August 23, 2010
According to Andrew Crawford, a former postdoctoral fellow at the Smithsonian Tropical Research Institute (STRI) and a current researcher at the Universidad de los Andes, the amphibian skin disease chytridiomycosis (known as chytrid) has already eliminated nearly 100 different frog species in Panama and threatens one-third of all amphibian species worldwide.
A recent study suggests that some frogs species were wiped out by chytrid even before scientists knew of their existence. In another new study, three new frog species have been discovered in an area of Panama not yet affected by the deadly pathogen. The newfound frogs give even more urgency to those researchers already feverishly working to save species from extinction.
The three species—including two frogs from the genus Pristimantis and a robber frog from the genus Craugastor—were discovered in the disease-free mountains of eastern Panama. In Panama and the Central American highlands, chytrid is spreading at a rate of 19 miles per year. Scientists at the Panama Amphibian Rescue and Conservation Project—an initiative sponsored by the National Zoo to save the frogs of Panama—anticipate that chytrid will soon sweep across the site, perhaps within the next six years. When it comes, it will be there to stay. And as of yet, nobody has found a way to stop it.
The amphibian disease was first detected in Queensland, Australia in 1993, and genetic evidence suggests that it was present in Africa even before that and traveled the world on the back of a carrier frog, the African clawed frog. Not susceptible to the disease, the African clawed frog is traded globally as food, as a pet and as a laboratory animal.
One bizarre use of the creature was for pregnancy tests in Europe, Australia and the Americas in the middle of the 20th century. (The frog was injected with a pregnant woman’s urine and if it spawned, well, that was like getting a plus sign.) With the advent of modern pregnancy tests, the frogs were no longer needed. Many were subsequently released or escaped into the wild, where they spread the disease. Now amphibian populations around the world are in grave danger.
“The diversity of species getting hit by this one pathogen is remarkable,” says Crawford.
The project is on the hunt for a solution, however, and its members have initiated a two-pronged approach to save threatened frog species. First, the project is attempting to capture frogs and raise them in captivity, where they can be protected from chytrid. The frogs will ideally be reintroduced to their native habitats at a later date. “We have a decent idea of susceptible species,” says Crawford, who has worked with the project. “We don’t know when we’ll solve the problem, but until then we can get those species in captivity, and try to get at least 100 to 200 individuals of a certain species, to ensure breeding potential.”
The newly discovered robber frog is one such species that is particularly vulnerable to chytrid.
The second step—finding a cure—is a bit more complicated. “Either we have to kill the fungus or make the frogs resistant,” says Crawford. “The best hope right now is finding a bacteria that can confer resistance to frogs.” Field researchers have been painting frogs with cultures of various bacteria and then testing the frogs’ resistance to chytrid in their habitat. Recently, one frog species in the infected Sierra Nevada mountains of California has experienced a high survival rate from chytrid with the help of a specific bacteria. “It’s one avenue for now that seems to show some promise,” Crawford says.
In the face of this global threat, Karen Lips, a University of Maryland wildlife biologist teamed up with Crawford to make the discovery that the disease is already killing species yet to be documented by scientists. By analyzing the genomes of frog specimens that Lips collected in the 1990s (using a technique called “DNA barcoding”), Crawford and Lips identified several previously undescribed frog species that were no longer present today in the Panamanian site where they were first collected.
As if the battle against chytrid weren’t tough enough already, evidence suggests a correlation between higher temperatures due to climate change and the increased rate of frog deaths from chytrid. “The solutions to climate change and infectious disease and contaminants are not always obvious. And these are big, wicked problems that are complex, they’re synergistic, they interact, and so if you’re dealing with problems like climate change or infectious disease, its not enough to go stake out another park,” says Lips. “The thinking has to change.”
The global reach of chytrid will require a large-scale solution. Instead of thinking globally and acting locally, as the saying goes, Crawford believes scientists and conservationists will have to do the reverse.
“It’s as if somebody were ripping chapters out of the book of evolutionary history,” says Crawford. “The truth is, if we never see it, then we never know what we’re losing.”
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