Why Has the Darwin’s Frog Likely Gone Extinct?

Deep in the forests of Chile, a frog has gone silent, possibly forever—and an epidemic fungus may be the culprit.

Northern Darwin’s frog (Rhinoderma rufum) is likely extinct due to the effects of the fungal disease chytridiomycosis that’s killing amphibians around the world, a new study says.

Photo of a male Darwin's frog.
A male Darwin’s frog carries tadpoles in his vocal sac. Photograph by Michael and Patricia Fogden, Corbis

“Only a few examples of the ‘extinction by infection’ phenomenon exist,” study lead author Andrew Cunningham, a zoologist at the Zoological Society of London, said in a statement. (Related: “30 Amphibian Species Wiped Out in Panama Forest.”)

Its sister species, the southern Darwin’s frog (R. darwinii) has also suffered catastrophic losses and is near extinction. Both frogs are unique in that fathers incubate fertilized eggs in their vocal sacs—no other amphibians are known to care for their young this way.

Watch a video of a father spit up its babies.

Charles Darwin first described his namesake frog in December 1834, when he visited the island of Lemuy in the Chiloé Archipelago (map), just off Chile’s western coast.

“Amphibians have inhabited the earth for 365 million years, far longer than mammals. We may have already lost one species, the northern Darwin’s frog, but we cannot risk losing the other one,” Soto-Azat said.

Scientists thought the northern and southern species were the same until 1975, when further research showed that they were two separate species. By this time, the northern Darwin’s frog was already well on its way to extinction. It was last spotted in the wild in 1980.

Tracking a Killer Fungus

Conservationists focused on the visible threats to these frogs, such as habitat loss and deforestation. But Cunningham and ZSL colleague Claudio Soto-Azat—currently completing his Ph.D. at Andres Bello University in Santiago, Chile—weren’t convinced that habitat loss was the sole explanation.

That’s because the northern Darwin’s frog had disappeared from every area where it was found, and the southern Darwin’s frog was declining even in areas where its habitat wasn’t disturbed. (Read about vanishing amphibians in National Geographic magazine.)

Chytrid disease, caused by the fungus Batrachochytrium dendrobatidis (Bd), has been killing amphibians worldwide during the past two decades. An outbreak of the illness was first discovered in frogs in Queensland, Australia, in 1993, although it may have been present in other amphibian species for longer. The fungus had previously been found in South America, which led Cunningham and Soto-Azat to hypothesize that chytrid may also be killing both species of Darwin’s frog.

To find out, researchers caught Darwin’s frogs and found that 12.5 percent of the specimens were infected with chytrid. They compared this with rates of chytrid found in preserved specimens collected between 1970 and 1978, of which only one percent tested positive for chytrid—suggesting the fungus was to blame for the species’ declines. (Related: “Deadly Frog Fungus Spreads in Virus-Like Waves.”)

“Amphibians have inhabited the earth for 365 million years, far longer than mammals. We may have already lost one species, the northern Darwin’s frog, but we cannot risk losing the other one,” said Soto Azat, whose study appears November 20 in the journal PLOS ONE.

“There is still time to protect this incredible species.”

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Meet the Author
Carrie is a freelance science writer living in Virginia. When she's not writing about cool critters, she's spending time outside, drinking coffee, or knitting. You can visit her website at http://www.carriearnold.com