Abstract
BACKGROUND: Supergenes are chromosomal regions with tightly linked clusters of alleles that control compound phenotypic traits. Supergenes have been demonstrated to contribute to the maintenance of polymorphisms within populations in traits as diverse as mimetic wing coloration in butterflies, mating strategies in birds, and malarial susceptibility in mosquitoes. A large supergene also underlies variation in social organization in Formica ants. Alternative supergene haplotypes are associated with the presence of either a single queen (monogyny) or multiple queens (polygyny) within colonies. Here, we assess the social structure and supergene status of the North American species Formica neoclara. RESULTS: We sequenced a subset of the genome in 280 individuals sampled in populations from California to northern British Columbia using ddRADseq. We determined that F. neoclara is socially polymorphic in queen number, and we show that the social polymorphism is associated with alternative haplotypes at the social supergene. Intriguingly, polygyne colonies can harbor workers that are homozygous for both haplotypes as well as heterozygotes. CONCLUSIONS: This colony genetic composition contrasts with other Formica species, in which almost all individuals in polygyne colonies have the polygyne-associated haplotype. The social polymorphism is present in widely distributed and genetically subdivided populations of F. neoclara. In studying this system in F. neoclara, we expand our understanding of the functional evolution of supergene haplotypes as they diverge in different lineages.