Isozymes and genetic divergence in the nasuta-albomicans complex of Drosophila

The nasuta-albomicans complex is a hybrid-zoned artificially created in the environs of the laboratory 1 . The members of this complex include D. nasuta, D. albomicans and a number of Cytoraces. The Cytoraces are the products of hybridization between D. nasuta and D. albomicans and have been maintained in the laboratory for 350 to 500 generations 2 . The degree of genetic diversity encompassed by the parental races and the four Cytoraces at eleven isozymal loci has revealed the existence of 122 alleles with 52 alleles being common to all the six races, 70 being shared by at least two races and 9 alleles being unique to one of the races. Based on our study, the divergence time between the parental races, D. nasuta and D. albomicans, is 264,000 years, which is the least divergence time so far postulated between these two chromosomal races from studies with different parameters. On the other hand, the Cytoraces, which are of recent origin, have accumulated extensive genetic variation within a span of 15 years, in comparison with the parental forms. These findings are discussed with reference to the critical role of hybridization in raciation