Unexpected absence of a multiple-queen supergene haplotype from supercolonial populations of Formica ants

Abstract

Ants exhibit many complex social organization strategies. One particularly elaborate strategy is supercoloniality, in which a colony consists of many interconnected nests (= polydomy) with many queens (= polygyny). In many species of Formica ants, an ancient queen number supergene determines whether a colony is monogyne (= headed by single queen) or polygyne. The presence of the rearranged P haplotype typically leads colonies to be polygyne. However, the presence and function of this supergene polymorphism have not been examined in supercolonial populations. Here, we use genomic data from species in the Formica rufa group to determine whether the P haplotype leads to supercoloniality. In a Formica paralugubris population, we find that nests are polygyne despite the absence of the P haplotype in workers. We find spatial genetic ancestry patterns in nests consistent with supercolonial organization. Additionally, we find that the P haplotype is also absent in workers from supercolonial Formica aquilonia and Formica aquilonia × polyctena hybrid populations but is present in some Formica polyctena workers. We conclude that the P haplotype is not necessary for supercoloniality in the Formica rufa group, despite its long-standing association with non-supercolonial polygyny across the Formica genus.