Population and quantitative genetic analyses of life‐history trait adaptations in Amaranthus palmeri S. Watson

Amaranthus palmeri populations can evolve life‐history traits despite its high levels of genetic diversity and gene flow. However, it was not known whether those differences were due to selection or other evolutionary processes. We used microsatellite markers to quantify genetic differentiation among 10 Amaranthus palmeri populations and determined whether the differences in life‐history traits among the populations could be attributed to selection. Genetic differentiation was small (Φ ST  = 0.093), indicating that there were high rates of gene flow among populations. AMOVA showed that only 9% of the genetic variability was explained by variation among populations and 90% was found within populations. Using Φ ST as a surrogate for F ST in the Q ST −F ST analysis, we confirmed that most traits followed the same pattern as neutral markers and were not under selection. However, important traits for weediness such as plant height, dry weight and nitrogen use efficiency were under selection. These results provide evidence that selection forces in agroecosystems can increase weediness in A. palmeri , and that those forces should be identified to develop strategies to counter them when possible.