Recurrent horizontal gene acquisition in the evolutionary history of ants

Horizontal Gene transfer (HGT) from bacteria has often led to Horizontal Gene Acquisition (HGA), subsequently contributing to phenotypic innovation. Ants are interesting potential targets for HGA because they host many mutualistic associations with vertically transmitted symbionts, but the overall prevalence of HGA across the ants and other insect lineages remains virtually unexplored. Here, we systematically screened the genomes of 163 ant species and identified 497 HGA events of protein-coding genes, predominantly derived from intracellular symbionts, in 85 species belonging to eight subfamilies. Apart from convergent horizontal transfers of Wolbachia-derived ankyrin repeat proteins into the genomes of 45 ant species, we identified dozens of other HGAs that likely offered adaptive innovations of phenotypic functions, primarily mediating immune-system adaptations or facilitating nutritional niche expansions. We provide in-depth characterizations of multiple clade- and species-specific HGAs, some as old as 40 MY, consistent with strong evolutionary conservation. Our study is the first of its kind in ants and considerably expands our general appreciation of the evolutionary significance of HGA from bacteria to eukaryotes.