The frog which loses its lungs
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| CALL FOR CONSERVATION: Dr David Bickford in Kalimantan where the lungless frogs are found. Inset: The B Kalimantanensis, flatter than normal frogs. |
The jungles of Borneo have yielded the world's first recorded lungless frog. Researchers led by Dr David Bickford, Assistant Professor with the Department of Biological Sciences at NUS, have confirmed that this rare species of frogs called Barbourula kalimantanensis are indeed completely lungless. Living in clear, cold-water streams, the frog gets all its oxygen through its skin.
The team made this discovery during a visit to a site many kilometers upstream from where the species was described from some 30 years ago. Dr Bickford,
an evolutionary biologist, explained that they had not dissected the specimen back then, as there was no real reason to believe that they could be lungless.
The amphibians are slightly more than two inches long, slippery and can swim surprisingly fast for short bursts. Moreover, they are very difficult to find. "We had a team of 11 people looking for these frogs and it took us almost two weeks before we found any," Dr Bickford recalled.
Snorkelling in the rivers where the frogs live, the researchers were forced to stop after 45 minutes as the water was too cold.
"Nobody knew about the lunglessness before we accidentally discovered it doing routine dissections," said Dr Bickford in an interview with National Geographic News. Their findings will also be featured in Current Biology (May 2008).
The evolution of lunglessness in four-limbed amphibians is exceedingly rare. So far, it is known to occur only in two families of salamanders, and a single species of caecilian, a species of earthworm-like amphibian.
The frog lives in cold water which has higher oxygen content than warm water. The team surmises that the frog has a low metabolic rate and hence needs less oxygen anyway. It is also severely flat compared to other frogs and this would increase the surface area of the skin, allowing it to take in oxygen more efficiently, suggested Dr Bickford.
Having lungs also means being more buoyant and hence, more easily swept away by fast-flowing waters. Thus the loss of lungs as an adaptation to living in very fast-flowing streams seems to be a rational hypothesis as well.
Virtually nothing is known about how they reproduce, eat, and escape predation. Further studies of the frog, however, may be hampered as the species is extremely rare and its habitat is endangered. The water in the cold stream where they live is being clouded by sediments and contaminated by mercury from illegal gold mining. Logging in the surrounding areas also increases runoff into the streams — and climate change poses a grim future for the frogs, said Dr Bickford.
He calls for conservation of this "evolutionary enigma", with the urgent protection of the remaining habit. The evolution, development, and maintenance of lunglessness in this frog, could be significant research. The next step for him and his team is to better understand the extinction risk of the species, to map its exact geographic range and to make a more complete assessment of potential habitats.
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