Sperm competition and the evolution of multiple mating

The "sexy-sperm' hypothesis proposes that multiple-mating females have a selective advantage over single-mating females because the former are fertilized by the most competitive sperm and have sons that produce competitive sperm. A deterministic genetical model of the sexy-sperm process assumes one locus that influences sperm competitive ability and a second locus that influences female mating behavior. There must be tight linkage between the two loci, positive linkage disequilibrium, and no fitness cost associated with multiple mating. When there are costs for multiple mating, the sexy-sperm mechanism fails; the multiple-mating tendency increases initially but is eliminated when linkage disequilibrium decays. Linkage disequilibrium, rather than intergenerational payoff, is the driving force in this model. Under the assumptions of this model, sperm competition plays no special role in the evolution of female mating frequency. -from Author