The Story That Croaked?

by Howard Fienberg
April 29, 2002

Those amphibians seem to have it rough.


For over six years, we’ve seen news stories about a global decline of frogs and toads, as well as increasing numbers of amphibian deformities. No one knows exactly what is causing them, but a link to chemical pollution has been the most popular candidate.


For a public raised on a cartoonish diet of toxic scares, it has a visceral appeal. Monty Burns nuclear power plant on the Simpsons dumps toxic waste into the river, which produces three-eyed fish. Why shouldn’t we suspect the same kind of culprit when we encounter four-legged frogs in real life?


But these stories are not just about frogs. After all, unless a frog’s name is Kermit, he is not likely to evoke significant public sympathy. In some ways, these stories are really about humanity. The frogs serve as environmental warning signs, implying that the pollution we produce could easily cause the same problems in us. So it should be no surprise that a new study linking deformed frogs to a widely-used weed killer found an eager, if frightened, audience.


Published in the Proceedings of the National Academy of Sciences (PNAS), the study linked the common herbicide Atrazine to developmental defects in a species of frog. Laboratory experiments with the herbicide seemed to disrupt the hormones in a species of male African frogs, adversely affecting their sexual development. So, the decline in frogs could be linked to males with, ahem, diminished capacities or, even scarier, hermaphroditic tendencies.


Only the results were limited to the lab. The real world might be quite different.


Expanding suppositions


Do researchers actually know what is harming frogs? Unfortunately, no. Do they know that humans are also at risk? No. It is not necessarily unreasonable to propose that amphibians could serve as a kind of leading health indicator for future human health difficulties. But chemical pollution is not the only possible cause of the frogs’ foibles. Many other factors have been fingered, including global warming, excessive ultraviolet light radiation (caused by the depletion of the ozone layer), heavy metal contamination, acidification of the water, viruses and bacteria.


Following hard on the heels of the PNAS study came yet another frog study, this one with a different focus. Rather than toxic pollution, this study centered on a common parasite. Examining many different species of amphibians, researchers found that trematode parasitic infections were strongly associated with the frequency of limb deformities. This study, published in a less prestigious journal Ecological Monographs (EM), appeared unlikely to garner any media reporting whatsoever.


But Carl T. Hall paid attention. Hall, a superb science writer for the San Francisco Chronicle, happened to write the only lengthy, intelligent article on the PNAS study. He followed up four days later with a lengthy story on the EM study. The only other journalist to report on the EM study was Jeff Barnard, whose Associated Press story has languished on the wire, unpublished.


Which study to believe?


Just because the EM study found a possible link to parasites does not mean that the PNASs proposed link to Atrazine is wrong. It is possible they are both correct or both incorrect. Even if the parasite theory wins out, humans may still be to blame for the problem. It may be that increased fertilizer runoff could be increasing algae levels, which could lead to more snails (coming to eat the algae) which could be carrying the parasite.


But there’s not a lot to go on. We don’t even know for certain if the observed deformities are all that unusual, or that the frog populations are actually declining. Frog deformities appear much more common nowadays than in the past, but we have no baseline measurement for comparison. Frog-focused researchers have been trying to collect systematic population data worldwide, but the work is still in its infancy.


So, there’s no end in sight to our amphibian confusion.


Toad Tales


The sometimes poor media coverage of the amphibian decline has not helped public understanding. But some toad tales are more embarrassing than others. Boston’s Metrowest Daily News had a scary article April 15 about a mutant toad discovered by four-year-old Casey Dicken in a backyard swimming pool. Publishing a photo, the newspaper described these two toads as “conjoined, un-identical twins.” It even included a reference at the end of the story to the pollution-deformed frogs link. But three days later, the newspaper admitted it had hopped to conclusions too quickly.


“Looks can be deceiving. It’s as simple as that. To the untrained observer, two toads enjoying a romantic moment together could easily be mistaken for an exotic, two-headed mutant. ... But in the end, it was nature, not science-fiction, that explained the apparent phenomenon. It was just a couple of horny toads.”


Maybe we all should stop hopping to conclusions.

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