Hymenopteran inquiline species have been proposed to originate by sympatric speciation through intraspecific social parasitism. One such parasite, Myrmica microrubra, was recently synonymized with its Myrmica rubra host, because comparisons across Europe indicated insufficient genetic differentiation. Here, we use microsatellite markers to study genetic differentiation more precisely in a sample of Finnish M. rubra and its inquilines collected at two localities, supplemented with mitochondrial DNA sequences. The parasite had much lower genetic variation than the host at three of the four loci studied. Genetic differentiation between the host populations was moderate (F ST = 0.089), whereas the parasite populations were more strongly subdivided (F ST = 0.440). The host and parasite were highly genetically differentiated both across populations (F ST = 0.346) and in strict sympatry (0.327, 0.364), a result that remained robust both in a haplotype network and in PCA ordination. Individual assignments of genotypes indicated that gene flow between sympatric host and inquiline populations is reduced by about an order of magnitude relative to the gene flow within the morphs. Our results suggest that the parasitic morph of M. rubra may be an incipient species, but it remains unclear to what extent the observed genetic differentiation between host and inquiline is due to possible assortative mating and selection against hybrids or to recurrent bottlenecking and genetic drift. We conclude that an explicitly functional species concept would be unambiguous in treating this inquiline as a full species, as it begets its own kind and maintains its integrity in spite of occasional interbreeding with the host.

Myrmica scabrinodis is one of the commonest European ant species, but field observations of variable ecology and behaviour have suggested the existence of several ecotypes or even cryptic species within this ant. To address this hypothesis, we reconstructed the molecular phylogeny of M. scabrinodis and 15 related species based on 1089 base pairs of mitochondrial genes cytochrome B (Cyt‐B) and cytochrome oxidase subunit I (COI). We show that two major lineages occur throughout Europe. The observed sequence divergence between the two M. scabrinodis lineages is similar to or greater than that observed between the other investigated species. On a local scale, the lineages are both observed at the wet and dry extremes of the overall M. scabrinodis niche distribution, but analysis of the Myrmica communities in two sympatric populations shows that lineage B tends to avoid the drier habitat patches. Our inferred phylogenetic relationship of intra‐ and inter‐specific mitochondrial lineages within the M. scabrinodis species group in general shows several inconsistencies with the presently accepted taxonomy, suggesting the potential existence of more unrecognised cryptic species. The separate status of other species is not supported, particularly the differentiation between Myrmica sabuleti and Myrmica lonae, and specimens identified as Myrmica tulinae have highly inconsistent mitochondrial haplotypes, suggesting that the morphology associated with this taxon does not reflect phylogeny. The existence of multiple lineages within M. scabrinodis, and the apparent synonymy between M. lonae and M. sabuleti has implications for the conservation of Maculinea butterflies, for which these are major hosts.

We describe the isolation and characterization of five dinucleotide microsatellite loci in the ant Myrmica scabrinodis, which were obtained using a magnetic bead hybridization selection protocol. The PCR primers were tested on nine to 11 individuals. The number of alleles ranged from two to 13, and the observed heterozygosity from 0.200 to 0.778.