SREL Reprint #3857

Spatial and temporal variation in nest temperatures forecasts sex ratio skews in a crocodilian with environmental sex determination

Samantha L. Bock1,3, Russell H. Lowers4, Thomas R. Rainwater5,6, Eric Stolen4, John M. Drake1,2, Philip M. Wilkinson5, Stephanie Weiss4, Brenton Back4, Louis Guillette Jr7, and Benjamin B. Parrott1,3

1Odum School of Ecology, University of Georgia, Athens, GA 30602, USA
2Center for the Ecology of Infectious Diseases, University of Georgia, Athens, GA 30602, USA
3Savannah River Ecology Laboratory, Aiken, SC 29802, USA
4Integrated Mission Support Services, John F. Kennedy Space Center, FL 32899, USA
5Tom Yawkey Wildlife Center, Georgetown, SC 29440, USA
6Belle W. Baruch Institute of Coastal Ecology & Forest Science, Clemson University, Georgetown, SC 29442, USA
7Medical University of South Carolina, Hollings Marine Laboratory, Charleston, SC 29412, USA

Abstract: Species displaying temperature-dependent sex determination (TSD) are especially vulnerable to the effects of a rapidly changing global climate due to their profound sensitivity to thermal cues during development. Predicting the consequences of climate change for these species, including skewed offspring sex ratios, depends on understanding how climatic factors interface with features of maternal nesting behaviour to shape the developmental environment. Here, we measure thermal profiles in 86 nests at two geographically distinct sites in the northern and southern regions of the American alligator’s (Alligator mississippiensis) geographical range, and examine the influence of both climatic factors and maternally driven nest characteristics on nest temperature variation. Changes in daily maximum air temperatures drive annual trends in nest temperatures, while variation in individual nest temperatures is also related to local habitat factors and microclimate characteristics. Without any compensatory nesting behaviours, nest temperatures are projected to increase by 1.6–3.7°C by the year 2100, and these changes are predicted to have dramatic consequences for offspring sex ratios. Exact sex ratio outcomes vary widely depending on site and emission scenario as a function of the unique temperature-by-sex reaction norm exhibited by all crocodilians. By revealing the ecological drivers of nest temperature variation in the American alligator, this study provides important insights into the potential consequences of climate change for crocodilian species, many of which are already threatened by extinction.

Keywords: American alligator, crocodilian, climate change, machine learning, temperature-dependent sex determination, nesting ecology

SREL Reprint #3857

Bock, S. L., R. H. Lowers, T. R. Rainwater, E. Stolen, J. M. Drake, P. M. Wilkinson, S. Weiss, B. Back, L. Guillette Jr., and B. B. Parrott. 2020. Spatial and temporal variation in nest temperatures forecasts sex ratio skews in a crocodilian with environmental sex determination. Proceedings of the Royal Society B 287(1926).

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).