Light-dependent pupation site preferences inDrosophila. II.Drosophila melanogaster andDrosophila simulans

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Abstract
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 F 1 individuals were tested. Progeny from the cross ofD. melanogaster females withD. 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 preference are highly specific, being restricted to the time just before pupation. During the first two larval instarsD. melanogaster is quite photopositive whileD. simulans is comparatively photoneutral. These differences in light-dependent behavior could aid in reducing competition between the two species.