Disentangling the mechanisms linking dispersal and sociality in supergene-mediated ant social forms

The coevolution between dispersal and sociality can lead to linked
polymorphisms in both traits, which may favour the emergence of
supergenes. Supergenes have recently been found to control social
organization in several ant lineages. Whether and how these “social
supergenes” also control traits related to dispersal is yet unknown. Our
goal here was to get a comprehensive view of the dispersal mechanisms
associated to supergene-controlled alternative social forms in the ant
Formica selysi. We measured the production and emission of young females
and males by single-queen (monogyne) and multiple-queen (polygyne)
colonies, the composition of mating aggregations, and the frequency of
crosses within and between social forms in the wild. We found that males
and females from alternative social forms did not display strong
differences in their propensity to leave the nest and disperse, nor in
their mating behaviour. Instead, the social forms differed substantially
in sex allocation. Monogyne colonies produced 90% of the females flying to
swarms, whereas 57% of the males in swarms originated from polygyne
colonies. Most crosses were assortative with respect to social form.
However, 20% of the monogyne females did mate with polygyne males, which
is surprising as this cross has never been found in mature monogyne
colonies. We suggest that the polygyny-determining haplotype free rides on
monogyne females, who establish independent colonies that later become
polygyne. By identifying the steps in dispersal where the social forms
differ, this study sheds light on the behavioural and colony-level traits
linking dispersal and sociality through supergenes.