The estimated rate at which common morning glory populations can adapt dropped 96 percent over nine years, according to a University of Michigan-led study published in Evolution Letters. The decline occurred even though the newer plants still carried substantial genetic variation, the raw material evolution needs.

The researchers suggest the plant is caught in an evolutionary tug-of-war. Larger flowers can help attract pollinators that are becoming scarcer, while flowering earlier can help a plant respond to changing environmental conditions. In these populations, flower size and flowering time became increasingly linked, and selection for bigger blooms appears to be taking precedence over the potential benefits of earlier flowering.

That matters beyond one vine. Common morning glory is an annual weedy vine found across the eastern, midwestern, and southern United States, frequently seen along roadsides and crop fields, and farmers often regard it as a troublesome weed. The study offers a real-world example of pollinator pressure and climate pressure pulling in different directions. It remains a single-species result, and the authors do not claim it applies to all plants.

Linked Traits Put a Brake on Adaptation

The work was led by recent doctoral graduate Sasha Bishop with University of Michigan ecologist Regina Baucom and University of Toronto researcher John Stinchcombe. The team used a resurrection experiment, growing plants from seeds collected from wild populations at two points nine years apart so older and newer generations could be compared directly.

The researchers measured the date of first flowering, flower size, nectar sugar, flowering time and the distance between the pollen-producing anthers and the pollen-receiving stigma. They then estimated the populations' capacity to adapt using a statistic called R, which accounts for how traits influence one another instead of treating each trait separately.

The key shift involved covariance, or how traits change together. In the original populations, adaptation was estimated at about 76 percent of the rate expected if links between traits were ignored, the university release said. Nine years later, that figure had fallen to roughly 9 percent, pointing to a substantial increase in evolutionary constraint over a short period.

"The plant isn't running out of evolutionary fuel," Baucom said, describing a population that is "increasingly locked into a trajectory that favors pollinator attraction, potentially at the expense of climate adaptation."

Earlier work from the same group provides context. Michigan researchers reported in 2023 that common morning glory grown from seeds collected in 2003 and 2012 along soybean and corn fields in Tennessee, North Carolina and South Carolina produced wider flowers over that span, about 4.5 centimeters versus 4.8 centimeters across, and began flowering about four days earlier on average, with the strongest changes at more northern latitudes.

What the 96 Percent Figure Does and Does Not Show

This is a peer-reviewed study that compared plants grown from field-collected seeds. Its scope is one weedy species sampled at two points in time. The 96 percent figure is the university's summary of the drop in the estimated rate of adaptation, a statistical measure of evolutionary potential rather than a count of plants lost.

The study did not prove that pollinator decline caused the change. Bishop noted that temperature and precipitation both changed in the areas where the seeds were collected and offered her interpretation: "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." That is a plausible mechanism, not a demonstrated one.

The climate-related trait at issue is flowering time, which plants can shift in response to changing temperature and rainfall. The study also cannot say whether the weed will become easier or harder for farmers to control. Baucom said that outcome is "hard to predict," adding that "that unpredictability is itself part of the story."

Why Pollinator Stress Matters for Farms and Gardens

The study lands amid wider concern about pollinators. According to the USDA Natural Resources Conservation Service, about three-fourths of the world's flowering plants and about 35 percent of the world's food crops depend on animal pollinators to reproduce, and habitat loss, disease, parasites, and environmental contaminants have contributed to declines in many pollinator species. The U.S. Fish and Wildlife Service says insect pollination adds more than $34 billion a year in value to U.S. crops, including almonds, apples, blueberries and cherries.

The Michigan team points to habitat loss and widespread pesticide and herbicide use as contributors to pollinator declines. Growers of insect-pollinated crops and commercial beekeepers have the most at stake if pollination weakens. Whether crops would show the same trait conflict has not been tested, since most are bred and managed by people rather than shaped by wild selection alone.

Households and farmers can still act. Gardeners can plant native flowering species that bloom across the season and follow pesticide label directions closely. Farmers interested in pollinator habitat can ask their local NRCS office about technical and financial assistance, which the agency offers through programs such as the Environmental Quality Incentives Program.

Open Questions for the Next Round of Research

Important unknowns remain. Researchers do not yet know whether other wild plants show the same linkage, whether it persists beyond nine years, or how it affects survival and seed production in the field. More sampling points and more species would help show whether this is a broad pattern or specific to morning glory.

The researchers frame the work as part of a larger puzzle. Theory suggests organisms can sometimes adapt quickly when environments change fast, yet many wild populations do not appear to keep pace. "Instead of evolving, there are all these wild populations that are dying off, declining or going through genetic bottlenecks," Bishop said.

No follow-up publication dates have been announced. For now, the study adds a specific warning to a familiar concern: when a plant faces two pressures at once, responding to one may make it harder to respond to the other.

What Readers Want to Know

What did the morning glory study find? The estimated adaptation rate of common morning glory fell 96 percent over nine years as flower size and flowering time became linked.

Does this mean morning glory is dying out? No. The study measured estimated evolutionary potential, not population counts, and the plants still had substantial genetic variation.

Did pollinator decline cause the slowdown? That has not been proven. It is the researchers' interpretation of why selection for larger flowers appears to be taking precedence.

Does this affect food crops? Crops were not studied. USDA says about 35 percent of the world's food crops depend on animal pollinators, which is why pollinator health matters.

What can gardeners do? Plant native flowering species that bloom through the season and follow pesticide label directions closely.