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Gators: Sex Determined by Temperature

Young Gators, Big Cypress National Preserve.

I was intrigued to learn that alligators and crocodiles (and most turtles) lack sex chromosomes. “The sex of these creatures is actually determined by the temperature at which their eggs incubate. This phenomenon is called TSD (for temperature-dependent sex determination). In an alligator nest, the eggs that incubate between 90 degrees and 93 degrees F become males, while those incubating between 82 degrees and 86 degrees F become females. From 87 to 89 degrees, the ratio of males to females is about equal. Since the eggs at the top of the gator’s nest are likely to be heated more by the sun that those below, males usually come from the top part of the nest while females come from the bottom. On the contrary, with crocodiles, females come from the warmest eggs.” Source: Florida’s Fabulous Reptiles & Amphibians. [Photo: D.F.G. Hailson]

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