eastern hellbender range-wide microbiome

Multicellular hosts maintain complex associations with diverse microbial communities. While microbial communities often serve important functional roles for their hosts, our understanding of the local and regional processes that structure these communities remains limited. Metacommunity analyses provide a promising tool for investigating mechanisms shaping microbiome heterogeneity, which is essential for predicting functional variation between hosts. Using a metacommunity framework, we examined heterogeneity in the skin microbiome of the eastern hellbender (Cryptobranchus alleganiensis alleganiensis), which is broadly distributed throughout river systems in the eastern United States. The large range of the species and history of population fragmentation suggest that local and regional processes contribute to the distribution of cutaneous symbiont diversity. Therefore, we characterized the skin and planktonic bacterial communities at eight rivers throughout the range of the species. We observed variation among hellbender populations in skin microbial community diversity and proportion of shared OTUs between animal and planktonic communities. Among populations sampled, we noted significant clumped OTU turnover resulting in unique cutaneous communities. In addition, we observed a significant correlation between skin community divergence and hellbender population genetic divergence. Host-population skin community dissimilarity did not correlate strongly with distance between sampling locations, indicating a weak spatial effect on the distribution of symbionts. These results suggest that species sorting mechanisms structure local skin microbial communities in hellbenders. The variation in skin community composition observed among host populations foreshadows a similar pattern in important functional characteristics (e.g, resistance to dysbiosis). Future work should focus on investigating forces shaping microbiome structure in eastern hellbenders, and evaluating effectiveness of microbiome management recommendations.