Mutant Frogs

It sounds almost like the start of an X-Files episode: Some school children are taking a routine field trip in the woods. Happy to be out of school for the day, they see frogs and start to pick them up. Someone notices a deformity, then another weird-looking frog is found, and another. Finally, they determine nearly half the frogs they encounter are either missing limbs or have additional limbs. This happens in Minnesota.Elsewhere in the world, frog populations are diminishing; whole species have become extinct and frogs that should be green are pink or orange and some are albinos. There appears to be no single answer as to why.Don't call Scully and Mulder, though, there are already droves of scientists on the case and not one suspects either aliens or a conspiracy. The apparent world-wide phenomenon of missing a deformed amphibians is one that has drawn more attention since a group of students in Minnesota found a large number of deformed frogs over a year ago. However, even before that incident, scientists have been carefully recording data about the movement and fortunes of amphibians all across the globe.SRS has longest studyIn fact, the longest study of this has been done at the Savannah River Site. Dr. Whit Gibbons, Professor of Ecology at SRS, said that for 18 years, every day without fail, SRS scientists monitor the various traps set throughout the site for amphibians. This allows them to track the movement of the amphibians in the various areas of SRS, as well as their general state of health. Personally, Dr. Gibbons does not think the reported sightings of deformities in frogs is anything to be alarmed about. "That happens naturally," he said. "Everywhere in nature you see deformities."Dr. Joe Pechmann, Post-Doctoral Fellow at SRS, is one of the scientists working on the amphibian project there. He says that originally, the research was begun to monitor the effect of the Defense Department's Nuclear Waste site construction on amphibians. However, it is no longer funded by th defense Department. Instead it functions well as a control site for amphibian research. That is, the wetlands area monitored for 18-plus years has experienced no spraying or other direct man-made impact."It's important people understand the difference between what is a hypothesis and what is proven," says Pechmann. He called the rash of unexplained deformities and the declining numbers of amphibians "a real puzzle" with "a number of hypotheses but very little data." He cited one example. "One hypothesis is the null hypothesis that the deformities are a natural condition caused by a parasite that people simply didn't notice before. That is something you set out to disprove. It's anyone's bet if it's natural. That's what peoplexample. "One hypothesis is the hypothesis that the deformities are a natural condition caused by a parasite that people simply didn't notice before. That is something you set out to disprove. It's anyone's bet if it's natural. That's what peoplpeople assume but there's no data."Pechmann said that some chemicals mimic hormones and can certainly affect the development of embryos. Such chemicals, often found in pesticides, were once thought to have no effect in small enough quantities, but now it is known that even a small amount can affect development, especially if there are mixtures of such chemicals."It's no mystery why Atlanta doesn't have a lot of amphibians," said Pechmann. "human destruction of habitat certainly has an impact. What is mysterious is when populations decline in isolated areas not affected by humans."While Pechmann sees no reason to jump to conclusions or panic, he is concerned about the total disappearance of some species such as the gastric brooding frogs of East Australia and the Golden Toad in Costa Rica. "No one knows why they're gone but they are, totally. Not all frogs are more sensitive [to environmental changes] and you can't say what happens to them will happen to humans but it's like in a horror movie when your next door neighbor dies and you wonder, are you next?"While SRS has charted no unusual deformities or extinctions, they have followed some real fluctuations in populations that appear to be normal. "What we hope will come out of all the research will be how to preserve the creatures we share the earth with."Frogs decline in number Scientists elsewhere all agree that the situation bears close watching and more study. Several groups have formed to do precisely that. One such group, DAPTF -- Declining Amphibian Populations Task Force -- argues strongly that the declining numbers of amphibians bode ill for all other groups of life on earth. This group points to such examples as the tree frogs native to Australia. These small animals are important as insect control, as a source of chemicals with medicinal potential and because people simply like them. This illustrates what DAPTF believes are the important reasons to be concerned about the declining numbers of frogs: It is a measure of the general health of the environment, it may impact current or future generations of the aesthetic qualities of frogs, some of which are considered quite beautiful.DAPTF says the "current global loss of bio-diversity" is a "process generated by the activities of humans." They point to the depleted atmospheric ozone levels, pollutants accumulating in the natural systems, altered weather patterns and other gradual but fundamental changes affecting the ecosystem. "As we modify our environment for our own ends, ittof other species is clear that the destruction of the habitats of other species leads directly to their disappearance."DAPTF has "working groups" all over the world. Each group monitors amphibians in their area and reports back to DAPTF. For example, a group in the former Yugoslavia, now Serbia and Montenegro, reports that one million green frogs were allowed to be exported in 1996 compared with only a maximum of 11,000 allowed in the entire period from 1975 to 1980. They also noted that the exported frogs weighed less. Despite warnings from herpetologists from the Biological Institute in Belgrade to halt the export, the profitable business continues and information concerning the trade is withheld from scientists as "business secrets" so that the impact is hard to access.So you think frogs are green?While exploitation is a direct example of man's impact on the amphibians' well-being, other, less direct effects may be seen all over the world. Another group studying this is NAAMP -- North American Amphibian Monitoring Program. In a paper by Annie Zuiderwijk of the University of Amsterdam's Institute of Systematics and Population Biology, NAAMP documents albinism [a lack of all color] and unusually-colored frogs in the Netherlands. Green frogs have been noted to be white or pink or blue. Grass frogs, green frogs and common toads have been observed since 1950 on occasion to have