Professor identifies troubling trend for global frog die-off

A brown frog sits on a rock with tree-covered mountains in the background

A decade after the Bd fungus devastated amphibian populations in a Peruvian cloud forest, researchers published a paper showing that Bd isn’t a hit-and-run disease. (Photo credit: Alessandro Catenazzi)

A decade after an outbreak, Peruvian frogs still haven’t recovered

Five years ago, San Francisco State University Professor of Biology Vance Vredenburg was hard at work in a laboratory. This wasn’t a place with gleaming floors and high-tech gadgets — it was a rustic field station almost 10,000 feet high in the Peruvian cloud forest. Ten years earlier, Vredenburg was part of a team that documented a fungus outbreak that devastated the area’s rich assortment of frogs and toads. This time, he joined the team back in the cloud forest to ask: What happens after the collapse?

That question has implications that extend far beyond Peru. Amphibians worldwide are in the midst of a mass extinction, and the fungus Batrachochytrium dendrobatidis (Bd) is one of the main reasons: It has attacked amphibian populations from California to Australia, driving as many as 200 species extinct. Scientists intensely study these outbreaks, but rarely check back in on the species that persist afterward. “The attitude is, once the fire burns through, the survivors are the survivors. And they should be fine,” said Vredenburg.

He and his colleagues suspected that the story might be more complicated. They captured 122 frogs of eight different local species in Peru and tested their susceptibility to Bd. One part of the team, not including San Francisco State researchers, also surveyed the area’s frog life to see whether populations had stabilized in the decade since the outbreak. 

Their low-tech laboratory meant using some creative methods. “We’re pushing the limits of what you can do in a really remote place,” Vredenburg explained. Lacking the onsite resources to test whether frogs were sick, they had to treat the animals with an antifungal drug and then re-infect some to measure their vulnerability to the disease. And without the equipment to keep the fungus alive in the lab, the team decided to infect frogs by housing them with Bd-ridden frogs bought at a local market. Afterward, they packed up their samples and analyzed them back in San Francisco.

What they discovered wasn’t encouraging: When exposed to the fungus in the lab, three of the eight frog species showed significant die-offs. None of the eight were totally free of the fungus in the wild either, with most species hovering around a 50 percent infection rate. Only one had managed to maintain its pre-collapse numbers. The researchers published the results last month in the journal PLoS ONE.

“The situation isn’t as good for the survivors as we thought it was,” explained Vredenburg. Rather than coexisting peacefully with the survivors, Bd appears to be keeping amphibian populations low in this part of Peru. The same is likely true in other parts of the world devastated by the fungus, too — but while the threat may go unnoticed elsewhere, this cloud forest will keep getting regular checkups. Vredenburg and his colleagues plan to keep returning to track the disease. “I’m really excited to keep following up,” he said.

The research was a collaboration with SF State Assistant Professor of Biology Andrea Swei and Alessandro Catenazzi, an assistant professor of zoology at Southern Illinois University Carbondale. The team also included three undergraduate students. The work was supported by the National Science Foundation, as well as by the Asociación para la Conservación de la Cuenca Amazónica, a Peruvian conservation organization.

Last update: 
2017-11-22 10:55
By: 
PJM