Data from: Population genetics and origin of the native North American agricultural weed waterhemp (Amaranthus tuberculatus)

Premise of the study: The evolution of invasiveness has been extensively studied in natural ecosystems; however, far less is known about the evolution of agricultural invasiveness, despite the major economic impact of weeds on crop productivity. Examining the population structure of recently arisen weeds can provide insights into evolutionary avenues to invasion of agroecosystems. Weeds that originate from wild plants are the most common yet least frequently studied type of agricultural invasive. Here we address several questions about the origin of the native North American agricultural weed waterhemp (Amaranthus tuberculatus), which invaded corn and soy fields in the midwestern United States in the 20th century. Methods: We genotyped 38 populations from across the species range with 10 microsatellite markers and used these data to assess genetic diversity and population structure within and outside the geographical region where waterhemp is agriculturally problematic. Key results: We found evidence for two ancestral genetic lineages in our data, supporting the hypothesis that A. tuberculatus was diverging into two evolutionary lineages prior to the 20th century. However, we found no support for the hypothesis that agricultural weed populations arose from admixture of these two lineages after secondary contact. Our data suggest that eastward movement of the western genetic lineage, facilitated by changing agricultural practices, is the source of the agricultural invasion of waterhemp. Conclusions: This research demonstrates that agricultural invasion by native, wild plant species can proceed via different evolutionary trajectories from weeds related to domesticated plants, which has implications for evolutionary biology and weed control

Data from: A phylogeny of the genus Amaranthus (Amaranthaceae), based on several low-copy nuclear loci and chloroplast regions

The genus Amaranthus (pigweeds) is a group of ∼74 monoecious or dioecious annual species native to every continent but Antarctica, frequently associated with natural and human disturbance, with several economically important domesticated and weedy species. We set out to reconstruct the phylogeny of Amaranthus, with broad geographic sampling, in order to answer questions about biogeographic relationships in the genus and the monophyly of the subgenera. Fifty-eight species were included inmaximum parsimony and Bayesian phylogenetic analyses based on ITS and three low-copy nuclear genes (A36, G3PDH, and Waxy), as well as two chloroplast regions (trnL5′-trnL3′ and matK/trnK). Topology tests were also employed to test taxonomic hypotheses about incongruence between trees and the monophyly of clades containing Galápagos species. Our analyses support the origin of the genus in the Americas, with a single long-distance dispersal event to the Old World, and both nuclear and chloroplast trees recover three to fourmajor clades, roughly corresponding to three subgenera recognized based on morphology. However, there are species in all of these clades that were not predicted based on morphology, and we discover previously unsuspected relationships between Galápagos species and species from the North American Southwest, which comprise small monophyletic groups outside of the three recognized subgenera. Additionally, an important herbicide resistant weed species (A. palmeri) and its sister species are placed into different large clades based on nuclear or chloroplast data, suggesting a chloroplast capture event. These results will provide a basis for further exploration of the evolution of weedy ecological strategies in the group