Positive selection and the molecular evolution of a gene of male reproduction, Acp26Aa of Drosophila

The gene for a male ejaculatory protein, Acp26Aa, in four sibling species of the Drosophila melanogaster subgroup has previously been shown to have a nonsynonymous rate (K-a) of nucleotide substitution that is indistinguishable from the synonymous rate (K-s). By examining this gene in two other species of this subgroup, we found that K-a is generally large and can sometimes be more than twice as large as K-s. This suggests that positive selection may be operating at this locus of male reproduction.