Polygyny

CHAPTER 6. QUEEN NUMBERS AND DOMINATION

The number of queens profoundly alters several of the key features of colonial organization, including the kinship of the nestmates, the rate of colony growth, and the number and distribution of nests. The past ten years have witnessed an explosive growth of knowledge about this complex subject, with investigators addressing the following questions:

• Why does the number of queens vary among species? The colonies of some species always have a single egg-laying queen. Those of others have up to thousands or, as in the case of the “supercolonial” Formica yessensis of Japan, millions of queens. In still other species the number ranges among colonies from one to many. In addition, the number often shifts through different stages of the colony life cycle.

• Which colony members control the number of queens? Is the number a consequence of dominance and elimination among queens, or do the workers regulate the number?

• How is the number controlled? Regulation of the queen population can be achieved by physical elimination, reproductive castration (perhaps mediated by pheromones), or emigration of supernumeraries.

• What are the consequences of varying queen numbers on the growth and genetic structure of colony populations?

It will be useful to begin with the generally accepted terminology of queen numbers in relation to the life cycle. Monogyny refers simply to the possession by a colony of a single egg-laying queen, or reproductive female--or "gyne," as it is often called in the myrmecological literature. Polygyny is the possession of multiple queens. Oligogyny is a special case of polygyny, in which two to several queens coexist in the same nest but remain well apart from one another (Hölldobler, 1962; Buschinger, 1974a). As a rule, oligogyny in ants is characterized by tolerance of workers toward supernumerary queens combined with intolerance among the queens, so that the queens space out in the same nest (Hölldobler and Carlin, 1985). The founding of a colony by a single queen is called haplometrosis; when multiple queens found a colony the condition is referred to as pleometrosis (Wasmann, 1910b; Wheeler, 1933b). The term metrosis can be used to refer generally to this biological variable. Monogyny can be primary, meaning that a single queen is also the foundress; or it can be secondary, in which multiple queens start a colony pleometrotically but only one of them survives. In a symmetric fashion, polygyny can be primary (multiple queens persist from a pleometrotic association) or secondary (the colony is started by a single queen and others are added later by adoption or fusion with other colonies).