dewlaps that possessed higher-than-average concentrations of pterins and 
carotenoids reflected less UV light and more long-wavelength (yellow) light (Figure 2 d).   
In contrast, dewlaps that contained lower-than-average concentrations of pterins but 
higher-than-average concentrations of carotenoids strongly reflected UV and yellow 
light.  In dewlaps that had either higher-than-average pterin concentrations but low 
carotenoid concentrations, or lower-than-average pterin and carotenoid concentrations, 
the spectral curves were intermediate between the two extremes (Figure 2 i).   
These data also showed that pterin concentration correlated significantly with hue 
(i.e., wavelength of maximum reflectance) in the lateral dewlap region (R
2
 = 0.199, df = 
19, P = 0.055), but carotenoid concentration did not (R
2
 = 0.003, df = 19, P = 0.812).  
The distribution of hues in male lateral dewlap regions studied here showed a range from 
yellow to orange to red, and red (690-700 nm) was the most frequent hue of the lateral 
dewlap region (Figure 2 j).  Orange hues (650-660 nm) were nearly as frequent, and 
probably resulted from a particular pterin: carotenoid concentration ratio.    
Condition dependence 
In males, pterin concentration did not correlate with dewlap area (R
2
 = 0.099, df = 
19, P = 0.177), but carotenoid concentration did (R2 = 0.235, N = 20, P = 0.03, Figure 2 
k).  Because male SVL was positively correlated with dewlap area (R
2
 = 0.389, df = 19, P 
= 0.002), high carotenoid concentrations occurred in the largest males. Of all possible 
significant principal components with respect to male dewlap region, only PC2 of the 
midline regressed significantly against BCI (Figure 2 l).  Hence, UV chroma increased 
 27
with increased body condition.  Neither pterin concentration (R
2
 = 0.05, df = 21, P = 
0.343) nor carotenoid concentration (R
2
 = 0.029, df = 21, P = 0.476) regressed 
significantly against BCI. 
Discussion 
We detected sex differences in visible- and UV-light reflectance from the dewlaps 
of Brown Anoles.  Female dewlaps had greater UV brightness and chroma than those of 
males, whereas dewlaps of males had higher long-wavelength brightness and chroma 
than those of females. Other studies of UV coloration between the sexes of vertebrates 
show that UV is sometimes sex-limited in its expression [e.g., among males in guppies 
(Kodric-Brown and Johnson 2002) and sticklebacks (Rick et al., 2004)], or is greater in 
males than females [as in butterflies (Rutowski et al., 1995), blue tits (Andersson et al., 
1998), and  wall lizards (Molina-Borja et al., 2006)].  In two taxa studied, however, an 
agamid lizard (LeBas and Marshall, 2000) and Starlings (Cuthill et al., 1999), however, 
females have greater UV brightness and chroma than males.  In all of these taxa, UV has 
been shown to be an important aspect of social signals between the sexes.  It is unclear if 
female UV reflectance in N. sagrei is used in signaling, though females do perform 
occasional head-bobs (and dewlap extensions) in social interactions in the Green Anole 
(Jenssen et al., 2000; Jenssen, 1970) and Brown Anole (personal observation).    
UV reflectance (in addition to structural iridescent and blue color) is the result of 
short-wave scattering by nanostructural elements in integumentary tissues such as  
feathers and scales).  In birds, such elements are found within the medullary ?spongy 
layer? of the feather barb and ramus (Dyck, 1971; Dyck, 1971; Prum, 1999; Shawkey, 
2005).  In butterflies, however, special ellipsoid structures called ?laminate ridges? in the 
 28
reflecting scales cause scattering of light (Ghiradella et al., 1972).  The proximate cause 
to UV color in lizards is unstudied, but it is thought that iridophores scatter light in a way 
that is analogous to feather barbs (Morrison, 1995).  Pigments are also thought to play a 
role in shaping UV reflectance peaks, by selectively filtering non-UV wavelengths, 
which influences the shape of the reflectance curve in the UV region (Bradbury and 
Vehrencamp, 1998).  Bird feathers containing xanthophyll carotenoid pigments, for 
example, produce spectral curves that have a peak in the UV, as well as the yellow 
portion of the spectrum, because these carotenoids absorb violet and blue light 
(MacDougall and Montgomerie, 2003).  Feather keratin itself reflects strongly at all UV-
VIS wavelengths, and hence is white (Shawkey and Hill, 2005), but  
increases in plumage carotenoid concentration causes absorption of  middle wavelength 
of light, which in turn increases the amplitude of reflectance in the yellow and UV 
wavelengths  (Shawkey et al., 2006).  The UV and yellow reflectance peaks we observed 
in the midline regions of male N. sagrei dewlaps are consistent with this mechanism of 
color production, because individuals that possess lower-than-average concentrations of 
pterins but higher-than-average concentrations of carotenoids showed a dual-peak 
spectral curve, with strong reflectance at UV and yellow wavelengths.    
 In many fishes, amphibians, and reptiles, the yellow and red-producing pigments, 
carotenoids and pterins, occur together in erythrophores (Bagnara and Hadley, 1973).  In 
a previous study, Steffen and McGraw (2007) showed that red pterins and yellow 
carotenoids are together in both regions of the dewlap in N. sagrei.  In the present paper, 
we quantified concentrations of pigments from each of these pigment classes and found 
that males had greater concentrations of pterins, but not carotenoids, in the dewlaps than 
 29
did females.  Given that males had larger dewlaps than females, male Brown Anoles must 
have greater quantities of pterins and carotenoids in their dewlaps compared to females.  
The sex differences in pterin concentration probably represent developmental differences 
in the conversion of purines to pterins, and may reflect selection for males to have 
dewlaps that are more visible than those of females, especially because the red color 
provided by pterins in lizards markedly contrasts with green backgrounds that are 
common in the lizards? environs (Endler, 1992).   The sex differences in carotenoid 
quantity, but not concentration, implies that males do not have a greater ability to enrich 
the integument than females.  The dewlaps of males do have greater quantities of 
carotenoid than females, and this is probably a function of dewlap size, at least in part.     
This study also details how pigment concentrations related to reflectance 
characteristics in the dewlaps of male and female Brown Anoles.  In male N. sagrei, both 
pterin and carotenoid concentrations contributed positively to total brightness in the 
lateral dewlap region.  In the midline region, however, carotenoids alone contributed 
significantly (and positively) to overall brightness of males.  In females, however, pterin 
concentrations contributed significantly (as well as positively) to chroma, but not total 
brightness, of the lateral dewlap region only.  Overall reflectance (PC1), was not related 
to pigments of female dewlaps, and may instead be the result of differences in scale 
number and/or ultrastructure in the throat region.   
The effects of pigment concentrations on dewlap chroma and brightness in our 
study differ considerably from comparable work on plumage pigmentation in birds.  In 
male Greenfinches and American Goldfinches, which use carotenoids but not pterins to 
color feathers, carotenoid concentrations have been shown to positively correlate with 
 30
feather chroma, but not brightness (Saks et al. 2003, McGraw and Gregory, 2004).  The 
difference in the way these two pigments influence brightness and chroma between birds 
and lizards may be related to the degree to which feather ultrastructure contributes to 
spectral variation compared to the degree to which scale ultrastructure, as well as 
iridophore structure and abundance contributes to spectral variation.  Investigations of 
how scale structure contributes to aspects of color has been studied in only a few lizards 
(Morrison, 1995; Morrison et al., 1996) and this possibility awaits further investigation in 
N. sagrei.   
Pterins and carotenoids also combine to create colorful skin patches in male 
Trinidadian Guppies (Grether et al., 2001). In this species, pterin (in particular 
drosopterin) concentration correlates positively with carotenoid (tunaxanthin) 
availability, and the pterin-to-carotenoid ratio is responsible for a particular orange hue 
that is maintained across a gradient of carotenoid availability in several streams.  In N. 
sagrei, however, pterin concentrations did not correlate with carotenoid concentrations in 
either sex or dewlap region.  Furthermore, hue did not appear to be a statistically 
significant source of spectral variation, because the PC coefficient analyses did not show 
multiple adjacent peaks in long wavelengths that would reveal yellow-orange-red hue as 
an important source of spectral variation (see methods for explanation).  Still, pterins and 
carotenoids are found together, especially in male lateral dewlap regions, and basic 
primary color theory suggests that yellow (carotenoid) mixed with red (pterin) should 
produce orange.  The distribution of hues in male lateral dewlaps studied here range from 
yellow, through orange, to red, with red (690-700 nm) and orange hues (650-660 nm) 
being most common.   
 31
Pterins found in dewlaps of N. sagrei (especially the lateral dewlap region) appear 
to absorb highly in the UV range, but permit strong reflectance of the long wavelengths.  
This is because dewlap regions (e.g., lateral dewlap regions in males) that possessed high 
pterin concentrations as well as high carotenoids have spectral curves low in UV and high 
in the long (i.e., yellow-orange-red) wavelengths of light.  In contrast, midline dewlap 
regions of male and female N. sagrei are pigmented mostly by carotenoids, and have high 
UV reflectance.  UV reflectance along the male midline dewlap region correlated 
positively with BCI, despite the finding that concentration of neither pigment  correlated 
significantly with BCI.  Still, the juxtaposition of a patch in males that is colored by UV 
absorbing pigments next to a color patch that is highly UV reflecting is curious and begs 
the question ?why ?  A possible answer lies in understanding the placement of pterins in 
Colias butterfly wings, and the influence of this pigment on UV reflectance.  Similar to 
N. sagrei, pterins found in the Colias absorb highly in the UV range (Rutowski et al., 
2005), and the pigments are thought to amplify aspects of low wavelength iridescence, 
because pterins increase the spectral purity and directionality of the UV signal especially 
when a butterfly is in flight (Rutowski et al., 2005).  We speculate that the UV absorbing 
lateral dewlap ?amplifies? the appearance of the UV reflecting midline dewlap via 
heightened spectral contrast between the two regions, and makes the midline dewlap 
region highly conspicuous to conspecific males and female N. sagrei. 
The size of UV-based color patches correlates with body condition index in an 
agamid lizard (LeBas and Marshall, 2001).  To our knowledge, however, our study is the 
first to show some aspect of color per se (and not color patch size) as a potentially 
condition-dependent trait in lizards.  The condition dependency of UV brightness may be 
 32
related to variation in the keratin-based integumentary microstructure, or in the 
abundance of iridophores underlying the pterin and carotenoid pigments, since neither 
pterin nor carotenoid concentration related to body condition index in Norops sagrei 
studied here.  Keratin structure may display information about health, independent of the 
susceptibility of pigments to environmentally-based variation (Keyser and Hill, 1999; 
Keyser and Hill, 2000; McGraw et al., 2002; Doucet and Montgomerie, 2003; Siefferman 
and Hill, 2003).  Although empirical evidence for the condition-dependence of structural 
color is accumulating, the proposed mechanism for an association between health and the 
quality of structural coloration remains a matter of debate (Prum, 2006; Hill, 2006).  
Investigation into the nature of UV coloration, and the condition dependence of 
structurally- and/or pigmentary-based colors in reptiles is an exciting area of research that 
awaits future investigation.  
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 40
Figure Legends 
 
 
 
 
Figure 2a & b.  a) Mean spectral curves (?S.E.) of male and female N. sagrei lateral 
dewlap regions; b) mean spectral curves (?S.E.) of male and female N. sagrei midline 
dewlap.  Gray line represents female spectral curve, black line represents male spectral 
curve. 
Figure 2 c - f. Top: Relationship of PC 1 coefficients (black) and PC2 coefficients 
(gray line) and spectral wavelength for (a) male midline, (b) male lateral, (c) female 
midline and (d) female lateral dewlap regions.  PC 1 represents variation in mean 
spectra across 20-nm intervals for male midline and lateral dewlap regions, and for 
female midline dewlap regions.  PC 2 represents variation in short wavelengths 
relative to medium and long wavelengths of light in male midline regions.  PC2 
represents variation in long wavelengths relative to short and medium wavelengths in 
male lateral dewlap regions.  PC2 represents variation in short wavelengths and 
medium wavelengths relative to long wavelengths of light in female lateral dewlap 
regions. 
 41
 
 
 
 
 Figure 2 l. Regression of carotenoid concentrations on male dewlap area (R
2
 = 0.235, N 
=      20, P = 0.030).  
 
