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November 2, 2009

Disappearing Frogs: Trying to Save the World's Amphibians


Frogs in fight for their lives from disease, pollution, habitat loss

Disease, pollution, and loss of habitat are killing off hundreds of species of amphibians. One of the biggest threats right now is an aquatic fungus called chytrid that infects the skin of these historically tough, resilient creatures.

While a few species (marine toads, American bullfrogs and African clawed frogs) seem to be resistant to the fungus, chytrid is usually fatal to most others.

Biologist Vance Vredenburg is using a National Science Foundation (NSF) grant to study the disease. An important part of his research is communicating with scientists who are dealing with this crisis on every continent where amphibians live.

"How is the disease affecting rainforest species in Central America versus those in Africa? And if there are differences, what can we learn from that? Because that might be the key to understanding this disease," explains Vredenburg from his office at San Francisco State University. "So we're talking somewhere between 200 and maybe 400 species of amphibians being driven to extinction by this disease. That's never happened before in recorded history."

Saving frogs in the field

As scientists try to find answers to the cause and spread of chytrid, they are at the same time doing whatever is possible to save threatened species. One of Vredenburg's projects involved collecting frogs near Mammoth Lakes, Calif. (an area overwhelmed by the disease), treating them in anti-fungal baths, and then releasing them.

"I was able to get permission from the National Park Service to go in and actually treat some of these animals with anti-fungals. It had been done in the lab before. You can actually clear the frogs of the fungus," he says.

But before Vredenburg let those treated frogs back into the wild in 2006, he "microchipped" them. During later research trips to the area, he re-captured many of the treated frogs and found some of them to be disease free. Others were infected but still alive.

... And in captivity

Other amphibian experts are using different tactics, such as captive breeding programs. "Sort of the Noah's Ark perspective of race out in front of the wave of death and collect everything you can to try to save them before they go extinct," says Vredenburg.

"Besides chytrid, most of the problems are human-related, so you've got to do anything you can," says San Diego Zoo herpetologist Jeff Lemm, who is the project manager for the captive breeding program for California's endangered mountain yellow-legged frogs.

"The U.S. Geological Survey found a lot of tadpoles drying up during a drought in 2006. Eighty-two tadpoles were rescued and brought to the zoo. Captive breeding is often difficult and a little nerve wracking, but I'm optimistic on this project," explains Lemm.

The goal is to eventually get healthy animals back into the wild, a challenge in California not only because of chytrid, but also because of habitat loss, water quality issues and wildfires. Adding to the threats for these amphibians is the impact of climate change, especially on the spread of chytrid.

Is climate change a factor?

"Some people think it's climate change itself that's triggering the release of this pathogen from potentially being something that doesn't cause a problem to something that's suddenly really, really deadly," says Vredenburg. "It's almost as if humans began dying by the millions from the common cold."

Robin Moore, amphibian conservation officer for Conservation International, says global warming is impacting animals on several continents. "For example, for many amphibians, the breeding season is triggered by weather and climate change can disrupt this," he says.

For zoos, conservation organizations, and even for field biologists like Vredenburg, public awareness of the amphibians' plight seems to be increasing. "Not only do people have an affinity to frogs, they are really interesting, beautiful animals. They live all over the planet," notes Vredenburg.

Before it's too late

Vredenburg says he is touched by the desire of so many non-scientists to do whatever they can to make a difference. After reading an article about Vredenburg's work in National Geographic, art therapist Jennifer Beasley of Louisville, Ky., wrote him a letter of appreciation.

"I have fond memories of chasing frogs and tadpoles when I was growing up in Georgia, and that love of frogs and tadpoles stayed with me. My children are small now but someday I would like to see their children enjoy the croak of a bullfrog or the crazy squiggle that is tadpole locomotion."

"Please continue to do the hard but important work and know that there are people in the wider world who feel that your work is inspiring," wrote Beasley.

"We share a lot of traits with amphibians. I think it's really important that we understand as best we can why these outbreaks of disease are occurring, why we are having these massive declines and die-offs all over the world," adds Vredenburg. "Because if it happens in humans or if it happens in species that are very economically important to humans, we need those tools to figure out what can be done, if anything."

Miles O'Brien, Science Nation Correspondent
Marsha Walton, Science Nation Producer


Any opinions, findings, conclusions or recommendations presented in this material are only those of the presenter grantee/researcher, author, or agency employee; and do not necessarily reflect the views of the National Science Foundation.