Evolution of theDrosophila obscuraSpecies Group Inferred from theGpdhandSodGenes

Abstract

TheDrosophila obscuragroup consists of several dozen Nearctic and Palearctic species, with a phylogeny that remains largely unresolved in spite of numerous morphological, cytogenetic, and molecular investigations. We have partially sequenced two genes,Gpdh(about 1000 bp) andSod(about 700 bp) in 12–13 species and 1 subspecies in order to settle the issues. Difficulties in resolving the phylogeny emanate from the rapid sequence of successive radiations. Nevertheless, the following conclusions are warranted: (1) The Palearctic species include two monophyletic subgroups,subobscura(which may be the most ancient clade of the whole group) andobscura,plus two other species with unresolved phylogenetic positions,D. bifasciataandD. subsilvestris;(2) the Nearctic species form a monophyletic group consisting of two monophyletic sister clades, theaffinissubgroup and thepseudoobscurasubgroup. The Palearctic radiation may have resulted from adaptation to expanding temperate forests in the Old World. A second radiation occurred during the colonization of the deciduous forests of the New World by the descendants of a single lineage that soon split into theaffinisandpseudoobscurasubgroups.