Genetic diversity of the newly invasive weed Flaveria bidentis (Asteraceae) reveals consequences of its rapid range expansion in northern China

Ma JW, Geng SL, Wang SB, Zhang GL, Fu WD & Shu B (2011). Genetic diversity of the newly invasive weed Flaveria bidentis (Asteraceae) reveals consequences of its rapid range expansion in northern China. Weed Research51, 363–372. Summary The South American weed Flaveria bidentis has spread rapidly across northern China since its introduction to the Tianjin area in 2001. To explore its introduction dynamics and mechanism of rapid range expansion in northern China, we examined genetic diversity in 26 populations across the invaded range, using inter-simple sequence repeat markers. We found relatively high intraspecies genetic diversity (He = 0.279; I = 0.415) and wide-ranging genetic variation within populations (He = 0.095–0.263; I = 0.160–0.383), with relatively high genetic diversity in both older established populations and some newly established populations. Approximately 78% of genetic variation resides within populations, according to analysis of molecular variance. The unweighted pair group method with arithmetic mean clustered populations into two groups, composed of most populations distributed along the G106 or G107 National Roads. Moreover, a Mantel test showed no significant correlation between geographical and genetic distances. The findings indicate that during F. bidentis invasion, sexual reproduction and multiple introductions have maintained high genetic diversity, while secondary introductions or admixtures of populations have mitigated losses of genetic variation caused by founder events and promoted local adaptation and colonisation. In addition, human-mediated long-distance seed dispersal, via National Roads, may have contributed to its weak geographical genetic structure and rapid range expansion in northern China. To prevent further introductions, imports should be monitored at Tianjin (the likely first arrival point). To control established populations, efforts should focus on populations with high genetic diversity, populations along the G106 and G107 National Roads and regions that are climatically similar to its native range.