cross-posted from: https://hexbear.net/post/9876937

Climate refuges may be key to restoring imperiled amphibians

Panamanian golden frogs (Atelopus zeteki) suffered significant declines due to chytrid. The species has not been seen in the wild since 2009. Credit: Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.

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 disease, according to new research from the Smithsonian’s National Zoo and Conservation Biology Institute (NZCBI) and Smithsonian Tropical Research Institute (STRI) published 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 well-suited to frogs.

Mapping seasonal disease risk

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 severity of chytrid disease fluctuates with temperature and humidity.

Using previously developed models that identified where the disease was present and when it was most severe, the authors built new chytrid suitability maps to identify places 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.”

Variable harlequin frogs (Atelopus varius) were the only species found surviving in chytrid-suitable sites, which scientists say is consistent with evidence that the species may have evolved resistance to the disease. Credit: Brian Gratwicke, Smithsonian’s National Zoo and Conservation Biology Institute

Surviving toads reveal potential refuges

Researchers found that most harlequin toad species in Panama persist only 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 at sites suitable for the disease, which scientists say is consistent with evidence that the species may have evolved resistance to chytrid.

The models not only identify potential reintroduction sites but also point to places where 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, a 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.”

Like other Atelopus species, the critically endangered Pirri harlequin frog (A. glyphus) has experienced significant declines due to the amphibian chytrid disease. Credit: Brian Gratwicke, Smithsonian’s National Zoo and Conservation Biology Institute.

A prior reintroduction trial conducted with Limosa harlequin frogs (Atelopus limosus) resulted in the deaths of numerous frogs due to chytrid. By choosing reintroduction sites considered unsuitable for chytrid, researchers hope to reduce losses in future reintroduction trials. Credit: Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.

Researchers established captive assurance colonies for numerous species, including the critically endangered Toad Mountain harlequin frog (Atelopus certus), at the Panama Amphibian Rescue and Conservation Project in Gamboa, Panama. Credit: Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.

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