What Determines the Gender of an Alligator?

By Jo Jackson

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In most animals, offspring genders are determined by sex chromosomes at the time of conception. But alligators and other crocodilian species, as well as some turtles and lizards, do not have sex chromosomes. Instead, the sex of the young is determined by the temperature at which the eggs incubate during a critical period of development.

Alligators

American alligators live in freshwater environments like marshes, wetlands, swamps, ponds and rivers. They range west from Florida to southern Texas and north to parts of the Carolinas. Alligators have broad snouts and are predators of fish, turtles, other reptiles, birds and small mammals. Adults range from 8 feet to 16 feet long -- males have been sighted up to 20 feet long. Females average 8 to 10 feet long.

Reproduction

Alligators reach sexual maturity when they reach 6 feet long -- around 10 to 12 years of age. The mating season runs from mid-April through May. After mating the female builds a nest of sticks, leaves, other vegetation and mud close to the water or on wet marsh. In late June or early July she will lay 20 to 60 eggs in the nest and cover them with vegetation. The eggs take 60 to 65 days to incubate, which means they generally hatch in mid-August. The young alligators actually call to their mother before they break out of their shells.

Nest Temperature and Gender

Incubation temperatures below 86 degrees F from days seven to 21 after laying results in all female alligators. Temperatures above 93 degrees F from days seven to 21 after laying causes all the young to be males. Temperatures between these two result in batches of both genders. After day 21 of incubation, temperature fluctuations do not alter the gender of the hatchlings that will emerge.

Young Alligators

Nests built on levees tend to be hotter than those built on wet marsh, so more females are born in the wetter areas. Females tend to be bigger when they hatch, though males ultimately grow larger. The young are born with a yellow band of color around their bodies; it gradually fades over several weeks. Their mother will protect them for several months. Young alligators grow 4 inches to 14 inches a year, depending on food and habitat.

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