Tropical frogs found coexist with a deadly mushroom

Amphibian biologists around the world watched with horror in 2004 as El Copé frogs (Panama) began to die in the thousands. Guilty party: Batrachochytrium dendrobatidis, a deadly fungus more commonly known as chytrid fungus. In a few months, about half of the native frog species in the area have disappeared locally.

A new study conducted by researchers at the University of Maryland suggests that in a decade, the remaining species in El Cope have developed the ability to coexist with the chytrid fungus. In a field study covering the years 2010-2014, the researchers found that frogs infected with the fungus survived at a rate almost identical to that of uninfected frogs.

The results, published on October 3, 2018 in the journal Ecological applications, suggest that frog populations in El Copé have undergone ecological and / or evolutionary changes that have allowed the community as a whole to persist despite severe losses of species. According to the researchers, the results could be good news for other hot spots of amphibian biodiversity hard hit by the chytrid fungus, such as South America and Australia.

"Our results are really promising because they lead us to conclude that the El Copé frog community is stabilizing and not sinking into extinction," said Graziella DiRenzo (Ph.D. & # 39). 16, Biological Sciences), now a postdoctoral researcher at the University of California, Santa Barbara and the lead author of the research paper. "This is a big problem with chytrids around the world, and before this study, we knew very little about the communities that survive an epidemic, and in some areas it's still a black box."

DiRenzo and his colleagues returned to the same small plot of 2 km2 in El Cope, every year from 2010 to 2014. They broke up the site into smaller sub-sites of 20 meters, sampling several times the subsites several days of after. in a season. Each time, the researchers tested the presence of the fungus in individual frogs while assessing the severity of the symptoms of the disease.

The researchers then captured this data in a statistical model developed to assess the dynamics of the disease in communities affected by an epidemic. Frequent and repeated sampling of individual frogs in the field allowed the team to minimize bias by correcting the model for all present but non-visible animals. The results allowed the researchers to conclude that infected frogs survived at the same rate as uninfected frogs. This observation strongly suggests that the remaining frog species in El Cope develop the ability to tolerate the fungus and survive its deadly effects.

"Our study found that even though there are many infected individuals, about 98% of them are at very low levels," said Karen Lips, professor of biology at UMD and lead author of the study. "We know that early on, several species played a key role in spreading the infection, like Mary Typhoid, but some of these species have now disappeared, so the ecosystem is totally different.This is almost not comparable to what it was before. "

DiRenzo, Lips and their colleagues suggest that the El Copé frog community has stabilized thanks to an effect called "eco-evolutionary rescue". In this scenario, some species may have developed tolerance to the fungus, while others highly infectious, "Typhoid Mary", would have died and would have stopped contributing to the spread of the pathogen. The mushroom itself may also have become less virulent and the frog community as a whole may have undergone other types of restructuring.

The researchers note that, since the El Copé frog community had been studied for years prior to the 2004 outbreak, the research site offers a rare opportunity to evaluate changes in a frog community as a result of 'a generalized chytrid infection. According to the researchers, if the community has stabilized here, it is likely that other communities of hard-hit frogs elsewhere in the world have undergone similar adaptations, even when the disease has reduced the total number of frogs. 39 species and / or individuals.

"El Cope's frogs are not doing very well, but they're hanging in. The fact that some species have survived is the most important thing," Lips said. "If a species disappears immediately, it has no choice – we know how all these species reacted to the initial invasion – we now know how survivors react to the continuation of the species." We know that there are several sites in the world that have probably experienced the same thing.If enough species of frogs in a given place can survive and survive, it is hoped that a new community frogs will replace what has been lost.

The research paper, "Eco-Evolutionary Rescue Promotes Host-Pathogen Coexistence," Graziella DiRenzo, Elise Zipkin, Evan Campbell Grant, J. Andrew Royle, Ana Longo, Kelly Zamudio, and Karen Lips, was published in the journal Ecological applications October 3, 2018.

Explore more:
What prevents mass extinctions? Lessons from the disappearance of amphibians in Panama

More information:
"Eco-evolving rescue promotes host-pathogen coexistence" Ecological applications (2018). DOI: 10.1002 / eap.1792