Costs and benefits of colony aggregation in the social wasp, Polistes annularis

Abstract

Females of the social wasp, Polistes annularis, nest in large aggregations onriverside cliffs in central Texas. Aggregations occur where there is an overhang under which wasps build their nests. Colony aggregations appear to occur partly because individual females do notdisperse far from the natal site where most colonies are successful. In most taxa greater reproductive success near the natal nest site is related to unique physical features or to advantages ofbeing in a group. In P. annularis, the physical factors and not the social factors appear to be most important. Advantages to remaining near the natal nest site include protection provided by the cliff overhang from rain and afternoon sun. Central colonies are as likely to suffer predation as are peripheral colonies, which indicates an absence of selfish herd advantages to being in the center of the group. A cost of being in a dense aggregation is often increased reproductive competition, and this is the case for P. annularis. Colonies in the center of the aggregation suffer high usurpation rates by unrelated females and in 1 of 3 years produced fewer reproductives than edge colonies.