There are more than one way to determine the gender in nature. We humans depend on who is the carrier of the Y chromosome - XX female, XY male -. Other species such butterflies or chickens depend on the W chromosome - ZZ male, ZW female. But there is still another surprising possibility: the environmental sex determination.
Temperature plays a key role in a special type of this system, being very common in crocodilians, turtles and other reptiles. This nongenetic way of determine whether an egg develops as male or female occurs after fertilization.
For instance, in some turtle species, like Trachemys, eggs from colder nests result in all
males, whereas eggs from warmer nests turn into females. In crocodilian
species — the most studied is the American alligator— both low and high temperatures result in females, and intermediate temperatures become males.
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| Temperature-dependent sex determination in three reptile species: the American alligator (Alligator mississippiensis), the red-eared slider turtle (Trachemys scripta elegans), and the alligator snapping turtle (Macroclemys temminckii). (After Crain and Guillette 1998) |
