Multiple introductions and genetic admixture facilitate the successful invasion of Plantago virginica into China

Population genetic surveys can reveal the patterns of genetic diversity and provide insights into the details of invasion history. Plantago virginica L. (Plantaginaceae) is a North America species that was first reported in China in 1951 and has rapidly spread into the south-eastern areas of China. Although previous work has examined phenotypic variation during this invasion, the genetic variation and structure of P. virginica remains unclear. We used two chloroplast and seven microsatellite loci to analyse genetic diversity and population differentiation in 17 populations of P. virginica from the invaded range (China, n = 688) and 10 populations from its native range (USA, n = 625). Chloroplast haplotypes from all populations were clustered into two lineages (I and II) and invasive populations had 28 haplotypes, whereas native populations had only 10 haplotypes. DIYABC simulations based on microsatellite data also suggest multiple invasions into China. Invasive populations displayed high genetic diversity that was similar to that of the native range. However, there was markedly less genetic differentiation in Chinese populations (FST = 0.051) than in NA populations (FST = 0.143), suggesting increased gene flow within China. STRUCTURE analysis also revealed significant gene flow and lineage admixture among Chinese populations and MIGRATE analysis suggested high levels of gene flow to inland China from both the coast of China and populations in the United States. These results suggest that multiple introductions and genetic admixture likely play important roles in facilitating the invasion and geographic expansion of P. virginica into China.