Invasion history of North American Canada thistle, Cirsium arvense
Aim Canada thistle (Cirsium arvense– Cardueae, Asteraceae) is one of the worst invasive plants world‐wide. Native to Eurasia, its unintentional introduction into North America now threatens the native
flora and is responsible for enormous agricultural losses. The goals of this study are to: (1) reconstruct the evolutionary history of C. arvense and estimate how often it may have colonized North America, (2) compare the genetic diversity between European and North American populations
to detect signs of demographic bottlenecks and/or patterns of population admixture, and (3) conduct bioclimatic comparisons to infer eventual niche shifts following this species’ introduction into North America.
Location Europe and North America.
A total of 1522 individuals from 58 populations were investigated with six microsatellite markers. Estimates of heterozygosity (H
E) and allelic richness (R
S) were quantified for each population, and population structure was inferred via analyses of molecular
variance (AMOVAs), principal components analyses (PCAs), Mantel tests and Bayesian clustering analyses. Climatic niche spaces were based on 19 bioclimatic variables extracted from approximately 32,000 locations covering the entire range, and compared using PCA and hierarchical cluster analysis.
Although there is evidence of multiple introductions from divergent European lineages, North American populations of C. arvense exhibited significantly lower levels of genetic diversity than their putative ancestors. Bioclimatic comparisons pointed to a high degree of niche conservatism
during invasion, but indicated that genotypes from the former USSR and Central European mountain chains were probably best adapted to invade North America upon entry into the continent.
Main conclusions Genetic and historical data suggest that C. arvense first entered
North America from Western Europe with the first European settlers, and was later introduced from Eastern Europe into the prairie states during the agricultural boom. The species went through a significant bottleneck following its introduction into the New World, but the level of genetic diversity
remained high owing to admixture between genetically differentiated lineages and to a highly efficient outcrossing breeding system.
Document Type: Research Article
Botany Department, University of British Columbia, Vancouver, BC, Canada
Institute of Biology, Geobotany and Botanical Garden, Martin-Luther-University, Halle-Wittenberg, Halle (Saale), Germany
US Department of Agriculture, Agriculture Research Service, European Biological Control Laboratory, Montpellier, France
US Department of Agriculture, Agriculture Research Service, Red River Valley Agriculture Research Center, Fargo, ND, USA
Publication date: October 1, 2012