Most of Panama’s harlequin toads hang on only where the climate turns against their killer fungus

In Panama, most harlequin toad species persist only at sites where more than 80 percent of seasons are unsuitable for medium- and high-intensity infection by the chytrid fungus. The pattern comes from a Smithsonian analysis that laid the toads’ surviving populations over a climate map of the disease. One species, the variable harlequin toad, breaks the rule entirely, holding on in places where the fungus ought to thrive.

Chytrid, formally Batrachochytrium dendrobatidis, has been wiping out neotropical frogs since the 1970s, and the toads of the genus Atelopus have taken some of the heaviest losses. What the mapping offers is a way to say which places the fungus cannot easily follow them into, and therefore where a captive-bred toad has a realistic chance of living long enough to breed.

The 80 percent line in Panama’s seasons

The work was led by Carrie Lewis, a doctoral candidate at George Mason University, with Brian Gratwicke of the Smithsonian’s National Zoo and Conservation Biology Institute as senior author and Roberto Ibáñez of the Smithsonian Tropical Research Institute among the team. It appeared in the Journal for Nature Conservation, and the Smithsonian’s own release on the paper states the central result in plain terms: most harlequin toad species in Panama only persist where more than 80 percent of seasons were unsuitable for medium and high-intensity infections.

A season, in this context, is a stretch of weather, scored by whether conditions would let the fungus reach medium or high infection intensity. Chytrid thrives in particular combinations of temperature and moisture, so a site can be climatically hostile to the fungus for most of the year and still hold amphibians, which is the situation the surviving Panamanian toad populations appear to occupy.

Satellite data and 4,900 samples behind the map

The refuge analysis rests on an earlier Smithsonian project. In that 2025 work, described in a National Zoo release on the climate-based disease maps, Lewis, Gratwicke and 16 coauthors from the zoo’s conservation institute and the Tropical Research Institute combined 13 years of satellite and atmospheric data with more than 4,900 disease samples collected at 314 Panamanian sites.

Higher elevations consistently supported the fungus, while rainy seasons produced outbreak conditions in the lowlands, so risk shifted with both place and time of year. Weather over the previous 15 days was enough to predict whether chytrid would be present at a site and how intense the infections would be. That predictive skill is what allowed the later study to score any location in the country by how often its seasons fall outside the fungus’s comfort zone. Smithsonian Magazine’s account of the 2025 paper, published in Diversity and Distributions, describes chytrid as thriving in cool, wet mountain regions and struggling in hot, dry lowlands.

The same release put the cost of the disease in Panama at nine frog species eliminated, and noted that the Panama Amphibian Rescue and Conservation Project has bred 12 species in captivity since 2009, a rescue colony waiting on places safe enough to release into.

The variable harlequin toad, the exception

The refuge pattern has a notable exception, and it is the reason the pattern holds for most species rather than all of them. According to the Smithsonian release, the variable harlequin toad, Atelopus varius, persists in disease-suitable sites, the kind of place where the fungus should be able to reach damaging intensities. The release frames that as a possible sign of resistance to chytrid in those populations, not a proven one.

The species has a long record of loss. The Panama Amphibian Rescue and Conservation Project describes it as critically endangered under IUCN criteria, with a range across central Panama into Costa Rica. Chytridiomycosis devastated its highland populations in Panama, and the first reintroduction trials of captive-bred animals began in January 2018 in the Donoso area. The species’ Wikipedia entry adds a Costa Rican benchmark: surveys near Monteverde between 1990 and 1992 found no frogs in an area that had held 751 adults.

Lewis, the lead author, said these persisting populations could provide a source of genes to bolster populations under human care, a role that makes the disease-suitable survivors valuable well beyond their own sites.

A ranking tool for release sites

For the captive-breeding programs, the refuge map answers a question that has stalled reintroductions for years: where to put animals so the fungus does not simply kill them again once they leave the safety of a breeding facility. Gratwicke described the mapping as a tool to rank potential release sites, so that managers can choose places where released animals have the best chance of survival.

The practical consequence is a shortlist. Sites where more than 80 percent of seasons are unsuitable for medium and high-intensity infection become the first candidates for releasing captive-bred toads, while the disease-suitable sites where the variable harlequin toad still hangs on become candidates for a different question, namely what those animals are doing differently.

The limit of the approach is also in the source. The 80 percent figure describes where most species persist, not where all do, and the Smithsonian release does not claim that a climate refuge protects a population from the fungus outright. It claims that the odds of surviving an infection season are better there, which is a narrower and more testable statement.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.