NESTMATE RECOGNITION IN LEPTOTHORACINE ANTS - TESTING FOR EFFECTS OF QUEEN NUMBER, COLONY SIZE AND SPECIES OF INTRUDER

The aggressiveness of the facultatively polygynous and polydomous ant, Leptothorax ambiguus Emery, was measured in response to alien conspecific and heterospecific (L. longispinosus Roger) workers. Queenless, monogynous and polygynous nests showed no significant differences in aggressiveness. However, larger nests were significantly more aggressive than smaller nests and heterospecifics were attacked more frequently and more intensively than conspecifics. Regularly polygynous species are often less aggressive than strictly monogynous species, and the absence of a similar relationship within this facultatively polygynous species suggests that queen number and reduced genetic relatedness may not be proximate causes of this correlation, but that differing (perhaps alternate) life history strategies among monogynous and polygynous species might result in differential selection on aggressiveness. Alternatively, genetic relatedness in polygynous L. ambiguus nests might not be low enough to produce an effect, or might be so variable that any effect is difficult to detect. Since competition should be higher within than between species, stronger aggression between species is paradoxical and may indicate that competition is not sufficiently reduced to influence aggressiveness or that the intensity of competition has little influence on nest defence. © 1991 The Association for the Study of Animal Behaviour.