Meeting Abstract
Fisherian sex-ratio theory predicts sexual species should have a balanced primary sex ratio. However, organisms with environmental sex determination are vulnerable to excessively skewed sex ratios when environmental conditions vary. Theory has emphasized two traits important for sex-ratio dynamics in animals with these mechanisms: (1) maternal oviposition-site choice and (2) sensitivity of embryonic sex determination to environmental conditions. Much research has since focused on how these traits influence offspring sex ratios. Still, relatively few studies have estimated univariate quantitative genetic parameters for these two traits, and the existence of phenotypic or genetic covariances among these traits has never been assessed. Here, we leverage work on three species of reptiles (two divergent turtle species and a lizard) with temperature-dependent sex determination (TSD). These studies measured maternal behaviors that relate to nest temperature under field conditions and assessed the corresponding sex ratio of offspring from eggs incubated under controlled temperatures. A strong concordant covariance between these traits would maximize the efficiency of sex-ratio selection. We detected no such covariance between nest-site choice and thermal sensitivity of sex determination in the three species studied. Consequently, our results suggest these traits are able to evolve independently. Even so, a comprehensive review of the existing literature on quantitative genetic estimates for traits related to TSD identifies minimal microevolutionary capacity in the wild, in most cases. Such information is critical for understanding how animals with TSD might respond to rapidly changing environmental conditions.
