Hybridization and speciation

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.

Differential effects of climate and species interactions on range limits at a hybrid zone: potential direct and indirect impacts of climate change

“…Finally, hybridization can act as an evolutionary stimulus by promoting the introgression of adaptive genetic material across species boundaries (Abbott et al. 2013). …”

“…However, interspecific hybridization can facilitate adaptive potential by introducing genetic variation (Abbott et al. 2013). Indeed, theoretical work suggests that introgressive hybridization can rescue an extinction‐prone species after an abrupt environmental change (Baskett and Gomulkiewicz 2011).…”

Geographic variation in hybridization across a reinforcement contact zone of chorus frogs (Pseudacris)

“…One outcome of reinforcement is the pattern of reproductive character displacement (RCD), where reproductive behaviors evolve to be more divergent between species in sympatry than allopatry (Servedio & Noor, 2003; Lemmon, Smadja, & Kirkpatrick, 2004; Nosil, 2012; but see Pfennig & Pfennig, 2009). Selection against hybridization in contact zones is not only thought to contribute to divergence between species but also to promote diversification within species as a result of different selection pressures across allopatric and sympatric populations (Abbott, 2013; Fuller, 2016; Hoskin & Higgie, 2010; Ortiz‐Barrientos, Grealy, & Nosil, 2009; Pfennig & Pfennig, 2009). …”

Surgeons and suture zones: Hybridization among four surgeonfish species in the Indo-Pacific with variable evolutionary outcomes

“…Ecological factors, on the other hand, may be a driving force behind species formation under sympatric or parapatric scenarios (Choat, 2006;Bird et al, 2011). Indeed, there are several recent examples of ecological speciation (Nosil, 2012) or speciation with gene flow (Feder et al, 2012;Abbott et al, 2013).…”