Journal of the Marine Biological Association of India

Volume 15 Issue 1

Evolution of the Hawaiian Drosophilidae (Insecta : Diptera).

D. Elmo Hardy

It is a well known fact that evolution has proceeded at an accelerated pace on various oceanic islands and the rich faunas of some of these islands offer unusual opportunities for evolutionary research. Because of special attributes some groups of Diptera are ideal for obtaining information concering evolutionary processess and speciation rates. In the Hawaiian Islands the family Drosophilidae is especially well suited for such studies.

The dipterous family Drosophilidae is most remarkably developed in Hawaii and represents one of the most striking examples of "explosive" evolution known in animal kingdom. We have now described approximately 500 species (97% endemic) and estimate that the total fauna may number 700 species. The Hawaiian species are unique among drosophilids in many different ways. They have structural peculiarities and picturesque wing markings which are extraordinarily diverse. They exhibit striking sexual dimorphism and elaborate courtship and mating behavior, including lek behaviour in the males. They have radiated into a great variety of habitats and their food and breeding requirements differ from those of species from other areas of the world. The fauna exhibits a high degree of endemicity by islands. It appears probable that 90-95 per cent of the species are restricted to single islands.

This amazing fauna has been under intensive study since 1963 by a team of about 20 senior scientists and over 100 assistants attempting to unravel some of the complexities in the extraordinary evolution of this group. These investigations have been aimed at determining the factors responsible for the evolution of such' a large number of species in these islands, why they have developed such an array and diversity of morphological and biological characteristics, why this adaptive radiation has occurred at such a rapid rate, the possible time required for speciation, the pattern of evolutionary development and spread of species and groups over the islands, and probable numbers of progenator species and their possible home land.

We have now determined the most primative, ancestoral type, species in the genus Drosophila and have traced the evolutionary paths of various groups from the oldest island (Kauai, ca 8-10,000,000) to the youngest island (Hawaii, ca 800,000 years and still volcanically active) and have documented the Founder Principal.

Evolutionary data have been obtained by the following types of studies: cytogenetics, hybridization, courtship and mating behaviour, ecology, biology, external and internal morphology, nutrition biochemistry, and ovarian transplantation. The results of these studies will provide a better understanding of evolutionary process under insular conditions and will have world wide application.

Date : 31-08-1973