Figure 2 g & h.  Carotenoid (a) and pterin (b) concentrations for male (black line) and 
female (gray line) by sex and dewlap region in N. sagrei (lat = lateral; mid= midline). 
Figure 2 i.  Effect of pterin absorption on carotenoid absorption in lateral dewlap 
region.  Treatments are higher than average concentration of pterins and carotenoids 
(gray solid line), high pterin concentrations but low carotenoid concentrations (black 
short dashed line), low pterin concentrations but high carotenoid concentrations (black 
solid line), and low concentrations of pterins and carotenoids (black long dashed line). 
Figure 2 k.  Regression of PC2 against BCI, midline dewlap region for male N. sagrei.  
See text for details about derivation of BCI and biological interpretation of PC2.  (R
2
 = 
0.182, P = 0.047. N = 22). 
Figure 2 j.  Frequency histogram of hues from male lateral dewlap regions.  Orange 
(650-660 nm) and red (690-700 nm) hues are frequent in frequency distribution of 
wavelength of maximum reflectance (a corollary of hue). 
 42
Figures 
 
 
 
 
 
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 47
 
 
 
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I
 49
 
Tables 
 
 
 
Table 2 a.  Backwards stepwise multiple regression.  Assessment of contributions of tri-stimulus concept of chroma (UV, 
blue, green, yellow and red) to PC1 by sex and dewlap region 
Sex & 
Region 
R2adj F, UV P, UV F, Blue P, Blue F, Green P, Green F, Yellow P, Yellow F, Red P, Red 
Mlat 1 695.512 <0.001 1729.557 <0.001 520.194 <0.001 removed 0.6498 2346 <0.001 
Mmid 1 927.094 <0.001 294.361 <0.001 37.826 <0.001 12.814 0.0038 134.8 <0.001 
Flat 1 877.404 <0.001 1795.39 <0.001 251.705 <0.001 removed 0.5629 1673 <0.001 
Fmid 1 320.464 <0.001 305.193 <0.001 20.025 <0.001 removed 0.7945 124.5 <0.001 
 
 50
 
 
 
Table 2 b.  Backwards stepwise multiple regression.  Assessment of contributions of tri-stimulus concept of chroma (UV, 
blue, green, yellow and red) to PC2 by sex and dewlap region 
Sex & 
Region 
R2adj F, UV P, UV F, Blue P, Blue F, Green P, Green F, Yellow P, Yellow F, Red P, Red 
Mlat 0.264 removed 0.438 removed 0.990 removed 0.355 removed 0.220 7.457 0.014 
Mmid 0.953 238.953 <0.001 removed 0.375 removed 0.383 12.113 0.004 13.544 0.002 
Flat none none none none none none none removed 0.815 none none 
Fmid 0.937 8.454 0.023 36.76 0.001 removed 0.828 removed 0.892 7.663 0.028 
 
 51
 
 
 
 
 
 
 
 
 
 
 
 
Male  
Mean
Male 
S
Female 
Mean
Female 
S
FP
PC1 midline 0.050 0.216 -0.101 0.306 0.163 0.690
PC2 midline -0.375 0.183 0.750 0.258 12.643 0.001
PC1 lateral -0.416 0.174 0.833 0.246 17.262 0.000
PC2 lateral  0.381 0.181 -0.763 0.256 13.274 0.001
Table 2 c.  Four separate 1-Way ANOVA?s that compare sex 
differences in Principal Component Scores by dewlap regions 
 52
 
 
 
 
 
 
 
 
 
 
R
2
R
2
ad Par 1 Par 1 
2
F, Par P, Par Par 2 Par 2 
2 
F, P, Par 
PC1 
0 0 
non
PC2 
0.5739 0.5266 
P 0.57 12.1 0.006
PC1 
0 0 
non
PC2 
no  p c 2 no  pc 2 
non
Table 2 d.  Multiple regression of male pigment concentrations (top table) and female pigment 
concnetrations (bottom table) against Principal components (PC1 & PC2).  For details about spectral 
identity of PC?s. see Figs 4a & b, and consult text.  Par ID = parameter identity (i.e. pigment identity).  
Par 1 = 1
st
 parameter entered into multiple regression model, Par 2 = 2
nd
 parameter entered into 
multiple regression model.  F = F statistic, R
2
 = amount of variance explained by each regression 
model, and P = probability of Type II error.   
R
2 
R
2 
ad Par 1 Par 1 
2
F, Par P, Par Par 2 Par 2 
2 
F, P, Par 
PC1 
0.179 0.134 
[Ct
0.179 3.934 0.063
PC2 0 0 non
PC1 
0.2828 0.2073 
[Pt 0.155 5.00 0.03 [Ct 0.282 3.37 0.08
PC La
0 0 
non
 53
CHAPTER 3: LIGHT ENVIRONMENT INFLUENCES DEWLAP 
CONSPICUOUSNESS OF MALE AND FEMALE                                                
BROWN ANOLES (Norops sagrei) 
Abstract 
 Signal theory hypothesizes that visual signals should evolve conspicuousness 
sufficient to allow for detection in some light environments at the cost of 
conspicuousness in other light environments.  We quantified the spectral variation of 
male and female dewlaps from a population of Brown Anoles, Norops sagrei that 
inhabited a semi-disturbed habitat in central Florida, using a UV-sensitive spectrometer.  
Norops sagrei display dewlaps that, to the human eye, appear to have a yellow or white 
midline dewlap region flanked by a pinkish-red lateral region. We applied these spectral 
data to a visual model that integrated information about Norops sagrei visual physiology 
and coloration of background vegetation to estimate the conspicuousness of male and 
female dewlaps in four classic light habitats, and in dim vs. bright illumination 
conditions.  The chromatic aspects of dewlap color of male and female Norops sagrei 
was most conspicuous in light conditions typical of woodland shade, and were slightly 
less conspicuous in light conditions typical of large and small gaps.  Green backgrounds 
generally rendered dewlap color more conspicuous than brown backgrounds, as did 
illumination intensity (bright illumination rendered dewlap spectral variation more 
conspicuous than dim illumination).   Sexes could be discriminated based on differences 
 54
in their dewlap color in woodland shade only.  Brightness of male and female dewlaps 
could be used to determine the sex of an individual in woodland shade only.  We discuss 
how these results may influence social behavior of Brown Anoles.     
Introduction 
Animal coloration has captured the interest of naturalists since the time of Darwin 
(Darwin, 1871) and this trait is used often in sex attraction, sex recognition, and mate 
assessment (Andersson, 1994).  The effectiveness of coloration as a visual signal is 
dependent not only on the spectral reflectance of the color patch but also on irradiant 
light environment and display background. Moreover, signal effectiveness is also 
influenced by receiver physiology (visual system) and behavior (between signaler and 
receiver (Lythgoe, 1979; Endler, 1990; Endler, 1992; Endler, 1993).  Forest-wide 
variation in at least two of these factors, irradiant light environment and display 
background, may influence microhabitat choice, mating success, and mortality (Ryan and 
Wylczyski, 1991; Endler, 1991, Endler, 1992; Endler, 1993, Endler, 1996).    
Forests throughout the world contain five major irradiant light habitats, when the 
sun is not blocked by clouds: forest shade, woodland shade, small gaps, large gaps, and 
early/late light habitats (Endler, 1993, Fleishman et al., 1997, Chiao et al., 2000). The 
overall light spectrum of a habitat is influenced by the relative amount of direct and 
indirect light, which is a consequence of light reflected from sky, leaves or other 
substrates.  The first four light habitats arise because of the way in which differences in 
forest structure contribute to relative differences in direct and indirect illumination, and 
assumes that the sun is directly overhead, while the fifth light habitat (early/late) 
represents differences in illumination intensity (i.e. dim vs. bright), and is a result of the 
 55
sun nearing the horizon.  For the purposes of this paper, we focus on the structurally-
based light environment.   
Recent advances in spectrometry have revealed that human-based vision has 
largely underestimated the spectral variation of bird coloration (Burkhardt, 1991; 
Burkhardt and Finger, 1989).  Evidence is accruing that this is also the case in lizards 
(Fleishman et al., 1993; LeBas and Marshall, 2000, 2001; Whiting et al., 2006; Molina-
Borja, 2006; Macedonia et al., 2001; Stuart-Fox et al., 2004; Thorpe and Stenson, 2003, 
Steffen and McGraw, Chapter 2).  In addition, microspectrometry has allowed 
researchers to identify and assess the spectral sensitivity of UV-sensitive cone 
photoreceptors that are present in the eyes of many species from all vertebrate classes.  
Although ethologists have long interpreted these colorful ornaments and visual signals 
from the perspective of the sensory physiology of the signal receiver (Guilford and 
Dawkins, 1991), recent models proposed by Voroboyev and colleagues (Vorobyev and 
Osorio, 1998; Vorobyev et al., 1998; Vorobyev et al., 2001) improve our ability to 
integrate information about light environment, display background, and integument 
reflectance to better understand the conspicuousness of visual signals. 
Male anoline lizards have large, colorful dewlaps that are displayed to conspecific 
males and females in social interactions (Jenssen, 1977), to predators during attacks 
(Leal, 1995; Leal and Rodriguez-Robles, 1997 a, b; Leal, 1999), and to congeners (Losos, 
1985).  Leal and Fleishman (2001, 2002, 2004) used visual cone sensitivities to model 
dewlap detectability in two sympatric species (Anolis cristatellus and A. cooki), as well as 
in one species (A. cristatellus) in two different habitats.  The relationship of dewlap 
reflectance relative to detectability, based on ambient light and cone sensitivities in both 
 56
of these studies, is consistent with sensory drive (selection for differential 
conspicuousness under different ambient light environments).  For example, the spectral 
reflectance that characterizes dewlaps of male Anolis cristatellus differs between xeric 
and mesic habitats, and correlates with differences in irradiance between these two 
habitats (Leal and Fleishman, 2004).   
Male Brown Anoles (Norops sagrei) have large dewlaps that are comprised of 
two spectrally-distinct, adjacent dewlap regions that vary in UV, red, orange, yellow and 
white colors (Chapter 2).  To the human eye, the male dewlaps generally appear to have a 
yellowish edge (midline) flanked by a pinkish-red, central (lateral) region.  Females also 
possess dewlaps, but these structures are reduced to a small patch on the throat 
possessing colors that range more extensively into UV but less extensively into red, 
yellow and white (Chapter 2).  The extent to which these colors are perceived by 
conspecifics is a question that is of fundamental importance to studies that attempt to 
determine the role of dewlaps in social communication of anoles.  To date, no research 
has focused on differences in male and female dewlap color conspicuousness, despite the 
potential for male and female dewlaps to act as an important communication device in 
social encounters (Jennsen et al., 2000, Leal and Fleishman, 2004).  
Brown Anoles are native to Cuba, the Bahamas, and related islands (Schwartz, 
1991), but are successful invaders of the southeastern United States (Lee, 1985, 1992; 
Means, 1990; Echternacht et al., 1995; Platt and Fontenot, 1994; Campbell and 
Hammontree, 1995), as well as Hawaii (McKeown, 1996; Goldberg and Bursey, 2000). 
Throughout their range, Brown Anoles occupy, and display in, a wide variety of habitats  
ranging from hammock forests (Paterson, 2002;  McMann and Paterson, 2003) and 
 57
tropical gardens (McMann and Paterson, 2003), to disturbed environments such as 
commercial buildings and houses (Echternacht et al., 1995).  Brown Anoles are notorious 
invaders because of their propensity to inhabit disturbed areas, but substantial populations 
persist in hammock forests throughout Florida.  Hammock forests contain the four 
structurally based light environments described above (Endler, 1993).   
In this study, we measured dewlap reflectance for a population of Brown Anoles 
in central Florida.  To describe the conspicuousness of male and female dewlaps, we 
integrate information about N. sagrei visual systems, background radiance, illumination 
intensity, and ambient light irradiation from four distinct ambient light habitat types.  
These light environments are associated with distinct forest and suburban habitats in 
which these animals reside.  The goals of this study were to investigate the extent to 
which illumination intensity, ambient light habitat, and background reflectance influence 
dewlap conspicuousness, and to determine light conditions under which sexes could be 
distinguished based on dewlap color.    
Methods 
Lizard collection and care 
Male and female Brown Anoles (N. sagrei) were purchased from a pet store 
(Glades Herp, Bushnell, Sumter County, Florida), where the animals had been captured 
from a forest surrounding a park on the west side of Lake Panasofkee in Sumter County.  
Individuals were identified as adult males if they possessed a large (minimum 50 mm
2
) 
extendable dewlap.  Anoles were identified as adult female if their dewlap was small and 
limited in its ability to be extended.  Individuals were housed in an screen-topped, 37.90 
liter (ie., 10 gallon), glass terrarium that contained a perch, and a water dish on a sandy 
 58
floor.  A UV-B fluorescent bulb provided light from 12 inches above the terrarium top.  
Lizards were fed crickets and meal worms ad libitum, which were dusted with repta-vite 
(Zoo Med laboratories, San Luis Obispo, CA).   
Spectrometry  
We measured spectral reflectance of dewlaps and background vegetation using an 
S2000 spectrometer (range 250-880 nm: Ocean Optics, Dunedin, Florida) with a 
bifurcated micron fiber-optic probe. The probe was held at 90?, 1mm from the sample 
surface, and shielded from stray light by a rubber sheath. The reading area was 
illuminated with both UV (D-2000 deuterium bulb, Ocean Optics, Dunedin, Florida) and 
visible (tungsten-halogen) bulbs.  All data were generated relative to a white standard 
(WS-1, Ocean Optics, Dunedin, Florida). 
Following Steffen and McGraw (2007), we measured two regions of the dewlap 
in both sexes: lateral (side) and midline (edge).  Male dewlaps were extended with a pair 
of forceps to allow measurement of the lateral region; the midline region was measured 
with the dewlap unextended.  Because female dewlaps are small and limited in the extent 
to which they can be extended, lateral and midline dewlap regions were measured by 
placing the spectrometer probe against an unextended dewlap.  In each dewlap region, we 
took three measures per male and two measurements per female.  We took fewer 
measurements of the dewlap regions of females because dewlap area was only large 
enough to measure two unique locations.   
Color was expressed as percent reflectance per nm wavelength and this output 
was processed using ColoRv1.5 software (R. Montgomerie copyright 2002).  We 
generated spectral curves for every measurement location, and determined mean spectral 
 59
curves for the two dewlap regions in each individual lizard. To characterize background 
colors for the study site, we measured spectral reflectance of tree trunks and leaves where 
lizards were observed to perch.  Specifically, we measured reflectance of eight types of 
wood substrate and eight types of green leaves found near perch sites used by N. sagrei, 
to represent variation in available brown and green backgrounds.   
Light environments 
Brown Anoles are heliophilic and thermophilic squamates (Loew et al., 2002, 
(Ferguson et al., 2005), that can invade shady habitats lacking a shade-tolerant 
competitor.  Therefore, we used irradiance spectral data for forest shade, woodland shade, 
and small gaps (John Endler, pers. comm.), and similar data for large gaps (courtesy of 
Jarrod Hadfield; http://www.bio.ic.ac.uk/research/iowens/spec/welcome.htm) to model 
dewlap visibility across the spectrum of habitats used by this invasive species.   
Forest structure and openness responsible for creating four of the major light 
habitats, described by Endler, 1993, is illustrated in Figure 1.   Forest shade describes a 
light environment in which the predominant light derives from leaf reflection or 
transmission.  This light habitat is associated with a relatively high density of trees and 
which contains both canopy and understory trees.  In this light environment, there is no 
direct sunlight, and little or no light comes from the open sky.  Green dominates the 
irradiance spectrum because of reflected light from leaves.   
In woodland shade, light derives from leaves, but a significant portion comes 
from the sky.  In this category, direct sunlight (white light) contributes little to the 
spectrum.  This light environment is associated with forests with lower density of trees 
and lacking an understory of woody vegetation.  In this habitat, bluish or bluish-gray 
 60
radiance from the sky dominates the irradiance spectrum.  This light habitat is not limited 
to forests, instead occurring anywhere that shade is insufficient to prevent significant 
amount of sky light to penetrate to the substrate (e.g., canopies of emergent forest trees, 
shaded of boulders, buildings (Endler, 1992 and pers. comm.). 
Large gaps are ?open areas? in forests that are created by tree falls and are often 
characterized by downed logs, but this definition also includes open areas created from 
some other cause, in an otherwise forested environment.  In large gaps, a significant 
fraction of light comes from the open sky, but a lesser yet significant amount comes from 
the sun and vegetation.  The sun, blue sky and clouds are much brighter than vegetation.  
This light environment is predominantly white.   
Small gaps are sunlit locations in the forest in which a small canopy hole allows 
direct sunlight to pass to some point in the forest.  In this light environment, a small 
portion of the available ambient light comes from the open sky and essentially all light 
comes directly from the sun and vegetation. These areas are characterized by yellow-red 
ambient light.  
Visual modeling 
Norops sagrei possess four types of single-cone, retinal photoreceptors: 
ultraviolet (UVS), short-wavelength (SWS), medium-wavelength (MWS), and long-
wavelength sensitive (LWS).  Brown Anoles also possess a double-cone photoreceptor 
that is associated with long-wavelength light but does not possess rod photoreceptors 
(Loew et al., 2002). In lizards, color discrimination is the result of opponent processing of 
pairs of different types of single cone photoreceptors (Loew et al., 2002).  The chromatic 
component of an object such as a dewlap can be represented by a point in perceptual 
 61
color space whose coordinate axes represent the quantum catches of these cone 
photoreceptors (Goldsmith and Bursey, 1990).   For animals with four types of single-
cone photoreceptors, this perceptual color space can be likened to a tetrahedron, with 
each of the four photoreceptor types located at a vertex of this tetrahedron (Burkhardt, 
1989; Goldsmith, 1990).  Variation in the detectability of different colors can be 
approximated by calculating Euclidian distances between two points in this 
tetrachromatic color space (Goldsmith, 1990).   
However, distances between points in such a color space do not correspond 
directly to perceived differences in color because these distances must exceed a certain 
threshold to be distinguishable. This discrimination threshold depends on noise that 
originates in photoreceptors and at further stages of neural processing (Vorobyev and 
Osorio, 1998, Vorobyev et al., 1998).  When stimuli occur below this threshold, signals 
will not be perceived to the extent that signals above the threshold will be perceived.   
Vorobyev et al. (1998) have developed a color space model that accounts for 
receptor-noise limited stimulation thresholds and integrates information about the 
transmission of the ocular media, light environment, visual background, and receptor 
noise, to estimate the relative conspicuousness of a color patch. We implemented a 
version of this model to calculate the conspicuousness of the two different dewlap color 
regions of male and female Brown Anoles.  All equations follow Vorobyev et al (1998) 
and (Hadfield, 2004).  Spectral sensitivities (including effects of photoreceptor-associated 
oil droplets) were measured by Loew et al. (2002) and provided in its present form by 
Leo Fleishman (Figure 2).  We used these spectral sensitivities to estimate photoreceptor 
quantum catch in N. sagrei.  
 62
In a particular light environment, a color pattern is most conspicuous when the 
adjacent color pattern elements vary greatly in brightness and chroma (Endler, 1992).  To 
quantify the extent that the bi-colored dewlap was perceived by a conspecific observer, 
we estimated conspicuousness of the two adjacent color patches.  To estimate 
conspicuousness, we first calculated quantum catch (Q) per photoreceptor type as a 
proportion of total quantum catch for each dewlap region of each individual lizard using 
the equation: 
 
