University of Pittsburgh

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Why are frogs disappearing?

Breakthroughs in the Making

Written by Ezra Christopher


Green friends, take heed! Insecticides, even in low doses, may be doing more damage to the environment than previously known. Pitt biological sciences professor Rick Relyea has spent nearly a decade investigating the environmental effects of common chemicals on tadpoles. The findings from his latest study, coauthored by alumnus Nicole Diecks (CGS ’05), affirm a link between the routine use of pesticides and the dramatic decline in the survival of tadpoles.

As part of the study, which was funded by the National Science Foundation, Relyea and his team applied multiple low doses of the pesticide malathion to artificial ponds containing leopard-frog and wood-frog tadpoles. Malathion—a popular pesticide in the United States—is used in agriculture and for controlling mosquitoes that carry malaria and West Nile virus. It has been detected in U.S. wetlands.

In Relyea’s experiment, the weekly application of low doses simulated the levels of pesticide that many tadpoles experience in nature. By the end of the study, 43 percent of the leopard tadpoles did not mature fully and faced an early death. Even more significantly, the research team discovered that the pesticide killed zooplankton, tiny animals that eat phytoplankton in the water. Without zooplankton, phytoplankton overproduces and slows the growth of a type of algae that is a critical food source for tadpoles. It appears that malathion decimates tadpole populations by destroying their food chain. Amphibians are considered to be an environmental-indicator species because of their sensitivity to pollutants. Ultimately, these findings sound an alarm for the future of other species, including humans.