THE DISSOLUTION OF COOPERATIVE GROUPS - MECHANISMS OF QUEEN MORTALITYIN INCIPIENT FIRE ANT COLONIES

In several species of ants, queens often form temporary cooperative as sociations during colony foundation. These associations end soon after the eclosion of the first workers with the death or expulsion of all but one of the queens. This study examined competition between foundre ss queens of the fire ant Solenopsis invicta. Although attacks by the workers contributed to queen mortality, queens gained no advantage by producing more workers than their co-foundresses. Restriction fragment length polymorphism analysis of mitochondrial DNA showed that the que en producing more workers during colony founding was no more likely to survive than the less productive queen. III experimentally manipulate d colonies in which all the workers were daughters of only one of the queens, the mother of the workers was no more likely to survive than t he unrelated queen. Queens producing diploid males reared fewer offspr ing but were as likely to survive as queens producing only workers. Th ese results suggest that workers do not discriminate between related a nd unrelated queens within colonies. Aggressive encounters between que ens were common. Queens were more likely to die or be expelled if pair ed with heavier queens or if they lost more weight than their co-found ress during the claustral period. Finally, when queens were separated by screens through which workers could pass, the workers usually attac ked and killed the queen farther from the brood. These results suggest that queen survival is promoted by a high fighting ability relative t o co-foundresses, rather than by increased worker production, and that workers respond to queen differences that are independent of kinship.