Mated Drosophila melanogaster females require a seminal fluid protein, Acp36DE, to store sperm efficiently

Mated females of many animal species store sperm. Sperm storage profoundly influences the number, timing, and paternity of the female's progeny. To in vestigate mechanisms for sperm storage in Drosophila melanogaster, we gener ated and analyzed mutations in Acp36DE. Acp3BDE is a male seminal fluid pro tein whose localization in mated females suggested a role in sperm storage. We report that male-derived Acp36DE is essential for efficient sperm stora ge by females. Acp36DE(1) (null) mutant males produced and transferred norm al amounts of sperm and seminal fluid proteins. However, mates of Acp36DE(1 ) males stored only 15% as many sperm and produced 10% as many adult progen y as control-mated females. Moreover, without Acp36DE, mated females failed to maintain an elevated egg-laying rate and decreased receptivity, behavio rs whose persistence (but not initiation) normally depends on the presence of stored sperm. Previous studies suggested that a barrier in the oviduct c onfines sperm and Acp36DE to a limited area near the storage organs. We sho w that Acp36DE is not required for barrier formation, but both Acp36DE and the barrier are required for maximal sperm storage. Acp36DE associates tigh tly with sperm. Our results indicate that Acp36DE is essential for the init ial storage of sperm, and that it may also influence the arrangement and re tention of stored sperm.