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The sex of sea turtles

Tortuga marina

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It is well known that female turtles make a tremendous effort to deposit their eggs high up on the beach. But why do turtles venture to such a distant place away from the protection of the water, especially considering that when the hatchlings are born, this distance exposes them to predators? The answer lies in the fact that females must choose a location where they can ensure the appropriate temperature for egg laying.

The sex of turtles, as in most reptiles, is not genetically predetermined but depends on the average incubation temperature. The eggs are incubated by the heat accumulated in the sand that covers them. The depth of the nest, the characteristics of the sand, and the climate of the area all influence the temperature at which the eggs will develop and the sex of the hatchlings. At a moderate temperature, half of the hatchlings will be female, and the other half will be male. If the temperature is higher than the normal average, more females than males will be born. However, if the temperature is slightly lower during the egg development period, the sex ratio is reversed, and males dominate. A difference of just 2.5°C in either direction is enough to disrupt the sex ratio, resulting in the birth of only males or females.

Perhaps one of the most serious problems for turtles, in particular, and reptiles in general, is global warming, as these animals tend to lay their eggs in the same geographic area. Another potential problem is the gradual destruction of coastal areas where dunes are disappearing to make way for human constructions. Many conservation plans worldwide collect turtle eggs from their nests to artificially incubate them and release the young turtles into the sea when they reach a size that reduces the risk of predation. In these cases, the temperature factor allows scientists to repopulate areas where either males or females are lacking.

“You cannot defend what you do not love, and you cannot love what you do not know.”