Females of many animal species store sperm for taxon-specific periods of time, ranging from a few hours to years. Female sperm storage has important reproductive and evolutionary consequences, yet relatively little is known of its molecular basis. Here, we report the isolation of a loss-of-function mutation of the Drosophila melanogaster Acp29AB gene, which encodes a seminal fluid protein that is transferred from males to females during mating. Using this mutant, we show that Acp29AB is required for the normal maintenance of sperm in storage. Consistent with this role, Acp29AB localizes to female sperm storage organs following mating, although it does not appear to associate tightly with sperm. Acp29AB is a predicted lectin, suggesting that sugar-protein interactions may be important for D. melanogaster sperm storage, much as they are in many mammals. Previous association studies have found an effect of Acp29AB genotype on a male's sperm competitive ability; our findings suggest that effects on sperm storage may underlie these differences in sperm competition. Moreover, Acp29AB's effects on sperm storage and sperm competition may explain previously documented evidence for positive selection on the Acp29AB locus.

No abstract

The egg-laying hormone ovulin (Acp26Aa) is among the most rapidly evolving proteins in the Drosophila genome. Against the background of ovulin's high sequence variability within and between species, we have identified highly conserved motifs that may play an important structural role. Using yeast two-hybrid and GST-pull-down assays, we show that ovulin interacts with itself. The C terminus of ovulin is necessary and sufficient for selfinteraction, with its C-terminal 45 aa playing a major role. Under nonreducing conditions, ovulin participates in a high-molecularmass complex, suggesting that it occurs in an oligomeric form. One or more of three predicted coiled-coil domains in the C terminus of ovulin may be involved in its self-interaction. These structural elements are conserved between species despite an overall rapid pace of evolution in ovulin's primary sequence. We therefore suggest that domains involved in ovulin's self-interaction form a conserved structural backbone for the protein, resulting in greater evolutionary flexibility at other sites.adaptive evolution ͉ conservation ͉ protein-protein interaction ͉ reproduction ͉ accessory gland proteins