The Mutant Frogs Rash Of Deformities In Amphibians Sounds Alarm At U.S.-Canada Conference, With Some Participants Pointing To Chemicals That May Affect Humans

In an isolated mountaintop lodge with the lights turned down, 80 scientists from the United States and Canada clustered around a projector to view slides of misshapen, mutant frogs.

The scientists looked at frogs with legs protruding from their stomachs and frogs with no legs at all. They heard about frogs with eyes staring disconcertingly from their backs and frogs with suction-cup fingers growing from their sides.

What, they wanted to know, is causing the gross deformities turning up with alarming frequency in North America’s frogs? And if they are the victims of a tainted environment, they wondered, can humans be far behind?

“Maybe these frogs are pointing out that there is a more widespread problem,” suggested Kathy Converse of the National Wildlife Health Center in Madison, Wis.

There have been reports of unusually high numbers of deformed frogs in Minnesota, Vermont, Wisconsin and Quebec, Canada. Clusters of deformed frogs have also been found in Idaho, Montana, California, Oregon, Colorado, Mississippi and Ohio.

At the conference last month in Shenandoah National Park, scientists ranging from molecular biologists to herpetologists examined theories that link the frog deformities to chemicals or parasites.

“My best guess is that it has more to do with pesticides,” Martin Ouellet of McGill University in Montreal said.

Ouellet and four other scientists have been studying deformed and normal frogs found in more than 100 ponds in the St. Lawrence River Valley during the past four years.

Normally, less than 1 percent of frogs are deformed, and that’s about what Ouellet found in frogs taken from pristine ponds. But in ponds where pesticides are used on surrounding land, as many as 69 percent of the frogs were deformed, he said.

If a pesticide is causing deformities, it’s probably a new brand because large numbers of frog deformities have not been noticed before, Converse of the Wildlife Health Center said.

“It’s less likely to be one of the older chemicals, like DDT or PCBs,” she said.

David Gardiner, a molecular biologist from the University of California, Irvine, believes that the deformities may be linked to a new generation of chemicals that mimic growth hormones.

Gardiner said the same kind of frog deformities that have been found in marshes and ponds - including extra legs and eyes - have been replicated in laboratory experiments.

“I can make a frog that looks like any frog you’ve seen at this meeting,” said Gardiner, who specializes in cell regeneration.

Scientists have induced the deformities with retinoic acid, a byproduct of a workhorse chemical called retinoid that is found in acne medicine and skin rejuvenation creams.

Retinoids powerfully effect development, and if they are inside a growing animal at the wrong place at the wrong time, they can cause deformities, he said. That’s why pregnant women are warned not to use skin medicines that contain retinoids.

Recent laboratory experiments have determined that a pesticide can mimic a retinoid and, conceivably, cause defects in frog development, he said.

“We should start screening chemicals, and we should start with pesticides, to see if they mimic naturally occurring retinoids in the body,” Gardiner said.

Stan Sessions, a developmental biologist, questioned whether a chemical could be the culprit because there were no deformed fish or other animals found in the ponds where the deformed frogs were captured.

He believes parasites cause the deformities.

Sessions, a professor at Hartwick College in Oneonta, N.Y., put a three-legged frog recently found in Vermont under a microscope and invited his colleagues to share in his discovery.

In his partially dissected specimen, tiny parasitic flat worms were packed into the joint where the frog was missing a leg. Sessions told of a lab experiment in which he mimicked the invasion of parasites in a tadpole and caused it to sprout an extra leg as it developed into a frog.

“The mystery is beginning to resolve itself,” Sessions said.

Some scientists in Oregon, trying to unravel the riddle of deformed frogs in that state, decided that trematodes, a parasite commonly known as flukes, were burrowing into the places where legs form when the frogs are tadpoles, causing additional legs to grow.

Some of Sessions’ colleagues at the conference were intrigued and some said he was on to something. But others were skeptical.

Finding the answer to the deformed frog mystery will probably take three to five years of research, said Joe Tietge, conference organizer and research biologist for the U.S. Environmental Protection Agency laboratory in Duluth, Minn.

One of the goals of the conference was to direct research, Tietge said. The scientists at the meeting determined what kind of data will be included in a national reporting system that the U.S. Geological Survey is developing.

At the end of May, the EPA and other federal agencies will award grants to scientists studying the phenomenon of the deformed frogs.