Symbiotic relationships between insects and bacteria are found across almost all insect orders, including Hymenoptera. However there are still many remaining questions about these associations including what factors drive host-associated bacterial composition. To better understand the evolutionary significance of this association in nature, further studies addressing a diversity of hosts across locations and evolutionary history are necessary. Ants of the genus Polyrhachis (spiny ants) are distributed across the Old World and exhibit generalist diets and habits. Using Next Generation Sequencing (NGS) and bioinformatics tools, this study explores the microbial community of >80 species of Polyrhachis distributed across the Old World and compares the microbiota of samples and related hosts across different biogeographic locations and in the context of their phylogenetic history. The predominant bacteria across samples were Enterobacteriaceae (Blochmannia - with likely many new strains), followed by Wolbachia (with multiple strains), Lactobacillus, Thiotrichaceae, Acinetobacter, Nocardia, Sodalis, and others. We recovered some exclusive strains of Enterobacteriaceae as specific to some subgenera of Polyrhachis, corroborating the idea of coevolution between host and bacteria for this bacterial group. Our correlation results (partial mantel and mantel tests) found that host phylogeny can influence the overall bacterial community, but that geographic location had no effect. Our work is revealing important aspects of the biology of hosts in structuring the diversity and abundance of these host-associated bacterial communities including the role of host phylogeny and shared evolutionary history.

Symbiotic relationships between hosts and bacteria are common in nature, and these may be responsible for the evolutionary success of various groups of animals. Among ants, these associations have been well studied in some genera of the Camponotini, but several questions remain regarding the generality of the previous findings across all the members of this ant tribe and if bacterial communities change across development in these hosts. This study is the first to characterize the bacterial community associated with a colony of the recently recognized genus Colobopsis and three colonies of Camponotus (two distinct species) and show how different the composition of the bacterial community is when compared across the different genera. Our data reveal that Colobopsis (species: Co. riehlii) and Camponotus (species: Ca. floridanus and Ca. planatus) have distinct microbiota, and we were able to verify that the identity of the species contributes more to the bacterial diversity. We also demonstrated that there were no significant differences between colonies of the same species (Camponotus planatus), and between stages of development from different colonies. We did find that some developmental stages have distinct bacteria, confirming that each stage of development could have a specific microbiota. Our results show species are one of the factors that shape the bacterial community in these Camponotini ants. Additional studies of the intra-colonial microbiome of other hosts and across development may reveal additional clues about the function and importance of bacteria in colony recognition, individual and colony health, and nutritional upgrading.

Wolbachia is one of the most common intracellular symbionts among insects, but the function of this infection and its effects on the host still remain largely unknown for many taxa. In the case of many social insects, living in colonies results in close interactions, facilitating the dispersion of the symbiont. However, having only one caste responsible for reproduction (queens) could restrict infections. Several groups of social insects have been reported to be highly infected with these symbionts. However, Wolbachia associations across social and closely related non-social insects in a comparative framework has not been examined to date, which may help us understand the role social behavior, geography, and ecology plays in structuring this association. Since 2006 the Multi-Locus Sequencing Type (MLST) approach has been shown to be appropriate for diversity studies, which consists of sequencing five genes spread across the Wolbachia genome. Over the past 15 yr, studies using this approach have been conducted worldwide and have generated large volumes of data. In this review article, we intend to produce a meta-analysis by combining MLST data from across social insects (ants, bees, termites, wasps) and beyond, together with their closest relatives to better elucidate the patterns behind the diversity of this symbiotic interaction. Our main findings reveal that the diversity of Wolbachia (supergroups) is correlated with the host insect taxonomy, biogeography, and social/solitary behavior. In addition, solitary insects such as bees and wasps can interact with a greater diversity of Wolbachia supergroup compared to their social representatives.