SEXUAL INTERACTIONS BETWEEN 2 DISTANTLY RELATED DROSOPHILA SPECIES, DROSOPHILA-MELANOGASTER AND D-WILLISTONI (DIPTERA, DROSOPHILIDAE)

Molecular analysis suggests that the pomace fly Drosophila melanogaste r acquired the P family of transposable elements from another-Drosophi la species, D. willistoni. Since the two species are distantly related , it has been assumed that transmission of P element DNA from D. willi stoni to D. melanogaster was mediated by a vector. The possibility of an alternative mode of transmission was assessed by characterizing the sexual behaviors of D. willistoni males and females, then observing D . willistoni and D. melanogaster males and females to see whether male s from one species interacted sexually with females from the other spe cies in a laboratory setting. We observed that D. melanogaster males c ourt D. willistoni females vigorously and, in some cases, stimulate th e females to be receptive to copulation. However, D. willistoni males perform relatively little courtship in response to D. melanogaster fem ales and do not attempt to copulate. Thus, it is unlikely that sexual interactions effected the transmission of P element DNA from D. willis toni to D. melanogaster in the flies' natural habitat.