Genetic variation among populations of commensal house mice was studied across the territories of the Czech and Slovak Republics and in some adjacent areas of Germany. We used six diagnostic allozyme loci (Es-2, Gpd-1, Idh-1, Mpi, Np, Sod-1) and the following molecular markers: B1 insertion in the Btk gene (X chromosome), Zfy2 18-bp deletion (Y chromosome), BamH I restriction site in the mt-Nd1 gene (mtDNA) and Hba-4ps 16-bp insertion (diagnosing the presence of t haplotypes). In total, 544 individuals taken from 49 localities were examined. Almost the entire territories of the Czech Republic and Slovakia were found to be occupied by Mus musculus, the only exception being the westernmost parts of the Czech Republic, where M. musculus meets the range of M. domesticus and forms a narrow belt of hybrid populations. Despite this, domesticus-type alleles of some allozyme markers (notably Es-2) were also found at sites well within the range of M. musculus, either tens or hundreds of kilometres behind the hybrid zone. This provides evidence of either: (1) introgression of some markers into the species’ genome due to free gene flow through the zone, or (2) human-mediated long-distance migrations, or (3) incomplete lineage sorting. Conversely, variants of molecular markers typical for M. domesticus in Btk, Zfy2 and mt-Nd1were only found in the westernmost populations studied. t haplotypes were quite frequent in some populations, irrespective of whether M. domesticus, M. musculus or their hybrids, yet no t/t homozygotes were found. The mean frequency of t/+ heterozygotes found within the study populations was 13%.
Crested newts (Triturus cristatus superspecies) are a group of closely related species with parapatric distributions that are likely to interbreed where their ranges meet. Coexistence of three species of the complex (Triturus cristatus, T. dobrogicus and T. carnifex) has been recently confirmed in central Europe. In this study we aim to elucidate the distribution of crested newts in contact zones in the Czech Republic and Slovakia, and determine the extent of hybridization and introgression using nuclear (microsatellites and Randomly Amplified Polymorphic DNA, RAPD) and mitochondrial DNA (mtDNA) markers. Nuclear markers reveal hybrid zones between T. cristatus and T. dobrogicus at the foothills of the Carpathians in southern Slovakia, and between T. cristatus and T. carnifex in the southern parts of the Czech Republic. Analysis of mitochondrial cytochrome b sequences reveals T. cristatus and T. dobrogicus-specific haplotypes in contact zones in southern Slovakia. Surprisingly, most T. carnifex and individuals with mixed ancestry between T. carnifex and T. cristatus possess haplotypes specific for T. dobrogicus, most likely as a result of historical mtDNA introgression. Only one T. carnifex-specific haplotype carried by a single specimen is found in the Czech Republic. Our study shows that genetic structure of central European populations of crested newts is complex and influenced by historical and contemporary hybridization.
Despite the long-term study of the house mouse hybrid zone in Europe knowledge of its course in some areas is still rather vague. Comparisons of different portions of the zone showed some common patterns, however, several discordances were also revealed, the most remarkable being introgression of the Y chromosome. We sampled mice along the presumed course of the secondary contact zone between two subspecies, Mus musculus musculus and M. m. domesticus, from Schleswig-Holstein to southern Bavaria, in order to localize more precisely its position. A second aim was to reveal whether introgression shows some general rules obscured until now by studies of geographically isolated transects of the zone. We employed maternally (mtDNA), paternally (Y), and biparentally inherited markers and related their introgression patterns to the hybrid index (HI) based on five X-linked loci. While transition of autosomal loci across the zone was congruent with changes in HI, mtDNA showed bidirectional introgression with alien alleles occurring far behind the zone. Finally, the Y chromosome displayed asymmetric unidirectional introgression of the musculus type into domesticus background. We discuss evolutionary forces shaping these patterns.