DIFFERENCE IN PHOTO-PREFERENCES AS A CAUSE OF COEXISTENCE OF DROSOPHILA SIMULANS AND D. MELANOGASTER IN NATURE

Abstract

Photo-preferences of the sibling species D. simulans and D. melanogaster were studied using an apparatus and population cage having a gradient of light intensities. D. simulans preferred to stay and to lay eggs at light places; D. melanogaster did not show such a strong light preference. Selections of eggs in the light gradient cages made it possible to segregate a mixed species population into different species populations; selection for photo-positive flies soon eliminated D. melanogaster, and selection for photo-negative or photo-neutral flies finally eliminated D. simulans. The difference of the photo-preference seems to be a cause of coexistence of the sibling species in nature.