%0 Generic
%A Kiefer, Christiane
%D 2008
%F heidok:8980
%K Phylogeographie , BoecheraPhylogeny , Phylogeography , Apomixis, Evolution , Boechera
%R 10.11588/heidok.00008980
%T Evolution and Phylogeography of the North American genus Boechera (Brassicaceae)and the Evolution of Apomixis
%U https://archiv.ub.uni-heidelberg.de/volltextserver/8980/
%X Boechera is a North American genus of the Brassicaceae named after the Danish botanist Tyge Böcher who cytogenetically studied members of the genus in great detail. Until the end of the 20th century most species which belong today to Boechera were still included in the genus Arabis. Molecular studies in the late 1990s revealed that Arabis was polyphyletic and subsequently a majority of North American Arabis species was transferred into Boechera. Boechera inhabits a wide range of habitats and reproduces sexually as well as apomictic (asexual reproduction via seeds).  The aims of the study presented inhere were (a) to reconstruct the phylogeographic history of the genus based on chloroplast DNA marker sequences and (b) to investigate the nrDNA ITS gene pool and reconstruct phylogenies based on nrDNA ITS and single copy gene introns. In the course of the experiments it appeared that eastern North American Boechera constitute different evolutionary lineages than the species centred in western North America. Hence the split of eastern and western North American Boechera species became a third subject (c). In our continental wide phylogeographic studies we detected a large amount of haplotype sharing indicating recurrent hybridisation on the one hand and non-differentiation of haplotypes since speciation on the other hand. We concluded that the chloroplast gene pool in Boechera pre-dates speciation in respect to the investigated markers. Unrelated from taxon identity we could show that the evolutionary lineages detected have a different phylogeographic history in terms of glacial refugia and recently recolonized areas. The study based on nrDNA ITS and introns of two single copy genes enabled us to obtain deeper insights into Boechera phylogeny and ITS type distribution across taxa. We could show that species specific lineages exist although the relationship among them is poorly resolved. Comparing gene tree topologies this indicates rapid speciation which probably happened in the second half of the quaternary. Hybrids could be identified by the comparison of the different marker systems together with chloroplast DNA types from an earlier study.  The comparison of eastern and western North American Boechera based on DNA marker sequences showed that eastern North American Boechera represent two evolutionary lineages within the genus Boechera (cpDNA) or among the tribe Boechereae (nrDNA). We also included the Siberian taxa Borodinia and Boechera falcata in the analysis and could show that they were resolved within Boechera.  The final task in the thesis was to unravel the origin of two apomict specific chromosomes (Het and Del). BAC-FISH analyses revealed that Het is a homologue of Boechera stricta linkage group 1 and Del appears only in 15 chromosome apomicts and is a fragment of Het. The thesis presented inhere offers deeper insights into the evolution of this complex genus and offers a good basis for ongoing and future research projects dealing with evolution and expression of apomixis as well as genome evolution in Boechera. CD mit großem Anhang erhältlich bei Verfasserin Email: ckiefer@hip.uni-heidelberg.de