Interspecific variation in sex-specific gustatory organs in Drosophila.

Drosophila males use leg gustatory bristles to discriminate between male and female cuticular pheromones as an important part of courtship behavior. In Drosophila melanogaster, several male-specific gustatory bristles are present on the anterior surface of the first tarsal segment of the prothoracic leg, in addition to a larger set of gustatory bristles found in both sexes. These bristles are thought to be specialized for pheromone detection. Here, we report the number and location of sex-specific gustatory bristles in 27 other Drosophila species. Although some species have a pattern similar to D. melanogaster, others lack anterior male-specific bristles but have many dorsal male-specific gustatory bristles instead. Some species have both anterior and dorsal male-specific bristles, while others lack sexual dimorphism entirely. In several distantly related species, the number of gustatory bristles is much greater in males than in females due to a male-specific transformation of ancestrally mechanosensory bristles to a chemosensory identity. This variation in the extent and pattern of sexual dimorphism may affect the formation and function of neuronal circuits that control Drosophila courtship and contribute to the evolution of mating behavior.