Population Genetic Analysis of Naturalized US Populations of a Post-Columbian Invasive, Sorghum halepense

Range expansions are commonplace in nature, such as post-glacial recolonizations or migration patterns of humans spreading to multiple continents. Yet we have very few studied examples for rapid colonization of continental scale that took place in recent times. Such ‘ecological timescale’ colonizations may have genetic signatures quite distinct from those that took place in deeper evolutionary scale. These signatures involve allelic gradients, allele surfing (variants that are rare in ancestral populations may persist in high frequencies in derived peripheral populations) and rare patches founded by long-distance dispersal with low diversity at the boundary of the colonization front that are hard to detect in established populations. Here we use a combination of tools to study SSR-based genotypes including traditional genetic tree building, principle coordinate analysis (PCoA), Bayesian structure, Fst-based population genetics, minimum spanning network and mismatch analysis for understanding colonization and diversity patterns of naturalized and geo-referenced Sorghum halepense samples collected from populations in most of its range across the continental United States.