Genetic population structure and dispersal patterns in Formica ants — a review

Human impact on boreal forests has been extensive during a fairly short evolutionary time scale. Character species of boreal forests, such as Formica ants, may face loss of genetic diversity, increasing inbreeding, and decreasing gene flow among extant habitat fragments owing to habitat loss and fragmentation. Here we review the genetic data on old-world boreal species of the genus Formica. In Formica ants colonies can have one or several queens (monoand polygyny respectively) and this trait is often assumed to be linked with dispersal propensity, such that monogyne species disperse well and polygyne species disperse less well. Our analysis of the available data reveals three important aspects of the social and dispersal biology of Formica. First, the traditional division in monoand polygyne species is too simple and we propose a population-based division into highly polygyne, weakly or moderately polygyne, and monogyne populations. Second, there is indeed an association between colony kin structure and dispersal in the predicted direction, i.e. restricted dispersal in polygyne species. However, this only holds for between-population differentiation, not within population genetic viscosity. When genetic viscosity within populations was examined most species nevertheless showed a negative relationship between FIS and relatedness, indicating that low relatedness (many queens) is associated with reduced dispersal also locally. Only one species (F. exsecta) showed a significant positive relationship. Finally, we predict that sex-biased dispersal may be a common trait in Formica species, although data on more species are needed to confirm this.