This chapter discussed speciation by genetic divergence following geographic isolation, which is expected to lead to reduced gene flow, a process known as allopatric speciation

Question

A more controversial form of speciation is the genetic divergence of populations without physical isolation, a process known as sympatric speciation. Can you envision a mechanism or process that would permit two coexisting populations of the same species to begin to diverge without being isolated from one another?

Answer 1

Sympatric speciation is thought to be uncommon but almost certainly has occurred. In one general scenario, a form of isolation "in place," or in sympatry, may occur if certain males or females begin (by drift, perhaps) to prefer different resources–say, a special site for mating or laying eggs. If their mates follow in this "imprinting" process, the two preference populations may begin to experience reduced gene flow between them, which if maintained long enough may bring about a degree of genetic divergence that would be selectively reinforced should some of the individuals from the two populations ever hybridize.