THE EVOLUTION OF REPRODUCTIVE ISOLATION AS A CORRELATED CHARACTER UNDER SYMPATRIC CONDITIONS: EXPERIMENTAL EVIDENCE

A set of experiments is described that tests the general hypothesis that sympatric speciation is genetically feasible whenever reproductive isolation evolves indirectly as a correlated character. We specifically test the hypothesis that disruptive selection on habitat preference can lead to sympatric speciation when individuals mate locally within their selected habitat. Drosophila melanogaster was used as a model system. A 35-generation experiment using a complex habitat maze led to complete reproductive isolation between subpopulations using different spatiotemporal habitats. The reproductive isolation that developed over the course of the experiment was a result of offspring returning to mate in the habitat type selected by their parents, i.e., a gradual breakdown in migration between habitats.