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Current species distribution in Europe was mainly influenced by massive climatic and environmental changes during the Quaternary period. Different theories concerning survival of tree species during the last ice age in Europe were proposed and up to date the position of glacial refugia and directions of migration routes are under active debate. My dissertation thesis aimed to combine information from fossil records and genetic analysis to improve knowledge on postglacial history of Alnus glutinosa and Alnus incana. The synthesis of palaeoecological data supports the idea that not only southern but also northern populations were important sources of postglacial Alnus expansion. The delayed Alnus expansion apparent in some regions was likely a result of environmental limitations. Our findings from molecular study showed differences in postglacial histories between temperate A. glutinosa and boreal A. incana. In the case of A. incana, we found an effective refugium in Central Europe located outside classical southern refugia confirming the existence of northern refugia for boreal trees in Europe. Fennoscandian populations are derived from Central-European ones that originated from populations in the Alps. For A. glutinosa, multiple southern refugia were revealed and three main directions of postglacial expansion were proposed: 1) from the northern part of the Iberian Peninsula to Western and Central Europe and subsequently to the British Isles, 2) from the Apennine Peninsula to the Alps, and 3) from the eastern part of the Balkan Peninsula to the Carpathians followed by expansion towards the Northern European plains. It has been shown that colonizing lineages have met several times and formed secondary contact zones with unexpectedly high population genetic diversity in Central Europe and Scandinavia. For the first time, we discovered tetraploid populations of A. glutinosa situated in the putative main glacial refugia on the Iberian and Balkan Peninsulas. Neither of them was probably involved in the colonization of Central and Northern Europe after glacial withdrawal. In conclusion, thanks to extensive population sampling, testing of hypothesis postulated based on fossil data by molecular data and using two molecular markers, i.e. chloroplast DNA and microsatellites, with different mode of inheritance and polymorphisms, this project revealed not only the position of glacial refugia of European tree species and discriminate between effective and non-effective ones, but also help infer the main migration routes. This approach enabled us to change some long-lasting paradigms and brought new pieces of knowledge about postglacial colonization of European tree species. |