odd colors, but in the last two years, according to Zuiderwijk, "an explosion" of pink, yellow, orange and blue frogs of yet another species, normally brown and greenish-brown, has occurred there. These sightings were from several different locations in the Netherlands. Other strange-colored frogs were noted in England in 1995. An article in the Independent, a journal, pointed to global warming as a possible reason for the colors.Mysterious deathsJust last month in Texas, during a routine survey at Zilker Park, scientists found 12 dead Barton Springs salamanders. While the deaths could not be attributed to any specific cause, it is the largest die-off of the species since scientists began monitoring it several years ago. Also, the Colorado Division of Wildlife released thousands of hatchery-raised western boreal toads into Rocky Mountain National Park in November to try to counteract the toads' endangered status. Scientists have no idea why the population of western boreal toads has crashed more than 90 percent in recent years but the Division of Wildlife says that reintroducing the toads is the quickest way to recover. A look at our future?This apparent amphibian decline has caused concern in both the general public and the scientific community. There is a general assumption that the anomalies are related to one or more environmental factors and could indicate a possible future problem for other animals and humans. At a workshop on Central North American Amphibian Deformities held last September in Duluth, Minnesota, the conclusion drawn was that there is no decisive evidence either for or against this assumption. In a summary by Joseph Tietge issued by the group, he states, "The predominant causes for amphibian declines are probably habitat destruction, habitat degradation, habitat fragmentation, and predator introduction. However, chemical contamination and ultraviolet radiation have also been hypothesized to contribute to amphibian population decline." Currently, plans are being discussed to create a national reporting center for amphibian deformities. Such a clearing house would receive, confirm and investigate reports of deformities. Deformities: UV light? Chemicals? Nature?The idea that ultraviolet light might be a plausible factor contributing to amphibian deformities has been put forth by Gerald T. Ankley of the U.S. Environmental Protection Agency. He points to some circumstantial evidence that could contribute to limb deformities. "There has been a clear documentation of recent increases in the intensity of UV light," he says. "Some of the largest relative increases in UV have been shown to occur in late spring and early summer, a period which coincides with reproduction and critical windows of development of amphibian species in northern latitudes." He goes on to say that the mechanism of action by which UV could cause limb malformation is not certain but might be related to alterations in vitamin A/retinoic acid metabolism. Vitamin A is an antioxidant that can protect against UV stress and is also a precursor of retinoic acid, which is critical for normal "limb bud" formation -- that is, when limbs first begin to form on an animal. He calls for further research in this area. In another study on deformed frogs by scientists in Canada, deformities were tracked in both pesticide-exposed and control populations and while preliminary statistical analysis indicates no significant difference in the occurrence of limb deformities, the scientists wrote, "However, the prevalence and diversity of deformities in some of the farmland habitats, their simultaneous occurrence in more than one species at given sites, their overall diversity, and the fact that many agents are potentially harmful to anuran (adult amphibians) development, emphasize the need for further studies..."Stanley K. Sessions of the Hartwich College Department of Biology in New York takes a very different tack. He says, "The occasional occurrence of high frequencies of limb abnormalities, including missing limbs and extra limbs, in natural populations of amphibians has long been a puzzle...Here I report the discovery of a population from northern California in which such limb abnormalities appear to be caused by a parasitic flatworm... I conclude that trematode cyst infestation (caused by the parasite) is sufficient to cause the majority of observed deformities in natural population of amphibians." He suggests the presence of such a parasite be explored in all the reported but unexplained occurrences of limb deformities.Trace pollutants suspectedStill, Sessions' discovery cannot explain the virtual disappearance of the Yosemite Toad and Mountain Yellowlegged frogs from the wilderness of Yosemite's backcountry. An article from last January in The San Francisco Examiner cited pollutants from the Central Valley such as smoke, smog and pesticide residues as well as ozone, dust, sulfates and nitrates as possible causes for the missing frogs. In 1992 similar news of vanishing frogs and toads was noted in Australia, Canada, India, Europe and what used to be the Soviet Union as well as from Central and South America and most the western United States. At that time scientists from various areas compared notes and found disturbing declines across the globe. However, scientists cannot say with any assurance exactly what is causing the various problems -- or even if they are problems. One reason is the lack of continuous data over long periods of time. At SRS, where amphibians have been tracked the longest, their number goes up and down, sometimes wildly from year to year with no discernable trend.Natural random fluctuations in habitat can explain some of the observed amphibian difficulties, but most scientists involved either believe, or will not rule out, the possibility that something else may also be at work. As frogs such as the California red-leggeds are considered especially sensitive to subtle changes in the environment, they may also be indicators of what the future could hold for more complex animals. Right now the best guesses seem to include UV, parasites, pollutants, acid rain, or problems with the immune systems of the amphibians as well as natural fluctuations. But as noted by Ronald W. Russell of the Great Lakes Institute for Environmental Research, University of Windsor, "Amphibian declines are a complex and multifaceted problem which defy simple explanations. Although our evidence implicating contaminants in amphibian decline is correlational, the role of such contaminants should not be overlooked." He said that because some contaminants last a long time they can continue to remain toxic and can be transported by air, accounting for contamination far from the original site, even years later. The case of the missing and deformed frogs will not be easy to solve, but the truth is out there.

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