REINFORCEMENT - A NEW PERSPECTIVE ON AN OLD CONTROVERSY

A critical component of the reinforcement model, incomplete postzygoti c reproductive isolation, has been overlooked in the many selection ex periments designed to test this model. Many field observations are con sistent with the reinforcement model, but theoretical work predicts th at reinforcement should only work when nearly complete postzygotic rep roductive isolation has developed. The experiments described here used four levels of postzygotic reproductive isolation: complete, strong, moderate, and none. A significant decrease in heterotypic matings occu rred over 25 generations in the complete postzygotic reproductive isol ation treatment. No evidence for reinforcement was found in any of the other treatments using incomplete postzygotic reproductive isolation.