GENETIC POLYMORPHISM AND PHYLOGENY OF DROSOPHILA SUBOBSCURA.

Abstract

The genus Drosophila consists of more than 1,200 species which have arisen through several evolutionary radiations. One major radiation includes the subgenus Sophophora which comprises the melanogaster lineage evolved in the Old World tropics, the saltans-willistoni lineages in the New World tropics, and the obscura group distributed throughout the temperate zone of the northern hemisphere. According to Throckmorton (1975) the obscura group may have originated from a protomelanogaster lineage of the Old World tropics. After adaptation to temperate habitats, the obscura group diversified and eventually spread to North America prior to midMiocene times (i.e., more than 15 million years ago). Several species of the group have been the subject of intensive evolutionary and genetic studies. Lakovaara et al. (1972a,b) have attempted to reconstruct the phylogeny of the group on the basis of electrophoretic studies of gene frequencies. Among the Old World species of the obscura group, D. subobscura is particularly interesting. The species exhibits a considerable degree of chromosomal polymorphism that has been the subject of numerous studies (Goldschmidt, 1956; Knight, 1961; Sperlich, 1961, 1964; Pentzos-Daponte, 1964; Krimbas, 1964, 1971; Prevosti, 1966; G6tz, 1967; Andjelkovic and Sperlich, 1973; Zouros and Krimbas, 1973; and others). Recently, genetic variation has been studied in D. subobscura using electrophoretic methods. Particularly noteworthy is the work of Lakovaara, Saura, and their co-workers, who examined 32 gene loci coding for proteins in one study of geographically marginal populations (Lakovaara and Saura, 1971a) and 20 gene loci in a study of some central as well as marginal populations (Saura et al., 1973). The present paper reports the results of a study of 28 gene loci coding for proteins in a large sample of D. subobscura flies from Fruska gora, Yugoslavia. This is the first extensive electrophoretic survey of a D. subobscura population from southeast Europe (a region extensively studied with respect to chromosomal polymorphism) and of a population which is continental (more than 100 km from the sea). We have also made direct comparisons in the same electrophoretic gels between D. subobscura and the North American species D. pseudoobscura and D. persimilis. Thus, we have established the equivalence between the allelic designations used for a variety of obscura group species by Lakovaara and co-workers, and the designations used by American researchers working on D. pseudoobscura and its close relatives (e.g. Prakash, Lewontin, and Hubby, 1969). This equivalence has made it possible to estimate the genetic distance among several species of the obscura group in which the same protein loci have been studied by different workers.