SPERM DISPLACEMENT AFTER REMATING IN DROSOPHILA-MELANOGASTER

We examined sperm displacement in a fruitfly species in which females remate, D. melanogaster. Wildtype females were mated to males carrying dominant mutations, then given an opportunity to remate with wildtype males 6 h after the initial mating. The progeny were scored as first or second male progeny by the presence or absence of dominant mutations. Females that remated (about 40%) produced only about 25% of first male progeny that were expected on the basis of comparisons with control females not given a chance to remate, but produced about the same number of total progeny (first male and second male). Similar results were obtained using females with dominant mutations, but the total progeny for remating females was lower than for controls. Frequency distributions of progeny production for control, remating and nonremating wildtype females indicated that lowered first male productivity was not due to either preferential remating by females that initially stored few first male sperm or excessive depletion of first male sperm before remating. These results provide evidence that a large proportion of first male sperm are displaced by second male sperm when females remate within 6 h.