GENETIC VARIATION IN A COURTSHIP-RELATED MALE CHARACTER IN DROSOPHILA SILVESTRIS FROM A SINGLE HAWAIIAN LOCALITY

The large Drosophila species of Hawaii display sexual dimorphism and elaborate species-specific courtship patterns. Male characters related to courtship attract particular attention since they frequently constitute the most conspicuous taxonomic differences between Hawaiian species. The present study concerns intraspecific genetic variation in a courtship-related male character. D. silvestris, endemic to the geologically new volcanoes of Hawaii island, displays a brush of large dorsal cilia on the tibia of the foreleg of the male fly. This is used to stimulate the female during courtship. Genetic variation between local populations has previously been shown to exist for both sexual behavior and cilia number. The present paper reports the results of a study of cilia number variation in males collected at a single site over the period 1976-1980. Male progeny of females captured in nature were also studied. The mean number of cilia in the natural population was stable except for 1979 when it rose significantly, falling back again in 1980. The data indicate the existence of ample genetic variance for this character, existing as a balanced polymorphism in the natural population. The character appears to be under stabilizing selection. It is hypothesized that sexual selection is a contributing factor.