Description of a New Allopatric Sibling Species of Hawaiian Picture-Winged Drosophila

Abstract

A new picture-winged Hawaiian Drosophila species from the islands of Kaua'i and O'ahu that is morphologically indistinguishable from Drosophila grimshawi Oldenberg from the Maui Nui islands is described, based on differentiation in ecological, behavioral, cytological, and molecular characters as well as ultrastructural features of the chorion. The new species, D. craddockae, and D. grimshawi represent the first clear case of an allopatric sibling species pair among Hawaiian Drosophilidae (i.e., there is strong evidence for a profound set of intrinsic, genetically determined differences that are not easily diagnosable by the usual morphological methods). Ecologically, D. craddockae is a strict specialist, with oviposition restricted to the decaying bark of Wikstroemia. Drosophila grimshawi, on the other hand, is a generalist that breeds in the decaying parts of 10 families of plants. Data from cytological, behavioral, and molecular analyses are consistent with the geological evidence that species on the older islands are usually more ancestral than those that evolved on the younger islands. Thus, although long-standing ecological theory states that specialization is a derived condition, the biological and genetic evidence all indicate that specialism in D. craddockae is the ancestral condition and that generalism evolved in D. grimshawi on Maui Nui as a derived trait.