Colorful frogs downed by disease are making a surprising comeback | Science

No bigger than a strawberry and often more colorful, harlequin frogs suffered greatly as a rapidly spreading fungus killed amphibians around the world over the past several decades. More than 70 of the 94 named species in this charismatic group seemingly disappeared from their South and Central American homes by 2010, and researchers feared they had gone extinct. So, Juan Manuel Guayasamin could not believe his eyes when he spotted one of the missing frogs sleeping on a leaf in a cloud forest in Ecuador in 2008.

“My initial emotion was disbelief,” recalls Guayasamin, an evolutionary biologist at the San Francisco University of Quito. “And after that, of course, joy.”

Guayasamin’s fortuitous encounter with that Andersson’s stub-foot toad (Atelopus palmatus) isn’t the only potentially good news for harlequin frogs (sometimes called harlequin toads). Over the past 2 decades, other researchers have rediscovered 32 of the missing species, he and colleagues report today in Biological Conservation. The discoveries “give us hope” that the extinctions are fewer than once believed, Guayasamin says, and could ultimately aid conservation efforts by helping researchers understand how some species have managed to survive.

Given the drumbeat of bad news about biodiversity loss, “It’s good to talk about species being found again,” says Alessandro Catenazzi, an ecologist at Florida International University.

The frogs may still be struggling, however. “Rediscovery by itself is not evidence of recovery,” cautions Roland Knapp, an aquatic ecologist at the University of California’s Sierra Nevada Aquatic Research Laboratory and Earth Research Institute. Some of the rediscoveries are based on just a single sighting, he and other scientists note.

Over the past 50 years, the lethal chytrid fungus Batrachochytrium dendrobatidis has caused population declines in hundreds of amphibian species, researchers estimate. Species in the harlequin frog genus, Atelopus, have been among the most severely affected. The amphibians often live at higher, cooler elevations, where the fungus seems to thrive. Some 70% of harlequin frog species are now considered extinct or critically endangered.

In 2002, researchers surveying amphibians in Peru made the first rediscovery, of A. peruensis, which hadn’t been recorded in years. That find, which attracted little attention, was followed by scattered reports of other rediscoveries.

Two years ago, evolutionary biologist Sarah Fitzpatrick of Michigan State University’s W.K. Kellogg Biological Station and graduate student Kyle Jaynes began to tally the sightings, in part to see whether they might reveal clues to why some species had persisted. Working with Guayasamin and other ecologists, they found almost 90% of the rediscoveries came from four countries: Ecuador, Colombia, Peru, and Venezuela. In some cases, such as the 2019 rediscovery of Colombia’s starry night toad (A. arsyecue), it turned out that local people knew the species was there all along. In others, the evidence is thinner: For example, the rediscovery of Peter’s harlequin frog (A. petersi) in Ecuador is based on just a single photo taken by a park ranger in 2020.

Although the data were sometimes sparse, Jaynes and colleagues were able to test one idea about why the frogs persisted. Many researchers have suspected species living at lower, warmer elevations, where the fungus seems to have trouble gaining a foothold, would be more likely to persist. But the data didn’t support that scenario, as the rediscovered frogs were scattered across elevations ranging from 120 meters to 3600 meters.

That finding suggests “many factors” are contributing to the survival of some species, says ecologist Matthew Becker of Liberty University. The fungus might be becoming less virulent in some habitats, for example, or the frogs could be evolving better immune defenses. A change in the microbes that live on frog skins also could play a role. “The question of how these populations persist is not an easy one to answer,” says ecologist Delia Basanta of the University of Nevada, Reno.

The study also highlights the ongoing threats facing the rediscovered frogs. Many of the populations have very few individuals, so they are not “out of the woods,” Catenazzi says. In addition, analyses of DNA from six of the rediscovered species, conducted by Jaynes and ecologist Monica Páez-Vacas of the Indoamerica Technological University, suggest some have relatively low genetic diversity, potentially making the species more vulnerable to habitat loss, climate change, or new diseases.

Despite such concerns, “It’s incredibly exciting” to rediscover so many species, says Benjamin Scheele, a conservation ecologist at Australian National University. And the finds underscore the importance of protecting habitat that could host surviving populations yet to be rediscovered, Catenazzi says.

The rediscoveries are also inspiring others. Páez-Vacas, for example, has been working with study co-author Luis Coloma, director of the Jambatu Center for Amphibian Research and Conservation in Ecuador, to hunt for more Peter’s harlequin frogs. So far, their efforts—which have included collecting water samples to search for frog DNA—have come up empty.

Still, “We need to keep looking,” Catenazzi says. Rediscovered species, he believes, “are going to teach us important lessons about how we can make biodiversity more resilient.”

