THE BEHAVIORAL ECOLOGY AND CHEMICAL ANALYSIS OF MENTAL GLAND SECRETIONS OF BOTH SEXES OF GOPHER TORTOISES (GOPHERUS POLYPHEMUS)

Abstract

All living chelonian species (e.g., turtles and tortoises) are experiencing population declines, causing a new imperative to maintain the longevity of adults and to facilitate reproduction. One strategy in facilitating reproduction is to focus on sensory signaling in social interactions that could lead to mating. For example, olfaction and chemical recognition of pheromones represents the oldest use of senses, and yet, little is known about the chemical ecology of many vertebrates, especially chelonians, which are known to use chemosensory cues despite habitats that are becoming increasingly fragmented. This is especially true for threatened species like gopher tortoises (Gopherus polyphemus), which are endemic longleaf pine specialists in a rapidly declining habitat due to deforestation, urbanization, and poor land management (e.g., lack of fire maintenance). With these studies, I aimed to examine the behavioral ecology of the gopher tortoise through chemical signals found in chin or mental gland (MG) secretions. Chemical bioassays with paired treatments (MG secretion variants vs. controls) revealed MG secretions were used as pheromones in both males and females. Multimodal presentations with 3D tortoise models treated with MG secretions indicated MG secretions are chemical signals required to maintain social behaviors even with visual signals, leading to courtship or mating. To further understand MG secretion use in terrestrial habitats, I found that male tortoises were able to chemically discriminate visually identical models treated with 20X diluted MG secretions, supporting the ecological utility of MG secretions despite breakdown. In chemical analyses of MGs in both sexes from different locations, we identified several chemical classes in MG secretions not previously known in tortoises, with some differing by sex, body size, or location, including short-chained carboxylic-carbohydrate acids, aromatics, and amide compounds. All chemical compounds found may be signals used to identify conspecific characteristics. My studies are the first documented use of MGs as a source of pheromones in this species and the first thorough chemical composition analysis of MG secretions in both male and female gopher tortoises.