MOLECULAR EVOLUTION OF A DUPLICATION - THE SEX-PEPTIDE (ACP70A) GENE REGION OF DROSOPHILA-SUBOBSCURA AND DROSOPHILA-MADEIRENSIS

In Drosophila melanogaster; the Acp70A gene, which is involved in the postmating reactions of the female, is a single-copy gene. However, in Drosophila subobscura, the gene is duplicated and both copies are tra nscribed. To study the molecular evolution of the duplication, a 2.1-k b fragment encompassing both copies of the duplication was sequenced f or 10 lines of D, subobscura and one line of Drosophila madeirensis. E stimates of the divergence between the two copies of the duplicated re gion and between the two species studied, D. subobscura and D. madeire nsis, revealed that both copies of the Acp70A gene had evolved indepen dently since their duplication. The ratio of nonsynonymous to silent d ivergence between copies was generally higher than one. The McDonald a nd Kreitman test revealed an excess of nonsynonymous changes fixed sin ce the duplication and before the split of the D. subobscura and D. ma deirensis lineages. These results point to natural selection driving p rotein evolution after the duplication. Specifically, adaptive evoluti on appears to have caused the initial differentiation between copies o f the N-terminal parts: of the proteins, while purifying selection cou ld be responsible for the high conservation of the C-terminal parts.