| Summary: | Abstract Plants and animals colonized Northern Europe after the last Ice Age from different refugia, not covered by the ice sheet. Many plants, such as the northern rock cress (Arabidopsis lyrata ssp. petraea) adapted to the short growing season in the North. We thus expect that colonization of the new environment was accompanied by directional selection for traits conferring this adaptation. In this thesis I studied whether recent directional selection can be detected in two important genes, PHYTOCHROME A (PHYA) and FLOWERING LOCUS C1 (FLC1), related to the flowering time pathway. To detect directional selection, I compared DNA sequence variation from the samples of a southern (Plech, Germany) and a northern (Spiterstulen, Norway) population. I also studied the current response potential to changing conditions in the marginal Spiterstulen population. Adaptation potential was characterized by assessing plasticity and amount of additive genetic variation, focusing on flowering traits. In addition, associations of 21 flowering time candidate genes for phenological and fitness traits were studied. There were several lines of evidence for recent directional selection in both candidate genes, PHYA and FLC1, in the northern Spiterstulen population Variation was strongly reduced around both genes and in addition they were highly differentiated between populations. In the Spiterstulen population there was a remarkable reduction in additive genetic variation for flowering traits, for instance when compared with morphological traits. On the other hand, phenological traits showed high plasticity. Some of the photoperiodic pathway genes showed association to flowering or reproductive fitness. The results suggest that directional selection during the colonization of the northern areas has impacted the two studied genes. Genetic changes were likely involved in altered photoperiodic and vernalization responses which might be adaptive for a short growing season. Further, directional selection was probably responsible for ...
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