Intraspecific variation in Rhinanthus angustifolius. Local adaptation, phenotypic plasticity and geographical structure

Sammanfattning: Plant species often adapt to local environmental conditions, which can result in the formation of genetically and phenotypically distinct ecotypes. Ecotypes can evolve rapidly, and may be a first step in the process of ecological speciation. Consequently, ecotypes may constitute an important part of the biodiversity in regions with a young flora, where few endemic taxa at the species level have had the time to evolve. The lack of knowledge regarding species showing evidence of ecotypic differentiation may, however, hamper proper taxonomic treatment and identification of units for conservation. In this thesis we study the intraspecific variation of the annual hemiparasitic herb Rhinanthus angustifolius. The species is divided into several subspecies that generally are assumed to be ecotypes. Some of the putative ecotypes are connected to traditionally managed human-created habitats that are threatened by changes in management practices. However, the distinctness and conservation value of the putative ecotypes remain unknown. Phenotypic plasticity may, for example, blur or exaggerate genetically based differences. Here, we use a combination of common-garden experiments and molecular genetic analyses to study local adaptation, phenotypic plasticity and geographical structure within R. angustifolius. Moreover, we evaluate the distinctness of three putative ecotypes occurring in Sweden today. Our results support a history of genetic adaptation to local environmental conditions in Scandinavia after the last ice age. However, we observe a complex pattern of phenotypic variation rather than formation of distinct ecotypes. The major exception is a fen ecotype occurring in a few calcareous spring fens on the Baltic island of Gotland. In congruence with previous studies on R. angustifolius and closely related species, we show that phenotypic plasticity affects some characters that are used to delimit infraspecific taxa within the species. Results from our molecular genetic analyses indicate that geographically isolated populations of R. angustifolius have adapted to similar environmental conditions resulting in incongruent patterns of phenotypic and molecular-genetic variation, and repeated evolution of distinct fen ecotypes. We discuss the taxonomic value of ecotypes and currently recognized subspecies, and their usefulness as conservation units.