What Determines the Sex of a Sea Turtle?

The temperature of the sand in a sea turtle’s nest determines the sex of the babies. Below 85 degrees Fahrenheit (30 degrees Celsius), offspring are predominantly male. Above 85 degrees Fahrenheit, babies are predominantly female. This fascinating little fact even has its own acronym — TSD or Temperature-Dependent Sex Determination.

Apparently, there is a temperature that will give an equal ratio of male and female hatchlings. That temperature varies with species and with nest locations.

Interestingly, the heat produced by the eggs  can also affect the sex of the hatchlings. Eggs in the warmer center of the nest become females. Eggs on the periphery of the nest become males.

The temperature of the nest is the most common explanation for gender. There is an alternative explanation, still to do with temperature. In that theory, colder water during mating is responsible for males, warmer water for females.

Climate Change is a Problem

Sea turtle nests in the southern United States are predominantly female biased. If there’s even a 1 degree increase in average temperatures, even more females could be hatched. That isn’t a problem right now, but in 100 years there will not be enough males to fertilize the females’ eggs. And if there is a 3 degree increase in temperature, it is quite possible that fewer sea turtles will hatch.

Sea turtles may be able to prevent the female bias from developing further by:

  • nesting earlier when it is cooler;
  • nesting at more northerly locations;
  • changing the depth at which they bury their eggs,
  • or burying their eggs in lighter coloured sand because lighter coloured sand absorbs less heat from the sun than does darker coloured sand.

We humans can help too, by avoiding building hotels and resorts on the lighter coloured beaches.

Photo credit: USFWS/Southeast via VisualHunt / CC BY

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