Scientists work to save frogs from fungal pandemic

Scott Sutherland

Time is running out for many species of frog, as they are close to being wiped out by a plague called Chytridiomycosis. However, teams of scientists are working day and night, in isolated labs, to preserve these species so that they might, one day, be able to return to the wild.

Chytridiomycosis is a disease in amphibians caused by the fungus Batrachochytrium dendrobatidis (Bd). When Bd spores contact an amphibian's skin, they spawn small pods — called sporangia — which contain more spores, that then further infect the animal and any more around it when they open. The disease causes reddening and sloughing off of the skin, lethargy, a failure to seek shelter, a failure to flee when threatened, and failure of the 'righting reflex' — the instinctive reflex to reorient your body if you are upside-down. Eventually, the disease clogs the pours of the amphibians' skin, and they dehydrate and suffocate at the same time.

The outbreak of Bd has reached pandemic — or in this case panzootic — proportions, as frogs in North America, Central America, South America, Australia and Europe are threatened by or dying off from the disease.

Evolutionary biologist Cori Richards-Zawacki, who is a professor at Tulane University, in New Orleans, has been trying to find survivors of the panzootic in Panama — which has the golden frog as its national mascot — but with very little success.

"This sure is depressing," she said while making her way down the Rio Farallon, in central Panama. The area used to be teaming with golden frogs, who are 'explosive breeders', but where she would normally hear a cacophony of croaking, there is only silence now.

Scientists have gathered the last remaining specimens of some species in 'amphibian arks', in an effort to breed them and keep these species from going extinct. Keeping them isolated from the natural environment is necessary to prevent further infection.

The first such ark is located at the bottom of the crater of an extinct volcano, at the appropirately-named El Valle Amphibian Conservation Center (EVACC). The frog specimens there were collected in 2006 and 2007, by Edwardo Griffith, who helped found EVACC, and his team.

"It was a nightmare," Griffith said. "I saw frogs dying as we were collecting them. They would die in your hand. The only option we had was to buy some time, keep them alive."

The team first housed the frogs — hundreds of them, from a dozen different species — in a local hotel until the ark was built, monitoring the frogs day and night. The vigil continues now, but efforts are being made to breed the frogs so that they can reintroduce them back into the wild soon. This isn't as easy as just getting the frogs together, though. Some species require very specific conditions or stimuli in order to mate, so the three staff, working in rotating shifts, 24/7, must accommodate all these necessities.

“We have to do our job, for a while longer. We have to be successful. Maybe we’ll have too many frogs, maybe thousands and thousands. That would be great. But then what are we going to do with them?” said director of EVACC, Heidi Ross.

The problem lies with the fungus.

"Usually when Bd appears, it kills everything it is going to kill, and quickly," said Dr. Roberto Ibanez, who works at the Smithsonian Tropical Research Institute in Panama. "It kills some species, infects others, who serve as disease vectors, as carriers, so it doesn’t go away."

Although it is known that the fungus has difficulty with heat, such that exposing an infected frog to temperatures of 28°C or higher will kill the fungus, many of the places that the frogs inhabit — such as higher up in mountain chains — are where the rain forest canopy and persistent cloud-cover keep the environment cooler. Some species have a natural agent that coats their skin to protect them against the fungus, but no way has been found to transfer this to other species. One proposed solution is to expose captive frogs to the fungus, breed the survivors (if there are any), and then release their offspring into the wild, hoping that they had developed an immunity to chytridiomycosis. For now, though, the plan is to breed as many frogs as possible, simply to ensure the survival of these species until a solution is found.

"We basically have to become really good frog farmers and breed a lot of frogs," said Brian Gratwicke, project coordinator at the Smithsonian's Panama Amphibian Rescue and Conservation Project.

"But the last thing we want to do is release these precious, expensive frogs back into wild, just to see them consumed by the fungus all over again."