Inheritance of a secondary sexual character in Drosophila silvestris.

Reciprocal crosses were carried out between laboratory stock specimens obtained from two races of Drosophila silvestris from the island of Hawaii that differ in a quantitative secondary sexual character. The race from the Hilo side of the island has a novel attribute, consisting of an extra row of cilia on the tibia of males, which is used during courtship. With regard to this character, sex-linked genes contribute about 30% of the difference, and the remaining 70% of the difference between the races is produced by genes on at least two autosomes. The novel character appears to have been the outcome of altered sexual selection in the Hilo-side race. In an altered genetic environment, resulting from a founder event or random genetic drift, sexual selection may take a new direction. Such a shift may serve as a model for incipient speciation.