Do army ants and their associated arthropods share symbiotic bacteria?

Symbiotic microorganisms provide important services to their arthropod hosts, including digestion of dietary compounds, provisioning of nutrients deficient in their hosts’ diets, and defence against natural enemies and abiotic stressors. Such bacteria need to survive and compete against other microbes in internal environment of the host, which is known to vary between host species. Furthermore, they face ecological barriers to transfer between different hosts, and may be able to transmit more reliably between hosts of the same species. These factors are likely to promote host species-specialization of microbial strains. However, close associations and frequent interactions between different insect species could facilitate transmission of symbionts between such hosts.  Colonies of social insects, which are frequently inhabited by unrelated arthropods, offer a unique opportunity to compare bacterial communities of unrelated but closely associated organisms, enabling us to draw inferences regarding the specificity of their symbiotic bacteria. 

We are currently studying microbial communities of the neotropical army ant Eciton burchellii and its associated arthropods. They include hundreds of species of mites, beetles, flies, springtails and bristletails, many of which engage in trophic interactions with ants. Our results, obtained using 454 pyrosequencing, Sanger sequencing and T-RFLP, suggest that many bacteria are shared across host species. Particularly, Weissella sp. (Firmicutes: Lactobacillales) was among the most abundant bacteria in ants and beetles representing three families. This overlap in microbes found within ants and their associated arthropods indicates that colonies of army ants may serve as arenas for transmission of symbiotic bacteria between unrelated species. This may influence transfer of ecologically important traits conferred by microbial symbionts within an arthropod community, and can have important evolutionary implications.