Fertility in the male common shrews, Sorex araneus, from the extremely narrow hybrid zone between chromosome races

Selection against chromosomal heterozygotes causing a limitation of gene flow between parental forms could promote genetic changes leading to speciation. Hence, the analysis of the fertility of hybrids and the pure form individuals from chromosomal hybrid zones offers a possibility to study the role of chromosomes in the speciation process. In this study, meiosis and spermatogenesis of homozygotes, simple Rb heterozygotes and complex heterozygotes of the mate common shrews from the Dn/Bi hybrid zone were analyzed. It was found out that the Dn/Bi hybrids were not sterile, but they suffered from substantial germ cell death and were characterized by high level of chromosome non-disjunction at anaphase I. However, we suppose that speciation is not possible in the studied area, because effects of selection acting against hybrids are obliterated by inflow of pure race individuals and genetic drift. (c) 2006 Deutsche Gesettschaft fur Saugetierkunde. Published by Elsevier GmbH. All rights reserved.