                               Q
i
  = ?
?
 R
i
 (?)S(?)I(?)O(?)d ?                            (1) 
                                                   ?
?
 R
tot
 (?) d ? 
 
where ? represents wavelength, R
i
 (?) is the spectral sensitivity of receptor type i, S(?) is 
the reflectance of the color patch, I(?) is the irradiance of the light environment, O(?) is 
the transmission of the ocular media, and d ? symbolizes that integration is to be 
performed over the range of visual spectrum that is sensitive.  When spectral files are 
processed so that data are expressed as percent reflectance per nanometer wavelength, 
this integration is simply a summation of reflectance occurring throughout the range of i.  
Spectral sensitivities, irradiance, and ocular transmission were normalized to a mean and 
standard deviation of one using equation 1, from which we calculated receptor quantum 
catches for each single cone type (UVS, SWS, MWS, and LWS).  Photoreceptors 
undergo chromatic adaptation to pre-exposed or surrounding background stimuli, and we 
accounted for this by normalizing the photoreceptor quantum catches related to 
perception of spectra of male or female dewlap regions to the photoreceptor quantum 
 63
catches of the adapting backgrounds using the von Kries scaling algorithm (Wyszecki 
and Stiles, 1982): 
 
                                                                        q
i
 = k
i
 Q
i
                        (2) 
 
where the scaling factor, k
i
, is defined as: 
 
                                k
i
 = 1/?
?
 R
i
 (?)S(?)I(?)O(?)d ?                  (3) 
                                                    ?
?
 R
i
 (?) d ? 
 
and where S(?) is the reflectance spectrum of the background (Voroboyev and Osorio, 
1998).  This scaling factor is implemented to incorporate the assumption that receptors 
independently adapt to the background, and acts as a mechanism which can account for 
color constancy.  Spectra of green leaves and brown tree trunks were measured to serve 
as the background.  Fechner?s law states that the perceived magnitude of a visual 
stimulus is proportional to the physical magnitude of the stimulus (Wyszecki and Stiles, 
1982).  In mathematical terms, the receptor signal (f
i
) is proportional to the natural log of 
the quantum catch of a given receptor type (q
i
) and is calculated as follows:  
 
                                              f
i
 = ln (q
i
)                                           (4) 
 
And the difference in receptor signals (?f
i
) for two stimuli, a and b, (i.e. two dewlap 
regions, or a color patch against its background) is defined as 
 64
  
                                             ?f
i 
 =  f
i, a 
- f
i, b 
                                     (5) 
 
 Using equation 5, we calculated receptor signals that result from two adjacent 
dewlap regions, for each of the four cone types, for each sex.  Color perception is 
achieved by comparing receptor signals across different receptor types.  By extension, 
perceived differences in color between two objects can be determined by comparing 
differences in receptor signals across different receptor types.  For each receptor type, the 
difference in receptor signals between two color patches equal ?f
i
 .   
For a tetrachromat, we calculated the discriminability (?S) between two color 
patches (or two dewlap regions) using the following equation: 
 
                             (?S)
2
 = ((e
1
e
2
)
2
)(?f
4
 ? ?f
3
)
2
 + (e
1
e
3
)
2
)(?f
4
 ? ?f
2
)
2
  
                                           + (e
1
e
4
)
2
)(?f
3
 ? ?f
2
)
2
 + (e
2
e
4
)
2
)(?f
3
 ? ?f
1
)
2 
                                                                
 + (e
3
e
4
)
2
)(?f
2
 ? ?f
1
)
2
 + (e
3
e
2
)
2
)(?f
1
 ? ?f
4
)
2
)        (6) 
                                             / ((e
1
e
2
e
3
)
2
 + (e
1
e
2
e
4
)
2
 + (e
1
e
3
e
4
)
2
 + e
2
e
3
e
4
)
2
) 
 
As mentioned above, noise in receptor types influences the perception threshold 
of visual stimuli.  Noise in a receptor type i, (e
i
), can be modeled by the following 
equation: 
 
                             e
i
 = sqrt (((1/log(T(Q
i,a 
+ Q
i,b
)/2))
2
 + w
i
2
)/ n
i
 )              (7) 
 
 65
where T is a scaling factor which relates Q
i
 (which is expressed as a proportion of 
maximal cone catch) to an absolute quantum catch value for a receptor (Vorobyev et al 
2001), w
i
 = the Weber fraction for cone type i, and n
i
 = the relative abundance of cone 
type i in the retina.   
The mathematical expression 1/log(T(Q
i,a 
+ Q
i,b
)/2))
2
 models quantum-flux-
dependent noise whereby noise increases as the average absolute quantum catch for the 
two stimuli decreases.  This may be because colors are dark (i.e., Q
i
 is small), or colors 
are viewed under poor illumination (i.e., T is small).   
We compared two settings for T, 500 and 10,000., that roughly correspond to dim 
and bright illumination, respectively, for each ambient light setting.   Dim illumination 
represents irradiant light available during early/late parts of the day, and occurs when the 
sun is near the horizon.  Bright illumination represents irradiant light available when the 
sun is directly over head. 
The Weber fraction, w
i
, describes the inherent noise-to-signal ratio in receptor 
cells of type i, independent of the quantum catch.  This constant approximates noise-to-
signal ratios in photoreceptors, and permits predictions of suprathreshold differences 
between saturated color.  We used a default value of 0.05 for all cone types following 
Hadfield (2004).  Since no data are available for the relative abundance of cone types in 
anoles (Leo Fleishman, personal communication), we used relative abundance of cones 
from Blue Tits (Parus caeruleus, Class Aves) (Hart et al., 2000; UVS=0.37, SWS = 0.7, 
M = 0.99, L = 1).  Because the vertebrate eye is highly conserved between different 
classes, bird cone abundance should not differ greatly from squamate cone abundance, 
 66
and should suffice as a valid model parameter until data on squamate cone abundance 
become available (Campbell, 2006).  
Conspicuousness, or ?S
 
