How Rapidly Can Maternal Behavior Affecting Primary Sex Ratio Evolve in a Reptile with Environmental Sex Determination?

Theoretical models identify maternal behavior as critical for the maintenance and evolution of sex ratios in organisms with environmental sex determination (ESD). Maternal choice of nest site is generally thought to respond more rapidly to sex ratio selection than environmental sensitivity of offspring sex (threshold temperatures) in reptiles with temperature-dependent sex determination (TSD, a form of ESD). However, knowledge of the evolutionary potential for either of these traits in a field setting is limited. I developed a simulation model using local climate data and observed levels of phenotypic variation for nest-site choice and threshold temperatures in painted turtles (Chrysemys picta) with TSD. Both nest-site choice and threshold temperatures, and hence sex ratios, evolved slowly to simulated climate change scenarios. In contrast to expectations from previous models, nest-site choice evolved more slowly than threshold temperatures because of large climatic effects on nest temperatures and indirect selection on maternally expressed traits. A variant of the model, assuming inheritance of nest-site choice through natal imprinting, demonstrated that natal imprinting inhibited adaptive responses in female nest-site choice to climate change. These results predict that females have relatively low potential to adaptively adjust sex ratios through nest-site choice.