Effects of Social Organisation on Spatial Genetic Structures in Formica Ants

Abstract: The social organization of social insect colonies can be broadly defined as monogynous, single reproductive female or polygynous, several reproductive females. Monogynous organization is genetically simple while polygynous is more complex and the two social forms differ commonly in mating and dispersal behaviour as well as in colony foundation. The aim of the thesis was to study how social organization affects spatial genetic structures. Formica wood ants are suitable study organisms as both intra- and interspecific variation in social organization can occur.A set of microsatellite loci were characterized from a small insert library in the ant Formica exsecta. The microsatellite loci cross amplified among other Formica species. In a population of F. exsecta containing both monogynous and polygynous colonies, genetic differentiation was stronger in the polygynous form at both nuclear and mitochondrial DNA (mtDNA) markers. The data further suggests that female dispersal is restricted in the polygynous form.Female gene flow between the social forms appears to be absent in the ant F. truncorum as the social forms contained non overlapping mtDNA haplotypes. Strong nuclear genetic differentiation and profound allele frequency differences further suggest that male interform gene flow is weak. The social forms evolve largely independently when found in sympatry though the forms do not represent separate evolutionary lineages within the species.Spatial intraspecific genetic differentiation was similar in the species F. polyctena and F. rufa though quantitative differences in the level of polygyny existed. In polygynous populations of the ant F. lugubris, female gene flow was restricted but male gene flow was strong and homogenized nuclear allele frequencies.