Frogs in Panama Are Resisting a Deadly Fungus

Clown frogs (Atelopus varius) are just one of many frog species that have seen their populations decline. Brian Gratwicke/Wikimedia Commons

A deadly fungus has steadily ravaged the world's amphibian population since the 1980s, but there may be some good news.

According to a study published in Science, some species of frogs in Panama have demonstrated a steady recovery in their populations since the chytrid fungus (Batrachochytrium dendrobatidis) arrived in the country in 2004.

"It offers us all hope," Jamie Voyles, an assistant professor in the University of Nevada in Reno's biology department and one of the study's authors, told New Scientist.

Viva la resistance

The chytrid fungus works by growing on a frog's sensitive and all-too-important skin. Frogs rely on their skin to perform all kinds of functions, and when it's covered by a fungus, things go very badly very quickly.

"The reason why this is so deadly for amphibians is that their skin is really a physiological organ," Voyles explained to Wired. "Amphibians use their skin to drink water, to take in respiratory gases, and to balance things like electrolytes." Fungus-afflicted frogs eventually die of cardiac arrest.

Frogs have a defense mechanism against these sorts of diseases. They can secrete antimicrobial peptides that essentially serve as a kind of immune system to the skin, according to Wired. The fungus is just so tough that it overwhelms the frogs' defenses.

The result has been that plenty of frog species, including clown frogs (Atelopus varius) and common rocket frogs (Colostethus panamansis), have experienced severe drops in population. Clown frogs, for instance, are now critically endangered, in part because of the chytrid fungus.

A common rocket frog (Colostethus panamensis) against a white background
The common rocket frog (Colostethus panamensis) is an endemic species to Panama harmed by the chytrid fungus. Brian Gratwicke/Wikimedia Commons

Voyles and her colleagues discovered that nine out of the 12 frog species in Panama for which they have good data have shown a remarkable rebound in their numbers, however. At first, they assumed that the chytrid fungus might be weakening in some way, but when they compared samples collected in 2014 against samples of the fungus collected in 2004, when it first arrived in Panama, the fungus had barely changed on any level.

"At the outset I expected we'd find the opposite, that the pathogen had weakened," Voyles said. "I was completely wrong."

Obviously something was going on with the frogs themselves. The researchers collected frogs from areas where the fungus has decimated populations, as well as descendants of captive-bred frogs from before 2004. They exposed both groups to the fungus, and found that the frogs that lived in Panama were able to better fight off the fungus thanks to skin secretions.

No magic bullet

While the frogs evolving to combat the fungus is good news, it isn't great news. Evolution can move slowly, perhaps too slowly for species to survive, especially if the chytrid fungus itself end ups evolving against these new secretions. This becomes especially stark when the nine species that are recovering represent a mere 20 percent of the species that originally inhabited the area.

"We focused on the 12 species because we had reasonable numbers to work with," Voyles told New Scientist. "The remaining species may be lost or may be still out there, which is why we need to keep monitoring."

Conservationists are collecting uninfected wild frogs and breeding them in captivity to ensure a diverse gene pool in case the fungus wipes out the species in the wild. This tactic, while good for keeping the population up, means the frogs may not return to the wild, lest the fungus wipe them out again. Of course, if researchers are able to selectively breed the frogs that are exhibiting a resistance to the fungus, that could make a difference.

Another potential remedy is to coat the frogs with a fungus-protecting solution, but this may inhibit the frogs from developing their own methods of fighting off the fungus.

Even if the frogs survive the fungus, there are plenty of other threats to contend with — like habitat loss and climate change, which are reducing frog populations and genetic diversity.

But hopefully these frogs in Panama have demonstrated a resilience that will help them continue to rebound and continue to thrive.