Warming May Drive Gender-Bending Reptiles Extinct, Scientists Say

[dawn hilton]

Dave Hansford in Wellington, New Zealand
for National Geographic News
November 10, 2006

Less than one degree Celsius (1.8 degrees Fahrenheit) is all that stands between the tuatara—New Zealand's "living fossil" reptile—and extinction, scientists say.

The sex of tuatara—the sole surviving species of an ancient family of reptiles dating back 200 million years—is determined by the incubation temperature of its eggs. As the mercury climbs, so does the proportion of male hatchlings.

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The mechanism is so delicate that a flagging population on remote North Brother Island in Cook Strait is already running short of breeding females.

Nicky Nelson, a senior lecturer at Victoria University in Wellington, New Zealand, says experiments show that 21.7 degrees Celsius (71 degrees Fahrenheit) could be the pivotal temperature.

"At 22 degrees Celsius [71.6 degrees Fahrenheit], we got 100 percent males. At 21 degrees Celsius [69.8 degrees Fahrenheit], we got three males out of 80 eggs," Nelson said.

Nelson and her colleagues fear that such a finely tuned mechanism will become completely unbalanced as climate change warms the few remaining tuatara breeding grounds.

Intensifying the problem is the slow reproduction rate of the reptiles. On average, female tuatara mate once every four years, and eggs take between 11 and 16 months to hatch.

Different Kind of Disaster

Tuatara have endured climatic chaos before, Nelson says—they even survived the meteor strike many believe wiped out the dinosaurs. (Related: "Dinosaur Killer" Asteroid Only One Part of New Quadruple-Whammy Theory" [October 30, 2006].)

But the reptiles were far more abundant back then, bestowing them with enough genetic diversity to see them through the global catastrophe, Nelson says. Now, with their numbers already decimated, the species may face a much faster rate of warming.

"These creatures can live for more than a hundred years. We're talking perhaps a 5-degree jump in a single animal's lifetime," Nelson said.

"We're not talking adaptation—we're talking about the abilities of individuals to survive."