Monday, April 21, 2008

Evolutionary Oddity: Lungless Frog Found on Island of Borneo

The first recorded species of frog that breathes without lungs has been found in a clear, cold-water stream on the island of Borneo in Indonesia. The frog, named Barbourula kalimantanensis, gets all its oxygen through its skin.

Previously the only four-limbed creatures known to lack lungs were salamanders.

A species of earthwormlike, limbless amphibian called a caecilian is also lungless.

Tetrapods, or four-limbed creatures, that develop without lungs are rare evolutionary events, Bickford and colleagues write.

The researchers suggest lunglessness in B. kalimantanensis may be an adaptation to the higher oxygen content in fast-flowing, cold water.

"Cold water can hold more dissolved oxygen than warm water," Bickford explained.

The frog also has a low metabolic rate, which means it needs less oxygen.

What's more, the species is severely flat compared to other frogs, which increases the surface area of the skin.

"Along with the fact that having lungs makes you more likely to be swept away in a fast-flowing stream—because you would float—this [is] a very strong context for the evolution of loss of lungs," Bickford said.

(taken from google images)

(Article from National Geographic Website)

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