Universal versus taxon-specific drivers of helminth prevalence and intensity of infection.

Two key epidemiological parameters, prevalence and mean intensity of infection, together capture the abundance of macroparasite populations, the strength of density-dependent effects they experience, their potential impact on host population dynamics and the selective pressures they exert on their hosts. Yet, the drivers of the extensive variation observed in prevalence and mean intensity of infection, even among related parasite taxa infecting related hosts, remain mostly unknown. We performed phylogenetically grounded Bayesian modelling across hundreds of amphibian populations to test the effects of various predictors of prevalence and intensity of infection by six families of helminth parasites. We focused on the potential effects of key host traits and environmental factors pertinent to focal host populations, i.e. the local diversity of the amphibian community and local climatic variables. Our analyses revealed several important determinants of prevalence or intensity of infection in various parasite families, but none applying to all families. Our study uncovered no universal driver of parasite infection levels, even among parasite taxa from the same phylum, or with similar life cycles and transmission modes. Although local variables not considered here may have effects extending across taxa, our findings suggest the need for a taxon-specific approach in any attempt to predict disease dynamics and impacts in the face of environmental and climatic changes.