Sex-ratio distorter of Drosophila simulans reduces male productivity and sperm competition ability.

The aim of the present study was to determine whether the effects of sex-ratio segregation distorters on the fertility of male Drosophila simulans can explain the contrasting success of these X-linked meiotic drivers in different populations of the species. We compared the fertility of sex-ratio and wild-type males under different mating conditions. Both types were found to be equally fertile when mating was allowed, with two females per male, during the whole period of egg laying. By contrast sex-ratio males suffered a strong fertility disadvantage when they were offered multiple mates for a limited time, or in sperm competition conditions. In the latter case only, the toll on male fertility exceeded the segregation advantage of the distorters. These results indicate that sex-ratio distorters can either spread or disappear from populations, depending on the mating rate. Population density is therefore expected to play a major role in the evolution of sex-ratio distorters in this Drosophila species. Copyright 2004 Blackwell Publishing Ltd