Nest site limitation and colony takeover in the ant Leptothorax nylanderi

Ecological constraints on the success of independent coloniesare thought to strongly shape the organization of ant societies.One of the most important factors is probably the availabilityof suitable empty nest sites. By population censuses, laboratoryexperiments, and microsatellite analyses, we investigated thecolony and population structure of the small, myrmicine antLeptothorax (Myrafant) nylanderi in a deciduous forest nearWürzburg, Germany, where nest sites appear to be stronglylimited, especially in late summer. Colonies of L. nylanderiinhabit cavities in rotting branches, hollow acorns, grass stems,etc. After hibernation, a temporary overabundance of empty nestsites facilitates the fragmentation of larger colonies intosmaller buds, which, because the species is monogynous, arein part queenless. Nest sites become scarce in summer due torapid deca and both established colonies and young foundingqueens face a severe shortage of suitable nest sites. This leadsto the fusion of established, unrelated colonies, which afterinitial fighting permanently merge and live together. Typicalyonly one queen survives after fusion. Similarly, young matedqueens may seek adoption in alien nests instead of foundingtheir own colonies solitarily, and here again only a singlequeen survives. This temporary intraspecific parasitism maybe an important first step in the evolution of obligatory permanentparasitism, which is widespread in the genus Leptothorax.