The significance of sexual reproduction for local adaptation in Taraxacum

Abstract

One of the aspects of sexual reproduction, such as is practised by most eukaryote, multicellular organisms, is that each offspring receives a random selection of alleles from its father and its mother. This way, existing genotypes are broken up and new ones are created in every generation. As each environment varies in time and space, to survive, species need to find ways for continuously matching their genotype to the changing conditions. It has often been assumed and modelled that, because of this continuous reshuffling of alleles, sexual organisms will adapt to their environment in different ways than do sexually reproducing organisms. Dandelions (Taraxacum) form an agamic complex with sexual, diploid genotypes and asexual (mainly) triploid genotypes. In many cases sexuals and apomicts occur in the same field. This makes dandelions a convenient species to study differences in adaptation between the two models of reproduction, though the difference in ploidy level complicates the picture. This thesis describes patterns of genotypic and phenotypic variation among and between sexual and apomictic Taraxacum under various environmental conditions. Based on existing models and models developed in this thesis, a theory is presented about the significance of sexuality for Taraxacum