Mecanismes de Communication NAM, URA-CNRS 1491, Bat 446, Universite Paris-Sud, 91405 Orsay, France,
Male courtship in Drosophila melanogaster, is composed of stereotypical behavioral sequences that depend upon the sensory stimulation exchanged by sexual partners. Chemical messages, or pheromones, are particularly important for mate recognition and discrimination. Both emission and perception of pheromones are genetically determined, and show substantial differences between the sexes.
It has been possible to modify both aspects of chemical communication by ectopically expressing the female cDNA of the sex-determination gene transformer (UAS-tra), in various cellular patterns (with different Gal4 strains). This approach allowed us to map the sexually dimorphic sites where the sex-pheromones are perceived and where they are produced. (1) Male flies feminized in a portion of their antennal lobes and/or in a portion of their mushroom bodies show bisexual orientation. It is possible that such mosaic flies are unable to discriminate male and female pheromones. (2) Male flies feminized in clusters of abdominal cells (the oenocytes) are only producing female pheromones and are stimulating other males to court them. We are currently studying how the variations of expression of the transgene UAS-tra during development can change these two phenotypes.
Although we have not noticed any obvious anatomical relationships between the cells controlling the perception and those controlling the production of chemical substances, we have found a first functional link between both aspects. Our data suggest that a male fly can change his chemical perception depending upon its own pheromonal bouquet: Males from strains of various geographical origin showing different predominant pheromones, particularly 7-pentacosene (7-P), exhibit different responses toward 7-P. The genetic factor(s)responsible for such a difference in chemical perception is currently being mapped.