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Fungus Pushes Frogs Towards Extinction

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The Panamanian Golden Frog is most likely extinct in the wild, but it survives in captivity.
Sabri Ben-Achour
The Panamanian Golden Frog is most likely extinct in the wild, but it survives in captivity.

It's been called a crisis in amphibian biology: more than a third of amphibian species are at risk of extinction. Habitat loss and climate change are both causes, but so is an invasive disease that's been called the smallpox of the amphibian world. Researchers from D.C., Virginia, and Maryland recently traveled to Panama to try to help limit the effects of the disease.

Combing the rainforest in search of frogs

It's the middle of the night, and the middle of the rainforest in Central Panama. A group of researchers is slogging through a stream. It's dark, and dozens of critters are watching -- just not the ones they're looking for.

"I can see the eyes glowing right there; it's probably just a spider," says one of the researchers, Brian Gratwick.

Gratwicke usually lives in D.C. He's a biologist with the Smithsonian's National Zoo. But right now, he's here looking for frogs. And nobody's having much luck.

"We're looking for little green blobs sitting on a green leaf; anything that makes the leaf hang unusually," says Brian Gratwicke.

They've been at it -- looking for this frog -- for more than an hour and a half. They've seen plenty of giant spiders and venomous snakes, not to mention a very large lizard -- but no frog.

Finally, success: a glass frog guarding a gelatinous pile of eggs.

"See those tadpoles wiggling inside the eggs?" Gratwicke says.

It's called a glass frog for a reason: its skin is transparent.

"Right above the stomach, you'll see a teeny white thing that's beating, and that's his heart - see his heart beating?"

It might've just been a bad night, but researchers have documented population crashes of 80 percent at lowland sites like this. Tonight has been frustrating, and they call it a night.

Searching for the source of frog epidemic

For a long time it was a mystery what was causing such disappearances. For years, scientists watched extinctions and die-offs sweep across Central America. It was the National Zoo in D.C. that first characterized the culprit back in 1999: a fungus called chytrid. And the more researchers looked, the more they found it wasn't just a problem here.

Humans have spread it around the globe, and it's left a trail of amphibian die-offs and extinctions in its wake.

"There's frogs all around the world being affected," says Gratwicke. "There's amphibians that have gone extinct in Australia, in the Caribbean, in North America, in South America, in Central America."

Gratwicke says 94 out of 122 frog extinctions since 1980 were associated with chytrid. Some research shows it was introduced from Africa by people moving frogs over the past several decades. Some scientists suggest climate change may sometimes make it worse. The fungus doesn't kill all frogs, but it does hit especially hard in highland species.

"Where chytrid hits in mountainous regions you lose massive amounts of frogs - you lose half of species and about 90 percent of frogs," he says.

Implications for humans, other amphibians

It's not just thousands of frog species that are affected, he adds. Some toads and salamanders are also susceptible.

"If you're to think of an analogy for the mammal world, think of a disease that could spread from dogs to cats to cows to bats, and cause the extinction of half of those species," Gratwicke says. "That's what we're looking at with this disease."

There is also a real cost to humans from the frog extinctions. Frogs' skins are anti-microbial factories. They've produced compounds that kill superbugs in hospitals.

"There's a species of frog in Australia that produces a chemical called caerin, which blocks HIV transmission to T-cells," Gratwicke says. "The untapped resources of our amphibian biodiversity are virtually unknown."

Researchers rush to quarantine affected species

When people started to figure out how the fungus was wiping out these creatures, biologists and zoos from Berlin to Houston tried to medevac frogs out ahead of the fungus' spread.

Edgardo Griffith runs the El Valle Amphibian Conservation Center in western Panama, where the fungus swept through several years ago.

"Once chytrid starts killing frogs, it kills them fast around these areas," he says. "So when chytrid arrived in El Valle, we didn't even have a facility, so we had to keep frogs in hotel rooms. From the get-go we were behind the chytrid wave."

Griffith is now working with the Houston Zoo and the Smithsonian and has a two-room building where he keeps 12 of the 30 most endangered species in aquariums under tight quarantine. Some look like like bright yellow decomposing leaves; others are black as tar and have a crown like a triceratops; and others wear a metallic green.

But being as exotic as they are -- and in some cases brand new to science -- also means there's no rule book on how to take care of them.

Scientists learn to care for newly discovered species

Nobody knows exactly what some of them eat, or what they need to mate. Sometimes they die if they don't get some vital nutrient or if they become allergic to a medicine.

"A lot of these have never been kept in captivity," Griffith says, looking over a lemur frog. "We lost a lot of them."

Keepers don't have much time to figure it out. Some of these frogs are already extinct in the wild.

"That's our worst nightmare, that they go extinct before we get to them," says Angie Estrada, a zookeeper at Panama's Summit National Zoo.

At Summit, modified refrigerated shipping containers hold row upon row of aquariums, fog machines, and UV lights.

"We call them arks, amphibian arks, because we're basically keeping them alive for future generations," she says of the frog-filled containers.

Estrada holds some tiny black and metallic green frogs. "These are some of our babies. These are Atelopus certus babies," she says. "One of the first Atelopus born in captivity, ever. It's really kind of cool, exciting, that they bred in captivity."

About 80 of the frogs hop around a critter keeper. They are from a sliver of mountainous forest at the western end of Panama called the Darien. It may well be the last highland tropical forest in the entire Western Hemisphere that is chytrid free.

There may be 150 species of frogs and toads there, and scientists estimate that chytrid will arrive there in a year or two.

"I know it sounds crazy, and really intimidating, but some of the individuals here are going to be some of the founders for repopulating these sites," Estrada says.

That is unlikely to happen soon, without a cure or some kind of transferable immunity to chytrid. Both are questions researchers are working on. Until then, at least 1,000 species of amphibians around the world remain under threat.


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