The insulin−like signaling pathway (IIS) as a regulator of life histories in Western terrestrial garter snakes

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

Austin, TX

Congreso; Annual Meeting of the Society for Integrative and Comparative Biology; 2014

Society for Integrative and Comparative Biology

Western terrestrial garter snakes(Thamnophis elegans) living aroundEagle Lake, California haveevolved two distinct ecotypes, differingin growth, maturation andreproduction rates, lifespan and skinmorphology. While these ecotypesnicely conform to life historytheory of trade−offs betweenlifespan and reproductive output, littleis known about the underlyingmechanisms. Studies in modelorganisms have hinted at a role ofthe insulin−like signaling (IIS)pathway in regulating these trade−offs.We raised neonates frombirth of both ecotypes under tworearing conditions that differed inthermal availability for 1.4years. At the end of the rearing period, wetested for differences among fourconstituents of the IIS pathway inthese snakes in response to our 2x 2 design (ecotype x thermalavailability): insulin−like growthfactor 1 and 2 (IGF−1 and IGF−2)and associated receptors (IGF−1Rand IGF−2R) correlating withgrowth. We analyzed protein levelsof IGF−1 and IGF−2 and mRNAlevels of IGF−1, IGF−2, IGF−1R,IGF−2R among the brain, liver,and muscle for significantecotype, thermal availability and ecotype xthermal availability interactions.The effects of ecotype and treatmentvaried across tissue types, genes,and protein expression. IGF−1 andIGF−2 mRNA levels were highest inthe liver and IGF−1R andIGF−2R mRNA levels were highest inthe brain; muscle levels wereintermediate. Unexpectedly, bothcirculating protein and mRNAlevels of IGF−2 were higher thanthose of IGF−1. Birth size (SVL)and sex also affected mRNA andprotein levels. In this talk, we willexplore the implications of theseresults.