Colony founding by queen association and determinants of reduction in queen number in the ant Lasius niger

摘要

After the nuptial flight, queens of Lasius niger occur in very high densities on the ground. Queens in this study avoided areas frequented by workers of established colonies, leading to additional clumping of nest foundations. In the field 18% of colony foundation-nests contained more than one queen (pleometrosis). Queens showed neither preference for nor avoidance of pleometrotic founding, indicating that foundress associations are facultative, promoted by crowding and intense inter-colony competition. Indeed, under laboratory conditions brood raiding occurred. In this situation groups of queens had an advantage because they produced more workers initially and the colony with the most workers was more successful in brood raids. The queens in a colony fight until only one is left alive. Removal of workers delayed fighting and addition of workers led to premature fights, indicating that the presence of workers induces fighting amongst the queens. As soon as workers started to forage, additional queens negatively affected colony productivity: colonies with three or four queens produced fewer workers than colonies with one queen. Workers also influenced the outcome of queen-queen interactions, by preferentially feeding the most fertile queen, which was therefore the most likely to survive. Neither weight of the queens by the time of the nuptial flight nor injections of juvenile hormone affected the outcome of fights between queens.