Dietary niche shapes bacterial community in Indo-Pacific ants

Ants are among the most ecologically diverse insects, especially in tropical forest ecosystems, yet what shapes their microbial associates remains poorly understood. Most research has focused on Neotropical ants, where strong microbial associations have been linked to shifts in diet—such as herbivory—and nesting ecology. In contrast, Indo-Pacific ants, which have independently evolved similar specialised lifestyles, remain largely unstudied for their microbial associations. Here, we integrate deep-coverage 16S rRNA sequencing with stable isotope (δ¹⁵N) analyses to characterise the microbiomes of 239 ants from 36 species across 24 genera from the Indo-Pacific region. These ants span a broad ecological range, from ground-dwelling predators to strict arboreal herbivores, allowing us to ask: which ecological traits shape bacterial diversity in tropical ants? Our results reveal that dietary niche—rather than nesting habitat—is the primary explanatory variable of microbial diversity and composition. Ants consuming protein-rich diets (predators and omnivores) exhibit significantly higher bacterial alpha diversity and distinct community composition profiles compared to their plant-based (herbivorous) counterparts, with Rickettsiales, Rhizobiales, and Enterobacterales as major contributors to these differences. Notably, herbivorous ants tend to harbour simpler, Enterobacterales-dominated microbiomes, whereas predators support more complex communities, frequently containing Rhizobiales bacteria. Phylogenetic comparative analyses suggest that the acquisition of specific bacteria, particularly Enterobacterales, are strongly correlated with evolutionary transitions toward herbivory. Our findings expand on previously documented trends in ant-microbe interactions whilst also offering new insights into how symbioses drive the evolution of dietary strategies in tropical ecosystems.