A Closer Look at Frog Deformities

By now the images are no longer surprising, even if they remain grotesque and disturbing tolook at: frogs with missing or extra legs, missing or misplaced eyes and other strange deformities.

Ever since children in Minnesota and Vermont discovered large numbers of abnormal frogs in the mid1990s, researchers have scrambled for answers in what has become an alarming environmental issue.

Speculation was rampant, with little research to back it up. But in the last two years there has emerged new research, some of it still unpublished, that begins to close in on potential causes. This report, based largely on scientific literature, summarizes new insights into what is known and unknown about frog deformities.

A breakthrough in the search for causes came in April, when the journal Science published research demonstrating that a parasitic flatworm, called a trematode, could induce a range of deformities in Pacific treefrogs. Although the study was front-page news, even the principal researcher agrees that the case is hardly closed on the causes of frog deformities.

While any number of factors may be responsible, the research is converging on several potential causes, acting singly or together: parasite infestation and disease, increased levels of predation, ultraviolet radiation and natural or anthropogenic (introduced by humans) chemicals, including pesticides and other toxic contaminants.