House mice are believed to be, unlike rats, only reluctant swimmers. If water is a barrier to mouse dispersal water bodies and streams can have a substantial impact on the genetic structure of populations. Previous studies revealed influence of rivers on the position and structure of the European hybrid zone between two house mouse subspecies, Mus musculus musculus and M. m. domesticus. In this study, we used a simple motivation experiment to test the disposition of both wild and inbred mice representing the subspecies to overcome a water barrier. As the more dispersing sex, males were chosen for the experiment. Mice were tested under two air/water temperature regimes, 20 °C and 10 °C. Contrary to a common belief tested animals entered water rather easily, often even engaging in repeated swimming. We found significant differences in scored behavioural parameters between the subspecies. Under the 20 °C regime, both wild and inbred domesticus males entered and crossed the water earlier and more often swam even when satiated. Strikingly, under the 10 °C regime, the results were rather equivocal but with the opposite tendencies, with musculus males being more willing to swim. We discuss implications of these findings for the hybrid zone dynamics.
Documented were the values of 7 morphological meristic and 37 mensural characters in samples of 0+ juvenile specimens of the sterlet reared in special aquacultural facilities in the Czech Republic (and originating from Russia), and in the Slovak Republic (originating from the Danube Slovak section). Individual character values were compared with literature data using the method size-pooled samples. Specimens reared in the Czech Republic (CR) and in the Slovak Republic (SR) did not differ in the maximum-minimum range of their meristic characters from the literature systematic description presented for sterlet (Acipenser ruthenus Linnaeus, 1758). Regards differences between mean values, the sample from the Czech Republic differed significantly in 4 (of 6) meristic characters, and in 14 (of 27) mensural characters compared. On the basis of multivariate morphometrical analysis (PCA, UPGMA) it was found that the sample of sterlet from the CR clusters well with other samples of the sterlet populations, being morphologically closest to a pair of samples from the Danube River. We suggest that, because of the numerous transfers into the Danube of sterlets reared by aquaculture in the CR, it will be impossible to discriminate them morphologically from those reared naturally in the Danube Slovak section.
We analyzed sequences of two variable segments of the mitochondrial control region (CR) and flanking regions in the house mouse (Mus musculus). Most of the material was sampled from the eastern Mediterranean and the Middle East, i.e., a source area for the colonization of Europe. These sequences were supplemented with other samples from the whole range of the species including the Yemeni island of Socotra. This island was shown to harbour mice bearing M. m. domesticus and M. m. castaneus CR haplotypes. In addition, we found 10 distinct sequences at the same locality that were markedly different from all known CR sequences. Sequencing of the whole mitochondrial genome suggested these sequences to represent nuclear fragments of the mitochondrial origin (numts). We assessed genetic variation and phylogeography within and among the house mouse subspecies and estimated the substitution rate, coalescence times, and times of population expansion. We show the data to be consistent with time dependency of substitution rates and recent expansion of mouse populations. The expansion of European populations of M. m. musculus and M. m. domesticus estimated from the CR sequences coincide with presumed time of colonization of the continent in the Holocene.
Geographic isolation of small populations in refugia during late Pleistocene glaciations resulted in population differentiation that in some cases lead to speciation. We report the karyotype of Microtus bavaricus, an evolutionary young and threatened rodent endemic to the Alps. Our results show that the karyotype of M. bavaricus is almost identical to that of M. liechtensteini (2N = 46, NF = 54). A close relationship between the two species was also supported by phylogenetic analysis of complete mitochondrial DNA sequences for the cytochrome b gene. The cytochrome b divergence between Microtus bavaricus and M. liechtensteini was 1.7 %, the lowest estimate observed among the 14 currently recognised species of Eurasian pine voles (subgenus Terricola).
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.