Summary, in English
Flowering plants display an extraordinary floral- and reproductive diversity. Variation in the size, shape, colour and scent of flowers, and in systems and strategies of mating, is ubiquitous in comparisons of different species, but also exists among different conspecific populations. Diversity in these characters is central to the evolution of flowering plants and the formation of new species. In this thesis, I use the arctic-alpine plant Arabis alpina to explore various causes of intraspecific variation in floral scent, and consequences of evolutionary shifts in plant mating system. By combining experiments in the greenhouse, genomic data and studies in the field, I examine how mating system, natural selection, genetic differentiation and phenotypic plasticity shape intraspecific floral scent variation, and investigate the impact of mating system shifts for the build-up of reproductive isolation. Comparing the floral scent of different A. alpina populations distributed across Europe, I found that self-compatible populations had a lower floral scent emission rate and partly different scent composition compared to self-incompatible populations. For both self-compatible and self-incompatible populations, there was limited phenotypic plasticity in floral scent, with some effect of nutrient availability, but not of water availability, on scent emission rates. Comparing the genomic and phenotypic differentiation among self-incompatible populations, it was evident that closely related populations could differ considerably in floral scent. Estimating selection on floral scent, I found some evidence that patterns of selection differed between populations. By crossing plants from self-compatible populations with plants from self-incompatible populations, I found considerable reproductive isolation, consistent with parental conflict over seed provisioning being higher in self-incompatible than in self-compatible populations. Taken together, the results of my thesis reveal some of the complex patterns behind floral scent diversification, and demonstrate the importance of mating system shifts for the evolution of floral signalling and reproductive isolation among flowering plants.