ON THE EVOLUTION OF PREMATING ISOLATION AFTER A FOUNDER EVENT

We present a new simple model for the evolution of premating reproduct ive isolation. Using this model we first analyze the level of genetic variability maintained by mutation in a large stable population. Then we consider the plausibility of the evolution of strong premating repr oductive isolation after a founder event. We demonstrate that after a founder event a new adaptive combination of genes may rise to high fre quencies in the presence of an old combination of genes. We compare th e probabilities of speciation after a founder event with those in a st able population and with those when reproductive isolation is due to v iability selection against hybrids. We argue that premating reproducti ve isolation is more efficient than postmating reproductive isolation in maintaining the integrity of sympatric species. This might have con tributed to the pattern of stronger premating isolation than postmatin g isolation between closely related pairs of sympatric species.