Host Identity Matters-Up to a Point: The Community Context of Batrachochytrium dendrobatidis Transmission

AbstractThe level of detail on host communities needed to understand multihost parasite invasions is an unresolved issue in disease ecology. Coarse community metrics that ignore functional differences between hosts, such as host species richness, can be good predictors of invasion outcomes. Yet if host species vary in the extent to which they maintain and transmit infections, then explicitly accounting for those differences may be important. Through controlled mesocosm experiments and modeling, we show that interspecific differences between host species are important for community-wide infection dynamics of the multihost fungal parasite of amphibians (Batrachochytrium dendrobatidis [Bd]), but only up to a point. The most abundant host species in our system, fire salamander larvae (Salamandra salamandra), did not maintain or transmit infections. Rather, two less abundant "auxiliary" host species, Iberian tree frog (Hyla molleri) and spiny toad (Bufo spinosus) larvae, maintained and transmitted Bd. Frogs had the highest mean rates of Bd shedding, giving them the highest contributions to the basic reproduction number, R₀. Toad contributions to R₀ were substantial, however, and when examining community-level patterns of infection and transmission, the effects of frogs and toads were similar. Specifying more than just host species richness to distinguish salamanders from auxiliary host species was critical for predicting community-level Bd prevalence and transmission. Distinguishing frogs from toads, however, did not improve predictions. These findings demonstrate limitations to the importance of host species identities in multihost infection dynamics. Host species that exhibit different functional traits, such as susceptibility and infectiousness, may play similar epidemiological roles in the broader community.