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Fish Can Adjust Gender Balance in Face of Rising Temperatures

Warmer waters mean fewer female reef fish. But, over generations, populations can restore the balance.

(Reinhard Dirscherl/Corbis)
smithsonian.com

For certain species—some fish, alligators and lizards—the temperature of their surroundings influences their gender. This is known as “temperature sex determination," and as global warming heats up the world's oceans, it could lead to yet another strange phenomenon—fewer female fish. In a study published in Global Change Biology, researchers found that a change of just 1.5 degrees Celsius decreases the proportion of female Spiny Chromis coral reef fish by more than 30 percent.

A decreased female population is bad news: fewer females means fewer fish being born into the next generation. But it doesn't necessarily mean these fish species are doomed: over time, the researchers found, the gender balance can be restored.

Study author Jennifer Donelson writes in The Conversation:

We reared three generations of marine fish, the Spiny Chromis coral reef fish, and found that when parents develop from hatching at elevated temperatures, they can adjust their offspring gender back to the ideal 50:50 ratio. This phenomenon is called “transgenerational plasticity.”

The researchers showed the gender balance of offspring was restored when three generations of parents spent their entire lives in the warmer waters. “[F]or parents to compensate for the effects of higher temperatures on gender, they must develop from early life at the warm waters themselves,” Donelson says.

How, exactly, the fish do this remains a mystery – and their capacity to adjust only goes so far. When the scientists raised the temperature to 3 degrees Celsius above average, the number of fish born male still outnumbered those born female, even after two generations. 

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