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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. [ABSTRACT FROM AUTHOR]

Male ornaments and other sex‐specific traits present some of the most dramatic examples of evolutionary innovations. Comparative studies of similar but independently evolved traits are particularly important for identifying repeated patterns in the evolution of these traits. Male‐specific modifications of the front legs have evolved repeatedly in Drosophilidae and other Diptera. The best understood of these novel structures is the sex comb of Drosophila melanogaster and its close relatives. Here, we examine the evolution of another male foreleg modification, the sex brush, found in the distantly related Drosophila immigrans species group. Similar to the sex comb, we find that the origin of the sex brush correlates with novel, spatially restricted expression of the doublesex (dsx) transcription factor, the primary effector of the Drosophila sex determination pathway. The diversity of Dsx expression patterns in the immigrans species group closely reflects the differences in the presence, position, and size of the sex brush. Together with previous work on sex comb evolution, these observations suggest that tissue‐specific activation of dsx expression may be a common mechanism responsible for the evolution of sexual dimorphism and particularly for the origin of novel male‐specific ornaments. [ABSTRACT FROM AUTHOR]