Girls Only

Climate change could push painted turtles toward heavily-female populations, a new study suggests.

A painted turtle’s sex depends on the temperature during its development. If the environment is warmer, the turtle tends to become a female; if cooler, it tends to become a male. So scientists worry that males could become more and more sparse with global warming, eventually driving the species extinct.

One possible escape route is that female turtles could start nesting earlier, when the weather is cooler. But it’s not clear whether this change would be enough to save the species.

A research team developed a model to test this scenario. If the region warmed by 4 degrees Celsius, the females could keep the soil temperature at the beginning of nesting the same by laying their eggs about three weeks earlier. But during the phase when the young turtles’ sex is determined, the temperature would still climb to 3.2 degrees Celsius higher than normal.

This trend would eventually result in “a 100% female sex ratio and ultimately population extinction,” the team writes in The American Naturalist. The turtles might have to adopt other measures to produce males, such as nesting in shadier spots. Roberta Kwok | 1 April 2013

Source: Telemeco, R.S., K.C. Abbott, and F.J. Janzen. 2013. Modeling the effects of climate change-induced shifts in reproductive phenology on temperature-dependent traits. The American Naturalist doi: 10.1086/670051.

Image © Gerald A. DeBoer |



  • tom April 3, 2013 at 7:27 am

    Why would not this temperature increase effect ALL other turtles and most other reptiles? The sex ratio of captive breeding of snakes can be effected by temperature. One would have thought that the researchers would have mentioned this.


    • roberta April 6, 2013 at 9:26 am

      Thanks for your comment. The authors do recognize that temperature-dependent sex determination (TSD) occurs in more than one species; in the paper, they note that “species with TSD might be at risk of climate change–induced extinction because directional changes in temperature could skew sex ratios.” They chose to focus on painted turtles in their study.


  • Mattias Wieland April 3, 2013 at 10:44 am

    Clearly, all reptiles face this problem with a changing climate and have done so in the last 200 Million years. Even though we don’t know how they cope with it or adapt to it, there must be a way. Otherwise I can’t see how sex determination by temperature could have turned out to be evolutionary so successful.


    • Becca April 3, 2013 at 4:24 pm

      While sex determination by temperature may have been evolutionary successful in the past, the climate was not changing as rapidly 200 million year ago as it is today. It is possible that many species, like these reptiles, will not be able to adapt to the current rate of climate change.


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