Abstract
There is growing appreciation of the important role of commensal microbes in ensuring the normal function and health of their hosts, including determining how hosts respond to pathogens. A range of infectious diseases are threatening amphibians worldwide, and evidence is accumulating that the host-associated bacteria that comprise the microbiome may be key in mediating interactions between amphibian hosts and infectious pathogens. We used 16S rRNA amplicon sequencing to quantify the skin microbial community structure of over 200 individual wild adult European common frogs (Rana temporaria), from ten populations with contrasting history of the lethal disease ranavirosis, caused by emerging viral pathogens belonging to the genus Ranavirus. All populations had similar species richness irrespective of disease history, but populations that have experienced historical outbreaks of ranavirosis have a distinct skin microbiome structure (beta diversity) when compared to sites where no outbreaks of the disease have occurred. At the individual level, neither age, body length, nor sex of the frog could predict the structure of the skin microbiota. Our data potentially support the hypothesis that variation among individuals in skin microbiome structure drive differences in susceptibility to infection and lethal outbreaks of disease. More generally, our results suggest that population-level processes are more important for driving differences in microbiome structure than variation among individuals within populations in key life history traits such as age and body size.
Highlights
Emerging infectious diseases represent a major threat to amphibian biodiversity around the globe (Daszak et al, 1999)
When controlling for variation among populations in our linear mixed effects regression model (LMER), we found that neither sex, snout to vent length (SVL) nor disease history explained a significant amount of variation in individual effective number of species score (Table 2)
We hypothesized that frogs originating from populations with a positive disease history of ranavirosis would possess distinct skin microbiomes compared to frogs that originated at populations that have remained disease-free during the time frame of ranaviral emergence in the United Kingdom
Summary
Emerging infectious diseases represent a major threat to amphibian biodiversity around the globe (Daszak et al, 1999). In recent decades both fungal and viral pathogens have been implicated in population declines and extinctions of multiple amphibian taxa, including toads, newts, and salamanders (e.g., Longcore et al, 1999; Price et al, 2014; Martel et al, 2014). The vast majority of research to date has focussed on the interactions between the amphibian microbiome and the fungal pathogen Batrachochytrium dendrobatidis (Bd) (e.g., Bletz et al, 2013; Woodhams et al, 2014; Becker et al, 2015; Kueneman et al, 2016; Antwis and Harrison, 2018), and comparative data from other pathogen groups is lacking (Federici et al, 2015; Harrison et al, 2017). Understanding the mechanisms by which the skin microbiome affects host-pathogen interactions, and the generality of those mechanisms across multiple pathogen groups, requires that we measure how skin microbiome covaries with disease severity in the wild across a broad suite of pathogen types
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