In the last two decades, the widespread application of genetic and genomic approaches has revealed a bacterial world astonishing in its ubiquity and diversity. This review examines how a growing knowledge of the vast range of animal–bacterial interactions, whether in shared ecosystems or intimate symbioses, is fundamentally altering our understanding of animal biology. Specifically, we highlight recent technological and intellectual advances that have changed our thinking about five questions: how have bacteria facilitated the origin and evolution of animals; how do animals and bacteria affect each other’s genomes; how does normal animal development depend on bacterial partners; how is homeostasis maintained between animals and their symbionts; and how can ecological approaches deepen our understanding of the multiple levels of animal–bacterial interaction. As answers to these fundamental questions emerge, all biologists will be challenged to broaden their appreciation of these interactions and to include investigations of the relationships between and among bacteria and their animal partners as we seek a better understanding of the natural world

We present a large-scale molecular phylogeny of the ants (Hymenoptera: Formicidae), based on 4.5 kilobases of sequence data from six gene regions extracted from 139 of the 288 described extant genera, representing 19 of the 20 subfamilies. All but two subfamilies are recovered as monophyletic. Divergence time estimates calibrated by minimum age constraints from 43 fossils indicate that most of the subfamilies representing extant ants arose much earlier than previously proposed but only began to diversify during the Late Cretaceous to Early Eocene. This period also witnessed the rise of angiosperms and most herbivorous insects.

Ants are a dominant feature of terrestrial ecosystems, yet we know little about the forces that drive their evolution. Recent findings illustrate that their diets range from herbivorous to predaceous, with ''herbivores'' feeding primarily on exudates from plants and sap-feeding insects. Persistence on these nitrogen-poor food sources raises the question of how ants obtain sufficient nutrition. To investigate the potential role of symbiotic microbes, we have surveyed 283 species from 18 of the 21 ant subfamilies using molecular techniques. Our findings uncovered a wealth of bacteria from across the ants. Notable among the surveyed hosts were herbivorous ''turtle ants'' from the related genera Cephalotes and Procryptocerus (tribe Cephalotini). These commonly harbored bacteria from ant-specific clades within the Burkholderiales, Pseudomonadales, Rhizobiales, Verrucomicrobiales, and Xanthomonadales, and studies of lab-reared Cephalotes varians characterized these microbes as symbiotic residents of ant guts. Although most of these symbionts were confined to turtle ants, bacteria from an ant-specific clade of Rhizobiales were more broadly distributed. Statistical analyses revealed a strong relationship between herbivory and the prevalence of Rhizobiales gut symbionts within ant genera. Furthermore, a consideration of the ant phylogeny identified at least five independent origins of symbioses between herbivorous ants and related Rhizobiales. Combined with previous findings and the potential for symbiotic nitrogen fixation, our results strongly support the hypothesis that bacteria have facilitated convergent evolution of herbivory across the ants, further implicating symbiosis as a major force in ant evolution. diversification ͉ Formicidae ͉ Rhizobiales ͉ symbiosis ͉ trophic level I dentifying the mechanisms underlying adaptation and diversification is a central goal of evolutionary biology. Great strides have been made toward this end through the development of fast and affordable molecular tools, and the joint application of molecular phylogenetics and comparative methods (1-3). One unanticipated theme that has emerged from this work is that bacterial symbionts have played key roles in the evolution and diversification of eukaryotes, starting with endosymbiotic origins of mitochondria and chloroplasts (4). Bacterial symbionts are also prevalent among insects that feed on inaccessible or nutritionally marginal diets such as blood, wood, xylem, and phloem (5). Given the demonstrated nutritional roles of these bacteria, their near-ubiquity in insects that specialize on nutrient-poor diets, their long histories of coevolution, and the diversity of the many groups that harbor nutritional symbionts, it is clear that bacteria have had a strong impact on the dietary evolution and diversification of their insect hosts (6).Symbiosis has played an integral role in the evolution of the ants (Hymenoptera: Formicidae). Throughout the course of their 115-168 million year history (7,8), these diverse and ecologically dominant insects...

The estimated 6000 species of Lycaenidae account for about one third of all Papilionoidea. The majority of lycaenids have associations with ants that can be facultative or obligate and range from mutualism to parasitism. Lycaenid larvae and pupae employ complex chemical and acoustical signals to manipulate ants. Cost/benefit analyses have demonstrated multiple trade-offs involved in myrmecophily. Both demographic and phylogenetic evidence indicate that ant association has shaped the evolution of obligately associated groups. Parasitism typically arises from mutualism with ants, and entomophagous species are disproportionately common in the Lycaenidae compared with other Lepidoptera. Obligate associations are more common in the Southern Hemisphere, in part because highly ant-associated lineages make up a larger proportion of the fauna in these regions. Further research on phylogeny and natural history, particularly of the Neotropical fauna, will be necessary to understand the role ant association has played in the evolution of the Lycaenidae.