Throughout my graduate career, I’ve worked on non-model organisms. I started researching reptiles because I find them fascinating, but have found that some questions are extremely difficult or outright unfeasible to answer in mammals. For my master’s thesis under Dr. Christy Strand, I investigated how testosterone influences home range size and spatial-related regions in the brain of western fence lizards (Sceloporus occidentalis). This avenue of research first arose from findings in side-blotched lizards (Uta stansburiana) that showed males utilizing different space-use strategies also had significantly different plasma testosterone levels. The idea that spatial demand positively relates to increased space-related regions in the brain is echoed in numerous species including mammals and birds, and even humans! Taxi drivers and not bus drivers have significantly larger hippocampi. Therefore, determining if testosterone induces an increase in spatial demand which in turn increases the size of spatial-related brain regions in reptiles would likely translate to other species.
So what did I find? Increased testosterone did not influence home range size in lizards and actually decreased dorsal cortex volume, a brain region in reptiles homologous to the hippocampus. One explanation for this finding is that testosterone-treated individuals had substantially less, and in some cases completely lacked abdominal fat stores. To expand on this finding, I sought to determine how energy stores influence life-history transitions surrounding the breeding season in red-sided garter snakes (Thamnophis sirtalis parietalis) for my PhD with Dr. Deborah Lutterschmidt. This population of red-sided garter snake is one of the most northerly-residing reptiles and resides in Manitoba, Canada. Snakes. In snow. Well, underground in snow; they overwinter for approximately 8 months and emerge from dens to engage in an intense mating season with hundreds, if not thousands of individuals. As the mating season progresses, individuals then migrate upwards of 17 km to summer feeding grounds where they gorge themselves for 2 months. These feats of aphagia, up to 9 months, are simply unheard of in mammalian species. And while many mammals endure periods of fasting for transitions between 2 life-history stages, say hibernation and breeding or migrating and breeding, these snakes are one of the very few species I’m aware of with the capacity to fast over 3 life-history transitions (i.e., hibernation, breeding, and migration).
I feel pretty confident in labeling this population of red-sided garter snakes as the champion of aphagia. Studying them can reveal the breadth of the physiological spectrum as it pertains to metabolism and reproduction. And since we know that metabolic factors can adversely affect reproduction in mammals, particular in its association with polycystic ovarian syndrome and endometriosis, investigating how other models accommodate huge fluctuations in energy stores may represent an untapped resource to inform aberrant reproductive physiology in humans. In this way, reptiles may present an opportunity to discover mechanisms we can exploit to treat metabolic-induced reproductive disorders, much like the novel pathways to repair DNA in sharks are being used to further research in cancer biology and age-related illnesses.
After completing her PhD at Portland State University this past summer, Rachel Wilson is a first year postdoctoral scholar at the Oregon National Primate Research Center. She is interested in researching the pathophysiology and etiology of endometriosis with the ultimate goal of utilizing non-invasive techniques to diagnosis the disease.