LONG-DISTANCE DISPERSAL AND HIGH GENETIC DIVERSITY ARE IMPLICATED IN THE INVASIVE SPREAD OF THE COMMON REED, PHRAGMITES AUSTRALIS (POACEAE), IN NORTHEASTERN NORTH AMERICA

Premise of the study : The Eurasian subspecies of the common reed (Phragmites australis subsp. australis, hereafter abbreviated as P. a. australis) was introduced to North America in the late 18(th) century and rapidly expanded its range, posing an ecological threat to wetlands. In this study, we aimed to determine whether admixture among multiple lineages, dispersal mechanisms, and high genetic diversity have contributed to the invasion of P. a. australis in the northeastern part of its range. Understanding mechanisms of the P. a. australis invasion will 1) contribute to a broader understanding of the factors that facilitate plant invasion, and 2) help us to develop effective management strategies for wetlands threatened by P. a. australis invasion. Methods : We used a population genetics approach incorporating nine microsatellite loci to study genetic diversity and population structure in relation to biogeography of introduced North American Phragmites a. australis stands in the northeastern continental region. Key Results : Phragmites a. australis is genetically diverse in the region studied here. Significant population structure exists, and population structure is likely influenced by both long-distance dispersal via major waterways, and short-distance dispersal overland. Different lineages sometimes colonize geographically proximate locations leading to opportunities for admixture. Clonal reproduction likely exaggerates geographical structure among some stands, although high genetic and clonal diversity within some stands implies that sexual reproduction occurs frequently in P. a. australis. Conclusions : A variety of factors, including admixture among multiple lineages, multiple modes of dispersal, and plasticity in reproductive strategy promote the invasion success of Phragmites a. australis. Wetland managers in the St. Lawrence River/Great Lakes region should focus monitoring efforts on the shores of conservation lands to prevent the establishment of propagules from novel lineages.