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Warming May Drive Gender-Bending Reptiles Extinct, Scientists Say

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.

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."

Rescue Plan

Tuatara once ranged throughout New Zealand before rats, cats, and stoats—introduced by human colonizers—wiped them out.

Now the reptiles are limited to remote, mostly small islands around the top of New Zealand's South Island and off the eastern coast of the country's North Island (map of New Zealand).

"On North Brother, most nesting is in very shallow soil, and there's already a male bias in the population," Nelson said. "There's probably no way to naturally resurrect that."

So scientists are gathering eggs from North Brother and from nearby Takapourewa, or Stephens Island, and raising them in artificial incubators.

"We can dial in whichever sex we like," Nelson said.

Another captive population is being reared in California's San Diego Zoo.

Hatchlings are reared in captivity before being introduced to other islands as part of an effort by New Zealand's Department of Conservation to reintroduce the tuatara to its former haunts.

But Alison Cree, a senior lecturer at the University of Otago in Dunedin, New Zealand, says rising temperatures are not the only threat climate change poses to tuatara.

"There are the potential impacts of rising sea levels, coastal erosion, and habitat loss in general," Cree said.

Researchers plan to release tuatara in a sanctuary protected by a specially designed predator-proof fence at Orokonui, near Dunedin. The site is well south of the tuatara's current distribution, and Cree hopes it will buy time for the species as northern New Zealand warms in the coming decades.

"Eight populations of northern tuatara live on islands of 5 hectares [12 acres] or smaller, often with only two or three hectares [5 or 7 acres] of suitable habitat," she said. "The higher the sea level, the smaller that will get. We're already concerned about the long term future of those populations—there are so few animals there already."

Revered Animal

Saving the tuatara is a matter of pride among New Zealand's indigenous groups. The animals are revered by the Maori as a taonga, or treasure.

Glenice Paine, the Te Atiawa Maori tribe's resource management officer, says something irreplaceable will be lost if tuatara can no longer survive in the wild. The archaic reptile is a living link with the ancestors of her people.

Paine says her people were initially reluctant to allow some to leave the country for the San Diego Zoo.

"But when you consider climate change, if anything catastrophic was to happen here... it's sort of like an insurance policy," Paine said.

"In the Maori worldview we believe that everything is connected, so that tuatara are part of our whakapapa—our genealogy," Paine added.

"We are kaitiaki—guardians—of those tuatara, so we have an obligation from our ancestors to ensure their well-being, to make sure they're protected. To lose them would be like losing part of ourselves."

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