Apart from the fungal disease, amphibians are also at risk because of habitat loss driven by urban development and agriculture, experts warn.

Measuring a bit more than 20 millimeters (0.8 inches), Pratt's poison frog (Colostethus pratti) is not the kind of frog that would get attention. Although part of the Dendrobatidae family, known for its bright colors and high toxicity that keep predators away, it can only boast a brown, stripy skin and low poison levels. It's not even endangered. But in Panama, a recent move of a dozen pairs of these tiny frogs may offer researchers new insights into how to help amphibians worldwide in a decades-long fight against a deadly disease.

Pratt's poison frog has been one of at least 500 amphibian species affected by the chytrid fungal disease, a pathogen that over the last 50 years, is estimated to have wiped out 90 species of amphibians and caused a 90% decline in population abundance in other 124, according to a 2019 study. The disease, caused by the chytrid fungus Batrachochytrium dendrobatidis, was only discovered in 1998 but is known to have peaked in mortality in the 1980s and early 2000s.

Pratt's poison frogs have been hit by chytrid too. Although their populations are not at risk, they have been declining, as the fungus, urban development and agriculture have been encroaching on them.

The species can be found in several locations within its range in Panama, but it is believed to have been wiped by chytrid from Altos de Campana National Park, the country's oldest national park, at least 19 years ago, according to Brian Gratwicke, a conservation biologist at the Smithsonian's National Zoo and Conservation Biology Institute. Locally, the frogs live only in a forest on private land in Bajo Bonito in the Capira district, about 30 kilometers (18.6 miles) northeast of the national park.

In an effort to boost their population, in July, researchers from the Panama Amphibian Rescue and Conservation Project (PARC) transferred 12 pairs of Pratt's poison frogs from Bajo Bonito to Altos de Campana National Park.

The move marks the first for this species and the third attempt to translocate frogs in Panama. If successful, it could provide important information about chyrtrid, which, according to experts, appears to have produced the biggest documented loss of biodiversity attributable to a pathogen.

"We just need a win right now," said Gratwicke. "We're excited about it. I've spent 15 years of my life doing work on chytrid mitigation and my track record is basically the journal of negative results."

Poison frogs hold a special place in Panamanian culture. The Panamanian golden frog (Atelopus zeteki), for example, is a national icon, revered as a sign of good luck and prosperity. Once, hotels in Panama City used to keep the yellow spotted amphibians in lobby tanks to welcome guests, and today the species lends its name to a national artisanal beer. Beyond their cultural value, poison frogs also play a crucial role in ecosystems by consuming decaying leaves and animals from the forest floor. Amphibians are vital to healthy ecosystems, said Maureen Donnelly, a retired herpetologist and a former president of the American Society of Ichthyologists and Herpetologists, because they "eat small things and are eaten by bigger things." By feeding on decomposing material and providing food for larger species, they help sustain what she called the "brown food web."

"When we looked at the Pratt's poison dart frog, we found it had actually recovered at another site we were working at and it was one of the most abundant frogs at that site," Gratwicke said.

Catching the 12 pairs of frogs presented one of the biggest challenges. The frogs are no larger than a U.S. quarter, making them notoriously difficult to spot in dense jungle. To locate them, conservationists used an acoustic monitoring device to track their calls. The males, which produce distinct calls to attract females, were all caught on the first day, but the females -- quiet and elusive -- took longer. Researchers had to sit waiting near the males as they called for a mate.

The 24 specimens were then taken to the amphibian research center belonging to the Center for Species Survival of the Smithsonian Tropical Research Institute (STRI) in Gamboa, a town in Panama's Colón province, which houses around 2,000 adult frogs, including golden frogs, lemur leaf frogs (Agalychnis lemur) and Gemini's dart frog (Andinobates geminisae), all critically endangered, according to the IUCN.

At the center, the Pratt's poison frogs spent one month in quarantine, being tested and receiving treatment against the fungus. Only one of the 24 tested positive. "That indicates that this species may have lower chytrid infection rates than all the other frogs that are currently around," Gratwicke said. "It's very positive."

After quarantine, the frogs were moved into small tented "biomes" in Altos de Campana National Park, designed to help them adapt to their new surroundings before release. Two weeks later, they were released, but before the frogs left, researchers found that one pair had successfully bred.

