Malformed frogs are documented in 44 states, in 38 species of frogs and 19 species of toads, with estimates of deformities running as high as 60 percent in some populations. To understand more about amphibian deformities, researchers from the U.S. Geological Survey completed an extensive study on bone changes in malformed frogs with advanced X-ray technology. Variables of time and site-specific environmental events may influence these malformations, according to the report, which will be published in the journal Teratology. The study revealed that similar deformities are occurring in frogs collected at the same time from a particular site, suggesting that malformations within a specific population may well come from the same environmental hazard. The deformities usually occur during the development from tadpole to frog, explained Carol Meteyer, a wildlife pathologist at the USGS National Wildlife Health Center in Madison, Wisconsin and co-author of the study.
Development is controlled by chemical signals.
The precision and patterns of some of these malformations are striking. An oversized leg with extra toes is another example of frog deformities found by researchers. Although extra limbs were found in only 5 percent of the frogs in the study, all of the frogs with multiple limbs came from the same sites in Minnesota and Maine. In Vermont, all of the 65 malformed frogs were missing all or a portion of their hind legs. Of the frogs that were missing entire limbs, X-rays revealed that 73 percent were also missing bones in the hip, evidence that development and not predation is to blame.