Light-dependent pupation site preferences in Drosophila. II. Drosophila melanogaster and Drosophila simulans.

Drosophila melanogaster prefers to pupate in the dark, while its sibling species, D. simulans, prefers the light when the species are tested in isolation and when cultured and tested together. Reciprocal interspecific hybridizations were carried out and the F1 individuals were tested. Progeny from the cross of D. melanogaster females with D. simulans males chose pupations sites exactly intermediate between those of the two parental species, while the reciprocal-cross offspring preferred light pupation sites. The pupation site preferences (PSPs) of the hybrids are compatible with a sex-linked locus or loci influencing light-dependent PSP in this pair of species. Examination of light preferences of larvae prior to the late third instar demonstrates that these preferences are highly specific, being restricted to the time just before pupation. During the first two larval instars D. melanogaster is quite photopositive while D. simulans is comparatively photoneutral. These differences in light-dependent behaviour could aid in reducing competition between the two species.