DIFFERENT FORCES DRIVE THE EVOLUTION OF THE ACP26AA AND ACP26AB ACCESSORY-GLAND GENES IN THE DROSOPHILA-MELANOGASTER SPECIES COMPLEX

The Acp26Aa and Acp26Ab genes that code for male accessory gland prote ins are tandemly arranged in the species of the Drosophila melanogaste r complex. An similar to 1.6-kb region encompassing both genes has bee n sequenced in 10, 24, and 18 lines from Spain, Ivory Coast, and Malaw i, respectively; the previously studied 10 lines from North Carolina h ave also been included in the analyses. A total of 110 nucleotide and 4 length polymorphisms were detected. Silent variation for the whole A cp26A region was slightly higher in African than in non-African popula tions, while for both genes nonsynonymous variation was similar in all populations studied. Based on F-st estimates no major genetic differe ntiation was detected between East and West Africa, while in general n on-African populations were strongly differentiated from both African populations. Comparison of polymorphism and divergence at synonymous a nd nonsynonymous sites revealed that directional selection acting on a mino acid replacement changes has driven the evolution of the Acp26Aa protein in the last 2.5 myr.