Human embryos grow at a comfortable temperature just a bit warmer than the mother’s body. Reptile embryos, however, are at the whim of outside temperatures. And, in many cases, the sex of the offspring is known to be decided by incubation temperature.  

In fact, a recent study published in the Journal of Experimental Biology found that the sex of American alligators (Alligator mississippiensis) is set by just a one- or two-degree difference. With environmental temperatures on the upswing, that could make for lopsided alligator populations.

Read more: “Animals Are More Rational Than You Think”

“Whenever a population is out of balance, it can impact population growth,” explained senior study author Benjamin Parrot, an ecologist at the University of Georgia. “If temperatures are biasing sex ratios, that’s a big issue.”

Researchers collected 145 gator eggs from seven wild gator nests at the Tom Yawkey Wildlife Center in North Carolina. Eggs were incubated in the laboratory under five different temperature conditions: 30°C, 31°C, 32°C, 33°C, or 34°C. Several weeks into their incubation—when sex is known to have been established—embryos were removed from eggs to determine sex based on their reproductive structures.

The development of viable embryos didn’t vary between the temperature treatments, but the sex did. The lowest and highest temperatures favored females, while the medium temperatures favored males. At the higher temperatures, just a degree or two could shift the sex. The results also showed that brief spurts of heat expected to damage the embryos—up to 35.6°C—instead boosted their chances of being female.

With wild alligator nest temperatures predicted to rise to as hot as 33.5°C by 2100 across their range, expect some truly gender-bending gator trends in the future.

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Lead Image: Adobe Stock / Charoenchai