MALE IDENTITY AND SPERM DISPLACEMENT IN DROSOPHILA-MELANOGASTER

In Drosophila melanogaster, most of the sperm stored in a female is often displaced by the sperm from a subsequent mating. The exact mechanism of sperm displacement in D. melanogaster is unknown. It is thought, however, that the process is mediated largely by the male accessory gland fluid that is passed to the female, with sperm, during mating. If a sperm incapacitation process is involved, a male's accessory gland fluid would have to be able to distinguish between self and nonself sperm, Otherwise a male would incapacitate his own sperm as well as the sperm already stored in the female. Accordingly, if displacement occurs by an incapacitation mechanism, a male should be able to displace his own sperm less than that of another male. This experiment investigated whether males differentially displaced stored sperm when it was their own as opposed to that of another male. Females were remated to the same or a different male that had been sterilised between matings, allowing the degree of displacement of first male sperm to be determined unambiguously. Although no differential displacement was observed, further evidence was obtained that sperm displacement is caused by accessory gland fluid. The results also suggest that sperm displacement is directed primarily against sperm stored in the seminal vesicle rather than the spermathecae.