Sexual isolation in Drosophila. I. Theoretical models for multiple-choice experiments

Several simple models are developed to calculate expected mating frequencies in ethological isolation experiments. They take into account the effect that the peculiar sexual behavior of Drosophila species can have in multiple-choice experiments. These models depend on only three basic parameters: male competitive ability (C), female receptivity (R) and the coefficient of females acceptance (A). Two types of model can be distinguished: (1) models with discrete preferences, in which A is a measure of the percentage of females accepting a particular kind of male and (2) models with continuous preferences, in which A represents the probability of acceptance for each courtship. It is demonstrated that the information rendered by just one experiment, although effective for determining whether sexual isolation exists, it is insufficient to estimate its degree or to demonstrate that it is asymmetrical. Further developments of the models under more complex conditions as well as their implications for reinforcement and founder effect theories are discussed.