THE CHYTRID FUNGUS THREATENS ENDEMIC AMPHIBIAN DIVERSITY IN ONE OF THE WORLD’S LAST INTACT REFUGIA
The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused catastrophic amphibian declines and extinctions worldwide, particularly in the tropical highlands of Central and South America. Yet, in the Sierra Nevada de Santa Marta (SNSM), an isolated mountain range in northern Colombia, exceptionally diverse and abundant amphibian communities appear to have escaped these devastating epidemics. Our recent study suggests that this region represents one of the last major refuges from highly virulent Bd lineages in the Neotropical highlands.
A remarkable refuge amid global amphibian declines
The SNSM harbors at least 48 amphibian species, including 25 endemic montane species found nowhere else in the world. Among these are several harlequin toads (Atelopus), a genus that has suffered severe Bd-induced declines throughout Central and South America.
Together with an international team of researchers, we investigated whether these amphibian communities have remained unaffected because they are resistant to chytridiomycosis, or because highly virulent Bd lineages have not yet reached the region.
We screened more than 2,200 amphibian skin swabs, alongside environmental DNA samples, and found no evidence of contemporary Bd presence in the SNSM and adjacent lowlands. Whole-genome analyses of the endemic harlequin toad Atelopus nahumae further revealed no signatures of past population collapses that could have indicated previous disease-driven decline. In contrast, we detected the highly virulent Global Panzootic Lineage of Bd in a neighbouring Andean mountain range, less than 20 km away.
A unique amphibian community at risk
Environmental models showed that the SNSM provides highly suitable conditions for Bd and Bd-induced amphibian declines. However, the surrounding hot and dry lowlands appear to form a climatic barrier that may have prevented pathogen dispersal into the mountain range.
Experimental infections with three endemic amphibian species further revealed that parts of the community are highly susceptible to chytridiomycosis. While the harlequin toad Atelopus laetissimus tolerated infection during the experiment, all infected individuals of the frog Cryptobatrachus boulengeri reached humane endpoints within seven weeks.
Together, our results suggest that the SNSM represents an epidemiologically naive refuge, where amphibian communities may have persisted largely because highly virulent Bd lineages have not yet become established.
Protecting the refuge before it is too late
Although these findings are encouraging, the proximity of highly virulent Bd and increasing human activities pose a substantial risk of pathogen introduction. Once established, Bd is extremely difficult to eradicate from natural ecosystems.
Our study therefore highlights the urgent need for strict biosecurity measures, continued disease surveillance and proactive conservation programmes for particularly vulnerable species. Protecting the SNSM before a devastating epidemic occurs may be critical to safeguarding its unique amphibian diversity, including 25 endemic species.
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