Male tuatara are desperate, and may soon be dateless (7/3/2008)

Tuatara in Invercargill (New Zealand)

A new study has predicted that temperature increases due to climate change will cause the tuatara, an endangered reptile, to produce only male offspring by 2085, guaranteeing its extinction.

The tuatara, a 'living fossil', is a cold-climate reptile found on some of New Zealand's smaller islands. Its two related species are the only surviving members of the Sphenodontian family that flourished about 200 million years ago. About 80cm long, they are greenish brown with a spiny crest along their backs.

The impact of climate change on the reproductive cycle of the tuatara, is being examined by a team including Dr Nicola Mitchell, a research fellow at The University of Western Australia's Centre for Evolutionary Biology, Dr Michael Kearney from the Department of Zoology at the University of Melbourne and researchers from other universities.

In a paper published today (2 July) in Proceedings of The Royal Society, the researchers document their unique model that demonstrates how climate, soil and topography interact with physiology and nesting behaviour to determine sex ratios.

In many egg-laying reptiles, including the tuatara, the sex of offspring is determined by the temperature experienced during a critical period of embryonic development -a phenomenon known as temperature-dependent sex determination (TSD). Tuatara have a rare form of TSD where male hatchlings are produced at higher constant incubation temperatures and in hotter natural nests.

Contemporary rates of climate change threaten their survival because their isolation on islands prevents them migrating south to cooler climates. Their best chance of survival, other than reducing the magnitude of global warming, lies in translocation to other islands or protected mainland areas predicted to have thermally suitable micro-sites for nesting.

"Translocations of tuatara to islands south of their current range are already occurring. We now have a tool to identify which locations would produce favourable sex ratios under climate change," Dr Mitchell said.

Tuatara were driven to extinction by mammalian predators on New Zealand's main islands but small populations (from 10 - 30,000) survive on offshore islands.

"Tuatara are ancient animals - their ancestors were scurrying around the feet of dinosaurs. It would be a great shame to lose them," Dr Kearney said.

(Ref: Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara? N.J. Mitchell et al. Proceedings of the Royal Society B: Biological Sciences)

Note: This story has been adapted from a news release issued by The University of Western Australia

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