Location: Sunflower and Plant Biology ResearchTitle: Invasion history of North American Canada thistle, Cirsium arvense) Author
Submitted to: Journal of Biogeography
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2012
Publication Date: 10/1/2012
Citation: Guggisberg, A., Welk, E., Sforza, R., Horvath, D.P., Anderson, J.V., Foley, M.E., Rieseberg, L.H. 2012. Invasion history of North American Canada thistle, Cirsium arvense. Journal of Biogeography. 39:1919-1931. Interpretive Summary: Canada thistle (Cirsium arvense) is an invasive weed in much of the world. In order to help identify potential biological control agents, for North American populations, it would be helpful to identify where the North American Canada thistle came from. Also, knowing where our Canada thistle came from could provide information on climatic conditions that could help predict the spread of this invasive weed. To answer this question, we investigated the similarities and differences between 6 small pieces of DNA (microsatellite markers) from 15-30 members each of 55 populations spread out over Europe and North America. We learned that there are three distinct populations in Europe, and that a minimum of five successful introductions into North America: at least two independent introductions from Western Europe, one that may have spread across most of North America and another that appears to be restricted to the Great Lakes region, and at least three independent introductions from Eastern Europe into the Midwest, into areas close to actual Minnesota, Montana, and South Dakota. We also learned that there is less genetic diversity in North American Canada thistle populations than is observed in European populations, but that the North American populations retain sufficient genetic ability to readily adapt to new environments and control measures.
Technical Abstract: Aim Canada thistle (Cirsium arvense – Cardueae, Asteraceae) is one of the worst invasive plants worldwide. Native to Eurasia, its unintentional introduction into North America now threatens the native flora and imposes enormous agricultural losses. The goals of this study are to: (i) conduct bioclimatic comparisons to predict which region(s) in the native range most likely served as source(s) for the introduction of Canada thistle into the New World; (ii) reconstruct the evolutionary history of the species to test the former hypothesis and estimate how often Canada thistle may have colonized North America; and (iii) compare the genetic diversity between European and North American populations to detect signs of demographic bottlenecks and/or patterns of population admixture. Methods Fifty-eight populations totaling 1522 individuals were compared across 19 bioclimatic variables and six microsatellite markers. Estimates of heterozygosity (HE) and allelic richness (RS) were quantified for each population, and population structure was inferred via analyses of molecular variance (AMOVA), principal component analyses (PCA), neighbor-joining (NJ) tree reconstruction, Mantel tests, and Bayesian clustering analyses. Results Bioclimatic comparisons indicated that the climatic conditions experienced by North American populations best matched those prevailing in Eastern Europe. Yet, both Eastern and Western Europe repeatedly served as sources for the introduction of Canada thistle into the New World. Estimates of genetic diversity further demonstrated that introduced North American populations of C. arvense exhibited significantly lower levels of genetic diversity than their European ancestors. Main conclusions Canada thistle invaded North America on a recurrent basis from both Eastern and Western Europe, contradicting our bioclimatic hypothesis that predicted the former to be the main invasion source. This study further shows that Canada thistle went through a significant bottleneck upon its introduction into the New World, but that the level of genetic diversity remained high due to population admixture and a highly effective out crossing breeding system. Within this context, this species was likely able to quickly adapt to the new environmental conditions encountered upon its arrival into North America.