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. Further, 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.