Invasion of Brassica nigra in North America: distributions and origins of chloroplast DNA haplotypes suggest multiple introductions
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Deciphering the origin of invasive plant species, whether or not there have been multiple introductions, and genetic differentiations between invasive and native ranges is crucial in testing hypotheses underlying biological invasions. Here, we applied traditional population genetic analyses to unravel the phylogeographical relationships among invasive (North American) and native (North African, Mediterranean region, and Eurasian) range populations of Brassica nigra using chloroplast DNA. We sequenced chloroplast DNA intron (trnF–trnL) for 284 individuals representing 36 native and 15 invasive range populations of B. nigra. Thirty-two haplotypes were found over the whole data set. A similarity between the invasive range and native range populations in genetic diversity combined with results from analyses of molecular variance and gene genealogies suggest that invasive B. nigra populations were introduced from multiple sources in the native range. More generally, this study adds to the growing body of data on the genetic patterns involved in biological invasions that is crucial to our understanding of the evolutionary trajectories of invasive populations.
KeywordsInvasive plants Brassica nigra Rapid post-introduction evolution Multiple introductions Population admixture Invasive and native populations Introduced range Native range
We thank Yedra García for help with DNA extraction and Sharon Y. Strauss for comments on an earlier version of this manuscript. This study was supported by a Grant from the foundation Banco Bilbao Vizcaya Argentaria (BBVA-BIOCON06/064). We are grateful to North Central Regional Plant Introduction Station (NCRPIS)-USA, IPK, Gatersleben (Germany) and Real Jardín Botánico de Madrid (RJB-CSIC) for providing us with Brassica nigra seeds from their germplasm collections. We received additional B. nigra seeds from field collections done by Richard A. Lankau, Mirka Marcel,and Jeffrey K. Conner. A.M.O. Oduor received further financial support from a Ph.D. scholarship granted by Agencia Española de Cooperación Internacional para el Desarrollo (MAEC-AECID).
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