New study finds heat shifts alligator egg sex ratios earlier than expected

Researchers at the University of Georgia have found that rising temperatures begin skewing alligator egg sex ratios toward females at a lower threshold than previously believed. The study challenges earlier assumptions about how climate change affects reptile populations.

The team incubated 146 alligator eggs under five different temperature ranges, spanning 86 to 93 degrees Fahrenheit. Unlike prior studies that often used constant temperatures, this research accounted for natural fluctuations. Alligators determine the sex of their offspring based on incubation temperature. Moderate temperatures typically produce males, while extreme heat produces females.

The data showed that the shift toward female production started at 93 degrees Fahrenheit. Previous research suggested this shift did not begin until temperatures reached 97 degrees Fahrenheit. The researchers noted that estimates for sex determination differed by up to 1.36 degrees Celsius, or approximately 2.49 degrees Fahrenheit, compared to constant-temperature models.

Benjamin Parrott, the study’s senior author and an associate professor at Georgia’s Savannah River Ecology Laboratory and Odum School of Ecology, emphasized the biological implications of this shift. “For population health and stability, I think it means that those small differences are really important,” Parrott said. “Whenever a population is out of balance, it can impact population growth. Whenever you start to lose females, then the population can really get in trouble.”

Parrott noted that monitoring nests confirms these temperature cycles fluctuate in the wild. “We also know that a small difference can lead to mostly males or mostly females being produced,” he added. “That’s really relevant for how the environment is going to be changing in the near future. If temperatures are biasing sex ratios, that’s a big issue.”

The findings offer a new tool for conservationists aiming to predict sex ratios in populations of alligators, sea turtles, crocodiles, and freshwater turtles. Parrott cautioned that further research is required to fully understand how these populations will respond to various environmental conditions. “How are those populations going to respond to different environmental conditions? We still have a long way to go,” he said.