Abstract
Hybridization tests among the available strains of three sibling species of the D. kikkawai complex were performed. All cases of intraspecific crosses were successful. All interspecific crosses involving D. bocki were completely unsuccessful; however, interspecific crosses between D. kikkawai and D. leontia in mass mating involving as many as 20-30 pairs in most cases were successful, producing variable numbers of F1 offspring. Fertility tests of F1 progeny revealed that the F1 males were completely sterile while the F1 females were fertile when backcrossed to the males of parental types, yielding considerable numbers of offspring. The data suggest that D. bocki is the most genetically isolated, although all are morphologically indistinguishable. D. bocki and D. leontia are found existing sympatrically. Although D. kikkawai and D. leontia are occurring sympatrically, the former species has so far not been found to coexist with D. bocki. D. kikkawai and D. leontia differ in gene sequences in chromosome 2L, 2R and 3L and most extensively in the X chromosome. Nevertheless, chromosomes 3R and 4 do not show any differences in gene order among the species. D. kikkawai is polymorphic for a sequence (3LB) which appears to be fixed in D. leontia, indicating that they have diverged recently from a common ancestor.
