Submitted by Larry Halverson

Unlike birds, turtles don’t sit on their eggs. The female just digs a nest in the ground and then leaves her eggs to develop. Whether an egg hatches male or female depends on the temperature of its nest. Painted turtles undergo a phenomenon called “temperature-dependent sex determination” while developing inside the egg. Unlike mammals, birds, and other creatures, whose sex is set by the chromosomes they get from their parents, the trigger that causes turtle embryos to develop into baby boys or girls comes from outside the egg. Warmer temperatures during incubation will make the hatchlings female. But keep the eggs just a few degrees cooler; they’ll come out mostly male.

So increasing average temperatures due to climate change could disrupt the ratio of males to females and even threaten the survival of the species. Researchers studying painted turtles determined that an average temperature increase of just 1.1 degrees Celsius would be enough to skew the population to all females, which would ultimately lead to extinction. Especially since they live in small areas where there is little choice about where to lay eggs, and they can’t migrate like birds. So this is one species that can’t stand the heat.