Skin deep: A lungless frog that breathes through its skin has been discovered in the jungles of Borneo.

Credit: AFP/David Bickford

Related articles

• No need for dissection with transparent frogs
• Amphibians in losing race with climate
• Frogs rafted to the Caribbean
• A cure for the amphibian plague?
• Shifting lungs make crocs smooth movers

JAKARTA: The discovery of a rare species of Indonesian frog that breathes without lungs could shed light on how evolution works, a scientist has said.

Dissection of the frog, which was found on Borneo last August, showed it breathed entirely through its skin, said biologist David Bickford of the National University of Singapore in Kent Ridge.

"It's like a cookie, it's almost completely flat. So initially when you pick it up in the water you know this thing is strange," said Bickford. "It's surprisingly cute, you know, like a bulldog is cute. It's one of those things that is so ugly, it's cute."

While many frogs breathe partially through their skin, the Bornean flat-headed frog (Barbourula kalimantanensis) is the first to have evolved entirely away from having lungs. This runs counter to one of the key events in evolution, when animals developed primitive lungs and moved from water to land.

"Here is a frog that has reversed that trend, it has totally turned against the conventional wisdom, if you will, of millions of years of evolution," said Bickford.

The frog appears to have shed its lungs over millions of years to adapt to its home in the fast-flowing cold water rivers in the island's rainforests, according to Bickford. Cold water contains more oxygen, making it possible to breathe through skin, he said.

Unused organs

Only three other amphibians – two species of salamander and a worm-like creature called a caecilian – are known to have evolved to breathe without lungs.

While many animals have organs they no longer use – such as the human appendix – evolution normally works on the principle of "if it's not broke don't fix it," Bickford said. "Most things we don't use don't get lost ... so there had to be a big negative side-effect of having lungs for them to be lost."

Bickford believes lungs may have made the frog's ancestors too buoyant in the fast-flowing water, increasing their risk of being swept away. The downside, he said, is that the frog cannot survive on land or even in still water.

Indonesian scientist Djoko Iskandar, who accompanied Bickford on the expedition, first heard about the strange-looking creature 30 years ago and had been searching for it ever since.

He said that every time he went to Borneo he found habitats had been destroyed by industry, with river pollution from gold mines apparently making it impossible for the frogs to breathe.

"We think that a little bit of pollution will affect the skin, and the skin is more important than for other species," said Iskandar, a scientist at the Bandung Institute of Technology in Indonesia, adding that even a small amount of pollution could be devastating.

Hundreds of new species of insects, animals and plants have been discovered on Borneo, with a find every month on average, conservation group WWF has said. Other recent exotic discoveries include poisonous "sticky frogs," "forest walking catfish" able to travel short distances out of water and the transparent "glass catfish".