Toad Beneath the Harrow

The amphibians of the world are disappearing at an alarming rate, for mysterious reasons. Of the 5,743 known species, 43 percent are in decline, 32 percent are threatened and 168 species, three percent, are believed extinct. By comparison, about 10 percent of birds and mammals are believed to be threatened, and only one percent of those taxa have gone extinct since 1600.

Colorado’s entry into this lamentable race is the boreal toad (Bufo boreas), once common in the southern mountains above 7,000 feet, but now listed as endangered by both Colorado and New Mexico, and as a species of concern in Wyoming. Another local species, the Wyoming toad (Bufo baxteri) is extinct in the wild.I’ve been way ahead of the curve in reporting on the frog crisis. When I worked for a Wyoming daily in the early 1990s, I did a couple of stories about the decline of Wyoming toad, to the general amusement of the newsroom. I was “the Frog Guy” forever after. In honor of my distinguished reporting on the subject, my wife gave me a stuffed green frog, which I still have, watching over me from its perch on my desk as I write this story.

Stuffed frog
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I can’t recommend the cutting edge of frog journalism as a career choice. It’s hard to get anyone to care much about them. Amphibians are so, you know, icky. They’re not cute like polar bears, or dangerous like grizzlies, or majestic like bald eagles. They don’t inspire mass movements on the order of Britney’s waistline or the use of four-letter words beginning with F and B in college newspapers.

But the decline of these animals in the wild is a glimpse of the future. One amphibian, the golden toad (Bufo periglenes) vanished from its habitat in the Monteverde Cloud Forest Preserve in Costa Rica in 1987. It’s the first animal species credited with being driven to extinction by global warming.

In the mid-1990s, a group of school children found a pond in which more than half of the leopard frogs had missing limbs or extra limbs. Since then, reports of deformed frogs have been widespread across the country. The reason for these deformities has been unclear, perhaps caused by pesticides, ultraviolet radiation or parasitic infection.

This week, a University of Colorado biologist and colleagues have found that, as far the deformities at least, the use of high levels of nutrients in farming and ranching may be causing them.

CU’s Pieter Johnson’s study:

“showed increased levels of nitrogen and phosphorus cause sharp hikes in the abundance and reproduction of a snail species that hosts microscopic parasites known as trematodes. The nutrients stimulate algae growth, increasing snail populations and the number of infectious parasites released by snails into ponds and lakes. The parasites subsequently form cysts in the developing limbs of tadpoles causing missing limbs, extra limbs and other severe malformations,” Johnson said in a release.

The parasite, Johnson says, “is undergoing a cloning, then there is a mass release in the infectious stage. They swim around actively looking for tadpoles. They dissolve the skin. That can interfere with limb development.”

Real frog, er, toad bufo boreas
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While extra or missing limbs are unlikely to be good for you, it’s not yet clear to what extent these parasites are contributing to population declines. Johnson said in an interview:

“We have some limited evidence showing that over time at sites where we do see high deformities, we’ve observed declines in the amphibian populations. But really a lot of data are required to make that case compellingly, because amphibians fluctuate so much years anyway. So even in wetlands where we can get to to 70 percent of the frogs coming out with malformations, and none of those animals come back to reproduce year after year, it still hasn’t been long enough for us to really show that it is taking a toll on the population.”

Nitrogen and phosphorous pollution is only one of the problems facing amphibians. A study by University of California-Berkeley scientists found that leopard frogs in the Great Plains were being “feminized” by absorbing the common herbicide Atrazine. Amphibians breathe through their skin, so they are very susceptible to absorbing environmental contaminants. Deformities in the Great Lakes are believed to be caused by parasitic flatworms. And one of the largest threats is simple habitat loss as wetlands are lost to farmland, shopping malls and housing development.

As CU’s Johnson noted, amphibian populations undergo large natural swings in population levels, so it was thought for a time that the current crisis might not be a crisis at all, just part of the natural cycle. This hypothesis was exploded, however, by J. Alan Pounds of the Monteverde Cloud Forest Preserve and Tropical Science Center in Costa Rica in 1996. Pounds found the current declines were too sharp and synchronous to be caused by natural cycles. Pounds is also the fellow who reported the loss of the golden toad to climate change.

Golden toad
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Currently, the lead assassin in the frog world is the fungus Batrachochytrium dendrobatitis, implicated by evidence from Australia and North and South America. Chytrid fungus exists on the skin of amphibians and usually lies there harmlessly, but certain environmental stresses can cause the fungus to become fatal to the animals — but no one is quite certain what those stresses are.

“Amphibians are one of nature’s best indicators of overall environmental health,” Russell A. Mittermeier, president of Conservation International, said a few years ago. “Their catastrophic decline serves as a warning that we are in a period of significant environmental degradation.”

In 2005, Colorado’s boreal toad has 37 breeding populations, only one of which was considered “viable.” The Wyoming toad was extinct in the wild, although there is a captive breeding program under way.

Years ago, coal miners carried caged canaries underground with them. The birds were hypersensitive to the toxic gases that accumulated in the mine shafts. So they would die at low concentrations of the gas, their deaths warning the miners of the impending danger in time for them to get out of the mine.

So the multi-pronged assault on amphibians may be serving this “canary in the coal mine” function to the rest of us about the environment we live in. Amid this overused metaphor, one thing is certain: No one wants to be the canary.

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About the Author

Dan Whipple

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