describes a relative stimulation threshold for which 
values are described in units of Just Noticeable Differences.  A value of <1 indicates two 
colors that cannot be discriminated, and values >1 can be discriminated.  Values >1 
represent the incremental magnitude that a value is above the detection threshold.  
Quantifying contrast 
We used ?S to quantify chromatic contrast.  The degree of contrast between 
different body regions influences short-distance conspicuousness.  From a close distance, 
dewlap regions with high values of ?S will be highly conspicuous.   
Brightness represents variation along the achromatic (black-grey-white) axis and 
is calculated as the summed light reflected across all wavelengths. Variation in brightness 
also influences the conspicuousness of signals.  Because brightness is the most abundant 
source of spectral variation in animal integument (Chapter 2, and Cuthill et al., 1999), we 
calculated measures of brightness contrast between the two dewlap regions for males and 
females.   
The role of double cones in squamate visual perception is unknown, but because 
double cones are thought to be used for achromatic signal detection in birds (Cuthill et 
al., 2000 a & b, Hart, 2001), we calculated receptor signals for double cones in N. sagrei 
(f
D
) as a proxy for brightness using the formulae described above and spectral sensitivity 
of long wavelength cones alone.  Loew et al., (2002) found photoreceptors with double-
cone morphology to be a subset of LWS photoreceptors.  Therefore f
D
 is equivalent to 
f
LWS
, and
 
we obtained f
D
 (or f
LWS
) by calculating f
i 
for
 
long wavelength cones from 
 67
equation 4.  Receptor noise is not known to significantly influence reception by double 
cones, and we estimated the perceived brightness of a dewlap region as f
D
, and the 
perceived difference in brightness of a color patch as ?f
D 
(i.e. f
D, patch 1 
- f
Dpatch 2
).  We 
measured achromatic contrast between the two dewlap regions (to measure short-distance 
conspicuousness), and against different perch backgrounds (to measure long-distance 
conspicuousness) in dim and bright light conditions of four different ambient light 
environments.   
Statistical Analyses 
Normality was tested using the Shapiro-Wilk test.  Color variables were normally 
distributed in all cases and were therefore not transformed.  All analyses were performed 
using JMP statistical software.  ?S and ?f
D
 values of males and females were modeled 
for the four different light habitats, against green and brown backgrounds, and at two 
levels of light intensity (T = 10,000, as a model of direct sun, and T = 500, as a model of 
crepuscular sun); values > 1 were considered conspicuous and values ? 1 but ? 2 were 
considered marginally discernable.  ?S and ?f
D
 values of males and females within each 
light habitat were compared using a 1-way ANOVA to test for significant sex differences.  
?S and ?f
D
 values of N. sagrei dewlaps against each background color within each light 
habitat were compared using a 2-way ANOVA to test for significant differences in 
background color. 
Results 
Under bright illumination color of the two dewlap regions was conspicuous (?S 
values >1) in woodland shade, and large and small gaps, and against brown and green 
backgrounds (Table 2 a).   Dewlaps were most conspicuous in woodland shade against 
 68
green backgrounds.   Dewlaps were slightly less conspicuous in woodland shade against 
brown backgrounds.   In small gaps, dewlaps were relatively conspicuous against green 
background, but marginally discernable against brown backgrounds.   In large gaps 
dewlaps were marginally discernable against green backgrounds, as well as against 
brown backgrounds.  In forest shade, dewlaps were not conspicuous against green or 
brown backgrounds. 
Sexes could be discriminated based on dewlap color in woodland shade only.  
Against green and brown backgrounds, males were significantly more conspicuous than 
females (F
green
 = 52.022, P < 0.0001, F
brown
 = 54.876, P < 0.0001; Table 2 a). ?S values 
did not differ between sexes in large and small gaps, although the dewlaps of both sexes 
were conspicuous.  
Under dim illumination dewlap color was most conspicuous in woodland shade 
against green backgrounds and brown backgrounds (Table 2 a).  Dewlaps were also 
relatively conspicuous under dim illumination in small gaps against green and marginally 
discernable against brown backgrounds.   Dewlaps were marginally discernable in large 
gaps against brown backgrounds but not noticeable against green backgrounds.  Dewlap 
colors were also not noticeable in forest shade against green backgrounds or brown 
backgrounds (Table 2 a).   
Under dim illumination, sexes could be discriminated based on dewlap color in 
woodland shade only (Table 2 a). Against green and brown backgrounds, male were 
significantly more conspicuous than females (F = 77.322, P < 0.0001).   
 69
The brightness of dewlap color was highly conspicuous in woodland shade only 
(Table 2 b).  Brightness against a green background was slightly more conspicuous than 
brightness against a brown background (Table 2 b).   
Sexes differed significantly in brightness in woodland shade only, against green 
and brown backgrounds, and males had greater brightness contrast than females (F
green
 = 
139.971 , P < 0.0001; F
brown
 =139.971 , P < 0.0001 )(Table 2 b).  No other light 
environments showed significant brightness contrast between dewlap regions.   
Finally, green backgrounds render the brightness aspects and chromatic contrasts 
of dewlap (in bright and dim lighting) more conspicuous than brown backgrounds, in 
general (Table 2 c).   There is a background color * light habitat interaction, however 
(F
brightness
 = 8.84, P < 0.0001; F
chromatic, bright
 = 20.241, P < 0.0001; F
chromatic, dim 
= 292.429, 
P < 0.0001. Table 2 c).    In light habitats where ?S and ?f
D 
are roughly one magnitude 
above the stimulation threshold (i.e. ranging from 1-2), brown backgrounds render the 
dewlap more conspicuous than green backgrounds. 
Discussion 
Because the conspicuousness of a visual signal is dependent on ambient light 
level as well as background reflectance, color patches should appear different to 
conspecific observers when displayed in different light habitats and against different 
backgrounds.  The hypothesis that light habitat, as well as background color, has a 
significant impact on the conspicuousness of visual signal was supported by our results.  
We found that the chromatic aspects of dewlap spectral variation in N. sagrei was 
sufficiently conspicuous to be detected by a conspecific observer in woodland shade, and 
large and small gap light habitats, but was not conspicuous in forest shade.   
 70
In woodland shade, ambient light increases conspicuousness of the dewlap color 
5-7 times compared to that of forest shade (depending on bright or dim conditions).    
Woodland shade describes light environments where predominant light derives from blue 
sky and leaves, but there is no direct sunlight.  This describes forest structure with a 
canopy, but where there is a relatively low density of trees, and which lacks an 
understory of woody vegetation.  This also describes light environments in the shade 
along forest edges, when the edge blocks the direct sunlight, as well as shade that is 
created as the result of a significant obstructions blocking direct sunlight, such as that 
provided by roofs of house, fences, etc.  Thus, in the shade provided by human dwellings, 
it appears that N. sagrei dewlaps are more conspicuous than in other light environments.   
The achromatic aspect of dewlap spectral variation (i.e., brightness, or variation in 
the black-gray-white axis) is roughly 22-times greater in woodland shade than in any 
other habitat.   Brightness variation is the largest source of spectral variation in animal 
integument, and is the primary source of spectral variation of N. sagrei dewlaps (Chapter 
2).  It also is related to movement detection in Anolis cristatellus (Fleishman and Persons, 
2001).  Therefore, irradiant light available in woodland shade renders both the chromatic 
and achromatic aspects of Brown Anole dewlaps relatively conspicuous compared to 
other light habitats.   
Male and female dewlap color is barely noticeable (i.e., 1 ? ? S ? 2 ) in large and 
small gap light habitats.  Brightness differences between the two dewlap regions could 
not be discerned in males or females, in small or large gaps.  Gaps often provide light 
appropriate for visual displays of many animals (e.g., butterflies and birds), but may be a 
trait associated with relatively mature forests.   Furthermore, gaps represent a 
 71
proportionately small portion of habitat space in forests and these environments may only 
be useful for signaling to those organisms whose populations can persist in such small 
spaces.   
Forest shade renders color and brightness of male and female dewlaps 
inconspicuous.  Forest shade is created by a dense tree canopy that contains canopy and 
understory-midstory trees, and where there no direct sunlight, and little or no light comes 
from the open sky. 
Sexes could be discriminated according to dewlap color and brightness in 
woodland shade only.  Therefore if a conspecific observer is to gather information based 
on dewlap ?color? that is sex-dependent, it can only be done when the display is presented 
and observed in woodland shade.  Granted, there are other ways for a conspecific 
observer to determine sex that are not solely based on dewlap color, such as dewlap 
extension, dewlap size, body shape, dorsal pattern, etc., that can provide an observer with 
information to help determine the sex of a nearby lizard.  Arguably, these other traits and 
behaviors are as equally strong a force as dewlap color in providing information about 
sex identity to conspecifics.  However, these results do show that dewlap color alone can 
provide information to a conspecific observer about a nearby lizard?s sex.   
It appears that woodland shade provides optimal ambient light for the dewlap 
color of N. sagrei from this population.  If dewlap color is used to assess phenotypic 
quality of a potential mate or rival, or as a signal of dominance and fighting ability, then 
it is most easily done in woodland shade.  Interestingly, sexes could not be distinguished 
based on dewlap color in woodland shade if dewlap color was presented under dim 
illumination against a brown background.  This means that conspecific observers must 
 72
use some other means of distinguishing sex (e.g., dewlap size, dewlap movement, body 
shape, dorsal patterns) when observing dewlaps against a brown substrate, that is present 
early or late in the day.   As mentioned above, these traits and behaviors are very likely to 
provide reliable information about sex.   
When dewlap color is distinguishable, and sexes differ significantly in 
conspicuousness, males are brighter than females.  In some sub-optimal light habitats, 
however, ambient light does not reflect against the dewlap and display background in a 
way that stimulates the photoreceptors above the stimulation threshold, and therefore are 
?inconspicuous? (? S < 1).  In a few light habitats such as these, females have higher ? S 
values than males.  But why aren?t males always brighter than females under all light 
environments, even when the dewlap color is not sufficiently conspicuous?  We speculate 
that this pattern reflects that the direction of differential sex colorfulness varies when it is 
freed from the strong selection associated with sensory drive in optimal visual habitats.   
Green backgrounds render dewlap color more conspicuous than brown 
backgrounds, in general, and this is true for dewlap brightness as well as chromatic 
variation under dim and bright illumination.  Therefore, dewlap color would be more 
conspicuous if a conspecific observer were to observe the dewlap against a leafy 
background, instead of a bark background.  Whether or not Brown Anoles take advantage 
of the increase in background contrast against green backgrounds is not known.  
However, in general it is thought that conspecific Anole observers often position 
themselves so that dewlap extension of a nearby lizard can be viewed from the side, so 
that the lateral dewlap is visible from a 90? angle (Fleishman et al., 2006).  Furthermore, 
displayers use trees to perch and extend their dewlap above the perch substrate, so that 
 73
more than likely, the dewlap viewing background is not the perch substrate itself, but is 
instead provided by the leaves, etc., surrounding the tree from which the displayer 
perches (personal observation).   
Our data suggest that signal senders could improve the visibility of the dewlap 
spectral variation by behavioral modification, for example, by displaying in woodland 
shade, when the sun is directly overhead, and against green backgrounds.   Direct 
observations of social interactions involving presentation of male dewlaps in different 
light habitats can test this prediction and tell us whether signal senders actually display 
most often under optimal light conditions, and whether or not observers respond most 
frequently to signals under optimal conditions.     
Lastly, our findings show that color of female N. sagrei dewlaps is nearly as 
noticeable to conspecifics in certain light environments and against different backgrounds 
as are male dewlaps.  The potential for female dewlap color to perform a social role in 
anoles has not been studied.  In a laboratory study of aggression in Green Anoles (Anolis 
carolinensis), females, which have colored throats that are non-extendable, have the same 
repertoire of aggressive signals (e.g., head-bobs and push-ups) as males, but they differ in 
the social context and frequency of display (Jennsen et al., 2000).  The authors speculated 
that directional selection on these displays has been less intense in females than in males 
because the outcome of consexual contests has fewer reproductive consequences for 
females than males.  Several authors have shown that female anoles are territorial, but 
less so than males, and that female territories are often contained within a male?s territory 
(Rand, 1967, Trivers, 1976, Stamps, 1977, Schoener and Schoener, 1982).  Because of 
this, female signal use might have important consequences for female competitor 
 74
recognition and male mate suitability (Leal and Fleishman, 2004).  Since our results show 
that female dewlaps are only visible in some light environments but not others, a color-
based female signal may go undetected in suboptimal light environments.  Furthermore, 
our data show that female dewlaps are conspicuous in the same habitats that males are 
conspicouous in.  This pattern is consistent with sensory drive because sensory drive 
predicts that visual signals will not be uniformally conspicuous across all light habitats, 
but that male and female visual signals will be conspicuous in similar habitats,  to aid in 
the use of visual signals for mating and reproduction.  There is at least one alternative 
explanation however: female dewlap color conspicuousness may be a correlated response 
to selection for male dewlap color.  If female dewlap color is not noticeable to predators 
because females do not extend their dewlaps, and if dewlap color has negligible 
production costs, then female color might become as conspicuous as we measured it to be 
because its expression is subject to genetic correlations with male dewlap color.   
The findings presented here show that the colors of N. sagrei dewlaps are highly 
visible in some light habitats, but not in others.  Moreover, green backgrounds generally 
render the dewlap colors more conspicuous than brown backgrounds.  These model 
predictions await empirical testing, and this will surely be an area of exciting research in 
the future.   
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 81
List of Figure captions 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3 a.  The major light habitat classes in forests when the sun is not blocked by a 
cloud.  Shaded colors in figure represent the following: Dark grey: light from reflected 
leaves.  Medium-gray: light from blue sky and leaf reflectance.  Light gray checkers: 
light from blue sky and vegetation. Ligh habitats are defined as follows: Forest Shade: 
canopy closed, or with very small or few gaps; all or virtually all incident light is 
either reflected from or transmitted through the vegetation.  Small Gap: skylight from 
a gap in the canopy, essentially no light from the direct sun and less than ~10% of the 
incident light is reflected or transmitted through the vegetation.  Woodland Shade: 
canopy open, a significant fraction of the incident light comes from the sky, but none 
comes directly from the sun.  Large Gap: direct sunlight and open (blue) sky account 
for most of the ambient light. Figure is redrawn from Endler, 1993. 
Figure 3 b.  Relative spectral sensitivities of photoreceptor cells in Norops sagrei.  
Spectral curves represent distinct single cell photoreceptor cone types, whose 
sensitivities are maximal in the following spectral regions, from left to right: UVS, 
SWS, MWS, and LWS.  Norops sagrei possess single- and double- photoreceptor cell 
cone types.  These spectral curves represent single-cell photoreceptors.  The double-
cell photoreceptors are used for achromatic discrimination in birds, and they are 
maximally sensitive in the long wavelengths, but their use in lizards is undescribed.    
For the purposes of this study, I assume they serve achromatic discrimination, as in 
birds, and are maximally sensitive in the long wavelengths.  Thus, I use discrimination 
in LWS cones alone, to model achromatic discrimination by N. sagrei.  Used with 
permission by Leo Fleishman. 
 82
Figures 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
FOREST SHADE SMALL GAP WOODLAND SHADE LARGE GAP
 83
 