Researchers hope now they will breed naturally in the wild, strengthening the genetic diversity of the species in Panama. To assess the initiative's success, the team will continue to monitor them by recording frog calls in the jungle and distinguishing those of Pratt's poison frogs using a computer program.

For Gratwicke, the frogs' release was about more than conservation science. "If this succeeds -- if the animals survive and breed -- we will have restored part of the soundscape of the forest," he said. "When we heard these animals calling in this place for the first time in 15 years, it was just a magical moment."

Researchers first began noticing an uptick in amphibian deaths in the 1980s. But it was not until the following decade that the cause was identified as chytrid. The fungus has been detected in 93 countries, according to a study, and is now known to affect more than 700 species.

Although Pratt's poison frogs managed to survive in one area in Panama, as well as parts of northern Colombia, not all species were so lucky. The beloved Panamanian golden frog has not been seen in the wild since 2009.

Edgardo Griffith, a Panamanian amphibian expert, remembers the height of the disease in 2004. "I watched the chytrid fungus come and it was devastating," he said. "I was going out two or three times a month for four years [working with frogs]. You get to know the animals. As they were dying, I had to pick up their bodies, and I recognized every single one."

To protect the animals, Griffith and his wife, Heidi, began collecting Panamanian golden frogs, keeping them in two hotel rooms in El Valle de Antón, a town in the crater of a volcano in central Panama. In 2006, Griffith founded the El Valle Amphibian Conservation Center (EVACC), which now breeds Panamanian golden frogs and other species at a small facility that includes a small museum and several shipping containers hosted by the hotel where the couple first kept the frogs.

Although the fungus has been decimating amphibian species worldwide, habitat loss is the biggest threat they face today, according to Donnelly. According to a 2023 report, habitat loss, driven primarily by agricultural expansion, timber and plant harvesting and infrastructure, is known to affect 93% of threatened amphibian species.

"Across the world, habitat loss is pretty much the biggest concern for most species," said Robert Hill, curator of herpetology at Zoo Atlanta. For example, "one of the major habitats that used to have [Panamanian] golden frogs was being converted to basically a large retirement community," he said. Zoo Atlanta is part of Project Golden Frog, a consortium of institutions that since the early 2000s have focused on breeding the frogs ex situ.

"Habitat loss doesn't necessarily matter for the fungus itself. It's moving through the system, it's going to find its host and take them out," Hill said. "However, if populations are already stressed with limited space and a lack of genetic diversity, then it can be a factor." He added that maybe the frogs could have survived the fungus had they had a more diverse habitat.

EVACC is in the early stages of developing an outdoor corridor that, Griffiths hopes, could simulate conditions in the wild while still protecting the golden frogs. The corridor, which could be completed by the end of this year, is wedged between two shipping containers with a mesh roof; once fully developed, the mesh roof would allow the elements in without giving access to predators or species carrying the fungus.

Funding remains an issue for conservationists, Hill said. "For amphibian conservation, we tend not to have these big, 'sexy' animals," he said. "It's easy to want to help a really charismatic panda or something. Those animals are certainly deserving of conservation work. But they're easier to sell, so to speak, than a little brown frog," he told Mongabay.

Hill said the frogs are worth saving not only for the toxins they produce, which could be used in medicine for people. "There's also just an intrinsic value of these animals that exist on our planet and that are being affected in large ways by our actions. They have just as much right to be here as we do."

Banner image: Pratt's poison dart frog is one of many species that declined rapidly as the amphibian chytrid fungus spread through Panama. Image courtesy of Brian Gratwicke.

Citations:

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

Olson, D. H., Ronnenberg, K. L., Glidden, C. K., Christiansen, K. R., & Blaustein, A. R. (2021). Global patterns of the fungal pathogen Batrachochytrium dendrobatidis support conservation urgency. Frontiers in Veterinary Science, 8. doi:10.3389/fvets.2021.685877

Lips, K. R. (2016). Overview of chytrid emergence and impacts on amphibians. Philosophical Transactions of the Royal Society B: Biological Sciences, 371(1709), 20150465. doi:10.1098/rstb.2015.0465

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