Population genetic variation and structure of the invasive weed Mikania micrantha in southern China: consequences of rapid range expansion.

Invasive plants such as Mikania micrantha provide valuable opportunities for studying population genetic consequences of rapid range expansion. Twenty-eight populations of M. micrantha throughout its introduced range in southern China were examined by using intersimple sequence repeat markers. Population genetic parameters were estimated by Bayesian approaches as well as conventional methods. Bottleneck signature, multilocus linkage disequilibrium, character compatibility, and cluster analyses were conducted to assay the factors that may act to shape population variability. High levels of genetic variation and differentiation were detected in the introduced populations of M. micrantha. All populations experienced severe bottlenecks. Most of them demonstrated significant linkage disequilibrium and matrix compatibility. Populations were mainly clustered into 2 groups, and those from different regions intermingled in the unweighted pair group method with arithmetic mean (UPGMA) dendrogram. No geographical signature was found in the pattern of population genetic variation. This research indicates that during M. micrantha invasion, multiple introductions mitigated the loss of genetic variation associated with bottlenecks. Nonetheless, bottlenecks enhanced the population differentiation. Human-mediated long-distance dispersal events of seeds or propagules explain the lack of geographic structure in genetic variation. Although asexual reproduction is the predominant mating mode in M. micrantha, it has little effect on the population genetic composition.