The structured diversity of specialized gut symbionts of the New World army ants.

Symbiotic bacteria play important roles in the biology of their arthropod hosts. Yet the microbiota of many diverse and influential groups remain understudied, resulting in a paucity of information on the fidelities and histories of these associations. Motivated by prior findings from a smaller scale, 16S rRNA-based study, we conducted a broad phylogenetic and geographic survey of microbial communities in the ecologically dominant New World army ants (Formicidae: Dorylinae). Amplicon sequencing of the 16S rRNA gene across 28 species spanning the five New World genera showed that the microbial communities of army ants consist of very few common and abundant bacterial species. The two most abundant microbes, referred to as Unclassified Firmicutes and Unclassified Entomoplasmatales, appear to be specialized army ant associates that dominate microbial communities in the gut lumen of three host genera, Eciton, Labidus and Nomamyrmex. Both are present in other army ant genera, including those from the Old World, suggesting that army ant symbioses date back to the Cretaceous. Extensive sequencing of bacterial protein-coding genes revealed multiple strains of these symbionts coexisting within colonies, but seldom within the same individual ant. Bacterial strains formed multiple host species-specific lineages on phylogenies, which often grouped strains from distant geographic locations. These patterns deviate from those seen in other social insects and raise intriguing questions about the influence of army ant colony swarm-founding and within-colony genetic diversity on strain coexistence, and the effects of hosting a diverse suite of symbiont strains on colony ecology.

Łukasik P ，Newton JA ，Sanders JG ，Hu Y ，Moreau CS ，Kronauer DJC ，O'Donnell S ，Koga R ，Russell JA ... -  《-》

Microbial symbionts are shared between ants and their associated beetles.

The transmission of microbial symbionts across animal species could strongly affect their biology and evolution, but our understanding of transmission patterns and dynamics is limited. Army ants (Formicidae: Dorylinae) and their hundreds of closely associated insect guest species (myrmecophiles) can provide unique insights into interspecific microbial symbiont sharing. Here, we compared the microbiota of workers and larvae of the army ant Eciton burchellii with those of 13 myrmecophile beetle species using 16S rRNA amplicon sequencing. We found that the previously characterized specialized bacterial symbionts of army ant workers were largely absent from ant larvae and myrmecophiles, whose microbial communities were usually dominated by Rickettsia, Wolbachia, Rickettsiella and/or Weissella. Strikingly, different species of myrmecophiles and ant larvae often shared identical 16S rRNA genotypes of these common bacteria. Protein-coding gene sequences confirmed the close relationship of Weissella strains colonizing army ant larvae, some workers and several myrmecophile species. Unexpectedly, these strains were also similar to strains infecting dissimilar animals inhabiting very different habitats: trout and whales. Together, our data show that closely interacting species can share much of their microbiota, and some versatile microbial species can inhabit and possibly transmit across a diverse range of hosts and environments.

Valdivia C ，Newton JA ，von Beeren C ，O'Donnell S ，Kronauer DJC ，Russell JA ，Łukasik P ... -  《-》

Highly similar microbial communities are shared among related and trophically similar ant species.

Ants dominate many terrestrial ecosystems, yet we know little about their nutritional physiology and ecology. While traditionally viewed as predators and scavengers, recent isotopic studies revealed that many dominant ant species are functional herbivores. As with other insects with nitrogen-poor diets, it is hypothesized that these ants rely on symbiotic bacteria for nutritional supplementation. In this study, we used cloning and 16S sequencing to further characterize the bacterial flora of several herbivorous ants, while also examining the beta diversity of bacterial communities within and between ant species from different trophic levels. Through estimating phylogenetic overlap between these communities, we tested the hypothesis that ecologically or phylogenetically similar groups of ants harbor similar microbial flora. Our findings reveal: (i) clear differences in bacterial communities harbored by predatory and herbivorous ants; (ii) notable similarities among communities from distantly related herbivorous ants and (iii) similar communities shared by different predatory army ant species. Focusing on one herbivorous ant tribe, the Cephalotini, we detected five major bacterial taxa that likely represent the core microbiota. Metabolic functions of bacterial relatives suggest that these microbes may play roles in fixing, recycling, or upgrading nitrogen. Overall, our findings reveal that similar microbial communities are harbored by ants from similar trophic niches and, to a greater extent, by related ants from the same colonies, species, genera, and tribes. These trends hint at coevolved histories between ants and microbes, suggesting new possibilities for roles of bacteria in the evolution of both herbivores and carnivores from the ant family Formicidae.

Anderson KE ，Russell JA ，Moreau CS ，Kautz S ，Sullam KE ，Hu Y ，Basinger U ，Mott BM ，Buck N ，Wheeler DE ... -  《-》

Deep Sequencing Uncovers Caste-Associated Diversity of Symbionts in the Social Ant Camponotus japonicus.

Symbiotic microorganisms can have a profound impact on the host physiology and behavior, and novel relationships between symbionts and their hosts are continually discovered. A colony of social ants consists of various castes that exhibit distinct lifestyles and is, thus, a unique model for investigating how symbionts may be involved in host eusociality. Yet our knowledge of social ant-symbiont dynamics has remained rudimentary. Through 16S rRNA gene deep sequencing of the carpenter ant Camponotus japonicus symbiont community across various castes, we here report caste-dependent diversity of commensal gut microbiota and lineage divergence of "Candidatus Blochmannia," an obligate endosymbiont. While most prevalent gut-associated bacterial populations are found across all castes (Alphaproteobacteria, Gammaproteobacteria, Bacteroidetes, and Cyanobacteria), we also discovered uncultured populations that are found only in males (belonging to Corynebacteriales, Alkanindiges, and Burkholderia). Most of those populations are not detected in laboratory-maintained queens and workers, suggesting that they are facultative gut symbionts introduced via environmental acquisition. Further inspection of "Ca. Blochmannia" endosymbionts reveals that two populations are dominant in all individuals across all castes but that males preferentially contain two different sublineages that are diversified from others. Clearly, each caste has distinct symbiont communities, suggesting an overlooked biological aspect of host-symbiont interaction in social insects.IMPORTANCE Social animals, such as primates and some insects, have been shown to exchange symbiotic microbes among individuals through sharing diet or habitats, resulting in increased consistency of microbiota among social partners. The ant is a representative of social insects exhibiting various castes within a colony; queens, males, and nonreproductive females (so-called workers) show distinct morphologies, physiologies, and behaviors but tightly interact with each other in the nest. However, how this social context affects their gut microbiota has remained unclear. In this study, we deeply sequenced the gut symbiont community across various castes of the carpenter ant Camponotus japonicus We report caste-dependent diversity of commensal gut microbial community and lineage divergence of the mutualistic endosymbiont "Candidatus Blochmannia." This report sheds light on the hidden diversity in microbial populations and community structure associated with guts of males in social ants.

Koto A ，Nobu MK ，Miyazaki R 《mBio》

Antagonistic bacterial interactions help shape host-symbiont dynamics within the fungus-growing ant-microbe mutualism.

Poulsen M ，Erhardt DP ，Molinaro DJ ，Lin TL ，Currie CR ... -  《PLoS One》