Queen acceptance and nestmate recognition in monogyne and polygyne colonies of the ant Formica truncorum

Abstract

In ants permanent polygyny (the permanent presence of multiple reproducing queens) commonly arises secondarily through the adoption of daughter queens. Polygyny decreases the relatedness among nestmate workers and consequently the genetic benefits from helping close relatives. Hence, studies on nestmate recognition and queen adoption may shed light on how queen numbers are regulated as well as on causes of variation in queen number. In this study acceptance of nestmate and non-nestmate young queens in monogyne (single queen) and polygyne colonies of the ant Formica truncorum was compared. Queen number varies in this species: in some populations colonies have a single queen (monogyne populations), whereas in others all colonies contain several functional queens (polygyne populations). Young queens introduced into the experimental colonies varied with respect to female origin (nestmate versus non-nestmate), dispersal prospects as reflected by wing status (wingless versus winged) and mating status (mated versus virgin). Monogyne and polygyne colonies differed in one fundamental way in their responses to introduced females. Workers of monogyne colonies, but not those of polygyne colonies, discriminated between nestmate and non-nestmate females. In both monogyne and polygyne colonies mated females were destroyed to a higher extent than virgin ones, largely independently of wing status. None the less, mated females may have a reasonable chance of becoming adopted in their natal colony both in monogyne and polygyne colonies. If so, the single-queen status of monogyne colonies may be retained by a high rate of female dispersal in combination with few intra-nidal mating opportunities. Polygyne colonies are characterized by both a low degree of female rejection and low levels of discrimination between nestmates and non-nestmates. Nevertheless, previous genetic and behavioural data on female dispersal suggest that the majority of new queens adopted into polygyne colonies are their own daughters.