Predators reduce Batrachochytrium dendrobatidis infection loads in their prey

Disease ecologists and wildlife managers are increasingly interested in understanding how predators regulate infection in prey populations. The healthy herds hypothesis suggests that predators may decrease infection prevalence by decreasing overall population size, reducing density-dependent transmission and culling infected individuals from a population. While this model incorporates density-mediated indirect interactions (DMIIs), it does not incorporate the potential role of trait-mediated indirect interactions (TMIIs). Using wood frog tadpoles (Lithobates sylvatica), we examined whether predator cues could alter the prevalence and intensity of infection by the fungal pathogen Batrachochytrium dendrobatidis [Bd] and whether both stressors could alter the host's life history traits. Exposure to predator cues caused tadpoles to have reduced Bd infection loads, potentially as a result of stress-induced immunoenhancement. Tadpoles exposed to Bd had faster development than tadpoles not exposed to Bd, but they did not differ in survival or growth. This suggests that, in this life stage of this species, Bd infection does not have fitness costs. These data suggest that the trait-mediated effects of predators on infection may alter epidemiological outcomes of Bd exposure.