Portland State University. Department of Biology
Deborah I. Lutterschmidt
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Biology
Red-sided garter snake -- Physiology, Adipose tissues, Fat cells, Glycogen, Red-sided garter snake -- Reproduction, Red-sided garter snake -- Sex differences, Hibernation
1 online resource (ix, 155 pages)
All organisms must prioritize investment in either reproductive or self-maintenance activities. Despite this established paradigm, our understanding of how organisms choose to prioritize certain behaviors and physiologies over others remains limited. It is likely that an organism's energy status not only influences variation in reproductive effort, but also transitions to and from reproductive activities. My dissertation aims to investigate how energy metrics (body condition index, adipocyte follicle size, and liver glycogen) relate to reproduction and associated life-history stages in red-sided garter snakes (Thamnophis sirtalis parietalis). Chapter two examines if energy metrics differ with migratory status and sex in red-sided garter snakes. We expected to find that snakes investing primarily in mating behaviors had elevated energy metrics compared to individuals that initiated migration to summer feeding grounds. However, we found that neither adipocyte follicle area nor liver glycogen differed with migratory status in red-sided garter snakes, and therefore a physiological mechanism underlying the decision to migrate remains elusive. In this chapter, we also found a sexual dimorphism in energy stores of red-sided garter snakes, with females having significantly larger adipocyte follicles and higher liver glycogen stores than males. In my third dissertation chapter, we aimed to investigate if energy stores influence reproductive behavior. We altered a snake's perception of adipose stores by injecting the peptide hormone leptin, as it is produced and secreted from adipocytes in proportion to cell size and thus accurately indicates the amount of stored fat. While leptin increased both appetitive and consummatory sex behaviors (e.g., courtship score and number of copulations, respectively) in male snakes, we found leptin only increased consummatory sex behavior in females. These results indicate that leptin exhibited sex-specific effects on reproductive behavior in red-sided garter snakes. Because energy metrics influenced reproductive behavior in red-sided garter snakes, in my fourth dissertation chapter we aimed to determine how hibernation duration and temperature influence energy metrics. Our findings suggested that red-sided garter snakes preferentially utilized liver glycogen stores for energetic demands during hibernation, a finding that conflicts with the established literature in mammals indicating the preferential use of adipose stores. Additionally, exposure to elevated temperatures during hibernation depleted energy stores to a greater extent than an ecologically relevant hibernation temperature. Expending more energy during hibernation results in less available energy for mating activities upon spring emergence. Collectively, these data support the hypothesis that energy stores help an organism pinpoint the appropriate time to invest in certain behaviors and physiologies, which in turn will increase its Darwinian fitness. In examining multiple stages of an animal's annual life-history cycle and connecting physiology to behavior and subsequently fitness, my dissertation provides a view into how exposure to different temperatures affects a whole organism's biology.
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Wilson, Rachel Catharine, "Energy Stores and Life-History Transitions in Red-Sided Garter Snakes (Thamnophis sirtalis parietalis)" (2020). Dissertations and Theses. Paper 5507.