Dominance and fertility in a functionally monogynous ant

Summary Colonies of some leptothoracine ants may contain several inseminated but sterile females in addition to a single, fertile queen (functional monogyny). We here report the first observations on the behavior of these supernumerary females in the nearctic ant Leptothorax sp.A, a species belonging to the L. muscorum complex.In four colonies, each with up to eight intermorphic females, ritualized or openly aggressive interactions between individuals were observed, similar to those among workers of some other leptothoracine ants. The responses of individual females during encounters with nestmates apparently reflect the existence of linear dominance hierarchies. In each colony, the highest ranking individual was fed and groomed significantly more often than other females, and was the only one to oviposit after hibernation and to become fully physogastric during the first weeks of spring. When these -females were removed from three colonies, several other females started to lay eggs. However, in each colony only the highest ranking individual remained fertile; the others either were pushed out of the nest and finally killed by the workers, or their ovaries degenerated again.Aggressive interactions among females may also play an important role in the foundation of new colonies either by inducing intermorphs to leave the maternal nest to found new colonies solitarily or by inducing colony fission. Offprint requests to: J. Heinze at his new address