Possible Cause Found for Frog Deformities: Sunlight

A possible cause for frog deformities has been found, ultraviolet radiation (UV-B), but some experts disagree.

Last spring, a number of biologists and conservation officials expressed concern over the increasing number of discoveries of deformed frogs in a number of midwest locations (1) (2). Alarm over deformed frogs was first sounded in mid-1995 by Minnesota schoolchildren who were studying frogs in a farm pond near Henderson, Minn. In 1996, the Minnesota Pollution Control Agency received 180 reports of deformed frogs from 54 of the state's 87 counties, according to an ABC News story.

Later, reports of deformed frogs came in from other states. Alarmed over the widespread distribution of deformed frogs, biologists began discussing the problem at meetings in 1996 (Workshop Summary of Central N. America Amphibian Deformities) and 1997 (Great Lakes Declining Amphibian Conference). Also that spring, some biologists began to study frog breeding habits in the areas where deformities occurred to try to identify a cause.

Biologists have proposed several potential causes for the deformities. One potential cause is the chemical methoprene, which is used against flies, fleas and mosquitoes that pester cattle and pets. Methoprene is suspect because lab studies on limb regeneration have shown that it can produce deformities similar to some of those found in the wild. In a report for ABC News, Chris Bury wrote: "Methoprene is so powerful that only one teaspoon of pesticide is enough to cover and entire acre. It should be considered a prime suspect."

Parasites are another suspect in the deformity mystery, but last month researchers from the U.S. Environmental Protection Agency suggested an even more likely cause of deformities: ultraviolet radiation (UV- B) in sunlight.

UV-B radiation consists of invisible short wavelengths in sunlight and is blamed for the increasing rate of human skin cancer and eye problems. Both of these effects on humans have prompted doctors to recommend serious skin and eye protection. Unfortunately, frogs spend most of their time in water so sun screen wears off, and sunglasses, well, just don't fit.

All told, EPA and others have mapped frog deformities in 14 states; deformities such as extra, shortened and missing limbs; missing combinations of toes; multiple lower limbs below the knee; misshapen limbs; eye and internal organ deformities.

According to an article in the Beacon Journal, at least one biologist, Cynthia Carey of the University of Colorado, is suspicious about blaming UV-B radiation. She says that if UV-B was responsible, then more amphibians at high altitudes (where there is more UV-B) would be affected but this is not the case. Minnesota herpetologist and wildlife specialist John Moriarty also questioned the UV-B theory because he believes that the level of natural UV-B is far less than the level used in the laboratories that demonstrated a link between UV-B and deformities.

More Information on Deformed Frogs