Effect of queen phenotype and social environment on early queen mortality in incipient colonies of the fire ant, Solenopsis invicta

In many ant species, including the fire ant, Solenopsis invicta, queens can found their colonies alone or in associations of two or more. Colonies fou nded by associations produce a larger worker brood,have higher survival and mature earlier than colonies founded by solitary queens. However, cofoundr esses almost invariably fight after the eclosion of the first workers. As a result, only one queen survives and monopolizes the colony's future reprod uctive output. Queen mortality also occurs before worker eclosion, but neit her the causes (e.g. starvation, conflict), nor the factors (e.g. social en vironment) potentially affecting its occurrence, have been investigated. We analysed the effect of social environment and queen body mass on early mor tality by keeping queens (1) solitarily, (2) within associations of four qu eens of the same initial mass, and (3) within associations of four queens o f random initial mass. Mortality was higher for queens within associations than for solitary queens. Within associations of equally heavy queens, mort ality significantly increased with the queens' body mass. In contrast, mort ality of solitary queens did not significantly depend on body mass. Early m ortality was significantly more frequent in associations of queens of rando m initial mass than in associations of equally heavy queens. Altogether the se results demonstrate that queen phenotype differentially affects early qu een mortality depending on the social environment, and suggest that reprodu ctive competition rather than starvation is the main cause of mortality in multiple-queen associations. (C) 1999 The Association for the Study of Anim al Behaviour.