Bickford on amphibian extinctions

Don’t let these amphibians croak their last,” by Grace Chua. The Straits Times, 20 Aug 2008.
Up to half of all amphibian species could become extinct

THAT croaky chorus you hear coming from drains at dusk could belong to one of Singapore’s most common amphibians – the Asian toad or the banded bullfrog.

The toad has a burpy ‘curr, curr’ call and rough, warty skin, while the bullfrog is rotund, brown and cream, and ‘sounds like a dying sheep,’ according to amphibian researcher David Bickford.

Both species number in the tens of thousands here, said the National University of Singapore assistant professor, who helped unearth the only known species of lung-less frog in Kalimantan last year.

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There are 27 species of amphibians here, according to the Singapore Zoo.

Among the rarest species are the spotted tree frog (Nyctixalus pictus) and the Malayan horned frog (Megophrys nasuta), whose populations number less than a hundred.

Humans are generally bad news for frogs; local amphibian populations are threatened by pollution and habitat loss.

A frog’s skin is water-permeable, so dissolved contaminants can enter their bodies easily.

They are especially sensitive to pollution, which can cause deformities. Dr Bickford said he has found frogs with seven toes on each hind limb. Normal frogs have four toes on each front limb and five on each hind limb.

When they are exposed to pesticides, frogs can become chemically castrated – male frogs turn female, while females are unable to produce viable eggs.

The bigger picture for amphibians is dire. A third to half of all amphibian species could go extinct in the immediate future, said conservation project Amphibian Ark, a programme that brings together conservationists, researchers and zookeepers.

Frogs and toads world-wide are threatened by habitat loss, climate change, pollution and pesticides, as well as over-collection as pets and food.

Disease is another threat. The deadly chytrid fungus, which infects a frog’s skin, has exterminated the Panamanian golden frog in the wild.

Though chytrid fungus disease has not found its way to Singapore, it has decimated frog populations in Australia, Japan and the Americas.

In Feb this year, Dr Bickford and a team of international researchers published a paper on amphibian extinction.

Frogs, which had small geographic ranges with high temperature and rainfall fluctuations, were most sensitive to pressures like global warming, the researchers found.

‘The big question mark is climate change,’ said Dr Bickford.

caiwj@sph.com.sg

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