Question

1) Can postzygotic isolation (low hybrid fertility or viability) be reinforced by natural selection in hybrid zones? Is this a way in which natural selection can reduce mixing between gene pools?

2) In many groups of plants, low levels of hybridization between related species are not uncommon, yet only a few cases of the origin of "hybrid species" by recombinational speciation have been documented. What factors make recombinational speciation likely verus unlikely?

Answer 1

1) Postzygotic isolation(low hybrid fertility or viability) can be reinforced by natural selection in hybrid zones. Reinforcement is a process by which speciation can be driven by natural selection,so in a hybrid zone,when two long time divergent populations come together,incompatibility occurs between them because of low hybrid fitness. So natural selection then drives the formation of a new species.

The degree of this type of isolating mechanisms is directly proportional to the distance between two gene pools,i.e it will occur only when two distantly related populations come together. So this is not a typical way to reduce mixing between two gene pools.