Abstract
Species composition within ecological assemblages can drive disease dynamics including pathogen invasion, spread, and persistence. In multi-host pathogen systems, interspecific variation in responses to infection creates important context dependency when predicting the outcome of disease. Here, we examine the responses of three sympatric host species to a single fungal pathogen, Batrachochytrium dendrobatidis, which is associated with worldwide amphibian population declines and extinctions. Using an experimental approach, we show that amphibian species from three different genera display significant differences in patterns of pathgen-induced mortality as well as the magnitude and temporal dynamics of infection load. We exposed amphibians to one of four inoculation dose treatments at both larval and post- metamorphic stages and quantified infection load on day 8 and day 15 post-inoculation. Of the three species examined, only one (the Pacific treefrog; Pseudacris regilla) displayed “dose-dependent” responses; survival was reduced and infection load was elevated as inoculation dose was increased. We observed a reduction in survival but no differences in infection load across pathogen treatments in Cascades frogs (Rana cascadae). Western toads (Anaxyrus boreas) displayed differences in infection load but no differences in survival across pathogen treatments. Within species, responses to the pathogen varied with life history stage, and the most heavily infected species at the larval stage was different from the most heavily infected species at the post-metamorphic stage. Temporal changes in infection load were species and life history stage-specific. We show that variation in susceptibility to this multi-host pathogen is complex when viewed at a fine-scale and may be mediated through intrinsic host traits.
Highlights
Most pathogens can infect and be transmitted among multiple hosts, but there may be considerable variation in responses to infection among species, individuals, or between life stages [1,2,3,4,5]
We show that intrinsic host traits, alone, can be important mediators of pathogen dynamics in the amphibian-chytrid fungus system
Previous studies have shown that some species are very susceptible to Batrachchytrium dendrobatidis (Bd) and succumb to mortality soon after exposure, [24,43] while other species show no signs of morbidity or mortality in the presence of the pathogen [22]
Summary
Most pathogens can infect and be transmitted among multiple hosts, but there may be considerable variation in responses to infection among species, individuals, or between life stages [1,2,3,4,5]. Differences in host responses to pathogens can influence disease dynamics by altering the probability and rate of pathogen transmission, disease induced mortality, and recovery from infection [6,7,8]. Reservoir hosts harbor and transmit a pathogen, often without incurring morbidity or mortality as a result of infection [3]. Species that act as reservoirs can facilitate long-term pathogen persistence in space and time and prevent periodic pathogen fade-outs based on density of susceptible hosts [3,7,9]. Species identity and composition in ecological assemblages can have a deterministic effect on pathogen invasion, spread, and persistence
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