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Larry Dodder's Whacky World of Science!
 

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What's behind the amphibian die-off?

  It's a fact. Even a blitherin, slitherin' whyzard can't make a decent potion without amphibians -- or amphib parts, at any rate. But the potion-masters down at the Pollywogparts Amphibian Academy are starting to worry about a lack of ingredients.

Black lizard with yellow blotches. Tiger salamander in Golden, Colorado. Courtesy W. Battaglin, U.S. Geological Survey.

Toads and salamanders, it seems, are disappearing from one habitat after another. "Amphibian populations fluctuate," says James Collins, an Arizona State University biology professor who heads a National Science Foundation project on host-pathogen biology and the global decline of amphibians, "but the decline is clear globally, starting in the 1960s."

Should we blame the disappearance on overharvesting by the adolescent wizards-in-training at Logdarts? Probably not. Larger forces from the dark side are at work.

We muggles (non-wizards) deserve a good slice of blame for turning huge swaths of the planet into farms, roads and cities. But why are amphibians disappearing from pristine mountain habitats? Is it ultraviolet radiation, disease, exotic species, toxic chemicals -- or some deadly brew concocted from these factors?

Certainly, diseases play a role in some declines: A fungus-like organism called the chytrid, for example, is blasting frogs.

Now we hear a virus is slaying salamanders in Canada and the Western United States.

One sick story
In the early 1990s, the destruction in Arizona was hard to ignore, with dozens or hundreds of dead tiger salamanders found floating in their pools. In 1996, Arizona State University biologist Elizabeth Davidson identified a new virus called ranavirus in those croaked salamanders. To prove that ranavirus was killing the salamanders, Davidson and Collins used the "gold-standard" test for pathogens. "We fulfilled Koch's postulates," Collins says. That means they extracted ranavirus from the corpses, grew it in culture, and used it to infect another salamander.

Collins says that ranavirus has also been found in die-offs in Saskatchewan, North Dakota, Colorado and Utah. The virus, he says, "shows a terrific amount of genetic similarity" in the various locations.

Flying the Virus 2000?
But how does the virus travel? Desert salamanders, after all, live in remote pools and water tanks, and don't even have a thumb for hitchhiking. To be sure, they have never been enrolled at Dogparts University (although there are rumors that they've been used in the odd potion or two by an over-eager freshman). Ranavirus has not been found in fish or frogs either, but it's possible that birds are spreading it -- since the deaths seem to occur under migratory paths.

Recipe card forBogstart's Wizard Whitener (Makes 2 servings)1 part frog's legs, ground fine2 parts salamander feet, mincedEye of newt, pureed1 brain of bird, pickled and lightly chopped1 dash, liquor of mercuryHeat carefully over smoky fire for 3 days....Scottish sheepgenetically engineered port

Another possible source of infection is cannibalism -- the tiger salamander eats its comrades. We can only say it serves them right.

Until pathogen movement is understood, the Arizona amphibian researchers are taking no chances. To block one route of infection, they use a bleaching ceremony to kill virus on clothing and equipment before visiting research sites.

Collins says that beyond preserving the 'manders, there are interesting lessons to be learned about disease ecology and pathogen-host relationships. Curiously, while chytrids seem to kill off frogs, the salamanders may be back at their old levels within a few months of a severe ranavirus attack.

And how does the virus work? Is it like measles and influenza, which sweep through populations, striking the susceptible? Or is it always present, but only infecting hosts when conditions are right?

Dearth of death data
Although it's obvious by now that amphibians are getting scarce in many parts of the world, the phenomenon is elusive to study. Populations of amphibians, like other wild critters, naturally oscillate. And since baseline data on amphibians and pathogens is scarce, doing ecological research can involve multiplying two unknowns. The reasons for the decline "are elusive and complex," Collins says.

Although disease is one factor, Collins suspects that global change also plays a role. Increased ultraviolet light caused by ozone destruction, for example, could harm the immune system, allowing normally benign viruses to run amok.

As amphibian researchers watch the disappearance of their favorite critters, they worry that this is a symptom of a larger ecological havoc. So for the sake of the amphibs, the wizards at Pigzits Academy, and even for us muggles -- it would be nice to know what's slaying them salamanders.

Salamanders are found in the best witches' brews. But what are witches?

 

 

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