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Study: Nutrient pollution drives frog deformities

September 25, 2007

High levels of nutrients used in farming and ranching activities fuel parasite infections that have caused highly publicized frog deformities in ponds and lakes across North America, according to a new study led by the University of Colorado at Boulder.

University of Wisconsin–Madison researchers Katherine Dosch, Richard Hartson, Daniel Sutherland and Stephen Carpenter were co-authors on the study, which published online this week (Sept. 24) in the Proceedings of the National Academy of Sciences. The National Science Foundation funded the work.

The study, which was conducted in Wisconsin, showed increased levels of nitrogen and phosphorus cause sharp rises in the abundance and reproduction of a snail species that hosts microscopic parasites known as trematodes, says Pieter Johnson, lead author of the study and an assistant professor in the ecology and evolutionary biology department at the University of Colorado. The nutrients stimulate algae growth, increasing snail populations and the number of infectious parasites released by snails into ponds and lakes, which subsequently form cysts in the developing limbs of tadpoles that cause missing limbs, extra limbs and other severe malformations, Johnson says.

“This is the first study to show that nutrient enrichment drives the abundance of these parasites, increasing levels of amphibian infection and subsequent malformations,” says Johnson. “The research has implications for both worldwide amphibian declines and for a wide array of diseases potentially linked to nutrient pollution, including cholera, malaria, West Nile virus and diseases affecting coral reefs.”