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Monday, Jul 09, 2007
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Case of the deformed frogs

Ravi Sharma

— Photo: Handout

Abnormal: A deformed frog which shows no evidence of a limb. Its hip region is smooth and the pigment pattern is not disrupted.

Bangalore: Scientists are puzzled over the fact that an abnormal number of frogs in the central parts of the Western Ghats are seen to have deformities.

Some are born with incomplete features. Their metamorphosis from tadpole to frog, when the tail gets absorbed in the body and the gill disappears, is affected. The deformities, which are not caused by predators or parasites, are generally confined to the periphery of the limbs and eyes. These include polydactyly (increase in the number of digits), brachydactyly (shortening of digits), amelia (absence of a limb) and ectromelia (an incomplete limb). While a few are without an eye, others have their eyeballs discoloured and shrunk.These are the findings of a group including Karthik Vasudevanwho works with the Dehra Dun-based Wildlife Institute of India and has been studying amphibians for over a decade; S. Murlidharan, an eco-toxicologist from the Dr. Salim Ali Centre for Ornithology and Natural History (SACON),Coimbatore; and Karkala Deputy Conservator of Forests Vir Ranjan Singh.

They are continuing the study. Water samples and tadpoles from streams have been taken to SACON.

It is seen that frogs endemic to the Western Ghats are significantly affected. Stream-breeding varieties are more affected than pool-breeders.

The findings of a Department of Biotechnology-funded study to evaluate amphibian biodiversity in the Western Ghats in terms of evolutionary aspects, showed that nearly one in 20 frogs covered by the study has a deformity.

What has puzzled them is that the deformities are different from those seen in other parts of the world where deformities have been reported. According to Dr. Vasudevan, the team has been specifically looking to studywhether insecticides such as pyrethroides (which chemically resemble Vitamin A) could be causing malformation of limbs in tadpoles. “We are looking at acause-and-effect relationship.”Surprisingly, most of the deformed frogs are found in streams deep in theforests, far from any agricultural or other activity.

The health of amphibians is one of the first pointers to environmental change in a given ecological context.

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