Adaptive Radiation in the Hawaiian Drosophila (Diptera: Drosophilidae): Ecological and Reproductive Character Analyses

The entomologist R. C. L. Perkins pioneered observations of breeding site ecology for the endemic Hawaiian Drosophilidae, a renowned group of flies that has undergone explosive speciation and adaptive radiation into a wide variety of breeding niches. Females of the various species groups and subgroups oviposit their eggs in either fungi, flowers, fruits, leaves, stems, bark, sap fluxes, or other novel substrates. Varied selective forces in these alternative breeding sites have apparently molded female reproductive characters and strategies into diverse outcomes; some species mature and oviposit only one egg at a time, whereas others oviposit hundreds. Here, we have analyzed the pattern of shifts in breeding substrate, and the associated evolution of selected ovarian, egg, and ovipositor traits, by mapping the various ecological and female reproductive character states on an independently derived phylogenetic hypothesis based on nuclear and mitochondrial DNA sequences. This comparative phylogenetic approach demonstrates a number of strong historical associations among female reproductive traits and between particular traits and the breeding substrate, although the overall pattern is complex and more data are needed. Identification of certain apomorphic traits associated with shifts in breeding substrate suggests an adaptational origin for some of the changes in egg load per fly, in the length of the respiratory filaments of the egg, and in the length and shape of the ovipositor. Although these hypotheses need further testing, it appears that the ecological diversification in breeding substrates has been an integral component in the radiation of drosophilids in Hawai'i

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

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

Effects of microclimatic changes on oogenesis of Drosophila mimica

Reports were scanned in black and white at a resolution of 600 dots per inch and were converted to text using Adobe Paper Capture Plug-in.The reproductive mode of Drosophila mimica, a species endemic to the island of Hawaii, was determined by analyzing the ovarian development of three natural populations during a nine month period. Qualitatively the developmental profile of the ovaries remained the same in all the populations and for the entire collecting period. Each developmental stage was represented only in a fraction of the ovarioles, and mature eggs were usually found in half of the ovarioles. Quantitative differences were found between populations and between collections and these differences were correlated with the environmental conditions. The relative humidity was found to be the most important factor in regulating ovarian development by interrupting the growth of oocytes at the stage of RNA-yolk synthesis. A seven day period of constant low relative humidity causes the degeneration of grown oocytes, while a constant high humidity for the same period of time reinitiates normal development. This mechanism serves as a device to assure the presence of not more than one mature egg per ovariole, and thus prevents the overpopulation of the natural breeding substrates after environmental stresses. The adaptive significance and the theoretical implications of such behavior were discussed.It is my pleasure to express my deepest gratitude to Professors D. Elmo Hardy and Hampton L. Carson for supporting, organizing and providing laboratory facilities at the University of Hawaii where this work was carried out. I am in debt to Dr. Garrett A. Smathers for accumulating the meteorological data, to Mr. Ken Kaneshiro for his assistance in specimen identification and to Mr. A. Kuniyuki for technical assistance. The hospitality and cooperation from the administration of the Headquarters of the Hawaii Volcanoes National Park was much appreciated. I am also grateful to Professor William B. Heed for his stimulating discussions during the progress of this work

IN VITRO DEVELOPMENT OF INSECT TISSUES. I. A MACROMOLECULAR FACTOR PREREQUISITE FOR SILKWORM SPERMATOGENESIS

Volume: 141Start Page: 527End Page: 54

IN VITRO DEVELOPMENT OF INSECT TISSUES. II. THE ROLE OF ECDYSONE IN THE SPERMATOGENESIS OF SILKWORMS

Volume: 141Start Page: 541End Page: 55