Nutrients cause increase in parasites and frog deformities

Extra and missing-legged frogs have become increasingly common in North American wetlands over the last decade. Research implicates a flatworm parasite, Ribeiroia ondatrae, as the culprit of these deformities. Reasons for the apparent increase in infection and malformations, however, have remained a mystery.

In the July issue of Ecology Letters, Johnson and Chase suggest a possible reason why this native parasite is on the rise. By surveying more than 75 wetlands across the western and midwestern United States, Johnson and Chase suggest that excess nutrient inputs into the ponds where tadpoles develop causes an increase in rams horn snails - the exclusive first hosts for the parasites.

Increased numbers of these snails correlate with higher levels of parasite infection and, in turn, frog deformities.

These results may help to both explain the recent increase in amphibian malformations and to suggest control strategies for reducing malformations and mortality associated with infection.

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