Courtship behaviour of Drosophila melanogaster revisited
Résumé
Nearly all studies of Drosophila melanogaster courtship have focused exclusively on male behaviour. Female precopulatory behaviour is often relegated to ‘accept' or ‘reject' mating, and how female behaviour interacts with that of males remains largely unknown. Using a video-computing approach, we measured 10 behavioural states and 22 elementary behaviours that occur during the precopulatory phase of Canton-S (Cs) flies. Male and female behaviours were studied under a variety of social conditions. This allowed us to identify which one(s) is relevant to courtship or to general activity. Our analysis showed that the courtship repertoire was not constant over time, as female and male behaviours varied during courtship, and that virgin Cs females showed several behavioural sequences whose frequency, latency and total duration could predict their mating success. The most striking index of females' willingness to copulate was the way they extruded the ovipositor: a partial extrusion stimulated male courtship, whereas total extrusion inhibited it. Furthermore, females that mated preened their abdomen more frequently than did females that did not mate. We also observed that male sexual activity was strongly increased when the female emitted a tiny volatile droplet at the tip of the ovipositor. We hypothesized that partial ovipositor extrusion, droplet emission and abdominal preening are related behaviours that result in the active dispersion of compounds spread on the female's abdomen. Such a detailed picture of the precopulatory behaviours should allow better characterization of the sensory stimuli exchanged during courtship in Drosophila.