Variation among males and females in reproductive success is a major determinant of effective
population size. Most studies of male mating success in Drosophila, however, have been done
under conditions very different from those in typical cultures. We determined the distribution of
male mating success in five laboratory populations of D. melanogaster maintained on a 14 d,
discrete generation cycle fairly representative of standard Drosophila cultures. Mating success was
measured as the number of matings a male could achieve under conditions closely approximating a
regular culture vial of these populations. Preliminary studies determined that most mating in these
populations occurred within 14 h of the flies attaining sexual maturity. Consequently, individual
virgin males were marked with white paint on their thorax, put into vials with varying numbers of
unmarked virgin flies of both sexes, and monitored continuously for matings over a period of up
to 14 h. At various times during the assay, virgin males and females were added to these vials in
proportions simulating the pattern of eclosion in culture vials. The observed variation in the
number of matings per male in the five populations was, by and large, consistent with a Poisson
distribution, suggesting that male mating success in short-generation-time, discrete-generation
laboratory cultures of D. melanogaster may fulfil a fundamental assumption of the Wright–Fisher
model of genetic drift in finite populations.