Our Stolen Futurea book by Theo Colborn, Dianne Dumanoski, and John Peterson Myers
 
 

 

 
Frog deformities are being detected at levels drastically above any rate which might plausibly be thought to be natural.


[new research on frogs]


Chapter 9 of Our Stolen Future discussed evidence that frog populations in many parts of the world are declining and explored the unproven but plausible hypothesis that endocrine disrupters might be involved. The "frog story" has grown more dramatic since OSF went to press, with alarming deformities now showing up in frogs all across Minnesota and Wisconsin and in the St. Lawrence River Valley in Quebec. Researchers in Minnesota have found grotesquely deformed frogs at more than 100 sites. One animal had four legs sprouting from its stomach; another had a leg growing out of its neck. The most bizarre, perhaps, was a frog with an eye inside its mouth. The animals appear to be victims of severely derailed development. While scientists are exploring a number of theories to explain these developmental deformities, including disruption caused by parasites or by bacterial or viral disease, pesticides and synthetic chemicals have become leading suspects.

William Souder describes one deformity outbreak in A Plague of Frogs:

 

"The scene at the Bocks' lake deteriorated in front of Hoppe's (a herpetologist at the University of Minnesota) eyes. By midsummer the lake had become a watery nightmare. Each successive collection revealed a fresh perversion of nature. The frogs reproducing along the Bocks' shoreline--where the family had swum and caught their Sunday supper for years, and where Hoppe had seen nothing out of the ordinary only weeks before--were being ravaged. There were significant levels of deformity in every species. The most severe abnormalities--the worst yet seen anywhere in Minnesota--occurred among the mink frogs.

The mink frogs at the Bocks' lake exhibited every type of deformity previously seen at other places in the state--plus a ghastly parade of new ones. Some were missing legs or leg parts, but most had some sort of twisted addition to their normal complement of limbs. Many had the strange skin webbings--Hoppe started calling them "cutaneous fusions--that spanned the trailing edges of the hind legs, preventing their full extension and in the most extreme cases totally immobilizing the limbs. Hoppe found it hard to look at these animals and not wonder if they weren't likely to die by drowning.

Other frogs had stumps of legs or partly formed limbs protruding at odd angles from their hindquarters. There were legs that split, branching off in two or more directions, as well as legs that had extra feet, and feet that had extra toes. There were tapering, leglike appendages sticking of from the rear flank like wings on an airplane. One frog had a total of nine legs."

 

Some scientific progress has been made on the central question of what is causing these deformities, but it has been slow, halting and contentious.

  • Parasites can cause some of the deformities seen and may be involved in the natural background rate of deformities. This has been established through an elegant combination of laboratory and field research. Even the scientists who performed this research, however, do not believe that parasites are the only cause.
  • Field and lab experiments with wood frogs reveals that pesticides reduce the frogs' ability to resist parasitic infection. Frogs in contaminated areas have higher rates of infestation than those without contamination.
  • Careful studies of the geography of deformities, especially in SE Canada, show a striking relationship with the distribution of agricultural chemicals.
  • Deformed frogs have been found with no sign of parasitic infection.
  • Water from areas where deformities occur in greatest abundance has been shown in experiments to produce deformities without any parasites involved.
  • Several agricultural chemicals when applied to developing frogs in the laboratory cause a range of deformities, including forms similar to virtually all types seen in the wild.

Thus the picture that is emerging is that frog deformities occur in some areas as a result of parasitic infections. In other regions, indeed where deformities are most common, parasites do not appear to be a major contributor. In these areas, particularly the upper portions of the US mid-West eastward to Ontario, agricultural pesticides are clearly involved. Which chemical(s) and via what mechanism is far from resolved.

Press coverage...

Two websites that monitor ongoing research:
Amphibian deformities
Minnesota Pollution Control Agency

For an excellent overview of the search for the causes of frog deformities, read William Souder's A Plague of Frogs.

A useful essay by Dr. Michael Lannoo on the scientific pursuit of frog deformities can has been published on a website HMS Beagle.


New research on deformed frogs:

Experimental laboratory work by James La Clair et al. (1998) shows that the breakdown products of a common insecticide causes deformities in toads similar to those found naturally in frogs. More...

Johnson et al. (1999) demonstrate that parasites can cause deformities in experimental ponds and these correspond with patterns of deformities observed in central coastal California. More...

A study by Sower et al. published in October 2000 finds that deformed frogs have hormones out of balance compared to normal frogs. More...

 
   
     

 

 

 

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