July 8, 2002 Frogs with limb deformities are shown with two normal frogs, top left and top right, for comparison. Please Register or Log in to view the hidden image! STATE COLLEGE, Pennsylvania (AP) -- Scientists debating whether high rates of deformities in frogs are the result of parasites or pollution may both be right, a study suggests. In an article published Tuesday in the Proceedings of the National Academy of Sciences, Penn State University biologist Joseph Kiesecker wrote that infection with trematode worms, a common parasite, actually causes the deformities in wood frogs, but that the deformity rates were substantially higher in areas where infected frogs were exposed to pesticide runoff. The exact role of pesticides is still unclear. But Kiesecker said the chemicals may lower frogs' immunity to infection, or pesticide runoff may boost the population of snails that transmit the trematodes to frogs. Since the early 1990s, researchers have found large numbers of deformed frogs, many missing limbs or growing extra limbs, across wide regions of the Pacific Northwest and the Northeast. Gayle Kraus, a marine biologist at the University of Maine at Machias, said a combination of natural and environmental factors makes sense. Kraus said environmental stresses -- whether it is heat on coral, or pollution in seals -- causes organisms to succumb more readily to naturally occurring diseases. "That same pattern seems to be occurring in different groups of organisms," Kraus said. Kiesecker's study examined frogs in six central Pennsylvania ponds both with and without pesticide runoff, and frogs in the lab. In ponds without pesticide runoff, deformities occurred in 5 percent to and 10 percent of trematode-infected frogs. In ponds where runoff was present, deformity rates were 20 percent to 30 percent. Copyright 2002 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed. http://www.cnn.com/2002/US/07/08/deformed.frogs.ap/index.html
