Historical amphibian declines and extinctions in Brazil linked to chytridiomycosis

The recent increase in emerging fungal diseases is causing unprecedented threats to biodiversity. The origin of spread of the frog-killing fungus <i>Batrachochytrium dendrobatidis</i> (<i>Bd</i>) is a matter of continued debate. To date, the historical amphibian declines in Brazil could not be attributed to chytridiomycosis; the high diversity of hosts coupled with the presence of several <i>Bd</i> lineages predating the reported declines raised the hypothesis that a hypervirulent <i>Bd</i> genotype spread from Brazil to other continents causing the recent global amphibian crisis. We tested for a spatio-temporal overlap between <i>Bd</i> and areas of historical amphibian population declines and extinctions in Brazil. A spatio-temporal convergence between <i>Bd</i> and declines would support the hypothesis that Brazilian amphibians were not adapted to <i>Bd</i> prior to the reported declines, thus weakening the hypothesis that Brazil was the global origin of <i>Bd</i> emergence. Alternatively, a lack of spatio-temporal association between <i>Bd</i> and frog declines would indicate an evolution of host resistance in Brazilian frogs predating <i>Bd</i>'s global emergence<i>,</i> further supporting Brazil as the potential origin of the <i>Bd</i> panzootic. Here, we <i>Bd</i>-screened over 30 000 museum-preserved tadpoles collected in Brazil between 1930 and 2015 and overlaid spatio-temporal <i>Bd</i> data with areas of historical amphibian declines. We detected an increase in the proportion of <i>Bd</i>-infected tadpoles during the peak of amphibian declines (1979-1987). We also found that clusters of <i>Bd</i>-positive samples spatio-temporally overlapped with most records of amphibian declines in Brazil's Atlantic Forest. Our findings indicate that Brazil is post epizootic for chytridiomycosis and provide another piece to the puzzle to explain the origin of <i>Bd</i> globally.