Phylogenetic relationship and habitat both impact the gut microbiome in two microendemic gastropods

Bacterial communities associated with eukaryotes play important roles in the physiology, development and health of their hosts. Additionally, the composition of microbes associated with eukaryotes can be indicative of evolutionary history, environment and life history. Here, we investigated the microbial ecology of two sympatric caenogastropod taxa belonging to the family Hydrobiidae, Juturnia kosteri and Pyrgulopsis roswellensis. The diversity and composition of the microbiota were described based on high-throughput Illumina sequencing targeting the V4 region of the 16S rRNA gene. The observed bacterial diversity was distributed over 16 phyla, with the greatest number of 16S rRNA gene sequences derived from Proteobacteria, Bacteroidetes, Tenericutes and Planctomycetes. These results document the presence of highly diverse gut bacterial communities in the two hydrobiid species. While alpha-diversity measures were consistent across species and sites, beta-diversity measures revealed significant differences in species, collection site and the interaction of both variables. These results indicate a mixed interaction, with both species and site impacting the microbiome. However, principal coordinate analysis indicated no separation between snail species at site BLU7 (Bitter Lake Unit 7). The high impact of site on microbial communities implies that although these species have different phylogenetic histories, they show similarities in their microbiomes when occupying overlapping habitats. Further investigation into biotic and abiotic factors is necessary to elucidate differences in microbial communities between sympatric snail species.