Relationships in the Drosophila obscura species group, inferred from mitochondrial cytochrome oxidase II sequences

We compare the sequences for the mitochondrial cytochrome oxidase II geneof 13 species of the Drosophila obscura group. The survey includes sixmembers of the D. affinis subgroup, four of the D. pseudoobscura subgroup,and three of the D. obscura subgroup. In all species, the gene is 688nucleotides in length, encoding a protein of 229 amino acids plus the firstposition T of the stop codon. The sequences show the typicalhigh-transition bias for closely related species, but that bias isessentially eliminated for species pairs of > 5% sequence divergence.The phylogenetic relationships in the species group are inferred using bothneighbor-joining and maximum parsimony. The two procedures give comparableresults, showing that the D. affinis and D. pseudoobscura subgroups aremonophyletic groupings that appear to have closer affinities to one anotherthan either has to the D. obscura subgroup. We use transversion distancesto estimate times of divergence, on the basis of three different estimatesof the time of separation of the D. obscura species group from the D.melanogaster group. If that event occurred 35 Mya, then we can estimate theorigin of the nearctic forms at approximately 22 Mya and the separation ofthe D. affinis and D. pseudoobscura subgroups at approximately 17 Mya.