Alternative reproductive tactics in females: the case of size polymorphism in winged ant queens

Summary:

Alternative reproductive tactics are common in males but rather rare in females. In this respect, ants are apparently an interesting exception. Ant queens can either start a new colony on their own or utilize the work force of existing colonies for dependent colony founding. As the success of these different options depends on body reserves of the queens, the finding of two different classes of alate queens in some ant species that differ only in size strongly suggests alternative modes of reproduction. Studies of queen size polymorphism from a number of ant species differ in scope and also in their results. Nevertheless, across taxa evidence exists that small queens found dependently while their larger conspecifics found colonies on their own. However, in most cases it is not clear whether the small queens exploit unrelated colonies (intraspecific “social parasitism”) or return to their natal colonies. In some ant species the queen size polymorphism might constitute an evolutionary transition to either interspecific social parasitism or a morphologically more pronounced queen polymorphism linked to dispersal. In others, queen size polymorphism might be a stable phenomenon. Although it is important in this context whether queen size polymorphism is caused by a genetic polymorphism or phenotypic plasticity, so far no conclusive evidence about proximate mechanisms of size determination has been presented. Some considerations are made about the question why female alternative reproductive tactics correlated with morphological adaptations are comparatively widespread in ants.