Phylogeny of the Island Populations of the HawaiianDrosophila grimshawiComplex: Evidence from Combined Data

The picture-winged speciesDrosophila grimshawiis unique among HawaiianDrosophilain its wide geographic range, having populations on several islands of the Hawaiian archipelago. This distribution contrasts with the pattern of single-island endemism observed in most of the picture-winged group; significantly, it does not concur with predictions of the founder theory, where speciation is the typical outcome of founder events involving colonization of a new island. To examine this anomalous situation, we have taken a phylogenetic approach in an attempt to resolve the relationships among taxa and decipher the most probable colonization scenario. We have obtained both morphological and molecular data for all theD. grimshawipopulations as well as the closely related speciesD. pullipes,and two outgroup species, using scanning electron microscopy to score ultrastructural features of the chorion or eggshell, and PCR amplification and nucleotide sequencing to acquire sequence data onYp1,one of the threeYolk proteingenes. In addition, we have used available data on Yolk Protein electrophoretic pattern and jousting, oviposition, and mating behavioral characters. Analyses of these data sets, either individually or in combination, indicate that there are two separate and ecologically distinct clades within this species complex. One clade includes the Kauai and Oahu populations ofgrimshawi,as well as the closely related speciesD. pullipesfrom Hawaii, all of which are classified as ecological specialists with respect to their oviposition and breeding substrate. The other clade includes all the ecologically generalistgrimshawipopulations of the Maui Nui island complex. The phylogenetic results do not concur with the previously proposed hypothesis thatD. pullipesoriginated from a founder derived from the Maui Nui complex and further suggest that these taxa are in need of taxonomic revision.