Comparative analysis of 163 ant genomes reveals recurrent horizontal gene transfer from bacteria to ants

Horizontal gene transfer (HGT) from bacteria can drive phenotypic innovation and adaptation in eukaryotes. Ants are likely carriers of HGT-derived genes, as they have repeatedly established mutualistic associations with vertically transmitted bacterial symbionts with direct access to the germline. However, the prevalence of HGT across ants and most other insects remains virtually unexplored.

Here, we systematically investigated the genomes of over 160 species of ants and uncovered 497 protein-coding HGT events in 85 species, predominantly derived from intracellular symbionts. Among these, we identified several HGTs likely underpinning functional innovations, primarily by mediating immune-system adaptations or facilitating nutritional niche expansions. Several of these HGTs were conserved in sequence and synteny across multiple species, consistent with strong signatures of purifying selection over up to 40 million years. Functional and structural analysis of a horizontally acquired Xanthine-guanine phosphoribosyltransferase gene of Cardiocondyla ants reveals deep entrenchment of this protein in basic energy metabolism of the host, facilitated by the enzyme's substrate promiscuity.

This study provides insights into the abundance and diversity of HGT from bacteria in the evolutionary history of ants. Furthermore, our comparative and functional analyses suggest that many of the horizontally acquired genes serve adaptive functions in ants, most prominently by expanding metabolic pathways or modulating immune responses.