| Abstract: | Sexual isolation between two species of the Drosophila auraria complex, D. auraria and D. triauraria is different in darkness and light. In darkness there is complete isolation while in light it is only partial. The sensory bases of these differences were investigated by behavioral studies in darkness and light. In darkness there was no normal courtship sequence but males of both species displayed attempted copulation to homospecific and heterospecific females, as well as homospecific males. After a few hours together, homospecific copulations were observed after females displayed a characteristic posture: spreading the wings. Such an acceptance posture, also observed in other Drosophila species, was probably released by the wing vibration of a homospecific male. In light, visual signals alone are able to elicit male's orientation and following, whether flies are housed together or physically separated. Intense homosexual courtships were observed. All these data suggest that males have a low discrimination ability and females play the main role in sexual isolation. |
