Is it a boy or a girl? For alligators, it may come down to one degree
by Savannah Peat, University of Georgia
Is it a boy or a girl? For alligators, it may come down to one degree
The future of the alligator species could come down to a one- or two-degree temperature difference, according to new research from the University of Georgia. The findings are published in the Journal of Experimental Biology.
A small change on the thermometer could determine whether a gator develops as a male or female. And that could have ramifications for alligator populations as temperatures rise.
Typically, incubations at cooler temperatures (think 86 to 88 degrees Fahrenheit) & hot spells (97 degrees Fahrenheit & above) result in more female gators. Moderate temperatures (90 to 92 degrees Fahrenheit) yield more males.
But these trends largely reflect controlled experiments in laboratories in which alligator eggs are incubated under constant temperatures.
Nests in the wild don't experience constant temperatures; instead, temperatures fluctuate due to heat waves or just going from day to night.
The present study gives scientists a better understanding of real-world nest conditions.
"For population health & stability, I think it means that those small differences are really important," said Benjamin Parrott, senior author of the study & an associate professor in UGA's Savannah River Ecology Laboratory & Odum School of Ecology. "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."
Hotter weather could skew gator hatchlings female
The researchers collected 146 alligator eggs from 7 nests in South Carolina. They incubated the eggs under 5 different temperatures, averaging 86 to 93 degrees Fahrenheit, with small daily fluctuations (around 5 degrees) to simulate realistic nest conditions. They then identified the resulting sex of the alligators & used that to create a new model that connects offspring sex with incubation temperature.
Their new model closely matched previous sex outcomes at cooler temperatures. But at higher temperatures, even a change of one or two degrees made a big difference in whether alligator embryos developed as male or female.
"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," Parrott said. "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 eggs' swap back to a female outcome occurred at a lower temperature threshold than anticipated. Whereas some previous models expected the flip to happen around 97 degrees Fahrenheit, the new model suggests that sex was more likely to be female starting at 93 degrees Fahrenheit. Temperatures between the 2 female-producing ranges still produce mostly males.
Previous studies also found temperatures above about 94 degrees Fahrenheit could hurt alligator embryos, with survival oftentimes limited at 97 degrees Fahrenheit. The present study, however, found that not only did short spurts of high temperatures (up to 96 degrees Fahrenheit) not harm the embryos, but they increased the likelihood of embryos developing as females rather than males.
"This work is important because it's trying to ensure that we have an accurate tool to be able to say, "Okay, here's a nest temperature. What sex will the alligators from this nest most likely be as a result?" We're able to know better what to expect," said Karin Ebey, lead author of the study & a doctoral student in the Odum School.
New model helps predict sex more accurately, easily
The model is the first of its kind to predict how incubation temperatures determine a creature's sex while accounting for daily temperature fluctuations. By better reflecting natural weather patterns, it could help researchers more accurately predict alligator sex ratios in the wild. Researchers say the method could also eventually be applied to other critters.
"Alligators are predators, but they are also ecosystem engineers. They're important to the environments they reside in," Ebey said. "Alligators are an abundant & well-studied species, allowing them to serve as a model for other crocodilian species.
"We're hoping what we learn in alligators can also inform conservation efforts for other species of crocodile."
Understanding how temperature impacts these reptiles is increasingly important as global temperatures change.
"It's one step forward, & it's a great tool, but we still need so much more research to be able to properly predict sex ratios in populations of sea turtles, alligators, crocodiles or freshwater turtles," Parrott said. "How are those populations going to respond to different environmental conditions? We still have a long way to go."
This study was co-authored by Christopher Smaga & Mathews Nascimento, graduates of the Odum School, & Thomas Rainwater.
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