title: Molecular phylogeny of the Drosophila obscura species group, with emphasis on the Old World species.
abstract: BACKGROUND
  Species of the Drosophila obscura species group (e.g., D. pseudoobscura, D. subobscura) have served as favorable models in evolutionary studies since the 1930's. Despite numbers of studies conducted with varied types of data, the basal phylogeny in this group is still controversial, presumably owing to not only the hypothetical 'rapid radiation' history of this group, but also limited taxon sampling from the Old World (esp. the Oriental and Afrotropical regions). Here we reconstruct the phylogeny of this group by using sequence data from 6 loci of 21 species (including 16 Old World ones) covering all the 6 subgroups of this group, estimate the divergence times among lineages, and statistically test the 'rapid radiation' hypothesis.
  
  
  RESULTS
  Phylogenetic analyses indicate that each of the subobscura, sinobscura, affinis, and pseudoobscura subgroups is monophyletic. The subobscura and microlabis subgroups form the basal clade in the obscura group. Partial species of the obscura subgroup (the D. ambigua/D. obscura/D. tristis triad plus the D. subsilvestris/D. dianensis pair) forms a monophyletic group which appears to be most closely related to the sinobscura subgroup. The remaining basal relationships in the obscura group are not resolved by the present study. Divergence times on a ML tree based on mtDNA data are estimated with a calibration of 30-35 Mya for the divergence between the obscura and melanogaster groups. The result suggests that at least half of the current major lineages of the obscura group originated by the mid-Miocene time (~15 Mya), a time of the last developing and fragmentation of the temperate forest in North Hemisphere.
  
  
  CONCLUSIONS
  The obscura group began to diversify rapidly before invading into the New World. The subobscura and microlabis subgroups form the basal clade in this group. The obscura subgroup is paraphyletic. Partial members of this subgroup (D. ambigua, D. obscura, D. tristis, D. subsilvestris, and D. dianensis) form a monophyletic group which appears to be most closely related to the sinobscura subgroup.
authors.affiliation: Laboratory for Conservation and Utilization of Bio-resources, Yunnan University, Kunming, Yunnan, China. gao-leyun@263.net <gao-leyun@263.net>
authors.forename: Jian-jun
authors.initials: JJ
authors.lastname: Gao
authors.forename: Hide-aki
authors.initials: HA
authors.lastname: Watabe
authors.forename: Tadashi
authors.initials: T
authors.lastname: Aotsuka
authors.forename: Jun-feng
authors.initials: JF
authors.lastname: Pang
authors.forename: Ya-ping
authors.initials: YP
authors.lastname: Zhang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004272:DNA, Mitochondrial; D004330:Drosophila / Q000145:classification / Q000235:genetics*; D019143:Evolution, Molecular; D017344:Genes, Insect; D049810:Genetic Speciation; D014644:Genetic Variation; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D004272:DNA, Mitochondrial