Sliver of hope as ‘mountain chicken’ frog shows resistance to deadly disease

The mountain chicken isn’t a chicken at all, but a huge frog three times as heavy as a can of soup and about as long as a large banana. These animals, also known as “chicken frogs” or “giant ditch frogs,” used to be abundant across several Caribbean islands. Locals regularly ate them, and it’s said that the frogs tasted like chicken, which is likely how the species, Leptodactylus fallax, got its common name.

But over the years, the species went extinct on several islands following the introduction of the invasive Indian gray mongoose (Herpestes edwardsii), which only left populations on the islands of Montserrat and Dominica. Then, 20 years ago, an infectious fungal disease known as amphibian chytridiomycosis — a disease responsible for the decline of more than 500 amphibian species and 90 species extinctions in the past 50 years — spread across the Caribbean.

The disease first appeared in Dominica in 2002, and within 18 months, it eliminated 85% of the mountain chicken subpopulation. On Montserrat, a similar scenario played out: a subpopulation went from “thousands” to four known individuals within a year. Now, the mountain chicken is believed to be extinct in Montserrat.

The fungus affects the skin of the mountain chickens, making it thicker and unable to absorb water and electrolytes. Eventually, the fungus will cause the frogs to go into cardiac arrest, said Andrés Valenzuela-Sánchez, a researcher at the Zoological Society of London’s (ZSL) Institute of Zoology.

“This was one of the quickest declines of any wild species on the planet,” Valenzuela-Sánchez told Mongabay. “It’s not something that occurs very often. But with this fungus, we have observed this rapid and complete collapse of the populations in other places on the planet.”

A team of international researchers recently conducted a survey and found that there were still 21 mountain chickens living in Dominica.

Valenzuela-Sánchez, who was involved in the survey process, said he and his colleagues detected the animals by following the loud calls of the males, which he compared to “barking dogs.” They also searched for them in the forest at night with flashlights.

“Because the frog is very big, you can see the reflection of the light on their eyes,” he said.

Andrew Cunningham, professor of wildlife epidemiology at ZSL’s Institute of Zoology, said discovering the 21 mountain chickens gives “reason for optimism.”

“Despite all the threats these frogs are facing, the team identified one particularly special frog,” Cunningham said in a statement. “He was tagged as a mature individual in a survey eight years ago, so we know that this frog is at least 11 years old — making him the oldest wild mountain chicken frog known to be in existence.”

“If this individual can persist in the face of endless challenges, it gives us hope for the future of the species more widely,” Cunningham added, “and we need those with the power to rewrite this story to invest in that future.”

Valenzuela-Sánchez said the researchers found some of the remaining animals in Dominica also appear to have “resistant genes” that may help them survive against amphibian chytridiomycosis.

“We hope that with time, and with proper protection of the habitat and the reduction of other threats,” Valenzuela-Sánchez said, “these animals can still thrive in nature and increase the population size.”

Banner image caption: Mountain Chicken Frog (Leptodactylus fallax). Image by Josh More / Flickr (CC BY-NC-ND 2.0 DEED).

Elizabeth Claire Alberts is a senior staff writer for Mongabay. Follow her on Twitter @ECAlberts.

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Citation:

Scheele, B. C., Pasmans, F., Skerratt, L. F., Berger, L., Martel, A., Beukema, W., … Canessa, S. (2019). Amphibian fungal panzootic causes catastrophic and ongoing loss of biodiversity. Science, 363(6434), 1459-1463. doi:10.1126/science.aav0379