Insect Molecular Biology (1999) 8(3), 419±421 SHORT NOTE Microsatellite analysis of sperm admixture in honeybee P. Franck 1 , H. Coussy 1 , Y. Le Conte 2 , M. Solignac 3 , L. Garnery 3 and J.-M. Cornuet 1 1 Laboratoire de Mode  lisation et de Biologie Evolutive, URLB-INRA, Montpellier, France; 2 Laboratoire de Biologie de l'Abeille, Unite  de zoologie ± INRA, Avignon cedex, France; and 3 Laboratoire Population, Ge  ne  tique et Evolution, CNRS, Gif/Yvette cedex, France Abstract Sperm usage was investigated in an instrumentally inseminated honeybee queen. Her progeny were examined in the ®rst 3 months of the egg-laying period using a microsatellite marker. Frequencies of dierent subfamilies diered signi®cantly from one month to another. However, there was no evidence for sperm displacement or sperm precedence of a speci®c male in the worker progeny. The variance of subfamily proportions decreased over time suggesting that sperm admixture in the spermatheca was incomplete at the beginning of the egg-laying period of the queen and improved progressively during the ®rst months after mating. Keywords: Apis mellifera, polyandry, sperm admix- ture, microsatellite, relatedness. Introduction The question of sperm admixture remains one of the central problems for the understanding of the evolution of polyandry in social insect (Boomsma & Ratnieks, 1996). Emlen & Oring (1977) presented a model which provided a general frame to test mating strategies and sexual con¯icts in animals. This model predicts that females should select mates according to male quali- ties in order to increase the ®tness of her progeny. A general view proposes that when a female mates multiply, she minimizes sperm admixture in order to favour sperm competition among males (Birkhead & Hunter, 1990). In social insect, polyandry reduces the average relatedness among nestmate workers, and hence the likelihood that selection favours altruism among them (Hamilton, 1964). A non-uniform utilization of the sperm by the polyandrous queens was also invoked some time ago (Trivers & Hare, 1976) as a way to maintain a high level of kinship within cohorts. However, increas- ing the genetic variability of the queen's ospring may also bene®t the colony (Keller & Reeve, 1994). In order to maximize this variability, the queen should mix the sperm of her mates. Honeybees provide an excellent model to test the evolution of polyandry, especially because of numer- ous observations on its reproduction biology (reviewed in Winston, 1987), which provide a frame to formulate predictable hypotheses. Honeybee queens mate with at least seven drones (e.g. Estoup et al ., 1994) during one or several mating ¯ights. Each drone injects into the queen's lateral oviducts an average of 6 million spermatozoa. However, a total of approxi- mately 5.5 million spermatozoa move to the sper- matheca after mating by active and passive mechanisms over a period of up to 40h. Most of the sperm is expelled by the queen through the sting chamber. Spermatozoa will last in the spermatheca for several years during the entire egg-laying life of the queen. In order to test the modalities of sperm admixture, the progeny of an arti®cially inseminated honeybee queen were genotyped with one microsatellite locus over time. This controlled condition enables testing of the hypothesis of equal distribution of patrilines, which is expected if the queen favours sperm admixture of her mate. Results and Discussion Patriline assignment A virgin queen was instrumentally inseminated with Received 14 September 1998; accepted 3 December 1998. Correspondence: Pierre Franck, Laboratoire de Mode lization et de Biologie Evolutive, URLB-INRA, 488 rue Croix de Lavit, 34090 Montpellier, France. Tel. (33/0) 4 67 41 68 25. Fax: (33/0) 4 67 54 94 58. e-mail: franck@ensam.inra.fr # 1999 Blackwell Science Ltd 419