Gene flow is maintained by polyandry and male dispersal in the army ant Eciton burchellii

The combination of haplodiploidy, complementary sex determination and eusociality constrains the effective population size (N (e)) of social Hymenoptera far more than in any other insect group. Additional limitations on N (e) occur in army ants since they have wingless queens and colony fission, both of which are factors causing restricted maternal gene flow and high population viscosity. Therefore, winged army ant males gain a particular significance to ensure dispersal, facilitate gene flow and avoid inbreeding. Based on population genetic analyses with microsatellite markers, we studied a population of the Neotropical army ant Eciton burchellii, finding a high level of heterozygosity, weak population differentiation and no evidence for inbreeding. Moreover, by using sibship reconstruction analyses, we quantified the actual number of male contributing colonies represented in a queen's mate sample, demonstrating that, through extreme multiple mating, the queens are able to sample the genes of males from up to ten different colonies, usually located within an approximate radius of 1 km. We finally correlated the individual mating success of each male contributing colony with the relative siring success of individual males and found a significant colony-dependent male fitness component. Our results imply that the dispersal and mating system of these army ants seem to enhance gene flow and minimise the deleterious effects associated with small effective population size.