Fungus imperils amphibians

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CHICAGO – A devastating fungus is sweeping the world, wiping out entire populations of amphibians at such a rate that biologists are helping pull together a massive “Noah’s Ark” project to capture frogs, toads and salamanders and put them in safe places.

A variety of factors already have combined to cause more than 120 amphibian species to vanish forever since 1980, in what one biologist has called “one of the largest extinction spasms for vertebrates in history.”

A third of the world’s nearly 6,000 amphibian species are threatened – their populations weak and susceptible to disease. If they go, ecosystems will tilt out of balance and potential medical breakthroughs – such as potent painkillers or HIV inhibitors – could be lost.

It is hard to determine just how many species have been affected by the fungus because they cannot be assessed fast enough, but it has factored into most of the recent extinctions and declines, said Bob Lacy, the population geneticist at Illinois’ Brookfield Zoo and chairman of the Conservation Breeding Specialist Group.

That leaves no time for anything but a triage attempt to get some of the animals out of harm’s way until this “tragically unique” disease can be further studied and countered, he said. “It is a race against time, and it’s a matter of months,” Lacy said.

Among zoologists, some have begun to face questions of which species should be saved and why.

“It’s terrible, I’ve never experienced anything like this,” said David Wake, a biology professor and curator of herpetology at the University of California at Berkeley, the first scientist to officially declare a pattern of global amphibian declines in 1989. “It’s really an awful prospect.”

When this fungal disease came along, amphibians the world over already faced stress from global warming, pesticides and herbicides, acid rain and habitat destruction.

Some scientists point to them as bellwether animals for the earth’s health. Their slippery, porous skin absorbs moisture around them, making them more vulnerable to environmental changes than mammals, birds and reptiles with their fur, feathers or scales.

But chytridomycosis, caused by the chytrid fungus, is adding a confounding new level of peril that is pushing many species over the brink – even in areas mostly untouched by human hands.

Dilemma

“This is a totally unusual conservation dilemma – species going extinct in a relatively pristine environment,” said Alejandro Grajal, Brookfield Zoo’s senior vice president of conservation, education and training. “Now we’re basically trying to save as many as we can as we try to figure out our next step.”

Chytridomicosis was first identified in 1998 and is not well understood. As it moves around the globe, it has caused massive amphibian die-offs in Australia and hit the population of boreal toads in the Rocky Mountains. In the Sierra Nevada, California-Berkeley researcher Vance Vredenburg found “piles” of mountain yellow-legged frogs dead from the disease two years ago.

The disease is filtering down Central America – one of the most biologically diverse areas on the planet – at a rate of about 17 miles a year, faster than a frog can hop to the next pond. With support from the Houston Zoo, Mauricio Caballero is leading an effort to build a field facility in Panama to preserve species, but the fungus caught up to his El Valle region before the roof was up.

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‘Starting to die’

“We knew what was going to happen and now we’re seeing the frogs starting to die,” he said after a meeting with other Latin American experts Monday in Brookfield. “We weren’t expecting it to hit so soon. We were predicting it was going to hit in the rainy season.”

Chytrid fungus is carried in water, but the disease is specific to amphibians, invisibly feeding on their skin’s carotin and causing it to thicken. The exact mode of death is unknown – it may produce a toxin or it may impair the amphibian’s ability to breathe and absorb water through its skin.

How it got around the world so swiftly is also uncertain.

It could have been carried by human travel – or by the global movement of ballast water and invasive species. Vredenberg says one hypothesis is the fungus always was around – but now amphibians are vulnerable to it, like humans suddenly dying of the common cold. One theory Grajal cited is it got around with African clawed frogs, which were shipped around the world in the 1940s and 1950s for use as pregnancy tests after it was discovered that a female injected with the urine of a pregnant woman began laying eggs.

There is some good news about the disease – besides the fact that it does not affect humans. Among some amphibian species it seems to kill only some individuals. Although scientists do not know how to stop the disease in nature, they can treat it in labs. And, so far, it is not believed to have reached areas of great amphibian diversity such as Madagascar, India and Indonesia.

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There could be even more at stake with all these dying frogs than their key roles in the food chain consuming insects and other small critters. Scientists say amphibians have great, largely untapped medical potential.

Last October, the Journal of Virology published a Vanderbilt University Medical Center study showing that compounds secreted by an Australian red eye tree frog’s skin appear to inhibit HIV infection. Poison dart frogs long have provided venom used by hunters in Central and South America, but pharmaceutical companies are researching a compound found in the frogs that could yield a painkiller 200 times more potent than morphine.

The total cost of holding 600 species captive to protect them will run about $60 million, Grajal estimated – a relative bargain compared to the costs of saving large animals like elephants or pandas.

“The very preliminary analysis we’ve done shows there’s an incredible potential (for medicines), and just because of that it’s worth the effort,” he said.



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