Climate Refuges May Be Key to Restoring Imperiled Amphibians

As a deadly fungal disease ravages wild frog populations around the globe, scientists have identified potential locations in Panama where amphibians might persist despite the presence of disease, according to new research from the Smithsonian’s National Zoo and Conservation Biology Institute (NZCBI) and Smithsonian Tropical Research Institute (STRI) published today in the Journal for Nature Conservation. 

The amphibian chytrid disease, also known as chytridiomycosis or simply chytrid, is caused by the fungus Batrachochytrium dendrobatidis. It has spread like wildfire through Central and South America since the 1970s and is now ubiquitous. It is believed to have driven numerous species of neotropical frogs to the brink of extinction, including many in the genus Atelopus, commonly known as harlequin toads. Now, as conservationists attempt to reintroduce captive-bred species to the wild, they hope to give the animals a leg up by identifying climatic refugia—places that are environmentally unsuitable for chytrid, but perfect for frogs. 

The chytrid fungus is present across almost all of the historic range of Atelopus species, but just as human influenza cases change with the seasons, the chytrid disease fluctuates in its severity depending on the temperature and humidity. Using previously developed models that identified locations where the disease was present and the seasons when the disease was most severe, the authors built new chytrid suitability maps where reintroduced frogs might thrive without the threat of chytrid.

“We have tried releasing captive-bred harlequin toads back into the wild and experienced high losses due to the amphibian chytrid fungus that persists in the environment,” said Brian Gratwicke, conservation biologist at NZCBI and senior author of the article. “By mapping climatic refuges, we finally have a tool to rank potential release sites, allowing us to select places where the released animals have the best chance of survival.”

Researchers found most harlequin toad species in Panama only persist at sites where more than 80% of the seasons were unsuitable for medium and high-intensity infections. Only one species, the variable harlequin toad (A. varius), was found in sites suitable for the disease, which scientists say is consistent with evidence that the species may have evolved resistance to chytrid. 

Not only do the models identify potential locations for reintroduction sites, they also provide locations where existing wild Atelopus populations might remain.

“Our ability to identify climate refugia is critical if we hope to locate populations that might have disappeared from most places in their former range,” said Carrie Lewis, doctoral candidate at George Mason University and lead author of the publication. “These persisting populations could provide a source of genes to bolster populations under human care and provide opportunities to augment wild populations.”

Although there are currently a limited number of potential refuges, additional opportunities have been identified. The models also forecasted areas that, while currently suitable for the disease, might become unsuitable in the coming years due to climate change. Researchers note the shifting climate could also have negative effects on frogs that are adapted to cooler mountainous habitats.

“Guided by these climate refugia and Atelopus habitat-suitability maps, we have already begun surveying potential sites for habitat suitability and potential release trials,” said Roberto Ibáñez, STRI staff scientist and co-author of the study. “These tools will allow us to experimentally test the climate refugia hypothesis through future release trials.” 

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Photo 1 caption: A captive-bred variable harlequin toad (Atelopus varius) at the Panama Amphibian Rescue and Conservation Project. Photo credit: Brian Gratwicke, Smithsonian’s National Zoo and Conservation Biology Institute.

Animation 2 caption: Research models show the seasonal suitability for a medium intensity chytrid infection across Panama. Animation credit: Smithsonian's National Zoo and Conservation Biology Institute. 

Photo 3 caption: A captive-bred toad mountain harlequin frog (Atelopus certus) inside a terrarium at the Panama Amphibian Rescue and Conservation Project. Photo credit: Brian Gratwicke, Smithsonian’s National Zoo and Conservation Biology Institute.

Photo 4 caption: A mated pair of Panamanian golden frog (Atelopus zeteki) and their offspring. Photo credit: Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.

Photo 5 caption: A limosa harlequin frog (Atelopus limosus) wearing a tracking device from an earlier reintroduction trial. The majority of the released frogs succumbed to chytrid. Photo credit: Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.