MORJAN, Carrie L.: Nest-site choice in reptiles with temperature-dependent sex determination and the evolution of maternal effects

Although maternal effects have traditionally been thought to hinder adaptive evolutionary responses, new theory suggests they play a key role in local adaptation through runaway processes. Oviposition-site choice by females coupled with progeny response to environment has often been used as an example for the adaptive potential of maternal effects. I evaluated the relative evolutionary potential of maternal and offspring traits affecting sex by developing a simulation model based on key parameters derived from a natural population of painted turtles (Chrysemys picta) with temperature-dependent sex determination (TSD). In contrast to predictions from theoretical models, the simulation model demonstrated that maternal nest-site choice is likely to evolve more slowly than thermal response of offspring sex, due to among-year climatic variation on nest temperatures overriding females’ ability to choose thermal nest qualities. A variant of the model, assuming inheritance of nest-sites through natal imprinting, demonstrated that natal philopatry to nest sites inhibited adaptive responses in nest-site choice to climate changes due to a runaway process favoring female-biased sex ratios. These results predict that both maternal and offspring traits, and hence sex ratios, will evolve slowly (or even maladaptively in the case of nest-site choice) as a response to biased sex ratios caused by predicted climate change scenarios. Thus, models assuming a critical role of maternal behavior in sex ratio evolution in TSD may need to be re-evaluated.