Evolution and Diversity of Inherited Spiroplasma Symbionts in Myrmica Ants.

Microbial partners play important roles in the biology and ecology of animals. In insects, maternally transmitted symbionts are especially common and can have host effects ranging from reproductive manipulation to nutrient provisioning and defense against natural enemies. In this study, we report a genus-wide association of ants with the inherited bacterial symbiont We screen ants collected from the wild, including the invasive European fire ant, , and find an extraordinarily high prevalence of this symbiont-8 of 9 species, 42 of 43 colonies, and 250 of 276 individual workers harbored -only one host species was uninfected. In our screens, each host species carried a distinct strain, and none were infected with more than one strain. All symbionts belong to the clade, allied most closely with pathogenic strains of infecting corn crops and honeybees, and there is strong evidence of host-symbiont persistence across evolutionary time scales. Genome sequencing of two symbionts revealed candidate genes that may play a part in the symbiosis, a nutrient transporter absent from other strains, and a ribosome-inactivating protein previously implicated in parasite defense. These results together suggest long-term, likely mutualistic, relationships atypical of -insect associations with potential significance for broad ecological interactions with Animal-associated microbial symbionts can dramatically affect the biology of their hosts. The identification and characterization of these intimate partnerships remain an essential component of describing and predicting species interactions, especially for invasive host species. Ants perform crucial ecological functions as ecosystem engineers, scavengers, and predators, and ants in the genus can be aggressive resource competitors and reach high densities in their native and invaded habitats. In this study, a novel symbiosis is identified between ants and the facultative bacterial symbiont Broad host distribution, high frequencies of infection, and host-symbiont codivergence over evolutionary time scales, an uncommon feature of associations, suggest an important likely mutualistic interaction. Genome sequencing identified highly divergent gene candidates that may contribute to 's role as a possible defensive or nutritional partner in .