Have symbiotic bacteria facilitated the evolution of herbivory in ants?

Many canopy-dwelling ants are known to feed extensively on nitrogen-poor food sources of honeydew and extrafloral nectar. Given their apparent N-deprivation and their common associations with gut bacteria, it has been proposed that microbes play important nutritional roles in these ant "herbivores". Through extensive universal and targeted 16S rDNA surveys, we have detected several novel lineages of gut symbionts from herbivorous ants. Most of those identified in our study are confined to the tribe Cephalotini. However, related bacteria from the order Rhizobiales were found in nearly exclusive association with ant herbivores from unrelated tribes and genera. Given these striking distributional patterns and the capacity for gut microbes to fix atmospheric nitrogen, we hypothesize that bacteria have played important roles in facilitating the evolution and maintenance of herbivory across the ants.