Combining morphological, acoustic, and genetic techniques to better understand hybridization of the most abundant toad in Alabama: Anaxyrus fowleri
Chivers, Jacqueline Marie
Type of DegreeMaster's Thesis
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The Anaxyrus americanus species complex has provided an interesting group of species to study hybridization. Two species in particular, Anaxyrus americanus and Anaxyrus fowleri, are known to hybridize in northern portions of their geographic range. In this study, I examined morphology, male anuran advertisement calls, and genetics for these species to determine the frequency of hybridization between these two species in Alabama and the reliability of morphology to detect genetic hybridization. I examined morphology for three hybridizing species of toads within the A. americanus species complex: A. americanus, A. fowleri and A. terrestris. Anaxyrus terrestris was included in morphological analysis due to its abundance in Alabama. I measured five key morphological characteristics and snout-vent length for all Auburn Natural History Museum specimens that were collected in Alabama: height of the junction of the interorbital and postorbital crests, width of largest tibial wart, size of largest dorsal wart relative to size of dorsal dark spot, and length and width of contact of the postorbital crest with the parotoid gland. Using discriminant function analysis (DFA), morphology revealed approximately 16% hybridization occurring among these three species. I then examined male advertisement calls of A. americanus and A. fowleri to determine if character displacement specifically occurred for A. fowleri in sympatry with A. americanus in current Alabama populations. New specimens were collected from extant populations in northern Alabama in order to examine advertisement calls as well as morphology and to perform genetic analysis on current populations of these species. Recordings from males calling in the field were measured using six call parameters: call duration, pulse rate, length of call, dominant frequency, length of pulse, and time between calls. No evidence of character displacement was seen between A. fowleri in allopatry and A. fowleri in sympatry with A. americanus. Nuclear DNA was extracted from tissue samples of the new specimens, sequenced using the next-generation sequencing technique, genotype-by-sequencing, and analyzed using fastSTRUCTURE. Only 5.4% of individuals genetically examined showed evidence of hybridization. High gene flow was seen between all A. fowleri populations regardless of location in Alabama. High genetic and acoustic variation was seen in A. americanus. The DFA of call parameter data showed individuals gave species distinct calls regardless of genetic influence. Through comparison of the morphological DFA and genetic analysis of the recently collected specimens, known genetic hybrids weakly correlated with morphological characteristics.
- Chivers Masters Thesis.pdf