Adaptive maintenance of European alleles in the Brazilian Africanized honeybee.

The Anthropocene is an epoch hallmarked by intensified human intrusion across ecosystems. One such intrusion is the movement and re-introduction of long-separated populations. By facilitating introgression - intraspecific genetic admixture - secondary contact can facilitate range expansion and the establishment of invasive species. The proximate mechanisms through which introgression facilitates expansion are rarely known (Bock et al., ; Rius & Darling, ), but managed species provide a useful avenue for exploration. Bee-keepers have been interbreeding highly diverged honeybee clades for centuries, often to introduce "useful" phenotypic variation to their stocks. Across the Western honeybee's (Apis mellifera) European range, this practice has not resulted in range expansion (Moritz, Härtel, & Neumann, ). In the Americas, however, introgression of European with African subspecies resulted in a widely publicized invasive population: The Africanized honeybee (AHB). In this issue of Molecular Ecology, Nelson, Wallberg, Simões, Lawson, and Webster () have made the first step towards understanding how this invasive species successfully spread across the Americas.