Geographic Variation, Hybridization and Evolution in the Bladder Campions, Silene vulgaris and S. uniflora (Caryophyllaceae)

Abstract: In the present thesis, I investigated the inter- and intraspecific variation in the Silene vulgaris/uniflora species-complex (the bladder campions). I have focused on the effects of past and present hybridization both on a large scale ? over the whole of Europe ? and on a local scale. Silene vulgaris and S. uniflora are perennial herbs and they are interfertile. The results from my studies suggest that hybridization between the closely-related species S. vulgaris and S. uniflora has influenced the evolution of both species in Europe. There is evidence for both ancient (predating the most recent postglacial migrations) and recent (local) gene flow between species and populations. The patterns of variation exhibited in allozyme and chloroplast DNA markers indicate considerable mixing of alleles and haplotypes and it is not possible, from the present results alone, to identify the source areas (refugia) from which northern Europe was recolonized during the postglacial period. On the Baltic island of Öland, a strong paternal effect on seed germination and germination time, in combination with differences in habitat preference, appear to constitute a strong barrier against hybridization and gene flow between the weedy S. vulgaris and the endemic S. uniflora ssp. petraea. My results are congruent with the hypothesis that the endemic subspecies S. uniflora ssp. petraea may have evolved as a result of hybridization between S. vulgaris and S. uniflora ssp. uniflora. It is further suggested that S. vulgaris ssp. glareosa and S. vulgaris ssp. prostrata (from S. Europe) may be better regarded as subspecies within S. uniflora, while S. vulgaris ssp. angustifolia should be retained within S. vulgaris.