Polyploidy, i.e., the duplication of entire nuclear genomes, has shaped the evolution of major lineages of eukaryotes, and is particularly important in the Plant Kingdom. Molecular analyses suggest that the genomes of most (>90%) of the present-day flowering plants retain evidence of one or more ancient genome-wide duplications, and that numerous species additionally have been through more recent polyploidisation events. Most of the world's threatened flora is polyploid. And most agricultural production of food, fodder and fibers comes from polyploids. Thus understanding the consequences of polyploid evolution is of vital importance for both conservation and economics. In this thesis, the candidate examines the origin of polyploid lineages and the consequences for gene flow between natural populations, focusing on four different case studies and using a wide range of molecular tools. Her results indicates that there are no general rules for the origins of different polyploid lineages; some are the result of multiple independent origins involving parents from populations distant in space or time, others are the result of a single polyploidisation event. Some polyploids are influenced by subsequent gene flow from the parental populations, some are immediately isolated, and the genome duplication acts as an instant speciation. The differences suggest that additional factors such as range fragmentation and expansion and occasional long-distance dispersals are important processes shaping the genetic structure of polyploids.
List of papers
(article II and V are removed due to copyright restrictions)
I. Jørgensen MH, Elven R, Tribsch A, Gabrielsen TM, Stedje B, Brochmann C. 2006.
Taxonomy and evolutionary relationships in the Saxifraga rivularis complex. Systematic Botany, 31: 702-729.
II. Westergaard K, Jørgensen MH, Gabrielsen TM, Alsos IG, Brochmann C. 2010. The extreme Beringian/Atlantic disjunction in Saxifraga rivularis (Saxifragaceae) has formed at least twice. Journal of Biogeography, 37: 1262-1276.
III. Jørgensen MH, Carlsen T, Skrede I, Elven R. 2008. Microsatellites resolve the taxonomy of the polyploid Cardamine digitata aggregate (Brassicaceae). Taxon, 57:882-892.
IV. Schmickl R, Jørgensen MH, Brysting AK, Koch MA. 2010. The evolutionary history of the Arabidopsis lyrata complex: A hybrid in the amphi-Beringian area closes a large distribution gap and builds up a genetic barrier. BMC Evolutionary Biology, 10: 98.
V. Jørgensen MH, Brysting AK, Takebayashi N, Steets JA, Beecher JJ, Wolf DE. Digging deeper into the allopolyploid origin of Arabidopsis kamchatica and its effect on molecular diversity. Manuscript.
VI. Jørgensen MH, Ehrich D, Schmickl R, Koch MA, Brysting AK. Interspecific and interploidal gene flow in Central European Arabidopsis (Brassicaceae).