In South American Highlands, Disease is Killing Frogs While Climate Change Threats Loom

A study of declining frog populations in the Andes Mountains reveals that disease is accelerating their death.

A deadly fungus is striking the mountain frogs, which San Francisco State University professor Vance Vredenburg said is notable because it's not the cause of death many had suspected. Increasing temperatures, even at the high altitudes of the Andes, were initially believed to play a role in the frogs' death.

Vredenburg and his colleagues found that frogs living at higher elevations can tolerate increasing temperatures. But as their habitat warms, it has fallen within the optimal temperature range for Batrachochytrium dendrobatidis, or Bd, a harmful pathogen responsible for the decline or extinction of 200 frog species worldwide.

"Our research shows that we can't just automatically point our finger at climate change," Vredenburg said. "We need to look carefully at what is causing these outbreaks.

Vredenburg and his team conducted their research in southern Peru at Wayqecha Biological Station on the eastern slopes of the Andes, near Manu National Park. The team devised an experiment to test frog's toleration to increasing temperatures by placing the amphibians in water baths of increasing temperature. If a frog placed on its back quickly flipped itself over, the researchers said it meant the frog could tolerate the warm water. If not, the researchers knew the frog had become overwhelmed and was unable to deal with the change.

The team also found the the optimal growth temperature for Bd lies within the normal temperature range of the frogs' habitat.

"This really suggests that the fungus is driving a lot of the declines in this place," said Alessandro Catenazzi, assistant professor of zoology at Southern Illinois University and the lead author of the study.

Climate change, however, is affecting frogs living at lower altitudes in the area. The area's lowland frogs are less susceptible to the threats of Bd, but their habitat is more likely to face climate change, meaning that if the frogs don't adapt or relocate, they could be in trouble.

"It's terrible news," Vredenburg said. "The frogs at the top of the mountain are in trouble because they are experiencing a novel pathogen. The guys at the lower elevations are not in trouble from the fungus, but they're really susceptible to changes in climate."

Vredenburg added that Bd is like no other pathogen in the history of the world. "Bd outbreaks make bubonic plague look like a slight cough," he said. "We need to understand the basic biology that's driving this terrible pathogen because it's the same biology that drives diseases that affect humans."

The research is published in the journal Conservation Biology.