The Acp26Aa seminal fluid protein is a modulator of early egg hatchabilityin Drosophila melanogaster

Drosophila melanogaster male accessory gland proteins (Acps) that are trans ferred in the ejaculate with sperm mediate post-mating competition for fert ilizations between males. The actions of Acps include effects on ovipositio n and ovulation, receptivity and sperm storage. Two Acps that modulate egg production are Acp26Aa (ovulin) and Acp70A (the sex peptide). Acp26Aa acts specifically on the process of ovulation (the release of mature eggs from t he ovaries which is initiated 1.5 h after mating. In contrast, sperm storag e can take as long as 6-9 li to complete. Initial ovulations after matings by virgin females will therefore occur before all sperm are fully stored an d the extra eggs initially laid as a result of Acp26Aa transfer are expecte d to be inefficiently fertilized. Acp26Aa-mediated release of existing eggs should not cause a significant energetic cost or lead to a decrease in fem ale lifespan assuming, as seems likely, that the energetic cost of egg layi ng comes from de novo egg synthesis (oogenesis') rather than from ovulation . We tested these predictions using Acp26Aa(1) mutant males that lack Acp26 Aa but are normal for other Acps and Acp26Aa(2) males that transfer a trunc ated but fully functional Acp26Aa protein. Females mating with Acb26Aa(2) t runcation) males that received functional Acp26Aa produced significantly mo re eggs following their first matings than did mates of Acp26Aa(1) (null) m ales. However, as predicted above, these extra eggs, which were laid as a r esult of Acp26Aa transfer to virgin females, showed significantly lower egg hatchability. Control experiments indicated that this lower hatchability w as due to lower rates of fertilization at early post-mating times. There wa s no drop in egg hatchability in subsequent nonvirgin matings. In addition, as predicted above, females that did or did not receive Acp26Aa did not di ffer in survival, lifetime fecundity or lifetime progeny, indicating that A cp26Aa transfer does not represent a significant energetic cost ibr females and does not contribute to the survival cost of mating. Acp26Aa appears to remove a block to oogenesis by causing the clearing out of existing mature eggs and, thus, indirectly allowing oogenesis to be initiated immediately after mating. The results show that subtle processes coordinate the stimula tion of egg production and sperm storage in mating pairs.