0
0.2
0.4
0.6
0.8
1
300 340 380 420 460 500 540 580 620 660
Wavelength, nm
R
e
l
a
t
i
v
e
 ab
s
o
r
b
an
c
e
UVS SWS MWS
LWS
R
e
l
a
t
i
v
e
 ab
s
o
r
b
an
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 84
Tables 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table 2.  Mean and standard error (SE) of male (M) and female (F) Norops sagrei dewlap chromatic  conspicuousness (?S), as viewed against green 
(left) and brown (right) backgrounds, under bright illumination (A; T = 10,000) and dim illumination (B; T= 500 ? see text for explanation). ?S > 1 
represents dewlap color contrast between dewlap regions that is conspicuous to brown anoles.  ** depicts significant sexual differences in male and 
female dewlap conspicuousness, where P < 0.001.  Light habitats are defined as in Endler (1993).  N (males) = 51, N (females) = 22.  
  Green Background    Brown Background     
A Light Habitat F ? S F SE M ? S M SE F P F ? S F SE M ? S M SE F P 
 Forest 0.489 0.091 0.691 0.058 3.498 0.066 0.489 0.091 0.691 0.058 3.498 0.066 
 Woodland  7.156 0.071 7.767 0.046 52.022 <.0001** 4.550 0.081 5.259 0.052 54.876 <.0001** 
 Large Gap  1.618 0.095 1.723 0.061 0.865 0.356 1.620 0.096 1.725 0.061 0.842 0.362 
 Small Gap  4.356 0.084 4.173 0.054 3.367 0.071 1.571 0.091 1.668 0.059 0.807 0.372 
 
  Green Background    Brown Background    
B Light Habitat F ? S F SE M ? S M SE F P F ? S F SE M ? S M SE F P 
 Forest  0.535 0.092 0.703 0.059 2.344 0.130 0.535 0.092 0.703 0.059 2.344 0.130 
 Woodland 5.803 0.048 6.121 0.031 31.344 <.0001** 3.731 0.062 4.378 0.040 77.323 <.0001** 
 Large Gap 0.797 0.041 0.843 0.027 0.894 0.348 1.533 0.096 1.648 0.062 1.004 0.320 
 Small Gap 3.901 0.092 3.811 0.059 0.674 0.414 1.640 0.101 1.756 0.065 0.937 0.336 
 
