A Bolivian frog species returns from the dead

Scientists feared this frog was extinct. No one had seen a Sehuencas water frog in the wild since 2008. Just one “lonely” survivor, nicknamed Romeo, remained in captivity. A fungal disease has been wiping out frog populations worldwide, and scientists suspected it had killed off this one, too. But after 10 years searching Bolivian mountain forests for the long-lost amphibians, scientists have finally turned up a tiny group of five.

“It’s just incredible,” says herpetologist Robin Moore. A herpetologist studies reptiles and amphibians. Moore is the communications director at Global Wildlife Conservation in Austin, Texas. He was among the scientists who announced the rediscovery of this species on January 15.

Sehuencas water frogs (Telmatobius yuracare) live only in the Bolivian mountain cloud forests, where the climate is moist and cool. And that’s where researchers found the five. Unfortunately, this frog’s native habitat also provides the ideal conditions for the growth of a fungal infection with an ungainly name: chytridiomycosis (Kih-TRIH-dee-oh-my-KOH-sis). Most scientists just refer to it (and the fungus that causes it) as chytrid (KIH-trid).

The disease has killed off most Sehuencas water frogs. It was believed to have eliminated them all. Why the five newfound animals survived remains a mystery. “It could be that this small population has immunity,” Moore says. A genetic difference might make them resistant to the fungus. Or there might be something special about their environment, such as an unusually warm patch of cloud forest.

It could also just be luck. “Many species of frogs that disappeared for years — decades in some cases — have been seen again later,” says Karen Lips. She’s an ecologist at the University of Maryland in College Park. For example, Ecuador’s marsupial horned frog was missing for more than 10 years. In December 2018, researchers announced they had rediscovered it.

Reappearances can happen for several reasons, Lips says. There might be changes in the frogs, the fungus or the environment. “The simplest explanation is that once most of the frogs are gone, the fungus declines,” she says. With fewer hosts to infect, the disease can die off, too. Any surviving frogs can then slowly rebound until, years later, one hops in front of scientists.

The five newfound Sehuencas water frogs raise hopes that even more are still hiding in the wild. They also offer researchers a chance to help the species recover. Scientists have taken the five back to the lab. There, the frogs will breed and make more frogs that can later be returned to the forest.

There’s currently no good way to get rid of the deadly chytrid fungus in the wild. So scientists are eager to study frogs that have survived exposure to the disease, Moore says. They could offer clues to how the animals pulled through.

Whenever a frog that scientists thought chytrid had killed off later reappears, “it’s just an opportunity to understand a little more about how this [disease] works,” Moore says. And, he adds, it’s an opportunity to bring the frogs back.