Imma Perfetto
Cosmos science journalist
There’s new hope for the survival of frogs facing the threat of a fungal disease ravaging their populations.
After nearly being wiped out by the disease chytridiomycosis, populations of yellow-legged frogs are again thriving across Yosemite National Park in the US.
The frogs have developed some resistance to infection by the fungus that causes chytrid, Batrachochytrium dendrobatidis(Bd), and higher tolerance to it once infected, allowing researchers to repopulate infested locations.
“It’s mind-blowing considering where we were 10 or 15 years ago,” says Roland Knapp, a biologist based at the University of California – Santa Barbara Sierra Nevada Aquatic Research Laboratory.
“When we weren’t sure if we were going to have this frog on the landscape anymore, to see how things are turning around. It’s incredible to see.”
Bd has devastated global amphibian biodiversity worldwide, with one estimate suggesting at least 501 species have declined due to chytrid, 90 of which are confirmed or believed to be extinct.
The Sierra Nevada yellow-legged frog (Rana sierrae) of California’s Sierra Nevada mountains have disappeared from more than 90% of their historical range and are now listed as endangered.
Over the course of 15 years, researchers and conservationists reestablished breeding populations of yellow-legged frogs by translocating Bd-resistant frogs back into 12 habitats where the species had been lost.
These frogs were taken from populations that had experienced outbreaks of Bd, but which had persisted and eventually recovered. These recovering populations show increased resistance against Bdinfection, either from natural selection for resistant genotypesand/or through acquired immunity.
The researchers found that yellow-legged frogs became established and formed reproducing populations at about 80% of the reintroduction sites, despite the ongoing presence chytridiomycosis.
“In our study, results from viability modelling suggest that many reintroduced populations have a high probability of persisting over 50 years,” Knapp says.
“These results provide a rare example of how reintroduction of resistant individuals can allow the landscape-scale recovery of disease-impacted species, and have broad implications for amphibians and many other taxa that are threatened with extinction by novel pathogens.
“We now have a proven strategy that is working in Sierra Nevada yellow legged frogs and is allowing us to recover the frog at a scale of Yosemite National Park.
“This frog that has been pushed to the verge of extinction by this pathogen is now becoming an example of how we might recover amphibians all around the world.”
Given how rare it is for amphibians to evolve resistance against Bd infection, the researchers say that understanding the factors behind it in yellow=legged frogs, and the effectiveness of selective breeding programs and other genetic interventions to enhance this resistance, may be important in the future.
The research appears in the journal Nature Communications.
