Herbicide-resistant "superweeds" change their mating strategies over time, an evolutionary shift that helps them hold onto valuable genes and outcompete other plants, according to a new study from University of Michigan researchers.

The study examined the relationships between plant mating systems and herbicide resistance in the common agricultural weed morning glory. The researchers found that morning glory populations that have evolved resistance to the herbicide Roundup rely on self-fertilization more than susceptible populations do.

The increased reliance on self-fertilization may help perpetuate Roundup resistance by blocking the flow herbicide-susceptibility genes from other plants, the researchers concluded.

The results highlight the potential unforeseen consequences of human activities—in this case the widespread use of Roundup Ready crops, which are genetically modified to tolerate the herbicide—on wild plants such as weeds.

"We need to fully understand how we are altering plant species through the use of agricultural chemicals. What kind of evolution are we causing due to impacts that we didn't quite foresee?" said U-M plant ecological geneticist Regina Baucom, senior author of a paper scheduled for online publication Nov. 30 in the journal Ecology Letters.

"This is further evidence that human activities can have unintended impacts on plant populations, in this case changes in traits that we weren't necessarily anticipating might evolve," said Baucom, an assistant professor in the Department of Ecology and Evolutionary Biology.

The first author of the Ecology Letters paper is U-M postdoctoral researcher Adam Kuester. The other authors are U-M undergraduate Eva Fall and Shu-Mei Chang of the University of Georgia.

Read the full press release from Michigan News

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Read more in these recent and related papers from the Baucom lab:

A resurrection experiment finds evidence of both reduced genetic diversity and potential adaptive evolution in the agricultural weed Ipomoea purpurea,” Molecular Ecology by authors Adam Kuester, Ariana Wilson, Shu-Mei Chang, Regina Baucom.

Fitness costs of herbicide resistance across natural populations of the common morning glory, Ipomoea purpurea,” Evolution by authors Megan Van Etten, Adam Kuester, Shu-Mei Chag, Regina Baucom.