Science on Purpose: Climate change makes turtles all-girl

With the rising temperatures on our planet, sea turtles could be facing a male deficiency.



By Jess Wind (The Cascade) – Email

Print Edition: May 21, 2014

A warming planet leads to an influx of female sea turtles in the Cape Verde Islands. (Image: Anthony Biondi)

With the rising temperatures on our planet, sea turtles could be facing a male deficiency. 

Turtle sex is determined by the temperature of the sand in which the female lays her eggs, unlike in humans where chromosomes make the sex distinction. The balanced temperature for a 50:50 sex ratio in turtles is 29°C — anything over that tips the scale in the female direction.

“The logic is that warming temperatures will lead to more female hatchlings being produced,” Graeme Hays told the Guardian.

Hays is the lead author of a paper published on May 18 in Nature Climate Change that looks at the rising temperatures of turtle rookeries in the Cape Verde Islands. 

“We combined in situ sand temperature measurements with air temperature records since 1850 and predicted warming scenarios from the Intergovernmental Panel on Climate Change to derive 250-year time series of incubation temperatures, hatchling sex ratios, and operational sex ratios for one of the largest sea turtles rookeries globally,” Hays explained in the paper. 

Researchers discovered that 70.1 per cent of turtles born in lighter-sand beaches were female, and darker beaches had risen to 93.5 per cent. 

“Over the next 20 to 30 years, it’s not going to create problems,” Hays told the Guardian. “In fact there’s going to be a benefit to the turtles, because there’s going to be more females produced, which means more females laying eggs. More females will lead to a population expansion.”

This is good news for turtle reproduction in the short term — more lady turtles to make more baby turtles. However, Hays and his team project that future generations of turtles may have trouble reproducing. 

“Ultimately, if you extrapolate long enough into the future … once you get 100 years or more into the future, then things start to look serious. You have so few males left that it’s likely to be a problem. There will be heaps of female but not enough males to fertilise all those eggs,” he said. 

Beyond 33°C embryos do not survive; as temperatures continue to rise, the fate of turtles and other temperature-dependant animals, like many species of lizard, could be in danger. 

“It will be end of story without human intervention,” Hays told the Sydney Morning Herald before going on to add that since these turtles have survived for millions of years, perhaps they will learn to adjust yet again. 

Possible natural solutions could include the turtles laying eggs at cooler times of the year, or moving to cooler regions, but for now Hays’ study could help steer conservation efforts to protect lighter coloured beaches from further development. 

“If you have to build a hotel, build it behind the dark-coloured beach,” he said.

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