Host tissues as microhabitats for W olbachia and quantitative insights into the bacterial community in terrestrial isopods

Animal–bacterial symbioses are highly dynamic in terms of multipartite interactions, both between the host and its symbionts as well as between the different bacteria constituting the symbiotic community. These interactions will be reflected by the titres of the individual bacterial taxa, for example via host regulation of bacterial loads or competition for resources between symbionts. Moreover, different host tissues represent heterogeneous microhabitats for bacteria, meaning that host‐associated bacteria might establish tissue‐specific bacterial communities. W olbachia are widespread endosymbiotic bacteria, infecting a large number of arthropods and filarial nematodes. However, relatively little is known regarding direct interactions between W olbachia and other bacteria. This study represents the first quantitative investigation of tissue‐specific W olbachia –microbiota interactions in the terrestrial isopod A rmadillidium vulgare . To this end, we obtained a more complete picture of the W olbachia distribution patterns across all major host tissues, integrating all three feminizing W olbachia strains ( w VulM, w VulC, w VulP) identified to date in this host. Interestingly, the different W olbachia strains exhibited strain‐specific tissue distribution patterns, with w VulM reaching lower titres in most tissues. These patterns were consistent across different host genetic backgrounds and might reflect different co‐evolutionary histories between the W olbachia strains and A . vulgare . Moreover, W olbachia ‐infected females carried higher total bacterial loads in several, but not all, tissues, irrespective of the W olbachia strain. Taken together, this quantitative approach indicates that W olbachia is part of a potentially more diverse bacterial community, as exemplified by the presence of highly abundant bacterial taxa in the midgut caeca of several A . vulgare populations.