Are novel or locally adapted pathogens more devastating and why?:
Resolving opposing hypotheses
Abstract
There is a rich literature highlighting that pathogens are generally
better adapted to infect local than novel hosts, and a separate
seemingly contradictory literature indicating that novel pathogens pose
the greatest threat to biodiversity and public health. Here, using
Batrachochytrium dendrobatidis, the fungus associated with
worldwide amphibian declines, we test the hypothesis that there is
enough variance in novel host-pathogen outcomes to pose substantial risk
of pathogen introductions despite local adaptation being common. Our
continental-scale, common garden experiment and global-scale
meta-analysis demonstrate that local amphibian-fungal interactions
result in higher pathogen prevalence, pathogen growth, and host
mortality, but novel interactions led to strikingly variable
consequences with the greatest risk occurring when susceptible hosts and
virulent strains interacted. Thus, while most pathogen introductions are
benign, enough variance exists in novel host-pathogen outcomes that
moving organisms around the planet greatly increases the chance of
pathogen introductions causing profound harm.