Genetic-Basis Of Reduced Eyes In The Hybrids Of Drosophila-Virilis Phylad Species

Structural anomalies were detected in F1 and backcross hybrids of Drosophila virilis and three of its sibling species Drosophila novamexicana, Drosophila americana texana and Drosophila americana americana. Similar but not identical anomalies have been described in D. virilis x D. lummei hybrids. F1 (D. virilis x D. novamexicana) hybrids had only slight disorders in the abdominal cuticula, but 5.3 % of the first backcross generation hybrids had reduced eyes. Eye defects in the second generation were due to interaction of the heterozygous fourth chromosome of D. novamexicana with the homozygous D. virilis chromosomes 2 and 3. Reciprocal F1 hybrids between D. virilis and D. a. americana and between D. virilis and D. a. texana had normal eyes, but in the second hybrid generation 4.9 % of D. virilis x D. a. americana and 1.6 % of D. virilis x D. a. texana hybrids had anomalous eyes. In D. virilis x D. a. texana hybrids, the heterozygous fourth chromosome of D. a. texana was incompatible with homozygous D. virilis chromosomes 2 and 3. Of the D. virilis x D. a. americana hybrids homozygous for D. virilis chromosomes 2 and 3, 10.2 % had the eye defect. The incompatibility system of non-conspecific chromosomes causing the eye anomalies in the hybrids of these three species pairs was different from those in D. virilis x D. lummei hybrids and has evolved independently after the diverging of the American lineage from D. lummei.