Queen phenotype and behaviour during cooperative colony founding in Polyrhachis moesta

Summary. Founding queens of the arboreal ant Polyrhachis moesta aggregate independently of kinship and cooperate in caring for their brood. In field studies, the number of queens in a founding nest varied from 1 to 8. The number of queens in the nests with multiple queens decreased significantly with time after the nuptial flight, resulting in monogynous or oligogynous nests. Single- and multiple-founding queens did not differ in characteristics representing nutritional states or body size immediately after the nuptial flight. Wet body weight decreased as days passed, whereas head width of founding queens who overwintered successfully were relatively larger. In laboratory studies, founding queens performed liquid food exchanges more frequently with queens from other founding nests or immature colonies than with those from the same nests. Queens in founding nests and immature colonies were observed to show no aggression against non-nestmate queens, whereas queens in established colonies showed aggressive behaviours against non-nestmates. This indicates that founding queens change drastically in their aggression levels before and after colony establishment. Multiple-founding queens started laying eggs earlier than single-founding queens under laboratory conditions. Higher brood productivity and lower brood mortality were observed in multiple-queen nests. These potential advantages in multiple-queen founding may support the cooperative association among unrelated founding queens.Received 1 December 2003; revised 25 March and 20 May 2004; accepted 3 June 2004.