Table 2 c.  Mean and standard error (SE) of male (M) and female (F) Norops sagrei dewlap brightness conspicuousness (?fD), as viewed against green 
(left) and brown (right) backgrounds.  ?fD > 1 represents dewlap color contrast between dewlap regions that is conspicuous to brown anoles.  ** 
depicts significant sexual differences in male and female dewlap conspicuousness, where P < 0.001.  Light habitats are defined as in Endler (1993).  N 
(males) = 51, N (females) = 22.  
Green Brown 
Light F ? f F M D M F P F F M M F P
Fores 0.06 0.00 - 0.05 0.00 155.69 <.000 0.066 0.00 - 0.0 0.00 155. <.000
Woodlan - 23.63 0.01 - 23.80 0.00 139.97 <.0001 - 22. 0.01 - 22.2 0.00 14 <.0001
Large 0.07 0.06 0.47 0.04 29 48 <.000 0.353 0.03 0.393 0.0 1.12 0.292
Small 0.07 0.06 0.47 0.04 29.48 <.000 0.353 0.03 0.393 0.0 1.12 0.292
 85
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table 2  d - f.  Two-way ANOVA results for effect of background color on three aspects of dewlap conspicuousness.  A = effect of 
background color on brightness of dewlap.  B = effect of background color on chromatic conspicuousness under dim illumination 
(T = 500).  C = effect of background color on chromatic conspicuousness under bright illumination (T = 10,000).  
D Light Habitat Bckgr Mea S.E. Bckgr Mean S.E. F d P
Forest Brown 0.008 0.17 Green 0.008 0.171 8.88 3 <.000
Woodland Brown - 21.684 - 0.1 71 Green - 23.182 - 0.171
Lg Gap Brown 0.373 0.17 Green 0.278 0.171
Small Gap Brown 0.373 0.17 Green 0.278 0.171
E Light Habitat 
Bckgr Mean S.E. Bckgr Mean S.E. F d P
Forest Brown 0.588 0.06 Green 0.588 0.067 245.74 3 <.00 1
Woodland Brown 4.803 0.06 Green 7.301 0.067
Lg Gap Brown 1.670 0.06 Green 1.668 0.067
Small Gap Brown 1.617 0.06 Green 4.263 0.067
F Light Habitat 
Bckgr Mea S.E. Bckgr Mean S.E. F d P
Forest Brown 0.617 0.05 Green 0. 617 0.059 292.43 3 <.0001
Woodland Brown 3.972 0.05 Green 5.832 0.059
Lg Gap Brown 1.589 0.05 Green 0.819 0.059
Small Gap Brown 1.696 0.05 Green 3.866 0.059
 86
CHAPTER 4: UV REFLECTANCE IS NOT USED TO INFLUENCE MALE-
MALE CONTEST OUTCOME IN LAB PAIRS OF NOROPS SAGREI 
Abstract 
Ultraviolet colors are an important visual signal in male-male competition in an 
increasing number of species of lizards.  I investigated the use of UV dewlap color as a 
signal in male-male contests in the Brown Anole, Norops sagrei, by performing UV-vis 
spectrometry on males of the same size, and then observing which one copulated with a 
female made available to both males.  I showed that males with less dewlap UV 
reflectance won contests for females significantly more than males with higher dewlap 
UV in a laboratory environment.  Based on these findings, I experimentally reduced UV 
in males with higher UV from a size-matched dyad, and found that males with artificially 
reduced UV lost contests for females compared to males with natural dewlap UV.  This 
suggests that dewlap UV color is correlated with some trait associated with dominance 
and winning access to females in the laboratory, but that manipulation of dewlap UV is 
not used as a basis of information about status by males in the lab.   
Introduction 
Animals use a diverse array of signals to communicate aspects of their social or 
reproductive status (Andersson, 1994).  Ultraviolet color is an important visual signal in 
butterflies (Ghiradella et al., 1972; Rutowski, 1985; Silberglied and Taylor, 1978), fish 
(Losey et al., 1999), birds (Cuthill et al., 2000) and lizards (Fleishman et al., 1993; 
 87
Stapley and Whiting, 2005; Stapley and Keogh, 2006; Whiting and Stapley, 
2006).  Previous studies investigating UV in fish and birds have focused on its role as a 
signal in female mate choice (Bennett and Cuthill, 1994, Losey et al., 1999).  The extent 
to which UV signals influence male reproductive success through their role in male-male 
contests remains unstudied.  However, signal theory suggests that visual signals should 
convey information used by resident males in assessing the competitive abilities of 
intruding or neighboring males in contests for territorial space and mates (Rohwer, 1975).  
For example, a status badge is a morphological trait (often a color patch) that reliably 
indicates the resource-holding-potential (i.e., fighting ability) of the individual displaying 
the trait, and allows assessment by nearby males.  Ideally, such traits are relatively 
inexpensive to produce but costly to maintain (Rohwer, 1981) because individuals are 
repeatedly tested on their dominance status through fight contests (Rohwer, 1982).   
Male-male rivalry is frequently found to be an important component to lizard 
mating systems, and most of the color patches studied in lizards appear to conform to 
definitions of status badges (Cooper and Greenberg, 1992).  In one example, UV has 
been shown to be linked to fighting ability, and acts as a status badge in Platysaurus 
broadleyi (Whiting et al., 2006).  In this species males assess their opponent?s UV 
reflectance, and asymmetries in amount of UV between males influence contest 
escalation (Stapley and Whiting, 2005; Whiting et al., 2006).  Males that were rich in UV 
were better fighters than males poor in UV.  Moreover, males that have UV reduced were 
contested more frequently than males that had natural UV colors.   
UV has been found to be a frequent component to dewlap color in many 
Caribbean anoles (Fleishman et al., 1993; Fleishman et al., 1997).  Dewlap UV varies 
 88
geographically in different groups of Anolis in ways that are habitat specific (Macedonia 
et al., 2000; Leal and Fleishman, 2002, 2004; Thorpe and Stenson, 2003).  For example, 
dewlap UV of four allopatric populations of Anolis cristatellus correlates positively with 
the UV light environment in a way that suggests that population abundance is highest in 
areas where dewlap color is most conspicuous (Leal and Fleishman, 2004).  This pattern 
is consistent with predictions of sensory drive, namely that signal diversity evolves 
species or populations come to occupy different habitat conditions where selection for 
effective communication promotes divergence in signal designs (Leal and Fleishman, 
2004).   These findings further support the hypothesis that dewlap UV reflectance is an 
important social signal. 
While several studies have focused on the role of dewlap extension in social 
communication of anoles (Crews, 1975; Evans, 1938 a & b; Greenberg and Noble, 1944; 
Leal, 1999; Tokarz, 2002; Tokarz et al., 2003; Williams and Rand, 1977), few studies 
have attempted to determine the role that dewlap color plays in social signaling.  Adult 
males from two species of sympatric sibling species on Hispaniola recognize species-
specific differences in dewlap color (Losos, 1985).  This experiment provides evidence 
for dewlap color serving a role in species recognition.   
The Brown Anole (Norops sagrei) is a small anoline lizard from Cuba, Jamaica 
and other Caribbean islands (Schwartz and Henderson, 1991) that is highly territorial and 
reaches extremely high population densities (Schoener and Shoener, 1978; Schoener, 
1980).  In nature, populations of anoles (including N. sagrei) exhibit sex-specific 
demographic differences, such that females aggregate around areas with high food 
abundance, and males aggregate in areas where females can be found (Schoener, 1980; 
 89
Guyer, 1988a).  This demographic pattern creates dynamic neighborhoods in anoles 
(Stamps, 1994, Stamps and Krishnan, 1997).  In these neighborhoods, males frequently 
engage in visual and physical contests for access to territorial space that includes access 
to one or more females, and this results in a few, large (old) males that appear to achieve 
dominance, and enjoy access to females and food (Stamps and Krishnan, 1994).    
Several lines of evidence suggest that dewlap color may serve a social role in N. 
sagrei.  UV color has been found to be sexually dichromatic in Brown Anoles, and 
correlates with body condition (Steffen and McGraw, in prep).  Moreover, UV of the 
Brown Anole dewlap is at least partially the result of xanthophyll (i.e., carotenoid) 
pigmentation (Steffen and McGraw, in prep).  Carotenoids have been implicated in their 
role as condition-dependent pigments in many animals, and results of nutritional stress 
experiments suggest that UV amplitude might indicate nutritional condition in N. sagrei 
dewlaps (Steffen and McGraw, in prep).  
Here I examine whether dewlap color plays a role in determining contest 
outcomes by investigating pair-wise differences in natural dewlap color among dyads of 
size-matched males.  I then investigate whether or not contest participants use UV color 
to convey information about dominance status by experimentally reducing UV in 
normally UV-bright males.  I discuss these outcomes with respect to male-male contests.     
Methods 
Lizard Collection and Care 
Lizards were collected from two sources. In 2005 and 2006, individuals were 
purchased from Glades Herp (Lake Thonotosassa, Hillsboro County, and Lake 
Withlacoochee, Marion County).  In 2007, lizards were collected from Lake George, 
 90
Marion County, Florida.  Data from the three populations were analyzed separately, 
although this site effect was confounded by the fact that each site was collected in a 
different year.  Collection sites are all within 72 miles of each other.   
In all years, all lizards were immediately identified as to sex, weighed (nearest 
0.001 g) and measured snout to vent (SVL; nearest mm) upon arrival at Auburn. They 
were then assigned a unique toe-clip.  After one day in captivity, the dewlaps of all male 
lizards were measured with an Ocean Optics S2000 UV-visible spectrometer following 
the methods for midline and lateral regions described in Chapter 2.  I also used all 
colorimetric variables (hue, brightness and chroma) related to UV, Blue, Green, and Red 
wavebands, as well as UV amplitude, as described in Chapter 2.   
Males were size-matched to another male that differed by no more than 0.5 mm in 
SVL but that differed naturally in dewlap UV brightness  Pairs of males were housed in 
37.90 liter terraria that were partitioned with particle boards into three compartments. The 
largest compartment (25.40 x 30.48 cm) represented half of the terrarium divided along 
its width. The other half was further divided into two small compartments (25.40 x 15.24 
cm) by a partition along the long axis of the aquarium. Separate males were placed into 
the separate small compartments. One female was placed in the large compartment of the 
terrarium.  The outside walls of the terraria were lined with green construction paper to 
facilitate visual detection of male dewlap colors (Endler, 1992).   The partition between 
males prevented them from seeing each other until an experimental trial was begun.  
Each compartment contained its own perch and water dish (filled with water 3 times per 
week).  Lighting strips containing full spectrum fluorescent tubes (Vitalite T8, 32 watt) 
were suspended 30.48 cm above the terrarium tops and all terraria were exposed to 
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natural light via a large window.  Lizards were sprayed with water daily, fed crickets 
three times a week (3 per feeding) and meal worms ad libitum.  All food items were 
dusted with repta-vite (Zoo Med laboratories, San Luis Obispo, CA) before being offered 
to a lizard.  Lizards were allowed to acclimate to a terrarium for a minimum of one week 
before experiment manipulations were performed.  Laboratory was maintained at 32.2 
?C, and 60% relative humidity. 
I performed natural color experiments during summers 2005 and 2007, and UV 
reduction experiments during the summer of 2006.  Lizards were never used in trials 
more than once.   
Natural experiments 
 Natural dewlap color trials were performed from May 1 -July 1, in 2005 and May 
1 ? June 15, in 2007.  At the beginning of each experimental trial the partitions in the 
terraria were removed to expose the size-matched males and the female to each other.  I 
then left the room and recorded all behaviors on an 8mm video camera.  All trials were 
allowed to run for 1 hour.   
From the video recordings all copulations were noted, and the identities of 
successful and unsuccessful individual males were noted.  Trial winners were easily 
identified because females never mated with more than one male in these trials.  The 
colormetric variables of each male contestant were placed in a file that contained each 
individual?s contest status (won copulation or lost copulation). To determine if color 
differed between the two contest outcome groups, pair-wise T-tests  were performed 
between the dependent variable, which were separate colorimetric / waveband 
combinations (i.e., UV chroma, Blue chroma, UV brightness, Blue brightness) and 
 92
contest outcome (won copulation / lost copulation) as the independent variable.  To 
reduce the probability of type I error (i.e., rejecting the null hypothesis when the null 
hypothesis is true) that arises from multiple comparisons, Bonferroni corrections were 
performed to the entire set of variables and only those that were significant after 
Bonferroni correction are reported.        
UV reduction experiment 
UV reduction trials were performed July 1 ? August 1, in 2006.  For these 
experiments I quantified the spectral variation of dewlaps as in natural experiments but 
noted which member of a size-matched dyad had higher UV reflectance. The lizards were 
placed into the partitioned terraria as described above, and acclimated with food and 
water for one week.  One hour before the beginning of each experimental trial, I selected 
the male from the pair that had higher UV reflectance, and I applied NOAD sunscreen 
(spf 30) to his dewlap.  This effectively reduced UV chroma in both dewlap regions, and 
UV reflectance in the midline dewlap region (Table 4).   The lizard with the lower UV 
chroma received a control treatment of water rubbed onto the open and closed dewlap.    
Lizards were returned to their respective compartments for one hour before beginning an 
experiment trial by removal of the partitions.    
Statistics 
Pair-wise t-tests of natural color variables between size-matched males were 
performed using SPSS statistical software (v. 9.1).  2-way ANOVAs were performed to 
investigate if some natural color waveband/colormetric combination (i.e., UV 
reflectance) varied with respect to year and copulation status, or as an interaction between 
year and copulation status.  Log-linear analysis was performed to determine if there was a 
 93
significant relationship between experimental treatments (sunscreen and water) and 
contest outcome.  JMP statistics was used to perform all statistics and alpha was set at 
0.05.   
Results  
Natural color contests 
 Males that copulated with females, had lower dewlap UV reflectance than 
unsuccessful males (Figure 4 a, pairwise t-test: t = -2.494, N = 24, P = 0.019, after 
Bonferrroni correction).  Unsuccessful males were an average of 13 % more UV 
reflectant than their successful rivals.   
UV-reduced experimental contests 
  Log linear analysis showed that individuals with reduced UV did not copulate 
with females significantly more than individuals with natural (and hence higher) UV 
reflectance (Figure 4 b, Chi-square likelihood ratio = 4.186, N= 8, P = 0.0408).  Out of 8 
UV reduction trials, lizards with sunscreen-treated dewlaps won contests for females 75% 
of the time.  
Discussion 
Because male and female anoline dewlaps differ in color (in human visible and 
invisible ranges), and because these dewlaps are displayed to conspecific males and 
females in social interactions, it has long been speculated that they serve a role in sexual 
selection, especially as a signal in male-male contests (Greenberg and Noble, 1944; 
Noble and Bradley, 1933; Evans, 1938 a & b; Crews, 1975).  My data demonstrate that, 
in male-male contests for access to females, male N. sagrei that win contests and copulate 
with females have dewlaps that reflect less UV (and have lower UV amplitude) than 
 94
males that lose contests, and these results suggested that UV could serve as a status badge 
in N. sagrei.   
In signals that serve as status badges, colors are hypothesized to be cheap to 
produce but expensive to maintain. Therefore, badge holders are constantly being tested 
through male-male disputes. Because production costs are cheap, both dominant and 
subordinate males can obtain sufficient amounts to be equally colorful, and the color that 
becomes associated with a dominant status relative to the status of a subordinate 
individual can be arbitrary.  Thus, according to this definition, it remains possible that 
less colorful males are dominant to more colorful males, as long as the information 
behind the signal is reliable (i.e., that you are dominant and willing to fight to prove it), 
and that the information is repeatedly tested (Rohwer, 1977; Rohwer, 1978). 
Interestingly, in the house finch (Carpodacus mexicanus), females prefer to mate with 
males with more colorful plumage (Hill, 1990), but drab males appear to be more 
dominant, at least during the breeding season (McGraw and Hill, 2000 a & b).  My data 
document a similar trend in anoles. 
To further explore the role of UV as a status badge, I decreased UV reflectance in 
naturally UV-bright males to see if a contest loser could become a winner via color alone.  
However, males with artificially reduced UV lost contests more frequently than did males 
with natural color. Thus, while there appears to be a consistent pattern of coloration that 
associates with dominance in natural color trials, it appears that altering it does not 
change the direction of the outcome.  That is, artificially reduced UV males (which are 
naturally brighter in UV) are still subordinate, despite altering them to look like dominant 
males.     
 95
 My results beg the question ?in naturally colored populations, why are winners 
less colorful than losers in N. sagrei??  One possible explanation emerges from the fact 
that testosterone negatively influences carotenoid-based integumentary color in other 
vertebrates.  In many vertebrates, aggressiveness is controlled largely by testosterone 
(Wingfield et al., 1987; Wingfield and Moore, 1987), a hormone that influences social 
contests for dominance (Wingfield et al., 1987).  Not surprisingly, testosterone has been 
shown to vary seasonally in male N. sagrei, and correlates with breeding season behavior 
[March-August, (Tokarz et al., 1998)].  Testosterone alters male contest behavior (e.g. 
increases dewlap extension frequency, Tokarz et al., 2002), as well as increases a male?s 
ability to acquire high social status (Tokarz, 1995).     
 Testosterone directly affects carotenoid-based integument color in the house finch 
(Stoehr and Hill, 2001).  In an experiment in which males were implanted with 
testosterone early or late in the breeding season, or left unmanipulated, unaltered males 
experienced minimum change in plumage color.  Males implanted with testosterone early 
in the breeding season metabolized the hormone before moult, and similarly showed 
minimum effect on plumage color change.  Males implanted with testosterone late in the 
spring, however, delayed moult timing and grew drab feathers.  This suggests that 
testosterone might effect plumage color directly (by delaying the moult past the time 
when carotenoids are abundant (see Nolan et al., 1992 ), or indirectly (by affecting the 
ability of males to utilize carotenoids indirectly via increases in parasite numbers that 
result from the immunosupressing effect of testosterone (Thompson et al., 1997; Brawner 
et al., 2000).  It is possible that testosterone affects the ability of males to utilize 
carotenoids via immunosupressive effect of testosterone in lizards. 
 96
Testosterone spikes, and not seasonal fluctuations in hormone levels, have been 
shown to be responsible for contest aggressiveness in vertebrates (Moore et al., 2007).  
UV color may change quickly in the Brown Anole based on xanthophyll carotenoid 
access (Steffen, in prep), and may be influenced by testosterone spikes at times of 
carotenoid acquisition (Moore et al., 2007).  Thus, in light of the un-manipulated as well 
as experimental dewlap color findings from this lab study, it seems plausible that UV 
serves a communicative role in natural settings, and may also serve as a signal indicating 
male testosterone levels.  These ideas await further investigation, and may be an exciting 
area of research full of new discoveries. 
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Tables 
 
 
 
 
 
 
 
 
 
 
 
Regio PW Mn SE Mn SE t d P
La UV 0.09 0.02 0.04 0.01 2.55 5 0.0
Mi UV 0.15 0.02 0.02 0.00 4.17 5 0.00
Mi UVV 0.18 0.02 0.03 0.01 6.51 5 0.00
Mi UV 1571.1 314.0 132.0 51.83 4.17 5 0.00
Table 4.  Sunscreen effectively reduces spectra in the UV wavelengths.  Lateral 
dewlap region required no Bonferroni correction, and P of significance for the 
midline dewlap region (after Bonferroni correction) was P = 0.01.  Ctrl = dewlap 
color before application of sunscreen.  SS = dewlap color after sunscreen 
application. 
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Figure Legends 
 
 
Figure 4 a. Significant pairwise difference in UV brightness and contest outcome in the 
midline dewlap region of Norops sagrei, after Bonferroni correction.  Trials from 2005 
and 2007 combined, t = -2.494, df = 24, P = 0.019.  
 
Figure 4 b. Significant difference in contest win percentage by experimental group (water 
as control, sunscreen as treatment) in male Norops sagrei.  Likelihood Ratio Test, Chi-
square value = 4.186, N= 8, P = 0.0408. 
 
