The truth about frogs

Scientists in the US are trying to find out the reason fordeformities in frogs

Published: Saturday 15 November 1997

 What should be blamed for abn (Credit: New Scientist)ever since deformed frogs were found in Minnesota, usa , scientists have been attempting to know the reason of such unusual cases. Recently, John Bantle, a researcher at Oklahoma State University, Stillwater, usa , has discovered that when methoprene -- a pesticide used against mosquitoes -- is exposed to sunlight, it produces chemicals that can lead to abnormalities as seen in the frogs. Methoprene is sprayed on mosquitoes to prevent their larvae from developing into adults (New Scientist , Vol 155, No 2099).

Although methoprene has a little effect on developing amphibians, if it is exposed to ultraviolet (uv) rays, it can cause serious deformities. When the researcher exposed frogs to two methoprene breakdown products such as cismethoprenic acid and transmethoprenic acid formed on exposure of uv radiation, they developed serious deformities within 96 hours.

Apart from Minnesota, frogs with high rates of abnormalities have also been reported in southern Canada and Japan. The deformities include missing limbs, extra limbs and even one frog has been found with an eye growing in its throat. Environmental scientists feel that if such abnormalities are reported in delicate species like amphibians, the human health may also face risk.

In another study, Ed Little at the us Geological Survey in Columbia, Missouri, has discovered that under uv radiation, the common insecticide carbaryl breaks down into a much more toxic substance that may harm tadpoles. The findings suit with the observations of Martin Ouellet at the McGill University in Montreal, usa , that frogs in ponds are likely to show deformities than those who are not.

In the mean time, Stanley Sessions, a developmental biologist at Hartwick College in Oneonta, New York, has found that fluke parasites also lead to malformations in tadpoles. These parasites take shelter in tadpoles and form small hard cavities. When the researcher inserted plastic particles of the same size as the cavities into tadpoles, the tadpoles developed deformed legs. Sessions has now been able to infect tadpoles with fluke parasites in the laboratory.

Whereas, a study conducted by Robert McKinnell of the University of Minnesota in Minneapolis, usa, suggests that internal abnormalities may also be a cause of deformed legs in frogs. He claims that some cases that he has come across, have not been caused by parasites.

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