Molecular phylogeny and divergence times of drosophilid species

The phylogenetic relationships and divergence times of 39 drosophilidspecies were studied by using the coding region of the Adh gene. Fourgenera--Scaptodrosophila, Zaprionus, Drosophila, and Scaptomyza (fromHawaii)--and three Drosophila subgenera--Drosophila, Engiscaptomyza, andSophophora--were included. After conducting statistical analyses of thenucleotide sequences of the Adh, Adhr (Adh-related gene), and nuclear rRNAgenes and a 905-bp segment of mitochondrial DNA, we used Scaptodrosophilaas the outgroup. The phylogenetic tree obtained showed that the first majordivision of drosophilid species occurs between subgenus Sophophora (genusDrosophila) and the group including subgenera Drosophila and Engiscaptomyzaplus the genera Zaprionus and Scaptomyza. Subgenus Sophophora is thendivided into D. willistoni and the clade of D. obscura and D. melanogasterspecies groups. In the other major drosophilid group, Zaprionus firstseparates from the other species, and then D. immigrans leaves theremaining group of species. This remaining group then splits into the D.repleta group and the Hawaiian drosophilid cluster (Hawaiian Drosophila,Engiscaptomyza, and Scaptomyza). Engiscaptomyza and Scaptomyza are tightlyclustered. Each of the D. repleta, D. obscura, and D. melanogaster groupsis monophyletic. The splitting of subgenera Drosophila and Sophophoraapparently occurred about 40 Mya, whereas the D. repleta group and theHawaiian drosophilid cluster separated about 32 Mya. By contrast, thesplitting of Engiscaptomyza and Scaptomyza occurred only about 11 Mya,suggesting that Scaptomyza experienced a rapid morphological evolution. TheD. obscura and D. melanogaster groups apparently diverged about 25 Mya.Many of the D. repleta group species studied here have two functional Adhgenes (Adh-1 and Adh-2), and these duplicated genes can be explained by twoduplication events.