Outliers exist everywhere in nature. Whether you're a scientist or not, chances are you've had experience with one of those things that is not like the others. Researchers are finding that loners, or small groups that don't react the way all others of their kind do, may be serving a crucial purpose; the flower that blooms late or early or the herd that misses the migration might actually be ecologically important, suggested associate professor of ecology and evolutionary biology Corina Tarnita. Evolution may actually select for the behavior of loners in some cases, according to a study in PLOS Biology by Tarnita and colleagues.
"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," Tarnita said. "Individuals that are out of sync with the majority of a population exist in humans, too. 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."
Unfortunately, Tarnita and other researchers face challenges in the study of collective systems; a locust swarm or wildebeest migration can't be used in an experiment that tests the impact of loners. In this work, however, they were able to find a model organism: the slime mold Dictyostelium discoideum. This enabled the scientists to select for loner behavior, and show that loners can act as a kind of protection that ensures a population stays diverse and will survive.
Slime mold expert John Bonner has shown (video above) that if the resources used by slime mold diminish and starvation is a threat, they aggregate into a tower that can grow upward. That enables spores from the colony to stick to passing insects and spread out into the world, even as the base of the tower is dying. Thus, collective behavior is necessary for survival. But in 2013, Tarnita began to take note of the slime mold cells that didn't take part in this activity.
"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," Tarnita said. "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."
While these loners had been dismissed by others as mere mistakes, she wondered about them and began to test them in her studies.
Careful studies by graduate candidate and co-first study author Fernando Rossine showed that loners couldn't be eliminated, even in a controlled environment. When he used wild slime molds, up to 30 percent of cells opted to act as loners. He was able to confirm Tarnita's hypothesis that they aren't random errors. If the slime mold population was small, all the cells behaved like loners. Over a certain limit, the tower-building starts, with a fraction avoiding the task. Once the population got to a certain size, the number of loners leveled off.
"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," said Tarnita.
The collective behavior of a group can have major benefits but also poses some risks, leaving loners as a kind of insurance policy.
"It's a social bet-hedging," said Rossine. "And a fascinating conclusion that follows from our findings is that, at least for slime molds, the decision not to become part of the collective is, in fact, taken collectively. All the cells kind of talk to each other chemically: 'Oh, you're going? I guess I'm staying.' There's communication involved in becoming a loner."
Tarnita is featured in the video above.
Sources: AAAS/Eurekalert! via Princeton University, PLOS Biology
