Frogs turn Palawan Paradigm on its head

Scientists reveal the ancient origin for the renowned Bornean lungless frogs

August 2010: What do Bornean lungless frogs and the rare Philippine flat-headed frogs have in common? The answer, scientists now conjecture, is tens of million years of evolutionary history and potential isolation of their ancestors on a small ‘raft' of islands that split from mainland Asia 30 million years ago.

ISLAND HOPPER:The Borneo lungless frog may not originally have come from Borneo at all, according to this latest research

The surprising findings were the result of the collaboration between scientists in four countries led by the University of Kansas's David Blackburn, who said the results ‘reveal a very ancient origin to these enigmatic frogs and suggest a new interpretation for the origins and history of animals living in the western islands of the Phillippines'.

Frogs became isolated on ‘raft' of islands
Dr Blackburn's co-author Arvin Diesmos added: ‘If our results are correct, the ancestors of lungless frogs may have become isolated on a small chain of islands that rifted from the Asian mainland 30 million years ago. This small, ancient archipelago, we now believe, later formed the mountains of Palawan Island.

‘These highly distinctive, threatened frogs may have acquired their unique characteristics during the period that they were isolated on the so-called "Palawan raft".'

In the study, the scientists sequenced a large number of genes and performed molecular clock analyses to date the evolutionary origins of lungless and flat-headed frogs. Scientists have long assumed that Philippine flat-headed frogs arrived in the western Philippine island of Palawan following dispersal to the north from Borneo, but now molecular data gathered by the team suggests that the frog's ancestors may have become isolated on the ‘Palawan Raft', a small, hypothesised chain of islands that broke off of mainland Asia, and eventually connected with the Philippines and Borneo.

If correct, these results suggest that the ancestors of the lungless frogs of Borneo may have dispersed south to Borneo, from Palawan Island of the western Philippines. These and results of several other recent studies contradict the 150-year-old Palawan Paradigm and the idea that western Philippines supports an unremarkable group of animals and plants, most of which were derived from Borneo.

CLOSE RELATIVE: The rare Philippine flat-headed frog. Picture: Dr Rafe Brown

Dr Mundita Lim of the Philippine Department of Environment and Natural Resources cited several other recent studies that, together with the new findings, emphasise the evolutionary uniqueness of the western Philippines - contradicting biologists' prevailing interpretation for the past 150 years.

Frogs survived in Philippines for 20million years before making it to Borneo
‘The Palawan Island chain is not the simple, unremarkable "faunal peninsula" of Borneo as previously thought by many biologists.'

Dr Rafe Brown, the curator of herpetology at the University of Kansas, said: ‘Our findings have the potential to turn the "Palawan Paradigm" on its head. Given our new data, we must consider the possibility that these unique amphibians survived 20 million years in the Philippines before dispersing to Borneo - not the other way around.'