Unearthing the impact of human disturbance on a notorious weed.

Large-scale anthropogenic changes in the environment are reshaping global biodiversity and the evolutionary trajectory of many species. Evolutionary mechanisms that allow organisms to thrive in this rapidly changing environment are just beginning to be investigated (Hoffmann & Sgrò 2011; Colautti & Barrett 2013). Weedy and invasive species represent 'success stories' for how species can cope with human modified environments. As introduced species have spread within recent times, they provide the unique opportunity to track the genetic consequences of rapid range expansion through time and space using historic DNA samples. Using modern collections and herbarium specimens dating back to 1873, Martin et al. (2014) have provided a more complete understanding of the population history of the invasive, agricultural weed, common ragweed (Ambrosia artemisiifolia; Fig. 1) in its native range with surprising results. They find that the recent population explosion of common ragweed in North America coincided with substantial shifts in population genetic structure with implications for invasion.