Long-Term Resilience of Primary Sex Ratios in a Species with Temperature-Dependent Sex Determination after Decades of Climate Warming

Species with environmental sex determination (ESD) have persisted through deep time, despite massive environmental perturbation in the geological record. Understanding how species with temperature-dependent sex determination (TSD), a type of ESD, persist through climate change is particularly timely given the current climate crisis, as highly biased sex ratios and extinction are predicted. Since 1982, we have studied primary sex ratios of a reptile with TSD (Chelydra serpentina). Primary sex ratios remained unchanged over time, despite warming in the environment. Resilience of the primary sex ratio occurred via a portfolio effect, realized through remarkable intra-annual variation in nest-level sex ratios, leading to a relatively consistent mean annual sex ratio. Intra-annual variation in nest-level sex ratios was related to variation in egg burial depth coupled with large clutch sizes, creating thermal gradients in the nest and promoting mixed-sex clutches. Furthermore, both locally and globally, sustained increases in nighttime air temperature contribute more to warming than increases in daily maximum temperature, but development rate was affected more strongly by maximum daily air temperature, conferring additional resilience to overall warming. Our study suggests that some TSD species may be resilient to warming and provides an example of how ESD may persist under environmental change.

Automated summary

This study found that reptiles with temperature-dependent sex determination (TSD) can maintain stable sex ratios despite climate change. The stability is achieved through seasonal variation in nest-level sex ratios, which is influenced by thermal gradients and mixed-sex clutches. Additionally, the impact of nighttime air temperature on warming is greater than that of daily maximum temperature, while the development rate is more affected by maximum daily air temperature, providing additional resilience to overall warming.