Prevalence of the novel amphibian pathogen Batrachochytrium salamandrivorans in Europe and its relationship to host richness and density

Abstract

Emerging infectious diseases are a growing driver of biodiversity loss. Fungal pathogens are of particular concern because many are generalists and can often persist in the environment in the absence of hosts. One recently described fungal pathogen, Batrachochytrium salamandrivorans (Bsal), has raised concern after causing extirpations of fire salamander ( Salamandra salamandra ) populations in western Europe. Research thus far has shown that temperature and moisture play a major role in the persistence of Bsal in the environment and that susceptibility to Bsal varies among species. However, little is known about host community composition and richness as drivers of Bsal prevalence. To investigate how community structure (i.e. host abundance and richness) affects Bsal prevalence, we compiled and analysed both published and unpublished data on the swabbing of 2625 amphibians from 49 sites in Europe comprised of 14 different amphibian species. We show that the amphibian‐Bsal system meets several prerequisites for a dilution effect, which describes a negative host biodiversity–disease relationship. Namely, there is variation in host susceptibility and, despite Bsal being associated with host declines, the most abundant species were the least resistant and most susceptible hosts of Bsal. On average across all communities, Bsal prevalence was associated positively with host density and negatively with host richness, supporting density‐dependent transmission and a dilution effect. Additionally, a dilution effect was observed for fire salamanders ( Salamandra salamandra ), the species experiencing the greatest declines from Bsal in Europe. However, for fire salamanders, Bsal prevalence was associated negatively with host density, presumably because Bsal is causing population declines in this species. Policy implications. These results suggest that conserving salamander species could reduce Bsal transmission and Bsal‐induced salamander population declines. Given that Bsal is a generalist pathogen that will be challenging to eliminate, conserving amphibian diversity should help to reduce Bsal prevalence and loads and thus protect highly susceptible amphibian species.