Polyergus is a Holarctic genus of five obligate slave-making species which enslave members of the genus Formica. The latter is the largest ant genus in the Holarctic region, comprising some 150 species divided into seven species groups. In North America, two geographically separated species groups of Polyergus are distinguished, each enslaving their own, specific members of the Formica species group. In such an ecologically and behaviourally close association between organisms, coevolution and occasionally cospeciation has been suggested. Here we propose to reconstruct a molecular phylogeny of Formica (hosts) and Polyergus (parasites) using mitochondrial and nuclear genes. We will then test whether the two phylogenetic trees are significantly congruent such that a large proportion of the branching patterns of the two phylogenetic trees match. This would suggest that the ancestors of present Formica species provided diversifying potential for Polyergus, and that evolving Polyergus species adapted readily to enslave Formica species that most closely resembled them. If the phylogenetic trees are not congruent, the two genera most likely evolved independently and the slave-making habit evolved later, presumably owing to close physical proximity caused by similar habitat requirements of the species.
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