Summer frogs

“Parasite Creating Deformed Frogs in Western U.S.

Hot spots of "grotesque" infections are shifting, research suggests.

Christine Dell'Amore

National Geographic News

Published August 3, 2011

Amphibians with "sick and twisted" deformities continue to be widespread in the western United States, new research says. (See more pictures of the deformed frogs.)

A flatworm parasite called Ribeiroia ondatrae infects several species of frogs just as they're developing their limbs, causing an assortment of defects such as no legs or even multiple legs that jut out at weird angles from the frogs' bodies scientists say.

The deformed frogs are often unable to move and either die or quickly get eaten by predators.

Scientists already knew that the parasite was the culprit in the frog malformations, but the researchers wanted to find out whether known hot spots of Ribeiroia populations in four western states had changed since they were last surveyed in 1999.

So in 2010 Pieter Johnson, an ecologist at the University of Colorado at Boulder, and colleagues gathered data on frogs and parasites in 48 wetlands inCalifornia, Oregon, Washington, and Montana.

The scientists found that the parasite infections were still pervasive in amphibians at the study sites.

"We found that, although the distribution of Ribeiroia across wetlands changed, there was little net effect on overall parasite prevalence, with 31 percent of wetlands gaining the parasite and 27 percent losing the parasite," according to the study.

But "what was most intriguing," Johnson said, "was that the locations of hot spots had changed substantially over the last decade."

For instance, ponds where scientists had found few "grotesque" frogs in 1999 now had 30 percent or more frogs with deformed limbs, he said. Likewise, former hot spots now had fewer of the diseased amphibians, according to their results, which are not yet published in a journal.

Because some of the hot spots can house threatened or endangered amphibians, conservationists need to know where the parasite is moving.

Predicting future hot spots by keeping track of environmental factors—for example how land is used—may also help scientists figure out what's happening to amphibian populations.

"These severe malformations—even though it's not in the headline news—these continue to occur in a lot of amphibian populations in the western U.S.," said Johnson, who received funding from the National Geographic Society'sCommittee for Research and Exploration. (The Society owns National Geographic News.)”