Turtle Embryos May Play A Role In Determining Sex

Scientists have found that turtle embryos can play a role in determining their own sex, which could help their species guard against climate change.

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Here's a reminder that NPR News reports on the news everywhere, including on the inside of a turtle egg. Before turtles hatch, when they're just tiny embryos inside their eggs, environmental changes may influence whether they become male or female. NPR's Merrit Kennedy reports this could protect turtles from climate change.

MERRIT KENNEDY, BYLINE: For a lot of reptiles, their sex depends on their surroundings.

RICK SHINE: It's a strange and wonderful aspect of reptile biology that in many turtles, all crocodiles and quite a few lizards, the sex that an animal develops into is determined by the temperature that it experiences within the nest.

KENNEDY: Rick Shine is a biologist at Macquarie University in Australia. He says that for some turtle species, eggs that incubate at lower temperatures produce all males and slightly higher temperatures produce all females. This could cause problems because temperatures are rising due to climate change. In parts of the world, virtually no male sea turtles are hatching because it's too hot for them to develop. So populations might have trouble reproducing and therefore surviving. But what if turtle embryos could do something that keeps the male-female ratio more even?

SHINE: Perhaps the embryos of reptiles could move around within the egg because it might be a little bit warmer at one end of the egg than the other.

KENNEDY: Shine worked with Chinese researchers to study the Chinese three-keeled pond turtle. He says its eggs can have hotter zones and cooler zones. The team wondered if an embryo could influence its sex simply by moving to find the sweet spot. To test that theory, they painted some eggs with a chemical so that the embryos couldn't sense heat.

SHINE: Just have to paint it on the eggshell, and you have an embryo inside that's no longer aware of the temperature differences within the egg.

KENNEDY: These embryos didn't move around much, and the turtles wound up being nearly all male or all female depending on whether the eggs were warm or cool. Embryos and eggs that weren't treated behaved very differently. They were more active and hatched with a much more even male-to-female ratio.

SHINE: It does seem as if the embryo has a lot more control over its destiny than we ever expected.

KENNEDY: That idea is controversial. Biologist Boris Tezak from Florida Atlantic University has a few questions, like whether an embryo would have the muscle strength to reposition itself at that point in its development.

BORIS TEZAK: I would like to see a little bit more of that data to be fully convinced, I think.

KENNEDY: Shine says the team's study in the journal Current Biology took Tezak's concerns into account. And he doesn't think the embryos are making a conscious choice about what sex to become. Moving around in the egg is more likely an unconscious behavior that the turtles evolved to shield against temperature shifts. It might act as a buffer against small temperature changes, but it's no defense against major swings.

SHINE: These organisms are far more sophisticated than we might think. They're capable of dealing with all kinds of unpredictable challenges that get thrown at them by the outside world.

KENNEDY: Shine says the danger is that humans are throwing so many challenges at these animals so quickly that in the future, they might not be able to cope.

Merrit Kennedy, NPR News.

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