Morning Glories May Be Evolving the Wrong Traits for a Warming World, Study Finds

Plants facing both a warming climate and declining pollinator populations may be getting pulled in competing evolutionary directions, according to a University of Michigan study of morning glories. The research, led by recent doctoral graduate Sasha Bishop working with professor Regina Baucom at Michigan and John Stinchcombe at the University of Toronto, was published in the journal Evolution Letters.

The team grew morning glory plants from seeds collected from the same wild populations at two points nine years apart. They measured traits including flower size, nectar sugar, the timing of the first flower, and the distance between a flower's pollen-producing anthers and its pollen-receiving stigma. The researchers then calculated each population's rate of adaptation using a statistic called R, which accounts for how multiple traits can become linked, or "covariant," rather than evolving independently of one another.

Flower size and flowering time became increasingly linked over the nine years. Larger flowers tend to attract more pollinators, while flowering earlier helps a plant track shifting temperature and rainfall, but the two traits pulled the population in different directions, with selection for larger flowers taking precedence. In the original population, adaptation proceeded at about 76% of the rate that would be expected if the traits were not linked; nine years later, that figure had fallen to roughly 9%, a 96% drop overall.

Importantly, the newer plant populations still contained substantial genetic variation, so the slowdown was not caused by a lack of raw material for evolution. "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.

Morning glory is also considered a troublesome weed by farmers, and Baucom said the slowdown in adaptation could affect how much of a problem the plant remains for agriculture, though whether that makes it more or less of an issue is hard to predict.