Tracing back the nascence of a new sex-determination pathway to the ancestor of bees and ants

In several Hymenoptera, sexual fate is determined by the allelic composition at the complementary sex-determiner locus, a sex-determination mechanism that can strongly affect population dynamics. To date, the molecular identification of complementary sex determiner has only been achieved in the honeybee, where the complementary sex-determiner gene was reported to have arisen from duplication of the feminizer gene. Strikingly, the complementary sex-determiner gene was also proposed to be unique to the honeybee lineage. Here we identify feminizer and complementary sex-determiner orthologues in bumble bees and ants. We further demonstrate that the duplication of feminizer that produced complementary sex determiner occurred before the divergence of Aculeata species (similar to 120 Myr ago). Finally, we provide evidence that the two genes evolved concertedly through gene conversion, complementary sex-determiner evolution being additionally shaped by mosaic patterns of selection. Thus, the complementary sex-determiner gene likely represents the molecular basis for single locus-complementary sex determination in the Aculeata infra-order, and possibly, in the entire Hymenoptera order.