Reinforcement during ecological speciation

Reinforcement of pre-zygotic isolation can result when any of several kinds of selection act against hybrids. This paper investigates the situation wh ere hybrids are selected against for ecological reasons, for example when t here is no niche for individuals that are phenotypically intermediate betwe en the parental species. The calculations here show how much ecological sel ection can lead to the reinforcement of a female mating preference or an as sortative mating trait that is expressed in both sexes. The model allows fo r the ecological trait to be affected by any number of loci, but assumes th at selection is weak and the introgression rate small. The effect of select ion against hybrids increases rapidly as the difference between the mean ph enotypes of the two populations increases. When genetic variation in the ec ological trait is caused by many loci, stabilizing selection on it further contributes to reinforcement.