MATING OF EBONY VESTIGIAL AND WILD TYPEDROSOPHILA MELANOGASTERIN LIGHT AND DARK

Abstract

Many observers have shown that there are sufficient differences in mating behavior between mostspecies of Drosophila to prevent transspecific matings under natural conditions or at least to reduce them to an extreme rarity (Dobzhansky, Mayr, Spieth, Stalker, Wallace and others). In most cases it is the female that refuses to take part in the courtship, the male being prepared to court with almost anything. That this is not always the case has been shown by Miller (1950) who observed that males of the species Drosophila affinis and Drosophila algonquin courted females of the same species more readily and more persistently than those of the other. Some studies have been made of differences in mating behavior between members of the same species. In recent years Mather 'and Harrison (1949) have demonstrated mating preferences between highly selected lines of D. melanogaster; Rendel (1945) showed that in Drosophila subobscura yellow males are distasteful to females that are not yellow, though yellow females mated normally. Merrell (1949) showed that yellow males in D. melanogaster appeared to behave similarly to yellow males in D. subobscura, and that cut females were not readily mated by any sort of male. It is 'not always possible in the earlier work to distinguish between a specific mating preference and an indirect effect of general vigor. For example, in competition with normal males, yellow-white males, because of their inferior all-round vitality, would inseminate relatively few females no matter what the females were. Studies of mating behavior are of interest in three ways: they demonstrate the extent to which separations of species can be brought about by mating preferences; they show to what extent mating is at random in populations; and they allow one to measure approximately the extent to which different mating behaviorscontribute to the fitness of the genotypes -determining them. This paper describes the result of matings using males from ebony, vestigial and wild type stocks under different illuminations. It shows that the mating behavior of homozygous males depends on whether matings are carried out in the light or the dark, and that this affects th-eir fitness. The investigation arose out of an attempt to discover if the presence of light facilitated mating in Drosophila melanogaster. In Drosophila subobscura light is necessary for mating to take place (Rendel, 1945). Although in other species, including Drosophila melanogaster, light is not necessary, it was thought possible that light might nevertheless have some effect if tests of sufficient discrimination could be carried out. During trials of this sort using flies from ebony, vestigial, and wild type stocks, the first observations were made which led to the more detailed investigation described here. It should be noted here that differences ascribed to the genes ebony and vestigial may be due to other genes in the stocks used although stocks are identified here according to the presence of ebony or vestigial.