All painted turtles might be hatched female by 2100, making it impossible for the species to reproduce. That’s the chilling projection from a team of researchers at Iowa State University based on 25 years of painted turtle hatchlings sexed by Fredric Janzen, who has demonstrated that the sex ratio of the baby turtles is determined by the temperature when the mother lays the eggs.
The beautiful painted turtle, Chrysemys picta, is currently believed to be North America’s most abundant turtle. However, if the team’s mathematical projections are right, it could be doomed.
Lead author Rory Telemeco and colleagues already knew that eggs laid at warmer temperatures are more likely to be females, while eggs laid during cool weather are more likely to be males.
Many other reptiles also have temperature dependent sex ratios, although warm doesn’t always mean female. In American alligators, males are hatched at temperatures greater than 93 degrees Fahrenheit, while females are hatched at temperatures lower than 86 degrees.
To a certain extent, the mother can adjust when and where she lays the eggs to make sure that there are equal numbers of males and females produced. For instance, in the alligator, she might lay in a darker, cooler marsh instead of on a hot, bright levee to make sure that she produced enough females.
In the painted turtle, all female hatches can be avoided if the mother starts laying earlier, when it is still cool enough to allow her to produce some males.
However, the Iowa State University team said that the painted turtle can only shift her egg-laying dates by about 10 days — and they believe that it isn’t enough. Based on current rates of global warming, they predict that every baby painted turtle will be hatched female by the end of this century.
[Western painted turtle photo by RexxS via Wikipedia Commons]