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Free keywords:
hybrid species; hybrid zone; incompatibility; introgression; reinforcement; reproductive barrier.
Abstract:
Hybridization has many and varied impacts on the process of speciation.
Hybridization may slow or reverse differentiation by allowing gene flow and
recombination. It may accelerate speciation via adaptive introgression or cause
near-instantaneous speciation by allopolyploidization. It may have multiple
effects at different stages and in different spatial contexts within a single speciation
event. We offer a perspective on the context and evolutionary significance of
hybridization during speciation, highlighting issues of current interest and debate.
In secondary contact zones, it is uncertain if barriers to gene flow will be strengthened
or broken down due to recombination and gene flow. Theory and empirical
evidence suggest the latter is more likely, except within and around strongly
selected genomic regions. Hybridization may contribute to speciation through the
formation of new hybrid taxa, whereas introgression of a few loci may promote
adaptive divergence and so facilitate speciation. Gene regulatory networks, epigenetic
effects and the evolution of selfish genetic material in the genome suggest
that the Dobzhansky–Muller model of hybrid incompatibilities requires a broader
interpretation. Finally, although the incidence of reinforcement remains uncertain,
this and other interactions in areas of sympatry may have knock-on effects
on speciation both within and outside regions of hybridization.
