Sexual isolation in Drosophila. III. Estimating isolation using male-choice experiments

It has been generally assumed that "choice experiments" are useful to measure sexual isolation between Drosophila strains or species. Theoretical models have demonstrated however that the results obtained using one of these designs, namely multiple-choice experiments, are insufficient to determine the degree of isolation, even under very favorable assumptions. In this work, a simple behavioral model is developed to test whether male-choice experiments can be used to measure sexual isolation in Drosophila. This model shows that, although the outcome of male-choice experiments is affected by differences in female receptivities, a procedure to estimate the minimum degree of isolation using this experimental design can be established. The application of the methods derived from the theoretical model to previously reported experimental data demonstrates that a substantial degree of isolation frequently exists intraspecifically, while isolation is far from complete interspecifically. These results have important implications for discussions based on the comparative analysis of Drosophila behavior, both intra- and interspecifically. Most especially, they are in contradiction with the expectations of the Recognition concept of species.