Fungus threatens state's frogs, salamanders
Dead frogs rarely tell tales. The delicate corpses usually decompose or are gobbled up so quickly researchers never find them. So Steven Wagner was...
Seattle Times science reporter
Northwest amphibians: www.northwestherps.com/home.html
Washington herp atlas: www1.dnr.wa.gov/nhp/
Maps of infections: www.parcplace.org/bdmap.html
ELLENSBURG — Dead frogs rarely tell tales.
The delicate corpses usually decompose or are gobbled up so quickly researchers never find them.
So Steven Wagner was intrigued when one of his students spotted a body floating belly-up in a lake near Snoqualmie Pass.
"I told him to bring it over," said Wagner, associate professor of biology at Central Washington University. "Then I looked down at my feet and saw another one."
Over the next few days, Wagner and his class collected 85 dead frogs and salamanders at Swamp Lake. What they found in their post-mortem exams sent a chill through the state's small cadre of amphibian experts: the first evidence that frogs in Washington are being attacked by a fungus blamed for wiping out amphibian populations around the globe.
Since that discovery in 2005, Wagner and his colleagues have detected the fungus across the state, from Auburn to Zillah.
"We're finding it pretty much everywhere we look," he said.
The infection has now struck Potholes Reservoir in Grant County, home to Washington's last remaining population of northern leopard frogs. Oregon spotted frogs, found at only three sites in the state, have been hit with die-offs — and the deadly fungus.
State wildlife managers say they're concerned but have so far not mounted any coordinated effort to better understand the danger or protect vulnerable frogs and salamanders.
"People are ignoring it," Wagner said. "But can we afford to do that?"
It may be too late for the state's leopard frogs, Wagner suspects. Habitat loss and predation from nonnative bullfrogs and fish have already hammered the species. The fungal infection could be the final dagger.
"They are probably doomed."
But it may be possible to save other amphibians, if researchers can get a better handle on the fungus and the way it interacts with the other threats that have pushed nearly a third of the world's amphibian species to the brink, he said.
A world with fewer frogs would almost certainly be buggier, as the amphibians consume vast numbers of insects. Birds, snakes and other species that feed on frogs would suffer. Humans could be affected, too, losing out on the pharmacopeia of compounds in frog skin that has already yielded promising treatments for pain and diabetes.
"Frogs made it through the mass-extinction events that knocked out the dinosaurs," said David Wake, a biologist at the University of California, Berkeley, who was one of the first to sound the alarm over declining amphibians. "Now there are more amphibian species at the edge of extinction than for any other group of vertebrates ... and that should be a warning for all of us."
"Ebola for frogs"
First discovered in 1998, the fungal disease called chytridiomycosis has been implicated in the collapse of amphibian populations in Central America, Australia, Europe and other places. Researchers documented its march across Panama and the carnage left behind. In North America, the fungus is rampant in California's Sierra Nevada. It has been linked to die-offs in Colorado, Wyoming and Arizona.
But in other parts of the world, notably South America and the Northeastern United States, the fungus is present but doesn't seem to be fatal, Wake said.
"In some places, when it arrives it's a death knell. Then there are places where it doesn't have an epidemic effect, and we don't understand why."
The latter seems to be the case in Oregon, said Michael Adams, a research ecologist for the U.S. Geological Survey in Corvallis. Though the fungus infects about half the amphibian populations Adams and his colleagues have surveyed, they haven't seen widespread deaths.
Then again, they haven't done the type of regular monitoring it would take to notice population crashes, he added.
It was luck that put Wagner and his students at Swamp Lake in the midst of a die-off. Over the next several years, they visited the lake repeatedly, watching the robust population of frogs and salamanders dwindle.
"There were so many frogs that the sound was deafening," said Jim Johnson, a CWU botanist who identified the fungus through DNA analysis. By the end of the second season, a student heard a lone male calling from the forest.
Nearly all of the dead frogs were infected with the fungus, which turns white bellies bloodshot and causes the skin to thicken, then slough off in sheets. Amphibians breathe and regulate body fluids through their skins.
"I think of this like Ebola for frogs," Wagner said.
Though the circumstantial evidence seems damning, it's impossible to say whether the waterborne fungus killed the frogs outright or just contributed to their demise, Johnson cautioned.
At a small pond on CWU's campus, Wagner and his students have been tagging frogs and swabbing them for fungus for more than three years. While healthy frogs might be recaptured several times, infected frogs are never seen again. During 2006, when the pond's amphibian populations plummeted, nearly 50 percent of frogs were infected. Even the normally ubiquitous Pacific tree frogs disappeared in droves.
"It's potentially a very big problem," said Marc Hayes, a senior research scientist for the Washington Department of Fish and Wildlife.
Fungus only one threat
No one knows where the fungus, part of a group called chytrids (kih-trids), originated. DNA studies suggest it's a relatively recent arrival in much of the world, said Joyce Longcore, the University of Maine mycologist who first purified the species, named Batrachochytrium dendrobatidis.
One theory is that it was carried out of Africa in shipments of frogs used for pregnancy tests in the 1930s. Bullfrogs, which become infected yet rarely die from the disease, also may be carriers, she said.
But killer fungus is only one of the perils amphibians face today, said Oregon State University biologist Andrew Blaustein, whose own research has shown that UV radiation can harm amphibians and their eggs. Chemical contaminants, parasites and other diseases also take a toll. Susceptibility varies by species, and factors interact, Blaustein pointed out.
A frog whose immune system is weakened by UV radiation or toxins may be more vulnerable to infection. Global warming adds another level of stress.
Or as Wake, the Berkeley biologist, puts it: "It's a great big ball of wax and a lot of things are connected — but we don't know all the connections yet."
Scientists disagree whether global warming has made the fungus more widespread or lethal. The species actually prefers cool conditions. Some researchers say heating in the tropics has had the paradoxical effect of creating more cloud cover, which favors the fungus. Others see no link between temperature and outbreaks.
Worried experts are exploring the use of fungicide or diluted bleach solutions to clean and treat infected frogs.
Washington also is laying plans for the worst-case scenario, said JoAnn Wisniewski, a state fish and wildlife biologist. She monitors leopard frogs in the Potholes area, and has collected about 10 dead or dying animals infected with the fungus.
Zoos around the world are mounting emergency, captive-breeding programs to try to preserve amphibian species on the verge of extinction, Wisniewski said. "It's definitely something that we're talking about here."
Sandi Doughton: 206-464-2491
Copyright © 2008 The Seattle Times Company
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