Abstract
BackgroundSpecies 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.ResultsPhylogenetic 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.ConclusionThe 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.
Highlights
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
Species of the Drosophila obscura group (41 species assigned to six subgroups) are mostly inhabitants of temperate forest throughout the Holarctic region, with some can adapted into high-elevation temperate-like habitats in the Afrotropical, Neotropical and Oriental regions
Recent molecular phylogenetic studies [9,10,11,12,13] clearly support the monophyly of the obscura species group and recover several well-supported lineages, for example, the affinis, pseudoobscura, and subobscura subgroups, the D. ambigua triad (D. obscura, D. ambigua and D. tristis), give essential support to the monophyletic origin of the New World species, i.e., those of the affinis and pseudoobscura subgroups
Summary
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. Species of the Drosophila obscura group (41 species assigned to six subgroups) are mostly inhabitants of temperate forest throughout the Holarctic region, with some can adapted into high-elevation temperate-like habitats in the Afrotropical, Neotropical and Oriental regions Some of these species (e.g., D. pseudoobscura and its close relatives) have served as favorable models for evolutionary biology since the influential works of Dobzhansky and his colleagues in the 1930's [1,2]. The relationship among the Old World obscura, subobscura, microlabis, and sinobscura subgroups, and their relationship to the New World clade are still poorly resolved This phylogenetic predicament was partially ascribed to the "rapid radiation" history of the obscura group [10,12]. None of the previous phylogenetic studies has dealt with the obscura group as a whole: different studies employed different set of taxa, with species from the Afrotropical region (5 species) and Oriental region (8 described + 2 undescribed species) have rarely been investigated [14,15], probably due to the difficulty in collecting and/or culturing these poorly known taxa
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