Phylogenetic relationships in Drosophila: a conflict between molecular and morphological data.

Grimaldi's recent cladistic classification of genera in the family Drosophilidae, based on adult morphological characters, is evaluated for those taxa for which alcohol dehydrogenase DNA sequences are also available. These data allow us to look at relationships of the Drosophila subgenera Sophophora and Drosophila with the Hawaiian Drosophila (Idiomyia) and with Scaptomyza, when Scaptodrosophila is used as an outgroup. The molecular data give strong support for the broad relationships hypothesized by Throckmorton, who contended that the subgenus Sophophora is a sister group to the remaining ingroup taxa. The Drosophila subgenus Engiscaptomyza, which Throckmorton regarded as intermediate between the Idiomyia (Hawaiian Drosophila) and Scaptomyza, is shown to be much more closely allied with Scaptomyza, in agreement with Grimaldi's results from adult morphology. The Hawaiian taxa, both Idiomyia and Scaptomyza, are firmly located as a sister group to the subgenus Drosophila, and these in turn all form a sister group to the subgenus Sophophora. Grimaldi's classification of these taxa is quite different and places the Hawaiian Drosophila (Idiomyia) as sister group to the remaining ingroup taxa (Scaptomyza and the subgenera Sophophora and Drosophila). Our results show that Grimaldi's new classification of these taxa results in paraphyletic groups, just as does the traditional classification under Throckmorton's interpretation of relationships. Additional data are required to produce a robust classification of this huge paraphyletic genus.