JANZEN, F.J.: Constraints on the Microevolution of Type II Temperature-Dependent Sex Determination

Sex determination is a fundamental trait of organisms that reproduce sexually, yet the tremendous diversity of sex-determining mechanisms remains largely unexplained. The origin of and variation in types of environmental sex determination (ESD) are particularly enigmatic. In this talk, I explore the ecological relevance and quantitative genetic underpinnings of an especially curious pattern of ESD called Type II temperature-dependent sex determination (TSD). I first evaluate temperatures measured in natural nests with respect to both pivotal temperatures (Tpivs) of Type II TSD determined in the laboratory. Subsequently, I estimate heritabilities of sex ratio at both Tpivs, GxE for sex ratio, and the genetic correlation between both Tpivs in common snapping turtles. The results suggest that the ecological relevance of Type II TSD is questionable and that this pattern of TSD may simply be maintained by genetic constraints.