Nest temperature and sex ratios in a crocodilian
Global shifts in temperature are yielding widespread impacts across diverse ecosystems and certain species are especially vulnerable to these changes. In particular, many reptiles – including all crocodilians and many turtles – rely on a system called temperature-dependent sex determination (TSD) in which the temperature an animal experiences during development determines whether it becomes male or female. Rapid environmental change threatens to skew offspring sex ratios in these species and potentially lead to adverse population-level consequences. Predicting and mitigating these impacts requires understanding the environmental factors shaping nest temperatures in the wild.
In this study, we measured temperatures of 86 alligator (Alligator mississippiensis) nests in Florida and South Carolina and examined the influence of climate factors and maternally driven nest characteristics on nest temperature variation. While maternally driven nest-site choice accounted for a proportion of within-year variation in nest temperatures, we detected a strong relationship between mean nest temperatures and air temperatures across years. Based on this relationship, nest temperatures are predicted to increase by 1.6 – 3.7˚C by the year 2100 with rising air temperatures. Importantly, this could yield dramatic changes in alligator hatchling sex ratios. In alligators and all other crocodilians, males are produced at intermediate temperatures while females are produced at low and high temperatures. As a result, the predicted changes in nest temperature could yield nearly 100% male hatchlings under one climate scenario and nearly 100% females under a more extreme climate scenario. These findings underscore the importance of active monitoring of hatchling sex ratios for the future conservation of crocodilians worldwide.