Insulin-like signaling and life history trade-offs in garter snakes with divergent life histories

ADDIS, E.A.; REDING, D.M.; SCHWARTZ, T.S.; PALACIOS, M. G.; BRONIKOWSKI, A. M.

Charleston, NC

Congreso; Annual Meeting of the Society for Integrative and Comparative Biology; 2012

Society for Integrative and Comparative Biology

Classiclife-history theory predicts trade-offs between the lifetime fecundity andlifespan of an individual. However, little isknow about the mechanisms that control these trade-offs. Two geneticallydivergent ecotypes of Thamnophis elegans, the Westerngarter snake, provide a natural experiment to explore genetic and hormonalmechanisms 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 ecotypehas on average eight young each year, and has an average life span of fouryears. In contrast, the slow-living ecotypelives in the mountain meadows above Eagle Lake, has an average lifespan ofeight years and average litter sizes of four,but reproduction is dependent upon food availability. One proposed mechanisminvolved in these trade-offs is the regulationof the insulin-like-growth-factor (IGF) axis. The IGF axis is involved in abroad spectrum of cellular functions, particularlythose of cell proliferation, cell differentiation, and the inhibition ofprogrammed cell death. At the organismal level,these genes affect an organism?s physiological processes, including those ofaging and reproduction. In this study, we exploredsequence and expression variation in the genes IGF-1, IGF-2, IGF-1R, andIGF-2R. We found little variation in gene sequencesbetween ecotypes. However, expression of IGF-2, IGF-1R, and IGF-2R mRNA wasseveral fold higher in the fast-livingecotype than the slow-living. No difference was observed in expression of IGF-1mRNA between ecotypes. We discussthe significance of these results in the context of variation in bothlife-history strategies between the two ecotypesand in environmental conditions between the two habitats.