Characterization of diallelic SNP loci via a reduced-representation Genotyping-by-Sequencing (GBS) approach, to investigate fine-scale population genetic structure across the native range of Ambrosia artemisiifolia L.

Common ragweed (Ambrosia artemisiifolia) is an invasive, wind-pollinated plant nearly ubiquitous in disturbed sites in its eastern North American native range, and present across growing portions of Europe, Africa, Asia and Australia. Phenotypic divergence between European and native-range populations has been described as rapid evolution. However, a recent study demonstrated major human-mediated shifts in ragweed genetic structure before introduction to Europe and suggested that native-range genetic structure and local adaptation could fully explain accelerated growth and other invasive characteristics of introduced populations. Genomic differentiation that potentially influenced this structure have not yet been investigated, and it remains unclear whether substantial admixture during historical disturbance of the native range contributed to the accelerated growth and other invasive characteristics of introduced European ragweed populations. To investigate fine-scale population genetic structure across the species’ native range, we characterized diallelic SNP loci via a reduced-representation Genotyping-by-Sequencing (GBS) approach. We corroborate phylogeographic domains previously discovered using traditional sequencing methods, while demonstrating increased power to resolve weak genetic structure in this highly admixed plant species. By identifying the exome polymorphisms underlying geographic genetic differentiation, we suggest that geographic differentiation of this important invasive species has occurred more often within pathways that regulate growth and response to defense and stress, which may be associated with survival in North America's diverse climatic regions.