Genetic structure and colonizing success of a clonal, weedy species, Pilosella officinarum (Asteraceae)

Introduced populations of weeds which are polyploid and reproduce primarily by apomixis are generally considered as having low levels of population genetic variation, highly differentiated populations and short evolutionary lifespans. Although polyploidy allows for habitat differentiation and colonization, lack of recombination because of apomixis means that long-term persistence is unlikely. However, variation can be introduced to a colonizing population by evolutionary changes in the mating system, or by somatic mutation and recombination. In this study hypersensitive genetic markers, inter-simple sequence repeats (ISSRs), were used to quantify genetic variation within Pilosella officinarum, a major weed of the New Zealand high country. Pilosella officinarum was introduced from Europe to New Zealand late in the 19th century and only polyploid, apomictic populations are thought to have survived. The combination of introduction history and breeding system has led to the assumption that New Zealand populations are necessarily genetically depauperate. However, our studies reveal variable levels of genetic variation and patterns of clonal distribution which indicate varying levels of sexual reproduction within New Zealand populations.