For nearly half a century, scientists puzzled over why frogs had suddenly begun to disappear in Brazil's Atlantic Forest. From the 1970s onward, a sharp decline in populations was recorded in the area of the Boracéia Biological Station, but the cause remained a mystery.
Now, thanks to an analysis of museum specimens collected back in the 1970–1980s, the picture has become clearer. Researchers from the Smithsonian Institution and the University of Pennsylvania found that samples from before 1979 showed no traces of infection, whereas in collections from the 1980s the fungus Batrachochytrium dendrobatidis was present in more than half of the individuals.
This chytrid fungus, which causes chytridiomycosis, apparently entered the region during precisely that period and spread rapidly among amphibians that had no immunity. The species that suffered most severely probably died so quickly that infected specimens simply never made it into collections, while more resistant frogs carried the infection without mass mortality.
Modern surveys from 2022–2024 revealed an encouraging picture: of the 17 species represented in the old collections, 12 are once again found at the station. Most populations have recovered, although the fungus still circulates. Evidently, over the decades the surviving species have developed increased tolerance to the pathogen.
Museum collections have once again proven their value: what was kept in storage for decades made it possible to reconstruct an epizootic that no one knew about at the height of its outbreak. Such ecological "cold cases" help us better understand how new threats to biodiversity arise and spread.
The study highlights an important distinction: the presence of a pathogen does not always mean catastrophe, if species are able to adapt in time. This gives hope that even after severe losses, nature can recover, provided genetic diversity and suitable conditions are preserved.
Museum collections help uncover the secrets of past epidemics and prepare for future threats to amphibians.
