Competition Between Drosophila Melanogaster and Drosophila Simulans

Abstract

When a mixed population of D. simulans and D. melanogaster were kept in cages at 25[degree] C, melanogaster eliminated simulans in approx. 100 days in 19 out of 20 cages. In the exceptional cage melanogaster increased over simulans during the first 73 days, after which simulans increased until it comprised approx. half of the population on the 218th day. After this melanogaster gradually eliminated simulans. By selecting adult females from this cage on the 228th day a strain of simulans was developed which had undergone selection through competition with melanogaster, and a strain of melanogaster was obtained which had undergone selection through competition with simulans. These selected strains were caged with stock strains in various ways and the proportion of melanogaster males recorded over a period of 300 days. The melanogaster strain selected through competition with simulans was similar to or identical with the stock melanogaster in competition with stock simulans, whereas the selected simulans showed improvement over stock simulans in competition with stock melanogaster. Females were taken from the selected simulans stock, giving a strain which had competed with melanogaster for 329 days, and which, on testing was found superior to the 229-day strain in competitive ability. By further selection a simulans strain was obtained which had competed with melanogaster for 500 days. It was superior to the unselected simulans, but there was some doubt that it was better than the 329-day strain.