The Gut Microbial Community of Solitary Bees is Acquired through Host and Location Filtering.

Species traits and environmental conditions are among the many factors that shape bee communities. Their effective conservation is currently challenged due to global changes. The gut microbiome likely contributes to bee plasticity and resilience but is largely understudied in solitary bees. A stable core microbiome in social bees has been identified to be important for health and survival in changing environmental conditions, but knowledge on a host-specific core microbiome in solitary bees is very scarce. In the present study, we analyzed the gut bacterial and fungal communities of eight solitary bee species commonly found in apple orchards along a latitudinal gradient throughout Europe. We aimed to understand the intra- and interspecific variations in the gut microbial communities and the extent to which host species and local environment shape the solitary bee gut microbiota. The bacterial community showed strong host effects, with each bee species having a distinct core bacterial community that was mostly stable across locations. The fungal community was most strongly influenced by the local environment, while different environmental variables were responsible for the variation in bacterial and fungal communities. Our study demonstrated that the examined solitary bee species harbor a distinct microbial diversity and composition, which undergoes host- and location-specific filtering.