The blue world: the mystery of the sex of green turtles
Updated 15:45, 31-Dec-2020
By CGTN's Gao Yuxin

While the sex of many animals is determined by the sperm of the father and the egg of the mother, the sex of green turtles has nothing to do with their parents.

Green turtles are long-lived species with temperature-dependent sex determination; that is to say, the surrounding environment's temperature influences their sex. When spawning season comes, females go to the beach and create four to five nests, with about 100 eggs per nest. They are then covered with sand. During incubation in the nest, the warmer the egg, the more likely it is to hatch a female. Therefore, factors such as the nest's depth, the shading of the nest and the choice of nesting beach can affect a green turtle's sex.

Green turtles (Chelonia mydas), named for the greenish color of their cartilage and fat instead of their shells, are among the largest sea turtles and the only herbivores among the different species. They are found mainly in tropical and subtropical waters and spend their whole lives in the ocean, except for going ashore to lay eggs. 

In addition to ecological deterioration, pollution aggravation, et cetera, climate change poses a severe threat to green turtles. 

Warmer climates heat up the green turtle's nests. So, a slight change in temperature can alter the sex ratio of turtle hatchlings substantially.

Jana Blechschmidt and her research team from the faculty of biology at University of Bielefeld state in their research paper titled "Climate Change and Green Sea Turtle Sex Ratio – Preventing Possible Extinction" that in the northern Great Barrier Reef, the temperature of an individual turtle might have already increased by 0.8 degrees Celsius within its lifespan. The green turtles there have an approximate overall sex ratio of 80 percent female, with 99 percent of the non-adult turtles being female. The article says that when the temperature rises by only 1 degree Celsius, the female sex ratio rises from 50 percent to 80 percent.

The author also points out that global mean temperatures are expected to increase by 1 to 3.7 degrees Celsius until 2100.  

Increases in temperature can lead to biased sex ratios. When there are far more females than males, the few remaining males may no longer be able to fertilize enough females to sustain the population, which might make green turtles go extinct.

Green turtles have been on the International Union for Conservation of Nature Red List of Endangered Species since 2004, and their population continues to dwindle.

Keeping up with climate change would be a self-saving solution for green turtles, but whether it's possible remains a question.

(All images via VCG)

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