World's only lungless frog leaves scientists gasping

The Bornean flat-headed frog lives in fast-flowing streams and is the only known lungless frog (Image: D. Bickford)

An unassuming little frog from Borneo has been found to have an exceedingly rare anatomical feature - introducing Barbourula kalimantanensis, the only known frog with no lungs.

The Bornean flat-headed frog gets all of its oxygen through its skin. Local gold-mining operations, however, are fast polluting the streams where the frog lives.

A single specimen of Barbourula was described in the 1970s, but biologists had no idea, until now, that the frog had no lungs.

"I was just going to be happy if we simply rediscovered the frogs," says David Bickford of the National University of Singapore. "Most of what we presume is the frog's original range is completely uninhabitable due to illegal gold mining and land conversion."

Rare adaptation

Lunglessness is extremely rare in amphibians because, although the animals breathe through their skin, the method delivers only a fraction of the oxygen provided by lungs. It is only practical for cold-blooded animals, which use far less energy than mammals.

One family of salamanders and one species of caecilians are the only other lungless amphibians. There are no known lungless reptiles.

Bickford and his colleagues think that air-filled lungs may have made it difficult for Barbourula's ancestors to sink to the riverbed through fast-flowing water, so it evolved towards a lungless existence.

The clear, cold, fast-flowing streams they live in made this change possible. In the same way cold carbonated drinks hold more "fizz", cold water can hold more dissolved oxygen. And the rapidly flowing streams send a plentiful supply of the oxygen-rich water over the frog's body.

Collector threat

But deforestation and illegal gold mining is making the streams warm and sluggish - hostile habitat for the Bornean flat-headed frog.

"We should do all we can to conserve this novel species," says James Collins, co-chair of the International Union for the Conservation of Nature's Amphibian Specialist Group. "These rare biological insights have the capacity to give us a much deeper and richer understanding of the evolution of life on Earth."

"This is an endangered frog that we know practically nothing about with an amazing ability to breathe entirely through its skin, whose future is being destroyed by illegal gold mining by people who are marginalised and have no other means of supporting themselves," says Bickford. "There are no simple answers to this problem."

Bickford's team have no idea how many frogs remain and are not revealing where the two known populations are to be found, fearing that collectors might poach them.

Journal reference: Current Biology (vol 18, p 7)

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