The role of male accessory gland protein Acp36DE in sperm competition in Drosophila melanogaster

A crucial factor determining sperm fertilization success in multiply mated Drosophila melanogaster females is the efficiency with which sperm are stor ed. This process is modulated by the accessory gland protein Acp36DE. In th is study, we show that the effect of Acp36DE on sperm storage itself alters the outcome of sperm competition. As second-mating males, Acp36DE(1) (null ) males had significantly lower P-2-values than Acp36DE(2) (truncation) or Acp36DE(+) (control) males, as might be expected as the null males' sperm a re poorly stored. We used spermless males, which are null for Acp36DE, to s how that, in the absence of sperm co-transfer, Acp36DE itself could not dis place first-male sperm. The results therefore suggest. that males null for Acp36DE suffer in sperm displacement because fewer sperm are stored or reta ined, not because Acp36DE itself displaces sperm. Acp36DE(1) (null) males a lso gained significantly fewer fertilizations than controls when they were the first males to mate. Using spermless males, we also showed that signifi cantly more second-male offspring were produced following the transfer of A cp36DE by spermless first-mating males. This implies that the transfer of A cp36DE itself by the first male facilitated the storage or use of the secon d male's sperm and that co-transfer with sperm is not necessary for Acp36DE effects on second-male sperm storage. Acp36DE may persist in the reproduct ive tract and aid the storage of any sperm including these of later-mating males or prime the female for future efficient sperm storage. Our results i ndicate that mutations in genes that affect sperm storage can drastically a ffect the outcome of sperm competition.