These findings are the results of eight years of research by scientists around the world, and are presented in the February issue of Scientific American by researchers from Oregon State University and the University of Wisconsin.
Increases in ultraviolet radiation, contaminated water and a parasitic trematode are the leading culprits in the wave of deformed legs, eye damage and other ailments that have now been found in more than 60 species of frogs, toads and salamanders in 46 states and across four continents. Of these three leading causes, the parasite appears to be the major cause of many of the deformities, the scientists say.
"We've finally synthesized from a wide body of research the range of causes that are linked to amphibian deformities," said Andrew Blaustein, a professor of zoology at OSU and co-author of the report with Pieter T.J. Johnson, a doctoral candidate at the University of Wisconsin. "As is often the case in nature, it's now clear that there are multiple causes to this problem, some of which may act in concert," Blaustein said. "But the common thread that runs through the issue is that each cause can eventually be traced to human alteration of our climate or amphibian habitat. And one of the most common deformities, extra or deformed legs, is most often linked to a particular parasite."
The deformity problem first received widespread media attention when deformed frogs were spotted by school children in Minnesota in 1995, but it quickly became apparent that its scope was extraordinarily broad and the impacts severe in some frog populations, including one near Corvallis, Ore., 75-80 percent of the frogs are deformed.