Researchers at the University of Georgia collected 167 alligator eggs from South Carolina nests to study how daily temperature fluctuations shape hatchling sex ratios. Their findings reveal that a shift of just one or two degrees can alter whether alligator embryos develop as male or female.
University of Georgia Researchers Collect Eggs from South Carolina Nests
In June 2024, scientists discovered alligator nests by helicopter at the Tom Yawkey Wildlife Center located along the coast of South Carolina. The team gathered 167 freshly laid eggs from seven distinct nests to examine how realistic thermal environments influence embryonic development in reptiles.
While older laboratory experiments maintained constant temperatures in incubators, wild nests undergo daily thermal cycles driven by heat waves, sunshine, and nightfall. To replicate those conditions, researchers at the University of Georgia placed the collected eggs into five separate incubators. These units averaged temperatures between 86 and 93 degrees Fahrenheit while introducing daily fluctuations of about 5.4 degrees.
How Daily Temperature Swings Shift Gator Embryo Sex Ratios
Reptile incubation typically follows established patterns where cool temperatures and hot spells produce females, while moderate warmth yields males. However, the new model constructed from the South Carolina eggs demonstrates that temperature thresholds differ when daily swings are taken into account.
Traditional rules derived from steady laboratory conditions predicted that an even split between male and female hatchlings would occur at approximately 94.9 degrees Fahrenheit. By factoring in daily temperature curves, scientists discovered that the balance actually flipped to a roughly even split at about 92.4 degrees.
We know from monitoring nests that these temperature cycles fluctuate. But we also know that a small difference can lead to mostly males or mostly females being produced.
Benjamin Parrott, senior author and associate professor at UGA’s Savannah River Ecology Laboratory and Odum School of Ecology
At the warmest incubator setting averaging 93 degrees, the balance flipped decisively toward females, with 23 out of 27 embryos developing along the female pathway. The team noted that short daily spikes reaching up to 96 degrees did not harm the developing embryos.
Implications for Future Alligator Populations Under Climate Change
As global temperatures rise, shifting sex ratios pose distinct challenges for the long-term stability of alligator populations. Previous climate projections for the year 2100 estimated that under moderate emissions scenarios, average nest temperatures at the Tom Yawkey Wildlife Center would reach about 92.3 degrees Fahrenheit.
Relying solely on older steady-temperature rules would suggest that such warming would produce an overwhelming majority of male hatchlings, exceeding 90 percent. In contrast, the newly developed model accounting for daily temperature swings points toward a much more balanced ratio containing roughly 40 percent females.
Benjamin Parrott, senior author and associate professor at UGA’s Savannah River Ecology Laboratory and Odum School of Ecology, stated that for population health and stability, those small differences are really important, noting that whenever a population is out of balance, it can impact population growth, and whenever you start to lose females, then the population can really get in trouble.
Karin Ebey, a doctoral student in the Odum School of Ecology and lead author of the study, emphasized that the work provides a reliable instrument to connect nest temperatures directly to expected offspring sex. The findings were published in the Journal of Experimental Biology by a research team that also included Christopher Smaga and Thomas Rainwater.