Seasonal chytrid maps rank Panama release sites for captive-bred harlequin toads

Chytrid is present across almost all of the historic range of harlequin toads ^[4]. A map of where the fungus occurs would rule out nearly every site. The new maps count seasons instead, because chytrid disease rises and falls through the year the way influenza does, with temperature and humidity ^{[4] [6]}.

The study, by the Smithsonian's National Zoo and Conservation Biology Institute (NZCBI) and the Smithsonian Tropical Research Institute (STRI) in the Journal for Nature Conservation ^[1], checked its maps against the animals still alive. Most harlequin species in Panama persist only at sites where more than 80 percent of seasons were unsuitable for medium- and high-intensity infections ^[6]. At those sites, fewer than one season in five favors a serious infection ^[1].

The exception strengthens the result. If refuges protect toads by keeping the fungus down, a species that tolerates chytrid should be able to live outside them. The variable harlequin toad, Atelopus varius, is the only species found at disease-suitable sites, and the researchers say that fits evidence it may have evolved resistance ^[7].

The design is observational. It ties where toads survive today to where the fungus struggles. It does not measure whether a captive-bred toad released into a refuge outlives one released elsewhere, and the published account does not give the number of sites or species behind the 80 percent figure. The team intends to test the causal claim directly. "These tools will allow us to experimentally test the climate refugia hypothesis through future release trials," said Roberto Ibáñez, a STRI staff scientist and co-author ^[14].

Those trials matter because earlier releases lost many animals. "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, a conservation biologist at NZCBI and the paper's senior author ^[8]. "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," he said ^[9].

The forecast of new refuges comes with a complication. The researchers note that a shifting climate could also harm frogs adapted to cooler mountain habitats ^[12]. Ibáñez said the site surveys draw on both the disease maps and maps of where the toads themselves can live. "Guided by these climate refugia and Atelopus habitat-suitability maps, we have already begun surveying potential sites for habitat suitability and potential release trials," he said ^[13].

The maps also give field teams somewhere to look for survivors. "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 the paper's lead author ^[10].