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U study recreates evolution’s first steps

Researchers at the U evolved algae from single-celled to multicellular in 219 days.

Uncovering past scientific processes without a time machine seems impossible, but a University of Minnesota study offers a glimpse into biological history by evolving single-celled organisms into multicellular ones in the present.

Multicellular development is a process that many creatures go through to become more complex, but scientists don’t yet understand exactly how the process first occurred.

University researchers have taken a first step by showing how one type of unicellular algae can evolve into a multicellular one despite having no multicellular ancestors. They published the research in Nature Communications earlier this month.

“Understanding how multicellularity has evolved is really critical in understanding how complexity arises in nature,” said ecology, evolution and behavior postdoctoral fellow William Ratcliff, who worked on the research.

By putting the algae in test tubes and selecting the cells that settled faster, researchers forced them to evolve into larger cells. Some of those cells became multicellular within 219 days, a process scientists previously thought took millions of years.

“This is our back to the future thing,” associate ecology, evolution and behavior professor Michael Travisano said.

Genetics senior Katie Howell took microscopic photos of the algae so the researchers could analyze how many cells were in clusters. Out of 10 algae populations, one developed multicellularity.

This is only the second time researchers have recreated multicellular evolution in the lab, Ratcliff said. The first time, the team evolved brewer’s yeast, which has a multicellular ancestor and took only about 60 days.

In the most recent study, Ratcliff and Travisano chose a type of algae that doesn’t have a multicellular ancestor to see if they could replicate their results.

An important part of organisms’ success is multicellularity, said Indiana University-Bloomington professor and ecology, evolution and behavior expert James Bever. Since it’s difficult to study the origins, he called the research “remarkable.”

Travisano said scientists generally think of multicellular evolution as a lengthy, difficult process.

“The first steps in evolution to multicellularity are probably easier and faster than previously appreciated,” Ratcliff said.

The speed of the evolution probably means it happens more frequently than previously thought, Travisano said. But since the world is full of developed organisms already, he said, the newly evolved ones usually don’t survive, because established ones outcompete them.

NASA Astrobiology Institute postdoctoral fellow Matthew Herron from the University of Montana collaborated with Ratcliff and Travisano and analyzed the cell clusters. He discovered they were all identical, meaning they all came from the same line — called a single-cell bottleneck.

The researchers also found that cell competition decreased, but reproductive success temporarily increased.

Cells don’t need to compete if they are identical, Travisano said, because their genetic line is guaranteed to continue no matter which cell produces offspring.

Experts speculate multicellularity may have evolved to settle competition among cells, but the researchers said this study only found a side effect of decreased cell conflict.

“The single-cell bottleneck doesn’t have to evolve to settle among cell conflict,” he said. “It can evolve because … it has other benefits, like increasing short-term reproductive success.”

Now Herron said he’s working with the algae to see if they will evolve differently when he introduces predators into the environment.

Bever said the research sets up a model system for further studies about the origins of multicellularity.

“We can’t go back and study how humans are multicellular,” he said, “but we can go back and recreate this event.”

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