Abstract
Despite the negative economic and ecological impact of weeds, relatively little is known about the evolutionary mechanisms that influence their ability to persist and thrive in agricultural fields. Here, we use a resurrection ecology approach and compare the neutral and adaptive genetic variation of temporally sampled seed progenies of Ipomoea purpurea, an agricultural weed that is resistant to glyphosate, the most widely used herbicide in current-day agriculture. We found striking reductions in allelic diversity between cohorts sampled nine years apart, suggesting that populations of this species sampled from agricultural fields experience genetic bottleneck and/or founder events through time. We further found that populations of this species exhibit modest increases in herbicide resistance over time and evidence that this increase was due to adaptation and not genetic drift. Our results show that even in light of reduced genetic variation, populations of this noxious weed are capable of adapting to strong selection imparted by herbicide application. We likely uncovered only modest increases in resistance between sampling cohorts due to a strong and previously identified fitness cost of resistance in this species, along with the potential that non-resistant migrants germinate from the seed bank.
Significance Statement Although weedy plant species cause significant worldwide declines in crop production, we have a limited understanding of the evolutionary forces that influence their population dynamics. Here we use a novel “resurrection ecology” experiment and examine how both neutral and adaptive genetic diversity change over a nine-year period in the common morning glory, a noxious agricultural weed. By germinating stored seeds and performing genetic diversity and common garden assays we found consistent and striking declines in diversity through time, along with evidence that resistance to the herbicide glyphosate has increased. Our data indicate that weedy plant species are capable of adapting to agricultural regimes even as they experience genetic bottleneck.
