Variation of bacterial communities in bumblebees: Transmission and regulation by mating behavior

Bumblebees, as vital pollinators, serve as ideal models for investigating the relationship between hosts and their microbiomes. Mating behavior in bumblebees may influence microbial diversity, either through sexual transmission or immunity activation. Therefore, the study of mating-induced changes in microbiomes is crucial for understanding its biological and evolutionary significance. In this study, we examined microbiomes in a community context within both the gut and reproductive organs of bumblebees, using 16S rRNA sequences. Analysis of alpha and beta diversities revealed that the bacterial microbiome in the gut exhibits lower diversity than reproductive organs, with mating exerting a significant impact on the composition of microbiota in both gut and reproductive organs. By assessing Bray–Curtis dissimilarity at the amplicon sequence variant level, we observed a reduction in the divergence of bacterial communities between queen and drone reproductive organs following mating, a phenomenon not observed in the gut. This convergence is attributed to horizontal transmission and physiological responses post-mating. Notably, one bacterial genus in the gut and 13 genera in the seminal vesicle exhibited potential for horizontal transmission. Furthermore, the core bacterium Lactobacillus is suppressed in both gut and reproductive organs post-mating, while Weissella is increased in spermathecae. Our results reveal horizontal microbiome transfer between queen and drone bumblebees.