Frogs are bouncing back

Central America's amphibians are evolving resistance to a devastating fungal infection.

Harlequin-frog_Kike-Calvo-UIG-Getty623-9d4fd81

The harlequin frog population of Costa Rica was devastated by chytridiomycosis © Kike Calvo / UIG / Getty 

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Just a decade after the fungal skin disease chytridiomycosis swept through amphibian populations in Central America, there are signs that the region’s frogs are evolving resistance to it.

Discovered in the 1990s, chytridiomycosis, which is caused by the fungus Batrachochytrium dendrobatidis (Bd), has wreaked havoc with amphibian populations around the world. But a new study in Panama suggests that many species devastated by the disease – nine of 12 species surveyed – have recovered.

The biologists assumed that the fungus had evolved into a less virulent form. This is a common pattern in disease epidemics – parasites are better off keeping their hosts alive if they are to prosper. But experiments showed that the fungus is no less lethal to populations with no history of exposure, suggesting that this is not the case.

“I was very surprised,” says Jamie Voyles of the University of Nevada. “But the more tests we did, the more I became convinced that my initial ideas about what was happening were totally wrong.”

Instead, it seems to be the frogs that are evolving. Voyles’s team compared the susceptibility to the disease of two populations of clown frogs – one from a region where the fungus is endemic and a captive population that was established before the epidemic hit. This proved that the frogs have developed resistance to the disease, probably via anti-microbial skin secretions.

It’s not clear yet whether the frogs’ response is a sign of a global recovery. “We hope so,” says Voyles. “We were only able to focus on one aspect of frog defences but we expect they’re using lots of different ways to fight back.

“We know that the pathogen is still lethal so there may be some species out there in need of conservation intervention,” she adds. “We also know that amphibians are facing many threats, so protecting their habitats is critical.”

Read the paper in Science.

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