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Microbes May Come To The Rescue Of Endangered Frogs

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A golden frog before a bath.
Brian Gratwicke
A golden frog before a bath.

For years, researchers have been trying desperately to find a cure for a fungus that is killing frog populations the world over. Now, they think a D.C.-area man may have found a solution in his backyard.

A fungus known as amphibian bd or chytrid has been spreading around the world for the past few decades, wiping out amphibian populations in vulnerable areas. One-third of the globe's amphibians are now facing extinction from a host of issues, from habitat loss to pollution, and this fungus is an added assault they really don't need. Scientists are scrambling to find the answer.

Frogs on the brink

In a darkened, quarantined room in Panama's Summit Zoo, keeper Angie Estrada is about to open some special packages. "It's been a long trip for them," she says. "So we're trying to do things quick and not stress them out any more."

Wrapped inside wet balls of moss are six endangered frogs, waiting on a table. A field team spent weeks searching for them in a mountain forest where a human-introduced fungal plague has caused mass die-offs.

Estrada carefully teases away strands of moss, until a tiny hand with four little yellow fingers appears. The little frog turns out to be dead.

"Dammit," Estrada says. "It's not alive. This happens sometimes. It sucks." Not only is this frog dead, it's not even the especially rare one she was hoping for. But she says it's what they expected to happen with chytrid.

Bubble frogs: Species in quarantine

Rescued frogs and their progeny can now be found in zoos from Germany to Houston. Some are the last of their kind and exist only in captivity.

"Even if you're able to breed them in a lab, they're still susceptible to the chytrid fungus, so you can't really put them back in the rainforest because the chytrid fungus is still there," says Reid Harris, a professor of biology at James Madison University in Virginia.

While thinking about this problem and doing research in Virginia's George Washington Forest, Harris noticed something in the salamanders he was looking at.

"The females would squirm through the eggs periodically," he says. "If the parent deserted the nest, fungus would take over the nest fairly soon, and there would be no survival of the offspring."

Harris' observation eventually led to the discovery of bacteria on the skin of the salamanders. Those bacteria protected the animals against fungal attack.

"The exact mechanism, we hypothesize ,is that it's due to anti-fungal metabolites that are being produced by the bacteria," says Harris. "Maybe the bacteria is somehow stimulating the immune system of the frog. Maybe the bacteria is filling up all the attachment sites so the skin fungus can't find a place to attach."

When Harris removed bacteria from the skin of the salamanders and exposed them to chytrid, the salamanders got sick. When he slathered the salamanders with the bacteria, they did better. Researchers across the country took notice.

"When I heard about that, we immediately got in touch with Reid and said maybe that could help explain what's going on here in California, where you got these yellow-legged frogs that are dying from this fungus," says Vance Vrendenburg at San Francisco State University.

The yellow-legged frogs in the Sierra Nevada mountains were experiencing the same kind of die-offs as in Panama.

"When we started working on this problem, we had 500 populations remaining of these frogs," says Vrendenburg. "We're down to 80 populations left. So they're just dropping like flies."

But he found a few small populations of frogs that survived, and on their skin he found the same protective bacteria. He isolated it in the lab, grew broths full of it, and gave it to more frogs up in the mountains.

"We just capture individual frogs and we give them a little bacterial bath. It looks like soup, and it looks like it worked," he says. "I went back in 2011, I saw 23 frogs, that's it. Just 23 frogs. But of those 23, every single one was an experimental frog that got bacteria in 2010."

A promising start ... or a bandaid?

The bacteria approach to fighting chytrid fungus is one of several that have come up in the past decade. There's research showing some frogs could develop genetic immunity. And some strains of the fungus are less deadly than others, which could make breeding for resistance a little easier. There's even a type of aquatic crustacean found to eat the fungus. Brian Gratwicke, a conservation biologist with the Smithsonian, says those options would only work under certain circumstances.

"This is the only tool that we can think of at the moment that has a lot of promise in allowing a frog to be reintroduced back into the wild and survive chytrid," says Gratwicke.

As Gratwicke speaks, he and graduate student Matt Becker swab a bright yellow Panamanian Golden Frog in a lab in Front Royal, Va. These frogs, which are so yellow they seem to glow, are believed to be extinct in the wild. But in zoos, they've been multiplying like rabbits. When Becker tried to implant the protective bacteria from the Appalachians in their skin, it wouldn't stick. Not only that, but there were concerns about using non-native bacteria.

"So we went down to Panama in 2009 and collected bacteria from many different amphibian species in populations that were surviving with the chytrid fungus."

They sifted through 500 species of bacteria on frogs that survived local extinctions in Panama, looking for ones that fought chytrid. They found 50. Now, they're hoping one of those will stick to the Golden Frog so one day it might be reintroduced into the wild.

Heavy lifting left for evolution

But at least one scientist who's been trying to find solutions for two decades is not so sure.

"I'm quite skeptical, having seen what I've seen in the past 20 years," says Karen Lips, a researcher at the University of Maryland who was among the first to document frog die-offs. "I can't imagine anything is going to be the miracle cure. I hope I'm wrong."

Lips says it's unlikely anyone will be spraying bacteria from a plane, so each frog population would have to be hand-treated. With thousands of species at risk, it's no small task. And it's not clear if the bacteria will be passed from frog to frog, or generation-to-generation in the wild, though there is some promising research in that direction.

"Big scale, I think we have to depend on Mother Nature, on evolution, and hope for the best and do everything we can to stack the deck on the side of the frogs," says Lips.

Knowing more about how the fungus operates will help humans to better manage outbreaks in areas that haven't been hit yet, such as richly diverse Madagascar, adds Lips. The problem is, in many cases, the infection has been so swift and so severe it hasn't given vulnerable species the chance to evolve. For them, these microbes may buy just a little bit of time.

[Music: "Time After Time" by John Coltrane from Stardust]

Photos: Local Scientists Take Stock Of An Amphibious Species


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