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BURLINGTON FREE PRESS (Vermont) 01 August 07 Deformed frogs still a mystery (Candace Page)
A Yale University scientist says new studies are needed to discover whether farm chemicals are to blame for the missing hind legs and other deformities in Vermont frogs.
Ecologist David Skelly's study of thousands of frogs in 41 Vermont wetlands ruled out one likely cause -- a flatworm parasite -- of the abnormalities that have puzzled scientists in the 10 years since they were first widely reported here and elsewhere.
"We went to all these wetlands and cataloged where the deformities were found, and what kind of landscapes seemed to pose higher risks, if any," Skelly said Tuesday.
"The answer was, frogs growing up in proximity to agriculture were more than two times as likely to have deformities," he said. Skelly recently published the results of his research in the journal EcoHealth.
"This doesn't say it is chemical pesticides, but you can't credibly consider this problem of the frogs without at least evaluating whether pesticides are involved," he said.
Skelly chose Vermont for his study, which began in 2002, because the state has been "a real hot spot for deformities," he said. In addition, the state Agency of Natural Resources had assembled plenty of data about the frequency of frog deformities in the Champlain Valley.
Deformed frogs made national headlines in the mid-1990s after schoolchildren in Minnesota found frogs with missing or extra limbs and raised a cry.
When Vermont researchers went looking, they found plenty of abnormal frogs. At one marsh in West Haven in 1997, 45 percent of the 121 frogs collected were missing hind limbs or showed other malformations.
Alarmed environmentalists described the frogs as canaries in a coal mine, indicators of something seriously wrong with the global ecosystem.
Since then, the frogs have dropped out of the news. Some scientists concluded the deformities were the result of a naturally occurring parasite. In Vermont, at least, the frequency of missing hind legs has generally been much lower than in 1996 and 1997, when alarmingly high levels of abnormalities were found. When ANR researchers collected about 4,000 tadpoles and young northern leopard frogs from nine Champlain Valley wetlands in 2001, the overall rate of abnormalities was about 4 percent.
In Skelly's study, the overall rate was 3.4 percent among 3,400 tadpoles in the midst of developing into frogs. Both studies found a wide variation in the frequency of abnormalities from wetland to wetland and year to year.
"Should this trigger broader concern about what is going on in the environment? At this point, I would say no," Richard Levey, a Vermont ANR biologist said Tuesday.
Skelly isn't so sure.
His study focused on a kind of flatworm, Ribeiroia ondatrae, that has been proven to cause deformities in frogs in the Pacific Northwest.
If the flatworm were causing the deformities in Vermont frogs, that would suggest the problem was perhaps a natural occurrence that simply hadn't been noticed until the late 20th century.
Skelly's results showed that was not the case. He found none of the flatworm in any of the Vermont wetlands he studied; and the Vermont frogs' deformities -- mostly missing hind legs -- were different from those caused by the worm.
His finding confirmed Levey's observations over his six years studying Vermont frogs. The Vermont researcher had also concluded that here, at least, some other cause must be sought.
"It is still a mystery," Levey said, and the solution may be that there are multiple causes for the limb loss.
"I came to think of it as ordering off a Chinese restaurant menu," he said. Some abnormalities may be caused by problems with development, others by changes in water chemistry, and still others by insects that bite off the tiny limbs of developing tadpoles.
Levey found traces of two common farm pesticides, atrazine and metolachlor, in water from wetlands where malformed frogs were found. In all cases, the level was far below levels thought to have an effect on aquatic life.
Skelly said his findings re-open the question of whether tiny amounts of such chemicals can do damage to amphibians, Skelly said.
"Our whole regulatory system (for pesticides) is based on the assumption that more is worse. But maybe you can have instances where low concentrations can affect the genetic code. Are certain genes affected? What does that do to the animal? And what implication would that have for vertebrates, including humans?" he asked.
Skelly said he and a graduate student will begin laboratory tests to begin to answer those questions.
"We will come up with a list of chemicals used in Vermont that we think are candidates, and expose" frogs to those chemicals in the laboratory, he said.
For the time being, limbless frogs remain a mystery. Skelly expects scientists to find the answer one day.
"The tools are there. If we make the investment, we'll figure it out," Skelly said.
What's Wrong With Our Frogs? Scientists have begun to sort through the many theories for what is causing deformed frogs:
- Parasites: Disproved in Vermont. A new study by a Yale professor confirms earlier observations by Vermont researchers. No parasitic flatworms were found in a large sample of Vermont wetlands, including those with a history of frog abnormalities. The flatworms do cause deformities in frogs in the Pacific Northwest.
- Ultraviolet Radiation: Disproved. Research nationally has concluded frogs' exposure to UV rays is low.
- Predation: Unproven. Large aquatic insects may bite off the hind limbs as tadpoles turn into frogs.
- Chemicals: Unproven. Very low concentrations of agricultural and other chemicals may cause malformations as the tadpoles develop.
Deformed frogs still a mystery

I remember when that full thing happened years ago when I was a kid -- it seemed like every Leopard Frog metamorph was missing the same leg and nobody knew why. I even found one that had 3 extra malformed legs protruding from its chest and a Green Frog with two feet on its right hind leg in the same year. The Green Frog was quite large though so it could have been from a number of years earlier. The next year it just sort of went away without a trace and scientists have been working on it ever since. When I saw the Burlington Free Press article last week its timing was quite ironic because only hours before hand I had found a malformed Green Frog metamorph missing the same leg portion as the Leopard Frog on the front page.

One thing is nice though -- herps have been getting a lot of coverage in the BFP lately

Ok, my frog wasn't missng the exact same leg chunk but still...