The Wilhelmine E. Key 1996 Invitational Lecture. Sexual selection: a driver of genetic change in Hawaiian Drosophila

Within the last five million years, the Hawaiian archipelago has successively added 14, spaced, subaerial volcanoes at its southeast end. Each has received endemic terrestrial colonists; established populations appear to stem mainly from the immediately adjacent older island. Chromosome markers were used to trace the evolution of a phylad of 106 unique and closely related Drosophila species. With one exception, each species is restricted to one of the four groups of islands; 57 species appear to be restricted to single volcanoes. Founding of new populations across each of the three major oceanic channels appears to be infrequent. Genetic and morphological analysis suggests that each founding event has resulted in a newly organized, highly specific gene pool, not simply a transplanted colony of the source species. Progressive volcanic forces have thus provided an instructive spatiotemporal environment for the formation of new species. In Drosophila genetic change involves primarily spectacular premating sexual behavior, marked by novel male characters that appear to have evolved under the driving force of sexual selection. Permanent genetic changes in reproductive biology are thus elicited by selection for intrademe Darwinian fitness of individuals and are not the result of ad hoc selection for interpopulation reproductive isolation. The facts reinforce the view that reproductive isolation from other species is largely an incidental by-product of selection imposed by both the ambient and sexual environments in local populations.