Influence of food on frequency-dependent sexual activity of Drosophila melanogaster

When two types of Drosophila are in competition, the frequency dependence of mating successes frequently is measured by direct observation of copulating pairs in "Elens-Wattiaux" observation chambers, the relative frequency of both types being varied. The present experiments, concerning white-ebony mutants in competition with wild-type Canton-S flies, show that the presence of food in the mating chamber influences the sexual activity of flies, this influence differing in the two types when food is present. Thus, in order to have a realistic estimation of frequency dependence, it would seem prudent to conduct these experiments with food in the chamber. Three methods are used to analyze observation data: K coefficients of Petit and Ehrman, regression equations of Ayala and Campbell, and regression equations of Wattiaux and Lichtenberger. These three methods are compared and discussed.