Quantifying the rainforest ant gut microbiome

High-throughput amplicon sequencing is revealing a wealth of new data connecting gut microbial diversity with insect physiology, ecology, and evolution. But measures of microbial abundance, which may dramatically affect the interpretation of diversity data, have been largely ignored. In this study, we set out to investigate patterns in gut microbial abundance in rainforest ants, connections between bacterial abundance and diversity, and correlations of both with ant habitat, phylogeny, and ecology. Using in situ fluorescence microscopy of ~100 ant species from a field site in the Peruvian Amazon, we observed a roughly bimodal distribution in gut bacterial content, with most terrestrially nesting ants harboring very few visible bacterial cells, and arboreal ants typically harboring either very low or very high densities. Quantitative PCR of bacterial 16S gene copies indicated a range of cell densities spanning four orders of magnitude. Gut bacterial density appeared to be largely conserved within genera, but varied dramatically within subfamilies. Work is ongoing to generate amplicon sequence and natural stable isotope data for these samples. Our results indicate dramatic and phylogenetically conserved differences in gut bacterial densities in rainforest ants, patterns which correlate with previously described differences in feeding ecology and bacterial diversity.