Amphibian-killing fungus loses genetic diversity as it spreads across the New World

Emergent infectious diseases are a severe threat to global biodiversity, thus conservation biologists need to understand the emergence, spread, and evolution of pathogens to identify factors driving disease outbreaks. Amphibian chytridiomycosis is a recently emerged amphibian disease caused by the fungus Batrachochytrium dendrobatidis (Bd) that has led to species extinctions and declines worldwide. The spatio-temporal dynamics of pathogen occurrence and disease outbreaks, and comparative genomic analyses of global Bd strains, support the spreading pathogen hypothesis (SPH) with pandemics occurring after introduction of Bd into naïve host populations. Here we used population genetics of the amphibian-killing fungus to test for genetic consequences of pathogen spread. Our population genetic analyses are consistent with the spread of Bd from North to Central America, based on low genetic diversity, reduction in heterozygosity, and increased allele fixation in Bd from recently infected populations. Our findings confirm the spread of Bd in the New World, and indicate that future conservation efforts should focus on: (i) functional consequences (such as changes in pathogenicity) of these genetic changes, and (ii) public education and restrictions on wildlife trade to help slow spread of the pathogen at the invasion front.