Janzen and his collaborators studied mud turtles, sliders, snapping turtles and painted turtles that live in South Carolina, Nebraska, and along the Mississippi River between Iowa and Illinois.
An aspect of the study that surprised Janzen was the gender of the offspring.
The gender of turtle offspring, as with many reptiles, is typically determined by the temperature of the ground where they lay their eggs.
Janzen predicted that with warming temperature, the phenomenon of temperature-dependent sex determination would cause a disproportionate number of females since warmer conditions produce that gender.
Just the opposite seems to be happening. Male babies are outnumbering the females.
"Warmth produces females, so we thought we'd have more females," said Janzen. "But what we think is happening is, since the air feels warmer, the turtles are nesting earlier. But the ground is still cold, so the cold ground is causing us to get more males."
Janzen thinks that the overabundance of males will stress the species. Combined with the adult females being forced to change nesting habits, the stresses could mean the species is under real pressure to adapt swiftly, a pace not popularly considered to characterize turtles, he said.
|Contact: Fred Janzen|
Iowa State University