Refugia of Boreal Birds and Mammals in Eastern Central Europe

Comparison of phylogeographic structures in several Eurasiatic boreal species has shown that species associated with the taiga forest revealed essentially similar patterns. In the wood lemming (Myopus schisticolor), and also in most other boreal forest species, no substantial phylogeographic divisions across Northern Eurasia have been reported (Zink et al. 2002; Fedorov et al. 2008). The contraction of the range of these species to a single, probably Southern Siberian refugial area during the late Pleistocene followed by demographic expansion seems to be a general background for their shallow phylogeographic structure. The most important genetic discontinuity has usually been observed between the " Northern" Eurasiatic and the "Far East" clades. The limited distribution range of the South-eastern lineages suggests that their core areas ("Manchurian refugium" of de Lattin 1967) could not play an essential role in the post-glacial colonisation of Northern Eurasia by boreal forest species. A weak phylogeographic structure was also discovered in the flying squirrel (Pteromys volans), in which the divergence between the Far Eastern and Northern Eurasian groups may have been initiated during the Weichselian glaciation (Oshida et al. 2005). Mountain ranges in Southern Siberia and North-Eastern China may have isolated the Far Eastern group. Although the largest part of North-Eastern Europe and Siberia was not covered with ice during the last glaciation, most parts were overgrown by cold tundra-steppe ("mammoth steppe") under extremely cold and dry conditions (Svendsen et al. 1999, 2004; Simakova 2001; Schirrmeister et al. 2002). At that time, multiple isolated refugia of P. volans could be formed in

Eurasia. After the last glaciation, P. volans might have expanded throughout Northern Eurasia, along both sides of the Ural mountains.

Other boreal species show clear phylogeographical structures with well-differentiated populations in the coniferous forest zone of the South European mountains. They belong to rather different taxonomical groups. The brown bear complex can be mentioned as a classical example, (e.g. Taberlet and Bouvet 1994; Valdiosera et al. 2007). The discovery of 18,000-year-old charcoal of yew (Taxus baccata) and Scots pine (P. sylvestris) in Western Slovakia (Litynska-Zajac 1995) indicates that the climatic conditions at the Western Carpathians might have been suitable for the brown bear. The Eastern Carpathians served also as a refuge area for brown bears during the last glacial phase. Nevertheless, recolonization from the Eastern Carpathian refuge appears to have been less effective compared to the migration that began from the North-Western Carpathian refuge. This recolonization pattern can be explained by the more Northern position of the North-Western Carpathians (leading edge).

Southern European montane refugia have also been revealed in the capercaillie (T urogallus). It was suggested that the Southern European aquitanus lineage had expanded throughout Europe before the LGM, and the Eastern, urogallus lineage expanded in Asia and North-Eastern Europe. During the LGM, the two lineages were restricted into separate refugia (aquitanus: Iberia and Balkans, urogallus: Southern Siberia). During the post-glacial re-forestation, the urogallus lineage replaced aquitanus in Europe and forced them to the South-west into their refugia in the Pyrenees and Cantabrian Mts. (Duriez et al. 2007).

Different phylogeographical structures have been revealed in the root voles (Brunhoff et al. 2003), lemmings (Fedorov et al. 1999), collared lemmings (Fedorov and Stenseth 2002), and common voles (Haynes et al. 2003; Fink et al. 2004). In these cases, the Ural Mountains separated the Northern European and Siberian lineages. Root voles in Europe form a Northern and a central mtDNA phylogroup. Fossil records from the last glaciation have demonstrated that collared lemmings (Dicrostonyx) and true lemmings (Lemmus) used to be the most common small mammals in the periglacial tundro-steppe of central Europe. These species were regularly accompanied by several vole species, including the root vole. These species assembly always remained North of the "classical" Southern European refugia. Thus, central European root vole populations can be considered the sources of Northward expansion during the deglaciation. This model is corroborated by the data demonstrating that the fragmented populations in the Netherlands, Slovakia and Hungary all belong to a single mtDNA phylo-group. Consequently, the threatened populations in Hungary, Austria, Slovakia and the Netherlands represent glacial and post-glacial relicts (van de Zande et al. 2000).

Bilton et al. (1998) show that the Mediterranean populations of S. minutus, S. ara-neus and Clethrionomys spp. did not contribute to the present-day gene pools of the Central and Northern European populations. This view has also been supported by the high rate of endemism in the Mediterranean bank vole phylogroups. In contrast with some forest rodents (A. sylvaticus, A. flavicollis), bank voles would not be restricted to the Southern forest refugia during the last glaciations. Therefore, bank vole populations might have survived the Quaternary glaciations in their Northern refugia. This may have resulted in their present complex phylogeographic pattern including multiple glacial refugia in central Europe, in the Mediterranean mountains and possibly also in several Eastern regions. Based on fossil records, the Carpathian region has been suggested as a glacial refugial area for this species. These refugia were most likely to be located near the Alps or in the Carpathians and possibly at the network of streams in the marginal areas of the Carpathian Basin. Phylogeographic analyses of the bank vole have already suggested that glacial refugia located in central and Eastern Europe made a major contribution to the modern population of this species in Europe (Deffontaine et al. 2005; Kotlik et al. 2006). The analysis of nucleotide diversity also demonstrates that these Eastern Central European regions acted as core areas of expansion for the Western lineage of the bank vole. Another refugial area was proposed in the regions of Eastern Romania, Western Azov Sea and the Crimea (Jaarola and Searle 2002).

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