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UCSB researchers document abrupt evolutionary change in flowers

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Scott Hodges UCSB
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About a quarter of Colorado blue columbines in the area are spurless, more than can be attributed to mere chance.

Researchers from UC Santa Barbara have documented an abrupt evolutionary change in blue columbine flowers. The findings suggest that natural selection may not always be a sequence of gradual changes, but could instead happen more suddenly.

UCSB professor Scott Hodges is an evolutionary biologist with a focus on pollination systems. He studies Colorado blue columbine flowers.

Hodges' pollination research, with Ph.D. student Zachary Cabin, turned up something unexpected. Hodges said their data shows that about a quarter of the Colorado blue columbine plants have lost their petals and nectar spurs for pollination.

“To all of a sudden find an instance where we lost this feature of the plant that seemed so important was really surprising,” Hodges said.

Hodges said they initially thought the change put the plant at a disadvantage since pollination contributes to reproductive success.

“But it had nothing to do with pollinators. It had everything to do with being less likely to get eaten,” he said.

Cabin said deer and aphids prefer the flowers with nectar spurs, so becoming spurless is likely driven by selective pressure for the plant’s survival.

“The herbivores are applying such a strong pressure that the way to avoid that is to lose this sugary sweet attracting flavor,” Cabin said.

He said mutations are not unusual, but changes of this significance point to evolution.

“To be at such high numbers in the population is really unlikely due to what we call genetic drift or to random processes, we would expect selective pressure to be driving that,” he said.

Cabin said a change in the plant’s appearance was noted by botanists in Colorado about 120 years ago, but no thorough studies had been done.

With extensive field data and DNA analysis from a collaborative lab, Cabin said spurlessness can now be attributed to a change in a single gene. The gene, he said, is either on or off, and controls the entire development of the flower’s spurs and nectaries.

Professor Hodges said the research contributes to the understanding of evolution.

“Darwin’s idea was that evolution occurs in these really small changes, so you would make a very slight change and that would have a slight advantage, but you’d have to have another slight change, and another," Hodges said. "What we’ve been able to show here is that you can have a single change and make a really big jump all at once."

The study was published in the journal Current Biology.

Beth Thornton is a freelance reporter for KCBX, and a contributor to Issues & Ideas. She is a 2021 Data Fellow with the USC Annenberg Center for Health Journalism.
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