title: The structured diversity of specialized gut symbionts of the New World army ants.
abstract: 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.
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, USA.
authors.forename: Piotr
authors.identifier: http://orcid.org/0000-0002-4164-6487
authors.initials: P
authors.lastname: Łukasik
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, USA.
authors.forename: Justin A
authors.initials: JA
authors.lastname: Newton
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
authors.forename: Jon G
authors.identifier: http://orcid.org/0000-0001-6077-4014
authors.initials: JG
authors.lastname: Sanders
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, USA.
authors.forename: Yi
authors.identifier: http://orcid.org/0000-0002-1086-2072
authors.initials: Y
authors.lastname: Hu
authors.affiliation: Department of Science and Education, Field Museum of Natural History, Chicago, IL, USA.
authors.forename: Corrie S
authors.identifier: http://orcid.org/0000-0003-1139-5792
authors.initials: CS
authors.lastname: Moreau
authors.affiliation: Laboratory of Social Evolution and Behavior, The Rockefeller University, New York, NY, USA.
authors.forename: Daniel J C
authors.initials: DJC
authors.lastname: Kronauer
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, USA.
authors.forename: Sean
authors.initials: S
authors.lastname: O'Donnell
authors.affiliation: Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan.
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Koga
authors.affiliation: Department of Biology, Drexel University, Philadelphia, PA, USA.
authors.forename: Jacob A
authors.identifier: http://orcid.org/0000-0002-0131-6264
authors.initials: JA
authors.lastname: Russell
mesh_terms: D000818:Animals; D001000:Ants / Q000382:microbiology*; D001419:Bacteria / Q000145:classification*; D041981:Gastrointestinal Tract / Q000382:microbiology*; D064307:Microbiota; D010802:Phylogeny; D058974:Phylogeography; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013559:Symbiosis
chemical_list: D012336:RNA, Ribosomal, 16S
keywords: 
  Eciton burchellii
  ; 
  Labidus praedator
  ; Dorylinae; army ants; codiversification; ectosymbiont; gut bacteria; host specificity; strain-level diversity