Morning glories make bigger flowers to entice pollinators

Spring is arriving earlier as a result of global warming, and this phenomenon threatens to disrupt plant and pollinator interactions. In a new study led by the University of Michigan, researchers have discovered that some plants are not just flowering earlier, but are also producing bigger flowers to attract pollinators.

The experts found that between 2003 and 2012, the common morning glory in the southeastern United States increased the size of its flowers. This change was most pronounced at northern latitudes. Previously, scientists have reported finding more dramatic evolutionary responses to climate change in the northern part of a plant’s range.

According to the researchers, increased flower size suggests a greater investment by the plants in pollinator attraction. The morning glories had also invested more energy in nectar and pollen to attract more of the bees, syrphid flies, and wasps that pollinate them. 

“There is a major gap in our understanding of how traits that are crucial for plant-pollinator interactions may be evolving over time as a response to a changing climate,” said study lead author Sasha Bishop.

“We show that – in addition to well-documented shifts to earlier flowering – floral architecture and rewards can also play significant roles in the evolutionary response to contemporary environmental change.” 

In collaboration with Shu-Mei Chang of the University of Georgia, the experts used a “resurrection approach” for the study. They germinated morning glory seeds that were collected from the edges of agricultural fields in Tennessee, North Carolina and South Carolina in 2003 and 2012. 

Over these years, the region had experienced rising temperatures, an increase in the number of extreme rainfall events, and more extreme drought.

The researchers planted the seeds from both years in a greenhouse at the University of Michigan Matthaei Botanical Gardens. 

The results showed that morning glory corollas became wider over the course of nine years, jumping from 4.5 centimeters in diameter in 2003 to 4.8 centimeters in 2012. In addition, the study revealed that the morning glories from 2012 started flowering four days earlier.

“This is the first article to use the resurrection approach to examine the potential that traits responsible for plant-pollinator interactions may be evolving over time, concomitant to decreases in pollinator abundance and dramatic environmental changes due to changing climate and land-use regimes,” said Bishop.

The study is published in the journal Evolution Letters.

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By Chrissy Sexton, Earth.com Editor

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