 
 
 
 
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CHAPTER 5: EFFECTS OF NUTRITIONAL STRESS AND CAROTENOID 
ACCESS ON THE DEWLAP COLOR OF MALE                                                  
BROWN ANOLES, Norops sagrei 
Abstract 
Anolis lizard dewlaps are well known for exhibiting a diversity of colors, many of 
which strongly reflect in the UV spectral wavelengths.  These lizards are also well known 
for using their dewlaps as visual displays in intra- and intersexual interactions.  In 
previous studies, UV reflectance of the dewlap of Norops sagrei was found to correlate 
with body condition and male-male contest success.  Here I perform a two-factor, 
repeated-measures experiment to determine the effects of access to xanthophyll, a dietary 
carotenoid, and food provisioning rate, on dewlap color in the Brown Anole (Norops 
sagrei). Using this design, I test the hypotheses that dewlap color is dependent on access 
to xanthophyll and signals male condition in anoles.  Lizards fed a diet enhanced with 
xanthophylls had greater UV chroma on the lateral dewlap region and increased long-
wavelength chroma on the midline dewlap region than lizards without access to 
xanthophylls.  I also found that dewlap color of lizards with reduced provisioning rate, 
and reduced access to xanthophylls, had reduced UV amplitude. The colors that change 
due to access to xanthophylls are the same as those that determine male-male contest 
success in Norops sagrei.   These findings have implications for understanding dewlap 
signal content within and among species of anoles. 
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Introduction 
Carotenoid-based integumentary colors are well-known examples of an 
environmentally-determined class of ornaments that often serve in visual displays as 
signals of mate quality (Searcy and Nowicki, 2005).  For example, xanthophylls, a 
common carotenoid pigment class found in feathers, are known to produce UV and 
yellow spectral variation in the American Goldfinch (Carduelis tristis) by absorbing in 
the blue region of reflectance in an otherwise white feather (Shawkey and Hill, 2005; 
Shawkey et al., 2006).  Because no vertebrate can endogenously synthesize carotenoids, 
these chemicals must be ingested to be used as pigments in a visual display (Brush, 1978; 
Endler, 1980; Goodwin, 1984, Kodric-Brown, 1985; Hill, 1990; Endler, 1980).  
Carotenoids are important as indicator traits, because they have a high energetic cost to 
their obtainment and subsequent  metabolism compared to other ornamental pigments 
(Stradi, 1996; Stradi, 1995; Stradi, 1997, Hill, 2002).  Furthermore, parasites affect the 
expression of carotenoids.  For example, ectoparasites can inhibit integumentary 
expression of carotenoids in guppies (Houde and Torio, 1992), intestinal parasites can 
affect carotenoid ingestion and color displays in domestic chickens (Ruff et al., 1974) and 
sticklebacks (Milinski and Bakker, 1990).  Apicomplexan parasites (e.g., coccidia) can 
affect plumage coloration of house finches (Thompson et al., 1997; Brawner et al., 2000), 
and hemoparasites can reduce color expression in great tits (Horak et al., 2001).     
Carotenoids also have been speculated to represent a trade-off between immuno-
enhancement and ornament expression (Lozano, 1994a).  Carotenoids can act as free-
radical scavengers and, therefore, are potentially beneficial to an individual?s health (Di 
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Mascio et al., 1991; Diplock, 1991; Bendich, 1993; Olson, 1993; McGraw, 2005).  
However, carotenoids that are placed in the integument cannot be used for reducing 
oxidative stress (Von Schantz et al., 1999).  The logic of this trade-off hypothesis comes 
from the fact that carotenoids are a limited resource and are needed both for proper 
immune function and to create ornamental displays.  This puts carotenoid use for 
ornamentation in direct competition with use in maintaining health.  However, this is a 
matter of controversy (Hill, 1999; Lozano, 2001).  Despite the controversy surrounding 
the trade-off hypothesis, a great deal of evidence shows that carotenoids are used in 
ornamental displays as visual signals which communicate information to signal receivers. 
Despite mounting evidence of a role for carotenoids in sexual selection in many 
animals, squamates that use carotenoids for display might also use these pigments to 
facilitate species recognition (Wallace, 1889), and therefore, carotenoids might play a 
role in natural selection (Losos, 1985; Sigmund, 1983; Macedonia et al., 1994) within 
this diverse group.  In particular, anoline lizards belong to a species-rich genus, 
comprised of 380 recognized species (Nicholson, 2002), and are becoming recognized as 
a classic example of a group that has undergone adaptive radiation (Schluter, 2000).  
Most anoles are highly territorial (Stamps, 1983), and possess an enlarged throat fan, 
known as a dewlap, that is used as a social signal in intrasexual and intersexual 
interactions (Jenssen, 1977).  Dewlap spectra vary widely among species (Williams and 
Rand, 1977; Fitch and Hillis, 1984), and show a wide variety of patterns in which yellow 
is the most frequent color (Nicholson et al., 2007).  Interestingly, analyses of dewlap 
pigments have revealed that xanthophylls are a major contributor to yellow dewlap color 
 123
in Jamaican and Puerto Rican anoles (Macedonia et al., 2000), as well as one Cuban and 
one Central American anole (Steffen and McGraw, 2007).   
Yellow carotenoid-based colors are often correlated inversely with blue, but 
positively with ultra-violet reflectance because carotenoids function by strongly 
absorbing light from the blue wavelengths of the radiant spectrum (Bauernfiend, 1981) ? 
essentially they function like semi-transparent filters in feathers, which are structurally 
white in color (Shawkey and Hill, 2005).  The precise proximate cause to UV reflectance 
in vertebrate integument (including birds) is unknown.  In birds with carotenoid-based 
yellow colors, the pigments may interact with white feather microstructure in ways that 
create unexpected optical phenomenona, including UV chroma (Shawkey et al., 2006).  
Interestingly, they found that in the American Goldfinch (Carduelis tristis), UV color 
variation was only indirectly related to carotenoid concentration, in the context of the 
change in shape of the ?peak-trough-plateau? curve, typical of carotenoid-pigmented 
feathers (Shawkey and Hill, 2005; MacDougall and Montgomerie, 2003).   
UV is an important component to spectral variation in the dewlap of Puerto Rican 
anoles in that the degree to which UV is expressed is related to microhabitat-level 
differences in light availability (Fleishman et al., 1993; Fleishman et al., 1997).  In 
addition, color in anole dewlaps varies geographically in Anolis carolinensis (Macedonia 
et al., 2003), as well as in Anolis trinitatus (Thorpe, 2002).  Finally, dewlap UV of four 
allopatric populations of Anolis cristatellus correlates positively with the UV light 
environment in a way that suggests that population abundance is highest in areas where 
dewlap color is most conspicuous (Leal and Fleishman, 2004).  This pattern is consistent 
with predictions of sensory drive, namely that signal diversity evolves species or 
 124
populations come to occupy different habitat conditions where selection for effective 
communication promotes divergence in signal designs (Leal and Fleishman, 2004).   
Given the findings of Shawkey and Hill (2005), it seems likely that xanthophylls 
are at least partly responsible for the UV spectral variation in anoles.  Recent research by 
Steffen and McGraw (Chapter 2) shows that the lateral (red) portion of a dewlap in 
Norops sagrei is colored by a combination of xanthophylls and pterins (drosopterin), 
while the midline (yellow) region is colored predominantly by xanthophylls and has a 
strong UV component (Steffen and McGraw, Chapter 2).  Additionally, UV plays a role 
in allowing N. sagrei dewlaps to be visible against some background environments and 
not others (Steffen and Sieffermen in prep).  Finally, UV plays a role in determining 
which males wins contests for access to females in a lab setting (Steffen in prep).   
The manner in which anoles color their dewlaps, including UV, has not been 
studied.  Surprisingly, no study has traced the origin of carotenoids in dewlaps, despite 
the fact that scientists have recognized their presence in dewlaps for several years 
(Macedonia et al., 2000). In this paper I test the hypothesis that expression of dewlap 
color in adult male N. sagrei is dependent on access to dietary carotenoids, and examine 
whether expression of these colors is affected by nutritional condition.   
Methods 
Individual adult male lizards were collected on April 5
th
, 2007, from a forested 
dock on the east side of Lake George, Marion County, Florida.  Upon return to Auburn, 
Alabama two days later, lizards were assigned a unique toe-clip identity (no more than 
two toes clipped per individual), and were placed into 37.90 liter terraria, each of which 
was separated into four compartments so that lizards could be placed singly into a 
 125
compartment. Compartment walls were constructed from solid particle board which 
prevented lizards from seeing or physically contacting other individuals.  Each 
compartment contained a perch, water dish, and sandy substrate.  Lighting strips 
containing full spectrum fluorescent tubes (Vitalite T8, 32 watt) were suspended 30.48 
cm above each terrarium top.  Terraria, and the lizards in them, were exposed to natural 
light via sunlight that entered the holding room through a large window.  Water was 
sprayed into each terrarium daily, and water bowls were refilled three times per week.  
The room was maintained on a 14:10 hr photoperiod, at an air temperature of 32.2 ?C, 
with relative humidity ranging between 60-80%.   
Lizards were housed for a one week, pre-trial period, during which they were fed 
meal worms and crickets ad libitum.  At the beginning of the experiment, lizards were 
placed into one of four treatments: 1) high provision rate with carotenoid 
supplementation (see below), 2) reduced provision rate (see below) with carotenoid 
supplementation, 3) high provision rate with no carotenoid supplementation (see below), 
and 4) reduced provision rate with no carotenoid supplementation.   
Feeding level, one main effect in the experimental design, consisted of high and 
low provision-rate treatments. The high provision-rate group received 3 crickets per 
feeding repeated 3 times per week.  The reduced provision rate involved three crickets 
per feeding, once per week.  All crickets for all treatments were 3-weeks old (Golden 
Crickets, Alabama; raised on a protein-rich diet that lacked carotenoids) and were 
maintained on a diet of dog food (lamb, rice, oat and corn-based meal, supplemented with 
vitamins, including A) to eliminate the possibility that lizards obtained xanthophylls from 
the crickets.   
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Carotenoid access was the second main effect in the experimental design, and 
consisted of a carotenoid supplement treatment and a control treatment.  For the 
carotenoid treatment, I supplemented lizards with a xanthophyll carotenoid solution 
described in Navara and Hill (2003).  This solution was composed of 0.28 g of powdered 
lutein (5% tg/p) and 0.12 g of powdered zeaxanthin (5% cws/s-tg) dissolved in 3.79 liters 
of tap water.  The solution was shaken vigorously for two minutes. The solution was 
stored in a refrigerator where it was kept cool and protected from exposure to light.  
Carotenoids were donated by DSM, Nutritional Products, Parsippany, N.J.  Lizards were 
fed 2 ml of this carotenoid solution via a 10 ml syringe.  The blunt tip of a needle-less 
syringe was placed into a lizard?s gaping mouth, and the syringe plunger was slowly 
depressed so that the lizard ingested the solution.  For the control solution, a separate 
syringe was used to deliver water to lizards in an identical manner.   
Lizards were weighed to the nearest 0.001 gram at the beginning and end of the 
experiment using an electronic balance.  I weighed lizards three days after the last meal to 
minimize the possibility that weights reflected full stomachs instead of body mass. These 
measurements were used to document that the high and reduced food treatments 
represented reasonable extremes. 
Color of the lateral and midline dewlap regions (Chapter 2) was measured with an 
Ocean Optics S2000 UV-visible spectrometer.  Measurements were taken once per week, 
for 11 weeks (April 24, 2007 ? July 17, 2007).  Repeated measures of spectrometry data 
have notoriously high variance because the intensity of the light beam is sensitive to 
minute changes in electrical current (OOIbase lab manual).  Furthermore, the shape of a 
spectral curve is strongly dependent on probe positioning and ambient light (Fleishman et 
 127
al., 2006, Montgomerie, 2006).  Therefore, to minimize differences in electrical current 
associated with time of day, I took measurements consistently at 10:00 A.M.  To 
minimize geometric issues, I placed each lizard ventral side up on a flat black table and 
immobilized them with two pieces of athletic tape placed across their belly and nose.  To 
obtain spectrometry measurements on the midline dewlap region I placed the 
spectrometer probe at a 90? angle to the dewlap skin.  I visually inspected the probe to 
insure that it was placed flush against the dewlap skin and waited for a stable curve to 
appear on the screen before saving the spectral measurement as a spectral file.  To 
measure the lateral dewlap region I used blunt forceps to pull the dewlap away from the 
body, and I fastened the dewlap margin with a small blunt clamp suspended on a string 
through the opening of a threaded eye screw. This allowed me to adjust the height and 
tension of the clamp by turning the threaded eye screw until the string holding the clamp 
was taut, and the dewlap appeared to be maximally extended.  I then placed the 
spectrometer probe at a 90? angle to the extended skin of the dewlap.  To prevent the 
probe from differing in height among consecutive measurements, I placed a small black 
plastic stopper on the tip of the reflectance probe, so that there was a 2mm distance 
between the probe tip and the tissue being measured.  I took three spectral measurements 
per region for each lizard, and the data analyzed here represent the mean of the three 
spectral measurements per dewlap region.   
Spectral transmission files were processed using a program by Robert 
Montgomerie (?2002 used with permission).  This program is a series of Visual Basic 
macros that record each measurement as a series of readings representing the relative 
percent reflectance for each nanometer of wavelength reflected.  This program also 
 128
summarizes each spectral curve according to hue, brightness, and chroma.  Total 
brightness was defined as the sum of reflectance for values between 300 nm and 700 nm 
(Andersson and Prager, 2006).  Mean brightness was ? 
300
700 
Ri / n
w
, where
 
