Bafflement as toads go blind on Brazilian island

Why did toads which invaded a Brazilian island a number of decades ago begin going blind since arriving there?

Cururu toads have gone from normal sight to half-blind or fully blind while body parts have also malformed since arriving on Fernando de Noronha island off Brazil some decade ago

Cururu toads have gone from normal sight to half-blind, as in photo, or fully blind while body parts have also malformed since arriving on Fernando de Noronha island off Brazil some decade ago Image by Peter O'Connor aka anemoneprojectors / CC BY 2.0

That is a question scientists are trying to answer while also working out increased incidents of deformities among the same cururu toads on Fernando de Noronha island.

Fernando de Noronha island where important environmental studies on toads is taking place

Fernando de Noronha island where important environmental studies on toads is taking place Image by Henrique Pinto / CC BY 2.0

Latest research shows that nearly half of the toads have malformed limbs and mouth parts while one-in-five is either blind or half-blind – forcing them to hunt in direct ways for food.

The BBC reports that these changes have, in turn, led to a transformed lifestyle for the frogs. Instead of searching out prey, they wait for them to walk onto or into them before consuming them.

The study in the Journal of Zoology quotes amphibian biologist Luis Felipe Toledo as saying that because the frogs now eat less, they are not as big as traditional toads and also produce less eggs.

However Mr Toledo says they still produce eggs in sufficient number to ensure they will keep the population going.

He says that while everyone asks why toads are like that, the research hasn’t been able to answer it satisfactorily yet. His university in Sao Paolo has come together with people at San Diego Zoo in the US to test the reasons for the large-scale deformities in Fernando de Noronha.

Among items to be investigated are the possibility of bacteria or a virus being the root of the problem or the possibility of genetic issues due to inbreeding.

Researchers are also testing the water in and around the island as well as the soil to check for possible contaminants.

The quest to find the source of the malformations in the cururu toads is all the more urgent as there are fears the ailment could spread to other wildlife species, according San Diego Zoo’s Allan Pessier.

He added that the toads had acted as a sort of early warning device to potential problems in the environment.

Related content