Microbial gut symbionts and the origins of herbivory in ants

Gut communities of animals can be diverse and dynamic, showing variation between species and even among conspecific individuals. While dietary differences are likely to explain some of this variation, it is also likely that different animals—including insects—have evolved mechanisms to transmit and retain a select group of microflora. One reason for this is, essentially, dietary need. Organisms with nutrient poor diets are expected to rely upon microbes for the digestion recalcitrant materials, the recycling of nitrogenous wastes, or the production of essential nutrients. To explore the bacterial communities from insects, we performed a series of meta-analyses and molecular investigations, focusing largely on the gut communities from herbivorous ants that feed upon nutrient-poor liquid food sources. We have found that herbivorous ants harbor stable communities of gut bacteria belonging to derived, ant-specific lineages on 16S rRNA phylogenies. These bacteria are stably maintained in the laboratory, even after rearing on artificial diets. Other insects with low-quality diets show similar trends, revealing a common theme of community stability, in spite of some notable differences in community composition between these insects. Combined with experimental precedent and observations that unrelated herbivorous ants harbor related gut microbes, our findings suggest an important role for gut microbes in the dietary evolution of the ants, hinting that like other insects, nutritional bacteria have enabled the colonization of otherwise inhospitable dietary niches.