Ri refers to 
the sum of reflectance from 300-700 nm for an i, individual, and
  
n
w
 refers to the number 
of specified ranges being measured.  Chroma was defined as ?
?b
?a
 Ri/Bi, where a and b 
define the outer limits of some specified bandwidth range, and Bi is the total brightness 
defined above.   
I gathered data on brightness and chroma for UV, blue, green, and red using the 
output provided by the Montgomerie processing program.  UV described the portion of 
the spectral bandwidth ranging from 300 to 400 nm, blue spectra ranged from 400 to 512 
nm, green spectra ranged from 512 to 575 nm, and red spectra ranged from 575 to 700 
nm. The red spectral region captured wavelengths appropriate for dewlap carotenoids 
(Steffen and McGraw, in prep). Thus, although xanthophyll carotenoids are known to 
produce yellow colors, no separation of yellow spectra was necessary.  However, I used 
UV amplitude, a measurement that was not provided by the Montgomerie processing 
program, because this variable is important in describing spectral curves derived from 
xanthophyll carotenoids (MacDougall and Montgomerie, 2003).  Xanthophylls create 
yellow and UV spectral peaks by absorbing maximally in the blue region.  Lutein, 
thought to be a major xanthophyll in the dewlap of the Brown Anole (Macedonia et al., 
2000, Steffen and McGraw, 2007), absorbs maximally at 450 nm (Andersson and Prager 
2006).  Therefore, I defined UV amplitude as the difference between short-wave 
reflectance minima (435-500 nm) and very short-wave reflectance maxima (UV, 320-435 
nm).  By this definition, UV amplitude values have a negative sign. 
 129
I first performed two-way ANOVA?s to investigate effects of feeding level (high 
provision rate vs reduced provision rate) and carotenoid access (xanthophyll 
supplementation vs water) on mass loss. I then performed a two-way, repeated measures 
ANOVA to investigate potential change in dewlap color over time within individuals, 
and between main effects (food provisioning level and carotenoid access).  I used this 
statistical tool rather than MANOVA repeated measures because it is recommended for 
research designs that contain a small sample size and violate assumptions of sphericity 
(Tabachnik and Fidell, 2001).  All analyses were performed in SAS (SAS Institute, 2006) 
with a two-tailed alpha set at 0.05.  
Results 
 There was a significant main effect of feeding level on mass loss in lizards during 
the course of this study (F = 8.56, df = 1, N = 32, P = 0.007), indicating that the reduced 
feeding rate used for this experiment was an effective form of nutritional stress.  Lizards 
that were fed once per week lost an average of 1.22 g. of mass, from beginning to end of 
the study, while lizards that were fed 3 times per week gained 0.035 grams of mass 
(Figure 5 a).  There was no significant main effect of carotenoid access on mass loss (F = 
0.178, df = 1, N = 32, P = 0.6773), and there was no significant interaction between 
feeding level and carotenoid access (F = 0.0169, df = 1, N = 32, P = 0.8978).   
Feeding level showed a nearly significant main effect on UV amplitude in the 
lateral dewlap region (Figure 5 b; F = 3.23, df = 1, N = 32, P = 0.083).  Lizards in the 
high provision rate groups had greater negative UV amplitude (Mean = -1.584, S.E. = 
0.151, N = 16) than lizards in the reduced food provision rate groups (Mean = -1.000, 
S.E. = 0.215, N = 16, F = 3.2, df = 1, P = 0.083).  There was no main effect of carotenoid 
 130
access on UV amplitude (F = 0.87, df = 1, N= 32, P = 0.36), and there was no interaction 
between feeding level and carotenoid access (F = 0.66, df = 1, N = 32, P = 0.433).     
 Carotenoid access had a significant effect on UV chroma in the lateral dewlap 
region (Figure 5 c; F = 5.89, df = 1, N = 32, P = 0.022).  Male lizards from the carotenoid 
supplementation group had significantly higher UV chroma (mean = 0.113, S.E. = 0.006, 
N = 16) than lizards from the control group (mean = 0.086, S.E. = 0.004, N = 16).  There 
was no main effect of feeding level on UV chroma (F = 0.16, df = 1, N = 32, P = 0.17), 
and there was no significant interaction between feeding level and carotenoid access (F = 
0.62, df = 1, N = 32, P = 0.439).   
 Carotenoid access also had a significant effect on red chroma of the midline 
dewlap region (Figure 5 d; F = 89.15, df 1, N= 32, P < 0.0001).  Lizards in the carotenoid 
supplementation treatment groups had higher levels of red chroma (mean = 0.447, SE = 
0.004, N = 16) while lizards in the control group had lower levels (mean = 0.444, S.E. = 
0.006, N = 16).  There was no main effect of feeding level on red chroma (F = 0.06, df = 
1, N = 32, P = 0.815), and no significant interaction between feeding level and carotenoid 
access (F = 0.08, df = 1, N = 32, P = 0.776).  
Discussion 
In previous studies I have demonstrated that male Norops sagrei differ in the 
degree to which UV reflectance is expressed in their dewlaps (Steffen and McGraw in 
prep), that the intensity of UV reflectance plays a role in how dewlap signals are 
perceived in various habitats (Steffen and Siefferman in prep), and that males with 
dewlaps that reflect more weakly in UV wavelengths win contests more often than males 
with dewlaps that have stronger UV reflectance (Steffen, in prep).  In this study, I now 
 131
have demonstrated that UV reflectance depends on dietary access to xanthophyll 
carotenoids.  These findings solidify provide evidence that carotenoid-based dewlap 
color, especially the yellow midline region, is a condition-dependent trait in Norops 
sagrei.  In this regard, N. sagrei possesses features of color that mirror sexually-selected 
color variation in House Finches.  Red plumage coloration in male House Finches is 
maintained by a female preference for bright red plumage (Hill, 1990) created in part by 
dietary access to carotenoids (Hill, 2002; Hill et al., 1994).  Interestingly, males with drab 
yellow plumage to be dominant in agonistic interactions surrounding food sources 
surrounding perches (McGraw and Hill, 2000 a, b).  Unlike carotenoid colors in the 
dewlaps of N. sagrei, carotenoids used to pigment feathers of male and female house 
finches do not yield a strong UV component to color.  There is some reason to expect that 
female choice influences male reproductive success in the Brown Anole, however, 
because female home ranges overlap with multiple males home ranges, and females often 
copulate with more than one male during the reproductive season (Tokarz et al., 1998).  
One anole (Anolis carolinensis) has special sperm storage organs, which may allow for 
some pattern of differential sperm allocation for egg fertilization (Fox, 1963).  I have not 
yet tested for preferences of female N. sagrei, but all other aspects of color conform to 
the House Finch model.   
Access to lutein and zeaxanthin alters UV dewlap color in adult male N. sagrei, 
and it seems likely that this alteration is created by increased absorption of blue 
wavelengths in lizards that ingest greater quantities of xanthophylls, as happens in bird 
feathers (MacDougall and Montgomerie, 2003).   This effect in dewlaps of male N. 
sagrei causes a particularly striking decrease in UV amplitude in individuals with access 
 132
to xanthophylls and yields stronger reflectance in the yellow wavelengths in lizards 
consuming xanthophylls.  Previous research shows that UV color correlates positively 
with body condition (Chapter 2), and the results in the present paper add to evidence that 
carotenoid-based dewlap color may be used as a condition-dependent signal in social 
interactions.   
In nature, anoles appear to have access to xanthophylls via two sources.  Lutein 
and zeaxanthin are abundant in leaves of all plants.  Additionally, phytophagous insects 
assimilate these chemicals from plant matter.  Schoener (1968) presented a dietary 
analysis of male and female N. sagrei from the Bahamanian island of Bimini.   Stomachs 
of males contained a significant volume of leaves.  In adult males and females, 
lepidopteran larvae (which have a well-documented herbivorous life stage which 
sequesters carotenoids, see Czeczuga, 1986, 1990; Mummery, 1975; Rothschild and 
Mummery, 1985; Rothschild et al., 1986) constituted the greatest volumetric dietary item.  
Thus, both direct ingestion of plant material and indirect uptake through consumption of 
xanthophyll containing phytophagous insects seem a likely of xanthophylls in N. sagrei 
and likely for other anolines.  
These results also demonstrate that dewlap UV can be increased quickly upon 
ingestion of xanthophylls.  These experiments were run for 11 weeks, and significant 
increases in UV amplitude, UV chroma, and red chroma appeared after only two weeks.  
A typical breeding season for Brown Anoles in south Florida lasts for approximately 5 
months (Tokarz et al., 1998).  This rapid change in dewlap UV reflectance may be 
meaningful to an individual male who is attempting to send signals to receivers in order 
to alter its social status.  Furthermore, carotenoid availability may vary geographically 
 133
and differ among nearby forest locales because of differences in plant community 
composition, which may therefore influence breeding structure.  If there is a high density 
of carotenoid-rich insects in a particular area, and females aggregate in these areas, then 
males might follow females to areas where they will turn bright, and pay a higher 
defensive cost compared to males from carotenoid-poor environments.   
In Puerto Rico, two populations of Anolis cristatellus differ in habitat-based 
signal detectability (Leal and Fleishman, 2004).  In xeric populations, dewlaps tend to be 
darker than dewlaps from mesic habitats.  Furthermore, dewlap detection decreased 
significantly when a dewlap from a xeric habitat is detected under the spectral conditions 
of a mesic habitat, and visa versa.  The major spectral difference in dewlap design 
between habitats was in total reflectance, but UV comprised a significant portion of this 
variation, and also differed between dewlaps from the different habitats.  Thus, based on 
my findings, the differences in UV that contribute to habitat-specific differences in 
dewlap detectability may be proximately caused by habitat differences in carotenoid 
availabity.   
Food availability has been shown to have an important influence on demography 
of at least one Caribbean, as well as two mainland anoles.  Growth rates of juvenile 
Dactyloa aeneus in Grenada, West Indies, are influenced by food availability, and rainfall 
(Stamps, 1981).  Moreover, juveniles are highly selective in their dietary habits, and prey 
selectivity showed a negative correlation with relative abundance for all six major prey 
item classes.  In the lowland tropical forests of Costa Rica, experimental manipulation of 
food availability influenced female fecundity, male size, as well as male-male and male-
female homerange overlap (Guyer, 1988a).  Guyer (1994) presents demographic data that 
 134
suggests that males might focus on mating opportunities and females focus on food 
availability, and has since experimentally confirmed a differential willingness of male 
and female ground anoles (Norops humilis) to accept food.  Thus, food deprivation, in the 
form of reduced food availability or in the form of attention by males to other activities 
(like vigilance for mating opportunities), might change physiology enough to alter 
dewlap color in males.  Moreover, research on juveniles of one species suggests that 
individuals might actually be able to identify particular prey items.  If this is true, then 
anoles might actively seek (or avoid) particular prey items based on their perceived 
carotenoid content.  Even if anoles do not discriminate carotenoid-rich prey items, it 
becomes apparent that dewlap color might reflect the ecological processes of food 
availability, and relative prey abundance, and UV dewlap color might be influenced by 
what and how frequently the lizard is eating. 
Evidence for the use of UV-based visual signals in lizards is becoming 
increasingly common.  UV has been documented in socially displayed color patches in 
several lizards studied to date (Molina-Borja et al., 2006, Lappin et al, 2006, Stapley and 
Whiting, 2005 Whiting et al., 2006).  In these lizards, however, it appears that UV is used 
to establish dominance in male-male rivalry, and indicates something about ones? 
resource holding potential (RHP). Additionally, UV color has also been shown to be an 
important social signal in many other animals, especially birds (Andersson and 
Amundsen, 1997; Andersson et al., 1998; Siitari et al., 2002; Alonso-Alvarez et al., 2004) 
and fish (Kodric-Brown and Johnson, 2002; Rick et al., 2004, 2006; Siebeck et al., 2004).  
In all of these examples, UV shows phenotypic variation in males, which females assess 
and upon which they base preferences.  Female choice of male UV reflectance has yet to 
 135
be studied in Norops sagrei, and there is good reason to believe that female choice may 
occur through sperm competition and differential egg fertilization (Tokarz, R.R., 1998).  
Future research should investigate female preference for male dewlap color using 
behavioral experiments, and employ DNA paternity techniques to determine sire identity 
and dewlap color to understand if male dewlap color is used as an ornamental trait used 
by females to aid in mate choice decisions.  
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Figure Legends 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 5 d.  Effect of xanthophylls supplementation on repeatedly measured values 
of red chroma of the midline dewlap region (F = 89.15, df = 1, P < 0.0001).   
Figure 5 a.  Average mass lost in high (left) and low (right) provision rate 
treatments.  The two groups differ significantly in mass lost during the duration of 
the experiment (F = 8.56, df = 1, P = 0.007).  
Figure 5 b.  Effect of food deprivation on repeatedly measured values of UV 
amplitude in the lateral dewlap region (F = 3.23, df = 1, P = 0.083).  
Figure 5 c.  Effect of xanthophyll supplementation on repeatedly measured values of 
UV chroma for the lateral dewlap region (F = 5.89, df = 1, P = 0.022).   
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