‘Loners’ play important role in evolution, serve as nature’s insurance policy

PRINCETON, N.J. — At a time when many of us are experiencing extreme isolation due to the COVID-19 outbreak, people may feel they’re turning into loners. A study by Princeton University researchers finds being different from the pack isn’t a bad thing. Researchers say those outcast members of a species who hang back from the crowd play a vital role in evolution.

Study author Corina Tarnita says there are many examples of loners in the natural world: wildebeests that don’t migrate with their herds; locusts that separate themselves from the swarm; and bamboo that flowers before or after the rest of the crop.

“Now that we’re starting to look for it, we realize that a whole lot of systems are not perfectly synchronized — and it’s tantalizing to think that that there may be something to this imperfect synchronization,” the associate professor of ecology and evolutionary biology says in a university release.

“Individuals that are out-of-sync with the majority of a population exist in humans, too,” she adds. “We call them misfits or geniuses, contrarians or visionaries, very much depending on how the rest of the society feels about their behavior, but they certainly exist.”

The evolution… of slime?

The Princeton team says loners are an ecological and evolutionary insurance plan. They’re a way to diversify a genetic portfolio to make sure social and collective behaviors survive.

For their study, the authors investigated whether loners are random or if there’s always a predictable number of them in nature. They found a good subject for these tests in Dictyostelium discoideum, a cellular slime mold.

When starving, the humble slime mold amoebae consolidate into slug-like animals which then coalesce into large swaying towers. They grow upward until the slimy top of the tower sticks to passing insects. Starvation-resistant spores then hitch a ride on the insect while the individual amoebae in the tower die off. This collective phase disperses the slime mold while allowing some individuals to live.

Tarnita first noticed that not all slime mold cells were included in these towers in 2013.

“I was at a conference, and a speaker was showing videos of slime molds doing this very complex collective behavior, all determined to reach the center of aggregation,” the researcher explains. “All but some, I noticed: Here and there, some scattered cells on the plate just didn’t seem to react at all to this aggregation process.”

Loners were born to be different

Tarnita started studying the loners, testing to see if there is anything medically wrong with them. Studies find they eat when given food, divide to create offspring, and perform all the life functions normal slime does. Tarnita saw that the offspring of the loners would assemble in the tower when under threat of starvation.

In their experiments, Tarnita’s team reveals that even when they create an ideal condition for the slime mold to form towers, there are still loners left behind.

“This was exhilarating because it meant that we had originally been right that the loners were far from boring, but it also meant that, theoretically, we needed to go back to the drawing board,” says Tarnita.

The team took a few years to develop a modeling effort to predict the ratio of loners to individuals that formed the towers. The study authors theorize that loner behavior is a way to hedge against collective behavior. For example, if a wildebeest herd moves into a dangerous area, the behavior won’t wipe out the entire population.

The study was published in the journal PLoS Biology.

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