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Key words. Hymenoptera, Formicidae, ants, Myrmica rubra, isolation by distance, polygyny, relatedness, social insects

Abstract. Social insect colonies, especially of ants, often include several egg-laying queens that are not always closely related to each other. At least in some cases, the ants seem to accept non-related queens into their colonies. Here I test whether the colony queen status (with or without a queen), genetic and geographic differences between source and recipient nests and the average relatedness of the workers in the recipient colony affect the acceptance of alien queens. I used fi eld collected ruby ant Myrmica rubra colonies as a model system. Only the queen status signifi cantly affected the acceptance process. Colonies without queens accepted alien queens more frequently than colonies with a queen. The nests without queens and nest fragments may act as vectors for gene fl ow by the movement of queens between nests, i.e., queen fl ow.

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Breeding groups can be divided into colonial and social forms. Colonial nesting groups typically consist of several breeding pairs that share the same neighbourhood and have no non-breeding helpers, e.g., many seabirds (Danchin & Wagner, 1997). Social breeding groups are often family groups such as wolves where the helpers of the breeding pair are usually their own offspring (Mech & Boitani, 2003). Social insects such as ants, social bees and wasps and termites are often termed eusocial since they have special morphologically distinct castes for different tasks, e.g., queens, males/drones, workers (Wilson, 1971). Often one queen and one or several male mates are the reproducers in a social insect colony. The term "colony" in social insect studies means the combination of reproducers and helpers. While in many cases, the reproduction of a social insect colony is based on a single queen and the sperm contribution of her male mate or mates, many social insect colonies permanently have several reproducing queens at the same time, a situation called polygyny (Wilson, 1971; Bourke & Franks, 1995).

Among social insects, polygyny is especially common in ants, where over 40% of the species are classified as polygynous (Frumhoff & Ward, 1992). Polygynous ant colonies are often family groups where daughters of the mother queen have been adopted back into the colony, but also non-nest mate queens...

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