# Social organization and physical environment shape the microbiome of harvester ants

## TL;DR

This study shows that both the physical environment and social structure of harvester ant colonies influence their microbiomes.

## Contribution

The study demonstrates that both environmental and social factors shape the microbiome of harvester ants.

## Key findings

- Soil from different nests varied based on geographical distance, supporting the physical environment hypothesis.
- Bacterial communities in nest contents (ants, brood, seeds) differed from soil, supporting the social organization hypothesis.
- Nest soil resembled surrounding soil, indicating environmental influence on microbiome composition.

## Abstract

All animals harbor microbiomes, which are obtained from the surrounding environment and are impacted by host behavior and life stage. To determine how two non-mutually exclusive drivers - physical environment and social organization - affect an organism’s microbiome, we examined the bacterial communities within and around nests of harvester ants (Veromessor andrei). We collected soil and nest content samples from five different ant nests. We used 16S rRNA gene sequencing and calculated alpha and beta diversity to compare bacterial diversity and community composition across samples. To test the hypotheses that physical environment and/or social organization impact ant colonies’ community of microbes we compared our samples across (i) sample types (ants, brood, seeds and reproductives (winged alates), and soil), (ii) soil inside and outside the nest, and (iii) soil from different chamber types. Interestingly, we found that both the environment and social organization impact the bacterial communities of the microbiome of V. andrei colonies. Soil from the five nests differed from one another in a way that mapped onto their geographical distance. Furthermore, soil from inside the nests resembled the surrounding soil, supporting the physical environment hypothesis. However, the bacterial communities associated with the contents within the nest chambers, i.e., ants, brood, seeds, and reproductives, differed from one another and from the surrounding soil, supporting the social organization hypotheses. This study highlights the importance of considering environmental and social factors in understanding microbiome dynamics.

The online version contains supplementary material available at 10.1186/s42523-025-00390-3.