On the evolution of Dopa decarboxylase (Ddc) and Drosophila systematics

We have sequenced most of the coding region of the gene Dopa decarboxylase (Ddc) in 24 fruitfly species. The Dde gene is quite informative about Droso phila phylogeny. Several outstanding issues in Drosophila phylogeny are res olved by analysis of the Dde sequences alone or in combination with three o ther genes, Sod, Adh, and Gpdh, The three species groups, melanogaster, obs cura, and willistoni, are each monophyletic and all three combined form a m onophyletic group, which corresponds to the subgenus Sophophora. The Sophop hora subgenus is the sister group to all other Drosophila subgenera (includ ing some named genera, previously considered outside the Drosophila genus, namely, Scaptomyza and Zaprionus, which are therefore downgraded to the cat egory of subgenus), The Hawaiian Drosophila and Scaptomyza are a monophylet ic group, which is the sister clade to the virilis and repleta groups of th e subgenus Drosophila. The subgenus Drosophila appears to be paraphyletic, although this is not definitely resolved. The two genera Scaptodrosophila a nd Chymomyza are older than the genus Drosophila. The data favor the hypoth esis that Chymomyza is older than Scaptodrosophila, although this issue is not definitely resolved. Molecular evolution is erratic. The rates of nucle otide substitution in 3rd codon position relative to positions 1 + 2 vary f rom one species lineage to another and from gene to gene.