Behav Ecol Sociobiol (2000) 48:478–483 © Springer-Verlag 2000 Abstract When cooperation is based on shared genetic interests, as in most social insect colonies, mechanisms which increase the genetic similarity of group members may help to maintain sociality. Such mechanisms can be especially important in colonies with many queens be- cause within-colony relatedness drops quickly as queen number increases. Using microsatellite markers, we ex- amined the Old World, multiple-queen, swarm-founding wasp Polybioides tabidus which belongs to the ropalidi- ine tribe, and found that relatedness among the workers was four times higher than what would be expected based on queen number alone. Relatedness was elevated by a pattern of queen production known as cyclical oli- gogyny, under which, queen number varies, and daughter queens are produced only after the number of old queens has reduced to one or a very few. As a result, the queens are highly related, often as full sisters, elevating related- ness among their progeny, the workers. This pattern of queen production is driven by collective worker control of the sex ratios. Workers are three times more highly re- lated to females than to males in colonies with a single queen while they are more equally related to males and females in colonies with more queens. As a result of this difference, workers will prefer to produce new queens in colonies with a single queen and males in colonies with many queens. Cyclical oligogyny has also evolved inde- pendently in another group of swarm-founding wasps, the Neotropical epiponine wasps, suggesting that collec- tive worker control of sex ratios is widespread in polis- tine wasps. Keywords Split sex ratios · Microsatellite · Conflicts of interest · Ropalidiini · Altruism Introduction The suppression of selfish activity by group members is one of the major requirements for the maintenance of co- operation. Selfishness by group members can reduce the success of the group, and conflicts between individuals who are pursuing differing goals may destabilize cooper- ation (Trivers and Hare 1976; Ratnieks 1988; Frank 1995; Maynard Smith and Szathmáry 1995; Crozier and Pamilo 1996; Queller and Strassmann 1998; Keller 1999). When cooperation is based on genetic similarity, genetic bottlenecks to increase the homogeneity of the group may be important adaptations for the maintenance of cooperation (Grosberg and Strathmann 1998). Most cooperation in the social insects is based on the shared genetic interests of relatives, or kin selection (Hamilton 1964, 1972). Workers give up most or all of their own reproduction so that they may help relatives within their colonies to reproduce. They benefit through cooperation because the relatives they aid share a higher than average proportion of their genes with the workers, and effectively pass on copies of the workers’ genes to the next generation (Hamilton 1964). Thus, when relat- edness within the colony drops, the benefits of coopera- tion to the workers will decrease, and selection may fa- vor increased selfishness by the workers. Relatedness in a colony will decrease either when queens mate multiply, or when multiple queens repro- duce in the same nest (Queller 1993). Multiple mating will not lower relatedness as dramatically as multiple queens though, because even in extreme cases, the work- er offspring of a multiply mated queen will still be half- sisters related by 0.25. When multiple queens reproduce in a colony, the workers will be cousins at best, and in fact relatedness may approach zero, depending on the re- latedness among the queens (Hamilton 1972; Queller 1993). Communicated by R. Moritz M.T. Henshaw ( ✉ ) · J.E. Strassmann · D.C. Queller Department of Ecology and Evolutionary Biology, Rice University, P.O. Box 1892 Houston, TX 77251-1892, USA e-mail: henshawm@ent.umass.edu Tel.: (413) 545-2283, Fax: (413) 545-0231 M.T. Henshaw Department of Entomology, 102 Fernald Hall, University of Massachusetts, Amherst, MA 01003-2410, USA ORIGINAL ARTICLE Michael T. Henshaw · Joan E. Strassmann David C. Queller The independent origin of a queen number bottleneck that promotes cooperation in the African swarm-founding wasp, Polybioides tabidus Received: 22 May 2000 / Revised: 24 August 2000 / Accepted: 4 September 2000