No bigger than a strawberry and often more colorful, harlequin frogs suffered greatly as a rapidly spreading fungus killed amphibians around the world over the past several decades. More than 70 of the 94 named species in this charismatic group seemingly disappeared from their South and Central American homes by 2010, and researchers feared they had gone extinct. So, Juan Manuel Guayasamin could not believe his eyes when he spotted one of the missing frogs sleeping on a leaf in a cloud forest in Ecuador in 2008.

“My initial emotion was disbelief,” recalls Guayasamin, an evolutionary biologist at the San Francisco University of Quito. “And after that, of course, joy.”

Guayasamin’s fortuitous encounter with that Andersson’s stub-foot toad (Atelopus palmatus) isn’t the only potentially good news for harlequin frogs (sometimes called harlequin toads). Over the past 2 decades, other researchers have rediscovered 32 of the missing species, he and colleagues report today in Biological Conservation. The discoveries “give us hope” that the extinctions are fewer than once believed, Guayasamin says, and could ultimately aid conservation efforts by helping researchers understand how some species have managed to survive.

Given the drumbeat of bad news about biodiversity loss, “It’s good to talk about species being found again,” says Alessandro Catenazzi, an ecologist at Florida International University.

The frogs may still be struggling, however. “Rediscovery by itself is not evidence of recovery,” cautions Roland Knapp, an aquatic ecologist at the University of California’s Sierra Nevada Aquatic Research Laboratory and Earth Research Institute. Some of the rediscoveries are based on just a single sighting, he and other scientists note.

Over the past 50 years, the lethal chytrid fungus Batrachochytrium dendrobatidis has caused population declines in hundreds of amphibian species, researchers estimate. Species in the harlequin frog genus, Atelopus, have been among the most severely affected. The amphibians often live at higher, cooler elevations, where the fungus seems to thrive. Some 70% of harlequin frog species are now considered extinct or critically endangered.

In 2002, researchers surveying amphibians in Peru made the first rediscovery, of A. peruensis, which hadn’t been recorded in years. That find, which attracted little attention, was followed by scattered reports of other rediscoveries.

Two years ago, evolutionary biologist Sarah Fitzpatrick of Michigan State University’s W.K. Kellogg Biological Station and graduate student Kyle Jaynes began to tally the sightings, in part to see whether they might reveal clues to why some species had persisted. Working with Guayasamin and other ecologists, they found almost 90% of the rediscoveries came from four countries: Ecuador, Colombia, Peru, and Venezuela. In some cases, such as the 2019 rediscovery of Colombia’s starry night toad (A. arsyecue), it turned out that local people knew the species was there all along. In others, the evidence is thinner: For example, the rediscovery of Peter’s harlequin frog (A. petersi) in Ecuador is based on just a single photo taken by a park ranger in 2020.

Although the data were sometimes sparse, Jaynes and colleagues were able to test one idea about why the frogs persisted. Many researchers have suspected species living at lower, warmer elevations, where the fungus seems to have trouble gaining a foothold, would be more likely to persist. But the data didn’t support that scenario, as the rediscovered frogs were scattered across elevations ranging from 120 meters to 3600 meters.

That finding suggests “many factors” are contributing to the survival of some species, says ecologist Matthew Becker of Liberty University. The fungus might be becoming less virulent in some habitats, for example, or the frogs could be evolving better immune defenses. A change in the microbes that live on frog skins also could play a role. “The question of how these populations persist is not an easy one to answer,” says ecologist Delia Basanta of the University of Nevada, Reno.

The study also highlights the ongoing threats facing the rediscovered frogs. Many of the populations have very few individuals, so they are not “out of the woods,” Catenazzi says. In addition, analyses of DNA from six of the rediscovered species, conducted by Jaynes and ecologist Monica Páez-Vacas of the Indoamerica Technological University, suggest some have relatively low genetic diversity, potentially making the species more vulnerable to habitat loss, climate change, or new diseases.

Despite such concerns, “It’s incredibly exciting” to rediscover so many species, says Benjamin Scheele, a conservation ecologist at Australian National University. And the finds underscore the importance of protecting habitat that could host surviving populations yet to be rediscovered, Catenazzi says.

The rediscoveries are also inspiring others. Páez-Vacas, for example, has been working with study co-author Luis Coloma, director of the Jambatu Center for Amphibian Research and Conservation in Ecuador, to hunt for more Peter’s harlequin frogs. So far, their efforts—which have included collecting water samples to search for frog DNA—have come up empty.

Still, “We need to keep looking,” Catenazzi says. Rediscovered species, he believes, “are going to teach us important lessons about how we can make biodiversity more resilient.”