The role of hybrid zones in speciation: A case study on chromosome races of the house mouse Mus domesticus and common shrew Sorex araneus

Abstract

Although diverse complexes of chromosome races are of rather rare occurrence in mammals, this does not reduce their importance to an insignificant phenomenon unworthy of studying as a unique case without direct analogy. Moreover, these complexes represent virtually ideal models for estimation of the impact of hybridization on the process of microevolution. The chromosome races are characterized by an almost zero level of molecular genetic differentiation and well-defined distinctions between them, which are usually associated only with chromosome rearrangements. This review shows the valuable contribution of the studies on Sorex araneus and Mus domesticus chromosome Robertsonian systems to our understanding of the varied impacts of hybridization on the speciation process. It particularly promotes a better understanding of evolutionary phenomena such as the “reinforcement” of reproductive isolation in secondary contact zones between divergent populations, speciation without geographic separation (“divergence with gene flow”), and “zonal raciation.”