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Morning glories reveal 96% drop in adaptation as pollinator pressure reshapes evolution
Facing both climate change and a crashing pollinator population, plants may be evolving to attract pollinators rather than adapting to a warming climate, and the trade-off has resulted in a steep decline in plants' rate of adaptation, according to a University of Michigan study. The researchers, studying morning glories, observed a 96% decrease in the population's rate of adaptation over nine years. The declining rate of adaptation could affect farmers, who deal with morning glory as an agricultural nuisance. The research is published in the journal Evolution Letters.
"Because pollinator pressure strongly favors larger flowers, that linkage may limit how efficiently the population can respond to other selective pressures. Whether that ultimately makes the weed more or less of a problem for farmers is hard to predict—and that unpredictability is itself part of the story," said Regina Baucom, a professor in the U-M Department of Ecology and Evolutionary Biology.
The reason for the decline is an interesting one, Baucom says. Right now, the need to attract pollinators with larger flowers is winning out over the evolutionary advantage of an earlier flowering time, and the traits have become linked in a way that limits their ability to adapt. The decline is happening even though the newer plant populations had plenty of genetic variation, suggesting they should be able to adapt normally.
"The plant isn't running out of evolutionary fuel—it's increasingly locked into a trajectory that favors pollinator attraction, potentially at the expense of climate adaptation," Baucom said.
Human-caused global change
The researchers, led by recent doctoral graduate Sasha Bishop and in collaboration with University of Toronto researcher John Stinchcombe, were examining morning glory in the context of human-caused global change. In addition to a warming climate, they say, people have changed the environment in ways that affect both plants and animals. People build over previously untouched habitat, and widespread agricultural practices such as pesticide and herbicide use have led to a steep decline in pollinators.
Bishop says their study examines the gap between what theory suggests—that organisms should be able to adapt quickly to rapidly changing environments—and what scientists were seeing in wild populations of many plants.
"Instead of evolving, there are all these wild populations that are dying off, declining or going through genetic bottlenecks," Bishop said. "So we're looking at a situation in which there's a lag in what we're seeing in the adaptive rate in wild populations compared to what we think might be theoretically possible in terms of rapid evolution."
An adaptation trade-off?
For this study, the researchers grew morning glory seeds collected from wild populations at two different points in time, nine years apart. Focusing on plant traits that could be affected by climate change and pollinators, they recorded the date of each plant's first flower, flower size, nectar sugar, flowering time and the distance between flowers' anthers, or the pollen-producing part of the flower, and the stigma, the structure that receives pollen.
The researchers then examined the adaptation rate using a statistic called R, which calculates how a population is predicted to adapt when considering how traits within it are linked vs. focusing on a single trait at a time. This allowed them to study how one trait might "constrain" another—meaning that one trait could influence how another trait changes, or doesn't change.
When two traits become linked, they're considered "covariants." Bishop and Baucom's study also revealed that flower size and flowering time became linked in morning glories over the brief, nine-year period of the study.
They found that in their original populations of morning glories, the rate of adaptation was about 76% of what was expected without covariance. But nine years later, the rate of adaptation dropped to about 9% of what was expected without covariance.
"There are quite literally thousands of studies showing that flowering phenology is a really important adaptive path when it comes to climate change, particularly temperature changes and precipitation changes, both of which happened in these wild populations in the locations where they were collected from," Bishop said.
"The implication in my mind is that pollinator decline, or the lack of pollination and selective drive to attract pollinators, is making these plants potentially less able to adapt to climatic shifts."
Publication details
Sasha G D Bishop et al, A resurrection experiment reveals reduced adaptive potential in a common agricultural weed, Evolution Letters (2026). DOI: 10.1093/evlett/qrag026
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Citation: Morning glories reveal 96% drop in adaptation as pollinator pressure reshapes evolution (2026, July 9) retrieved 12 July 2026 from https://phys.org/news/2026-07-morning-glories-reveal-pollinator-pressure.html
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