Caste and Reproduction in Ants: Not All Mated Egg‐Layers are “Queens”

The existence of two classes of adult females is characteristic of the highly-eusocial insects, which comprise termites, ants, various bees (Bombus, Apis, Meliponini) and vespine wasps. Queen and worker castes differ phenotypically as a result of morphological adaptations for efficient reproduction (dispersal, egg-laying) and maintenance activities respectively. Reproductive role partitioning in highly-eusocial species is specified by caste membership, but exceptions exist (for example, ponerine ants without queens). By contrast, inprimitively-eusocial insects, adult females are all similar in form. Individual differences in size often occur as a result of environmental variations during larval growth (such as nutrition) and, together with age and insemination, are the basis for reproductive differentiation (reviewed by Wheeler 1986). Thus, although reproductive division of labor is a feature of both primitivelyand highly-eusocial insects, it is achieved in two distinct ways: role differentiation among monomorphic adults, or production of alternative adult phenotypes. This dichotomy is not reflected by the current use of "queen," "worker" and "caste." Each of these terms has alternative meanings, and this, we suggest, obscures various evolutionary processes associated with eusociality.