Sex in Drosophila mauritiana: A very high level of amino acid polymorphismin a male reproductive protein gene, Acp26Aa

Many genes pertaining to male reproductive functions have been shown to evo lve rapidly between species, and evidence increasingly suggest the influenc e of positive Darwinian selection. The accessory gland protein gene (Acp26A a) of Drosophila is one such example. In order to understand the mechanism of selection, it is often helpful to examine the pattern of polymorphism. W e report here that the level of amino acid polymorphism in the N-terminal q uarter of Acp26Aa is high in Drosophila melanogaster and is unprecedented i n its sibling species Drosophila mauritiana. We postulate that (1) this N-t erminal segment may play a role in sperm competition, and (2) D. mauritiana may have been under much more intense sexual selection than other species. Both postulates have important ramifications and deserve to be tested rigo rously.