GENETIC VARIATION IN HAWAIIAN DROSOPHILA. V. CHROMOSOMAL AND ALLOZYMIC DIVERSITY IN DROSOPHILA SILVESTRIS AND ITS HOMOSEQUENTIAL SPECIES

The evolutionary differentiation of populations and of species depends upon the existence of genetic variation in nature. How much of this variation contributes to the differentiation process at each level is questionable (Ayala, 1975), as is the precise nature of the genes involved, especially at the speciation step. In the final analysis, all new species derive from a divergent population of an ancestral species. Differentiation of populations can thus be considered as an early stage of species formation. Any analysis of the genetics of speciation must take into account the degree of differentiation achieved at the intraspecific level. Only then can we ascertain what proportion of the total interspecific differentiation is directly attributable to the actual speciation event. For studies of the speciation process, the Hawaiian Drosophila represent an ideal group of organisms, comprising some 700 endemic species which are well differentiated morphologically, ecologically and behaviorally (Carson et al., 1970). These species evolved in recent geological time via adaptive radiation throughout the several islands of the Hawaiian Archipelago. One important feature is that we can place upper limits on the ages of species (almost all are single-island endemics) on the basis of estimates of the time elapsed since the volcanic origin of