The shaping of male courtship posture by lateralized gustatory inputs to male-specific interneurons.

BACKGROUND: Unilateral wing vibration to generate "love songs" is a hallmark of male courtship posture in Drosophila melanogaster. In contrast, males of some other Drosophila species extend both wings simultaneously during courtship. Thus, the patterns of wing movement vary among species and are under stringent genetic control, although there are few variations among individuals within a single species. These observations prompted the postulation that the proper wing display by courting males of D. melanogaster does not require sensory inputs. RESULTS: Here we show that when males of D. melanogaster are deprived of gustatory inputs mediated by the sensory neurons expressing the taste receptor gene Gr32a, a close relative to the pheromone receptor gene Gr68a, they often fail to perform unilateral wing extension during courtship because they become unable to keep a wing in the resting position while extending another wing. The tarsal amputation of a foreleg, but not other legs, increased the occurrence of simultaneous wing extension, indicating that Gr32a-expressing cells in this structure are involved in the regulation of courting posture. A similar simultaneous wing extension was also observed in males in which the putative pheromone-binding protein gene Obp57d was inactivated. The axons of Gr32a-expressing cells project to the subesophageal ganglion, where their terminals unilaterally contact mAL, which are male-specific fruitless (fru)-expressing interneurons that have bilateral branches. CONCLUSIONS: Our observations strongly suggest that gustatory pheromone inputs ensure the correct laterality of wing vibration that conforms to the species-specific behavioral pattern.

Behavioral analyses of mutants for two odorant-binding protein genes, Obp57d and Obp57e, in Drosophila melanogaster.

The odorant-binding protein (OBP) functions in chemosensation in insects. Two OBP genes, Obp57d and Obp57e, are involved in the evolution of the unique host-plant preference in Drosophila sechellia. Comparative analysis of the Obp57d/e genomic sequences in the Drosophila melanogaster species group has revealed that the rapid evolution of Obp57d and Obp57e has resulted in functional divergence between the two genes. Here, using D. melanogaster knockout strains generated by gene targeting, we examined the roles of Obp57d and Obp57e in behavioral response to a series of fatty acids. In the taste-based oviposition-site preference assay, the knockout flies showed stronger preference for acids than wild-type flies, indicating that the normal functions of Obp57d and Obp57e are associated with the suppression of positive preference for C6-C9 acids. Heterozygotes for each knockout haplotype also exhibited a significantly different behavioral response compared with wild-type flies, suggesting that Obp57d and Obp57e have a gene dosage effect on behavior. In contrast, the wild-type and knockout flies exhibited similar responses in the feeding assay and the odor-based free-walking assay, suggesting that the two OBPs' contribution to feeding and olfactory behaviors is small. Taken together, our results demonstrated that each of Obp57d and Obp57e in D. melanogaster contributes to the determination of reproductive sites, suggesting that the two OBP genes play an important role in ecological adaptation of Drosophila.