Naturwissenschaften (2004) 91:400–403 DOI 10.1007/s00114-004-0547-3 SHORT COMMUNICATION CØdric Alaux · Fabrice Savarit · Pierre Jaisson · Abraham Hefetz Does the queen win it all? Queen–worker conflict over male production in the bumblebee, Bombus terrestris Received: 23 January 2004 / Accepted: 16 June 2004 / Published online: 10 July 2004  Springer-Verlag 2004 Abstract Social insects provide a useful model for study- ing the evolutionary balance between cooperation and conflict linked to genetic structure. We investigated the outcome of this conflict in the bumblebee, Bombus ter- restris, whose annual colony life cycle is characterized by overt competition over male production. We established artificial colonies composed of a queen and unrelated workers by daily exchange of callow workers between colony pairs of distinct genetic make-up. Using micro- satellite analysis, this procedure allowed an exact calcu- lation of the proportion of worker-derived males. The de- velopment and social behavior of these artificial colonies were similar to those of normal colonies. Despite a high worker reproduction attempt (63.8% of workers had de- veloped ovaries and 38.4% were egg-layers), we found that on average 95% of the males produced during the competition phase (CPh) were queen-derived. However, in four colonies, queen death resulted in a considerable amount of worker-derived male production. The different putative ultimate causes of this efficient control by the queen are discussed, and we suggest a possible scenario of an evolutionary arms race that may occur between these two female castes. Introduction Harmony and a high level of cooperation among nest- mates are a hallmark of social insects. However, evolu- tionary conflicts resulting from kin structure may emerge (Crozier and Pamilo 1996), mostly involving sex ratio and male production. In monogynous hymenopteran societies with singly inseminated queens, workers are more related to their sons (r=0.5) than to their nephews (r=0.375), and least to their brothers (r=0.25). Consequently, queen– worker conflict over male parentage is predicted to be well expressed. Workers are selected to collaboratively compete with the queen over male production, but also to compete between themselves for access to reproduction. Annual societies generally form relatively small- sized colonies that facilitate worker reproduction (Bourke 1999) and accentuate the queen–worker conflict. Bombus terrestris, being annual, monogynous, and monandrous (Schmid-Hempel and Schmid-Hempel 2000), provides a good example of such a system. The conflict over male parentage in B. terrestris is expressed at the end of the colony life cycle, at the so-called competition phase (CPh) during which both the queen and workers lay haploid eggs, and each attempts to replace the others’ eggs with its own. Although mutual oophagy at this phase is extensive, a large part of the haploid brood successfully develops to emergence. However, the parenthood of the emerging males is still elusive. Early behavioral obser- vations (based on only one colony) indicated that 82% of the total males produced are worker-born (Van Honk et al. 1981), whereas more recent studies attribute most of the emerging males to the queen (Duchateau and Velthuis 1989; Velthuis et al 2002). The use of genetic analyses to determine parenthood now enables a more accurate estimation of parenthood. To date, no genetic analysis regarding male parentage in B. terrestris has been done. In this paper we present a molecular analysis of male parenthood in B. terrestris as a means for determining the victor in the reproductive conflict: queen or workers? To discriminate between male origins we used two different genotypic populations, one from France (Fr) and one from Great Britain (GB). We manipulated the colonies in order to obtain Fr queens adopting GB workers and vice versa, and analyzed the genetic relatedness of the resulting males using micro- satellite DNA markers. C. Alaux ( ) ) · F. Savarit · P. Jaisson Laboratoire d’Ethologie ExpØrimentale et ComparØe, CNRS FRE 2413, UniversitØ Paris 13, 93430 Villetaneuse, France e-mail: Cedric.Alaux@leec.univ-paris13.fr Tel.: +33-1-49403259 Fax: +33-1-49403975 A. Hefetz G. S. Wise Faculty of Life Sciences, Department of Zoology, Tel Aviv University, 69978 Tel Aviv, Israel