Hybridization as a facilitator of species range expansion

Abstract

Explaining the evolution of species geographical ranges is fundamental to understanding how biodiversity is distributed and maintained. The solution to this classic problem in ecology and evolution remains elusive: we still do not fully know how species geographical ranges evolve and what factors fuel range expansions. Resolving this problem is now more crucial than ever with increasing biodiversity loss, global change and movement of species by humans. Here, we describe and evaluate the hypothesis that hybridization between species can contribute to species range expansion. We discuss how such a process can occur and the empirical data that are needed to test this hypothesis. We also examine how species can expand into new environments via hybridization with a resident species, and yet remain distinct species. Generally, hybridization may play an underappreciated role in influencing the evolution of species ranges. Whether-and to what extent-hybridization has such an effect requires further study across more diverse taxa.

Keywords: adaptation; admixture; hybridization; introgression; invasive species; range expansion.

Figure 1.

Hybridization can promote range expansion via its genetic effects. (a) Two species of fish (indicated by the different shapes and genotypes) that occupy different habitats (differential shading) hybridize and produce viable and fertile F₁ offspring, which (b) later backcross to one parental species. (c) As a result of introgression, one of the parental species acquires an allele (indicated as ‘a’) that enables adaptation and expansion into the other environment. Allele ‘a’ could encode for a key functional trait that is already adaptive in that environment. Alternatively, allele ‘a’ could represent additional genetic variation that interacts with other loci to take the species to a different adaptive optimum for that environment (see text).