Variation in social organization and supergene control along a latitudinal gradient

Widespread species often experience vastly different environmental conditions across their range. In species with polymorphic traits under strong genetic control, we can investigate how environmental variation influences the distribution of traits and whether the strength of genetic control is consistent across environmental gradients. Here, we investigate the distribution of phenotypic and genetic variation in the ant Formica podzolica across 30 degrees of latitude. This species shares a supergene that is associated with colony queen number and colony sex ratio with other congeners, but we detect a surprising six common supergene variants. Colonies with a single queen are more abundant in the north compared to those with multiple queens, although the queen number polymorphism is present throughout the range. In parallel, the frequency of supergene haplotypes also varies with latitude. Of the 170 colonies examined, 10.6% contained supergene haplotypes that did not match the queen number phenotype. The highest concentration of these 'mismatched' colonies occurred in one site, raising the possibility that the environmental conditions there override supergene function. While the supergene system in F. podzolica is complex, this species holds promise for understanding how an ancient supergene system evolves in a single species experiencing highly variable environmental conditions.