Natural selection could actually slow evolution, scientists say

When you hear the term natural selection, you probably think of change, but new research suggests that the mechanism can also maintain similarities between populations.

Biologists have a very strong understanding of the basic process of evolution. Genetic diversity in a population is the result of mutation, some of which creates traits that help individuals grow better in the current environment. These traits have a good chance of being passed on to future generations, while unhelpful traits tend not to appear in future generations. This is natural selection.

Evolutionary biologists often study variation within and between populations and species, but there is more to life than what makes us all different.

“We always talk about the great diversity in life, and we should. It's unbelievable.” He says Evolutionary biologist Jeff Conner of Michigan State University, lead author of the new study.

“Natural selection has given us much of this diversity, perhaps most of it. But natural selection can also cause similarities.”

Conner and colleagues from the United States and China worked on wild radishes (Ravanus ravanstrum). Whereas their pollen-producing organs used to be of equal length, today they have two short stamens and four long stamens.

unexpectedly, Previous search It has been suggested that selection maintains this length difference, known as “anther separation”, despite the fact that we do not know why.

Wild radish flower. (Jeff Conner)

Additive genetic variation—where multiple genes contribute to a trait—is necessary for the trait to evolve. In what is known as constraint, the lack of this variation tends to hinder evolution even if it is evolutionarily favorable.

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The constraint is based on the idea that as species change over time, they can lose their genetic flexibility in some respects, causing some traits to become stable across generations.

Where natural selection is the engine of change, constraint is the brake.

“Our work flips the script a little bit,” Conner said He says. “We suggest that selection can slow things down too, and can cause similarities as well as differences.”

The team wanted to know if the restriction could prevent the anther detachment from developing in the previous study. They used artificial selection to breed wild radishes to restore their appearance to their more primitive state, which consists of a smaller gap between the stamens.

“If a trait responds to artificial selection, it can clearly evolve,” the authors say. explained in their paper.

“But if the trait doesn't respond, there's a constraint caused by a lack of genetic diversity.”

The study included six generations, where 3,437 wild radish plants were grown and measured. Through artificial selection, the researchers were able to reduce the difference in stamen lengths by more than 30 percent.

Wild radish stems with visible stamens on a black background.
In nature, wild radishes have long and short stamens as seen on the left. Through artificial selection, the researchers succeeded in bringing the lengths closer to equality, as shown on the right. (Connor et al., New Botanist2023)

This change appears wild radish today, perhaps Relativesthey still have the genetic diversity they need to evolve, making it unlikely that they will be restricted.

Instead, natural selection appears to maintain variation in stamen lengths.

“This family of plants has maintained the trait of being four tall and short over a period of 50 million years, and we can eliminate a third of the difference in five generations, that is, five years.” He says. “I think if we keep going, we'll get back to six stamens of equal length.”

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Scientists have designed experiments to see whether varying stamen lengths confer any benefit R. Ravanistrum When it comes to the way pollinators interact with the plant.

“Natural selection is very important” He says Connor. “There are a lot of things that people thought election couldn't do, and we're learning that election can do.”

The research was published in New Botanist.

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