Variation of symbiotic gut communities across diets and colonies of the ant Cephalotes varians

Ants are ecologically dominant insects which feed on a variety of diets ranging from relatively balanced to extremely unbalanced in nutrient content. It has been hypothesized that herbivorous ants harbor stable, indigenous and coevolved gut bacterial communities and receive greater contributions from gut bacteria than those found at higher trophic levels, which feed on more complete diets. In this study, we aimed to explore the diversity and stability of gut associates in Cephalotes varians, an herbivorous ant from the Florida Keys. Our 454 pyrosequencing data showed that the predominant bacterial taxa from workers of C. varians were found across all field-collected colonies, although there was a slight trend of greater similarity of microbial gut communities within (versus between) ant colonies. In lab-based dietary experiments, we examined one of the possible causes of this variation, diet. T-RFLP analyses revealed high similarity between gut microbes in different ants, even those fed on different diets. However, gut bacterial communities of C. varians shifted in response to feeding on pollen due to an increase in relative abundance of bacteria from the order Rhizobiales. Ant gut microbial communities showed a slight shift in response to sugar-only diets in one of the studied colonies. Combined, these results indicated that C. varians harbor qualitatively stable bacterial gut communities that may supplement nutritional deficiencies for their hosts. Differences in the relative abundance of ubiquitous bacteria among ant colonies might be partially due to their consumption of different diets at varied geographic locations or during different seasons.