Genetical Processes of Evolution on High Oceanic Islands

The Hawaiian Drosophila project has been in progress for 20 years. Recently, emphasis has been placed on studies of genetic variability in natural populations. The data generated are of extraordinary interest for understanding the genetic basis of evolution. The findings are relevant not only to islands forms but also to species in continental ecosystems. Chromosomal, electrophoretic and morphometric studies of specimens from local populations (demes) of island species have shown them generally to be as rich in genetic variability as demes of widespread continental species. The main difference between continntal and insular species is that the latter have smaller total population sizes insular species have fewer demes. On high volcanic islands, the most striking mode of speciation is through one or a few inter-island or inter-volcano founders. The case of Drosophila silvestris from the island of Hawaii is presented. Enforced isolation appears to foster genetic divergence. An unexpected results is that the founder effect does not drasticaly reduce genetic variablity. Rather, it appears to induce a shift in the polygenic heterozygous balances that underlie the genetics of quantitative characters, especially those dealing with mating behavior.In view of these findings, the well-known exuberance of novel adaptations and species observed on isolated oceanic islands is understandable.