Frogs are disappearing around the globe, with species living in some of the most pristine areas among the hardest hit. The prime suspect: a fungus that destroys their sensitive skins. Now a paper published in the 5 October issue of PLoS Biology demonstrates that frogs infected with the fungus may survive for years in the wild, suggesting that frogs may be adapting to the scourge.
Queensland is the epicenter of frog declines in Australia. Fourteen of its frog species have dwindled or gone extinct since 1980, many from the untouched mountain streams of Eungella National Park. Since then, scientists have identified Batrachochytrium dendrobatidis as a major culprit; the fungus has been found on many dead and dying frogs around the world and often proves fatal to frogs infected in the lab.
To determine how B. dendrobatidis might have affected frogs in Eungella, Hamish McCallum of the University of Queensland, St. Lucia, and colleagues searched for the fungus in frogs living at four sites in the park. At the time, they believed that the fungus would have killed most of the susceptible frogs and then disappeared. The team looked for the fungus in 474 toe tips (the fungus typically attacks the extremities first) clipped from six species of park frogs over 4 years.
The scientists saw signs that frogs have developed some immunity to the fungus. There was very little if any trace of the disease in four species. In the two other species, the percentage of infected frogs remained stable from year to year, suggesting that the fungus was endemic. Among frogs captured more than once, those with the fungus were just as likely to have survived as clean animals. "That was quite a big surprise," McCallum says. "It suggests the frogs are existing quite happily with this disease."
It's good news if frogs can live with the fungus, says amphibian ecologist Ross Alford of James Cook University in Townsville, Australia: "Up until now, it was possible to imagine every frog we saw with the disease was dying." However, Alford cautions that not all frogs may be acquiring immunity to the fungus, as other Australian amphibians have not rebounded nearly as well.