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Abstract.
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).
Key words: Terricola, molecular divergence, glaciation
Introduction
Vole species of the genus Microtus (Arvicolinae, Rodentia) differ considerably in age and various evolutionary stages of speciation can be observed within the genus. The Eurasian pine voles, subgenus Terricola, include species groups that are especially suitable for analysis of recent divergence events (Jaarola et al. 2004). Geographic isolation of small populations in refugia during the late Pleistocene glaciations could have served as "speciation traps" for several of these young taxa, thus promoting speciation (Chaline 1987, Martínková & Dudich 2003).
The Bavarian pine vole, Microtus bavaricus (König, 1962), is an endemic species of the Alps with an extremely restricted range and rather enigmatic phylogenetic relationships. In fact, its distribution area covers only six known localities in the Innsbruck Alps in Bavaria, Germany (terra typica at Garmisch-Partenkirchen), and northern Tyrol in Austria (König 1982, Spitzenberger 2002, Carleton & Musser 2005). Because of the species' distributional pattern, it was suggested that M. bavaricus survived the last glacial period in a refugium situated in the northern Alps (Kratochvíl 1970, Spitzenberger 2002). Since the original morphological description by König (1962), affinities of M. bavaricus to the two other lineages of pine voles endemic to the Alps and some nearby mountain ranges, M. multiplex and M. liechtensteini, have been indicated (Kratochvíl 1970, Spitzenberger 2002) and confirmed by both morphological (Spitzenberger et al. 2000) and molecular genetic analysis (Haring et al. 2000). This group, the M. multiplex complex, including M. multiplex, M, liechtensteini and M. bavaricus, is characterised by low morphological divergence and M. multiplex and M....