57.2 Thursday, Jan. 5 The insulin-like growth factor axis as a mediator of life history trade-offs ADDIS, E.A.*; SCHWARTZ, T.S; REDING, D.M.; PALACIOS, M.G.; BRONIKOWSKI, A.M.; Iowa State University email@example.com
Classic life-history theory predicts trade-offs between the lifetime fecundity and lifespan of an individual. However, little is know about the mechanisms that control these trade-offs. Two genetically divergent ecotypes of Thamnophis elegans, the Western garter snake, provide a natural experiment to explore genetic and hormonal mechanisms that are involved in these trade-offs. Populations of the fast-living ecotype live along rocky outcrops of Eagle Lake, in the Sierra Nevada Mountains. This ecotype has on average eight young each year, and has an average life span of four years. In contrast, the slow-living ecotype lives in the mountain meadows above Eagle Lake, has an average lifespan of eight years and average litter sizes of four, but reproduction is dependent upon food availability. One proposed mechanism involved in these trade-offs is the regulation of the insulin-like-growth-factor (IGF) axis. The IGF axis is involved in a broad spectrum of cellular functions, particularly those of cell proliferation, cell differentiation, and the inhibition of programmed cell death. At the organismal level, these genes affect an organism’s physiological processes, including those of aging and reproduction. In this study, we explored sequence and expression variation in the genes IGF-1, IGF-2, IGF-1R, and IGF-2R. We found little variation in gene sequences between ecotypes. However, expression of IGF-2, IGF-1R, and IGF-2R mRNA was several fold higher in the fast-living ecotype than the slow-living. No difference was observed in expression of IGF-1 mRNA between ecotypes. We discuss the significance of these results in the context of variation in both life-history strategies between the two ecotypes and in environmental conditions between the two habitats.