In 1906 the zoologist Herbert Spencer Jennings published Behavior of lower organisms, a book that had a provocative idea: microbes can change their minds.
His subject was a single cell full of flapping hair Stentor. These trumpet-shaped predators are so big that fish can eat them and Humans can see them and so audaciously that they can catch and eat rotifers – real animals with hundreds of cells and a simple brain. In the microbial galaxy, stentors lie somewhere between the Star Destroyer and the Sarlacc Pit.
Jennings decided to tease it and see what happened. When faced with a stream of irritating carmine powder skillfully directed at her mouth by his steady hand, Stentor would bend down first, then reverse beating his hair (called cilia) to drive out the powder, then contract and finally peel off.
He noticed that the order of behaviors with different stimuli varied slightly (he tried different chemicals) and steps were sometimes left out. “But it remains true,” he wrote, “that under conditions which gradually interfere with the normal activities of the organism, behavior consists of successively” trying “different responses until one is found that offers relief.”
In short, stentors could confront a stimulus with behavior and then take a more costly approach if the irritant persists. For at least a short time (a time Jennings found experimentally difficult to determine and which was still unsolved) it could “remember” that it had tried one solution to no avail and decided on another.
In 1967, scientists from another school of animal behavior repeated his experiment and did not get the same result. And with that, Jennings’ results were thrown in the trash can.
About 10 years ago, Jeremy Gunawardena, Associate Professor of Systems Biology at Harvard Medical School, discovered the experiment and its defenestration and decided it deserved another look. To his surprise, he found that the 1967 team hadn’t used the right types of Stentor (As behaviorists who believed that variation came from the environment rather than from genes, they might feel that the species did not matter). The one they chose Stentor coeruleus, strong Unlike Jennings, he prefers to swim Stentor roeselii, who prefer to relax by the pool.
Gunawardena was intrigued by what repeating the experiment could tell about what individual cells are capable of. After years of unsuccessful working through the idea at laboratory meetings, he found that student Joseph Dexter and postdoc Sudhakaran Prabakaran were willing to try it out at night and on weekends – with no financial support.
This time the Harvard team managed to track down the right species in an English golf course pond and to build their own “stimulating device” Stentors” (As quantitative biologists, they lacked Jennings’ extreme pipette skills) and they discovered something extraordinary.
In your setup, Stentor did not respond to carmine powder as described by Jennings. However, when faced with the plastic microsphere barrage of the 21st century, it is individual Stentor Roeseli behaved in line with Jennings’ description – and in a remarkable way that Jennings did not observe in 1906.
If Stentor really can “decide,” it is certainly not the only path for the ciliates – the group of shaggy microbes to which they belong Stentor heard – resemble us. A ciliate works like an animal on the scale of a single giant cell, and the resemblance can be startling.
For example, some bundles of their cilia stick in structures called cirri and they can be used as legs, mouths, paddles, or teeth. Euplotes Skitters flit nimbly across surfaces on Cirri like some sort Close encounters-Class water flea. The Cirri are wired through nerve-like neurofibrils. When the fibrils are cut, the cirri go limp.
Some ciliates grab tiny tethered arrows that they can fire to attack prey, deter predators, or simply to anchor. Others have tentacles that catch on food. Like starfish, ciliates can regenerate entire bodies from shockingly small pieces in a day or two, provided that those pieces contain both a piece of the cell’s ciliated armor and a piece of nucleus, the cell’s genetic heart. Many ciliates divide in the usual way by pinching in two, but some stalked or sessile ciliates push small round larvae into the world through a special birth canal.
A ciliate called Diplodinium lives in the rumen of cows and other ungulates, a special environment that is home to all sorts of weird things, about half of which may be ciliates (keep this in mind the next time you see a cow peacefully chewing on its sprout ). Diplodinium Contains neurofibrils, cirri, muscle-like striped contractile fibers called myonemes, a “backbone” made of stacked plates, a mouth, an esophagus that contracts with the help of a ring attached to the outside, and an anus. But remember: single cell.
In short, ciliates have pushed the biology of the solo cell to its apparent earthly limit. Having something like a noggin in there is less gullible once you get it.
In the new study published in the journal Current biology in 2019, The scientists found that out Stentor in fact, behavior alternated in response to repeated poking of pearls, and the order of operations generally coincided with Jennings’ description. Detachment was always preceded by a contraction, and mathematical analysis showed that the cilia were far more likely to change or bend before the contraction than afterwards.
There is something else interesting about your datawhat i enCourage to check it out for yourself: It sure looks like stentors have personalities. Some contracted and relaxed repeatedly, or bent over, contracted, then relaxed and seemed willing to tolerate irritation – or live dangerously. They were the optimists.
Some contracted once or just a few times, never to relax again. Others contracted and broke up, and that was it. These were the pessimists (or maybe just those with a recent successful “door push”).
Some stentors always responded with one or two preferred behaviors, and never others, that they were certainly as biologically capable. A tireless person exposed to 13 bead explosions persistently responded by changing or contracting ciliary ciliary without bending or loosening.
Does Stentor have something like an agency – an ability to make decisions? This study and Jennings’ evidence undoubtedly suggest so.
There was one final provocative finding. Statistical analysis by this team found that choosing between contraction or detachment corresponds to the likelihood of a fair coin toss. In other words, it seemed completely random.
There is only one problem: no known cellular mechanism can achieve this result. This head scratch remains both inexplicable and unexplained.
Perhaps it is time to let go of our preconceived notions of what cells are capable of because they are just Cells, and the cells in our own Soviet-style bodies are the equivalent of worker bees. The abilities of crafty, gunslingers, and free-living cells can far exceed our faint conceptions of primates.