Surprise! Even Brainless Single-Celled Organisms Can Make "Complex" Decisions

By

CCSS NAS-1 NAS-3
The single-celled S.roeselli's complex behavior was first recorded by zoologist Herbert Jennings in 1906 (Credit:Dexter et al. & Current Biology)

With no brains or nerve cells, single-cellular microorganisms are often regarded to be simple, primitive beings with few capabilities. However, a new Harvard University study suggests that protozoans, like Stentor roeselii, have the smarts to make "complex" decisions when confronted with unpleasant situations.

The trumpet-shaped creature, found worldwide in freshwater ponds, lakes, rivers, and ditches, attaches itself to a firm surface such as algae or submerged waste. It then uses its large mouth-like opening, which contains thousands of tiny hairs called cilia, to suck in food.

The simple creature's decision-making prowess was first observed in 1906 by American zoologist Herbert Jennings. The researcher noted that when exposed to an environmental irritant, in this case carmine powder, the S. roeselii swayed away as though hoping it would pass and things would return to normal. If that failed to work, the microorganism tried several other clever tricks, such as reversing its direction or contracting, before finally detaching from its anchor and floating away in search of a more tranquil location. Unfortunately, Jennings' findings, which could not be replicated by other scientists, were met with skepticism and soon dismissed.

When faced with an irritant, S. roeselii will first bend away and alter the beating of its cilia to expel the particles from its oral cavity (Credit: Dexter et al, 2019)

Now, over a century later, a team led by Jeremy Gunawardena, an associate professor at Harvard Medical School, has finally verified the zoologist's research. However, while Jennings' observations indicated that all S. roeselii protozoa followed the same sequence to avoid the external irritant, the 2019 study found a variation in the order between individuals. While one specimen would start by swaying away before altering the direction of its cilia, another would switch between the two actions. Regardless of the order, they all contracted as the last resort, before finally detaching and fleeing.

“They do the simple things first, but if you keep stimulating, they ‘decide’ to try something else,” says Gunawardena. “S. roeselii has no brain, but there seems to be some mechanism that, in effect, lets it ‘change its mind’ once it feels like the irritation has gone on too long. This hierarchy gives a vivid sense of some form of relatively complex, decision-making calculation going on inside the organism, weighing whether it’s better to execute one behavior versus another.”

If bending and cilia alteration are insufficient, S. roeselii will contract onto its holdfast, or detach and swim away (Credit: Dexter et al, 2019)

The scientists, who published their findings in the journal Current Biology on December 5, 2019, believe the complex decision behavior makes evolutionary sense. "Organisms like S. roeselii were apex predators prior to multicellular life, and they are extremely widespread in many different aquatic environments," Gunawardena said, "They have to be 'clever' at figuring out what to avoid, where to eat and all the other things that organisms have to do to live. I think it's clear that they can have complex ways of doing so."

Besides vindicating Jennings, the Harvard University research may have broader implications for biology. For example, cancer researchers currently assume that diseased cells are "programmed" to do what they do. However, if single-celled organisms have a "mind" of their own, it may change the way we think about how cancer cells multiply and how the immune system works. Gunawardena said. "I think this experiment forces us to think about the existence of, very speculatively, some form of cellular 'cognition,' in which single cells can be capable of complex information processing and decision-making in response."

Resources: hms.harvard.edu, phys.org

Cite Article
Vocabulary List
algaeanchorcognitioncomplexconfrontedcontractingdismissedenvironmentalevolutionaryexecutehierarchyimmuneimplicationsmechanismmicroorganismspredatorsprimitiveprowessreplicatedresortsequenceskepticismstimulatingsubmergedtranquiltrumpetvariationverifiedvividwidespread
70 Comments
  • molynn_f
    molynn_fTuesday, January 21, 2020 at 6:35 am
    Wow. I can only imagine what would happen if those things romed the strrets. Lol.
    • im_happy
      im_happyThursday, January 23, 2020 at 1:30 pm
      Oh no XD
    • b3njam1n
      b3njam1nFriday, January 17, 2020 at 5:09 am
      Wut 'bout jellyfish dey smarts
      • follow-all
        follow-allFriday, January 17, 2020 at 11:04 am
        they super smarts
        • thisisit
          thisisitFriday, January 24, 2020 at 3:41 pm
          Octopus is the smartest by far
      • chanyag264
        chanyag264Thursday, January 16, 2020 at 6:50 pm
        you got to watch this video it is so wired
        • dragongirl08
          dragongirl08Thursday, January 16, 2020 at 3:46 pm
          Wow
          • hbcvfnmfb
            hbcvfnmfbThursday, January 16, 2020 at 11:54 am
            nasty
            • lovepup1
              lovepup1Thursday, January 16, 2020 at 11:18 am
              this is so creepy it is soo good
              • maxisecenuxoxa
                maxisecenuxoxaWednesday, January 15, 2020 at 12:54 pm
                can you like and follow me plz id like it if you did :)
                • maxisecenuxoxa
                  maxisecenuxoxaWednesday, January 15, 2020 at 12:52 pm
                  looks like a tape worm but really small
                  • meza
                    mezaWednesday, January 15, 2020 at 8:58 am
                    I wonder what applications can come out of this study.
                    • nmboss5
                      nmboss5Tuesday, January 14, 2020 at 11:13 am
                      i wonder what will happen if this happened to me