Polygenic adaptation from standing variation underlies rapid evolution under anthropogenic selection in an agricultural weed

Herbicide resistance serves as a prime example of rapid adaptation to intense human-induced selection. However, the origins and genetic makeup of this resistance remain unclear. This study investigates herbicide resistance in blackgrass, the most common and economically damaging weed in Europe. By analyzing genomes from pre- and post-herbicide populations, the researchers gain insights into the evolution of resistance over time and across different regions.

The study reveals that mutations conferring target-site resistance, which hinder the herbicide's intended effect, emerged recently and independently across Europe. On the other hand, non-target-site resistance, which reduces the herbicide's impact on non-target species, exhibits a polygenic architecture and is linked to a group of glutathione S-transferase (GST) genes along with other stress-response genes.

Most of these resistance-associated alleles were already present in historical populations before herbicide use, indicating that the species had previously adapted to stress and detoxification challenges. Additionally, the study uncovers evidence of positive selection predating herbicide use, suggesting that these stress and detoxification pathways were maintained by natural selection and later utilized when exposed to herbicide pressure.

Overall, this research highlights how herbicide resistance can evolve through different genetic pathways, with polygenic non-target-site resistance often emerging from pre-existing genetic variation, shedding light on the rapid adaptation processes driven by anthropogenic selection.