One theory on frog deformities

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(Host) If you’ve wondered about all the news pictures of frogs with a couple of extra legs or other deformities, commentator Ruth Page offers one scientist’s tested explanation.

(Page) “Look, Mrs. Page, isn’t this weird?” The six-year-old held out to me a frog with four weak, floppy back legs.
“Y’know, Betsy, there are a lot of frogs like that nowadays, and scientists are still trying to figure out why,” I said. That was last year; this year, there’s more information.

News media have published pictures of deformed frogs for years, with a mix of likely causes, from reactions to chemicals in the environment, to parasites, to more ultraviolet light striking earth. Proof was hard to find because any combination of causes was possible. Now, a Science News story offers one answer, headlined “Double whammy promotes frog deformities.”

In the past two or three decades, deformed frogs are turning up worldwide, much more often than in the past. Researchers have found evidence to make them suspicious of two environmental changes.

To pin down dome answers, Joseph M. Kiesecker, an ecologist at Penn State University, set up a study to check out both parasites and pesticides as agents of deformity. With plastic film, he set up six enclosures in six natural ponds in Pennsylvania.

All the ponds contained parasites. Half contained no other pollutants; the rest got pesticide runoff. Half the enclosures let new parasite larvae enter from the surrounding pond; half fenced them out. Kiesecker then put ten wood frog hatchlings in each of his 36 fenced spaces. After a month, he examined frogs in the early stages of changing from tadpole to frog.

Limb deformities occurred only in the enclosures with parasites – but if the enclosure also contained pesticides, more frogs were damaged. In the pesticide-polluted ponds, 29% of the creatures were deformed; in the ponds with only parasites, just 4% were affected.

Kiesecker tested frogs with the low pesticide amounts considered safe by the EPA; he found those were enough to damage the frogs’ immune systems. The researcher therefore concluded that the basic cause of frog deformities is attack by parasites, made worse by pesticides in the water. And there’s Science News’s “double whammy.” That helps explain why damaged frogs are found in vastly different regions of the U.S. Nature put the parasites in the water; we helped the parasites by providing pesticide residues.

This is Ruth Page, offering an example of how a controlled scientific experiment can help solve an environmental puzzle.

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