Natures wonders: nerveless multicellular movement (Introduction)

by David Turell , Sunday, March 27, 2022, 15:19 (755 days ago) @ David Turell

Research into a tiny moving sea animal:

https://www.quantamagazine.org/before-brains-mechanics-may-have-ruled-animal-behavior-2...

"The extremely simple animal Trichoplax adhaerens moves and responds to its environment with agility and seeming purpose, yet it has no neurons or muscles to coordinate its movements. New work shows that biomechanical interactions among the animal’s cilia are sufficient to explain how it moves.

"The animal beneath the lenses wasn’t much to look at, resembling an amoeba more than anything else: a flattened multicellular blob, only 20 microns thick and a few millimeters across, with neither head nor tail. It moved on thousands of cilia that blanketed its underside to form the “sticky hairy plate” that inspired its Latin name, Trichoplax adhaerens.

"This odd marine creature, classified as a placozoan, has practically an entire branch on the evolutionary tree of life to itself, as well as the smallest known genome in the animal kingdom. But what intrigued Prakash most was the well-orchestrated grace, agility and efficiency with which the thousands to millions of cells in Trichoplax moved.

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"In a trio of preprints totaling more than 100 pages — posted simultaneously on the arxiv.org server last year — he and Bull showed that the behavior of Trichoplax could be described entirely in the language of physics and dynamical systems. Mechanical interactions that began at the level of a single cilium, and then multiplied over millions of cells and extended to higher levels of structure, fully explained the coordinated locomotion of the entire animal. The organism doesn’t “choose” what to do. Instead, the horde of individual cilia simply moves — and the animal as a whole performs as though it is being directed by a nervous system. The researchers even showed that the cilia’s dynamics exhibit properties that are commonly seen as distinctive hallmarks of neurons.

"The work not only demonstrates how simple mechanical interactions can generate incredible complexity, but also tells a compelling story about what might have predated the evolution of the nervous system.

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"...single cells alone are capable of remarkable behaviors, and they can self-assemble into collective systems (such as slime molds or xenobots) that can achieve even more, all without the help of neurons or muscles.

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"In their models, the walking activity emerged naturally from the interplay between the internal driving forces of the cilia and the energy of their adhesion to the surface. The right balance between those two parameters (calculated from experimental measurements of the cilia’s orientation, height and beat frequency) resulted in regular locomotion, with each cilium sticking and then lifting away, like a leg. The wrong balance produced the slipping or stalled phases.

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"The cilia aren’t getting paced. There’s not some central thing that’s saying ‘Go, go, go.’ It’s the mechanical interactions that are setting up something that goes, goes, goes.”

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"Prakash, Bull and Kroo’s cilia models turned out to map very well onto established models for action potentials in neurons. “This kind of unique phenomenon admits itself to a very interesting analogy with what you see in the nonlinear dynamics of single neurons,” Bull said.

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"Eventually, Prakash and Bull found that they could write down a set of mechanistic rules for when Trichoplax might spin in place or move about in lopsided circles, when it might follow a straight path or suddenly veer to the left, and when it might even use its own mechanics to rip itself into two separate organisms.

“'The trajectories for the animals themselves are literally encoded” in these simple mechanical properties, Prakash said. (my bold)

Comment: this study is entirely of mechanical principles in motility. It must sense food chemically as other simple animals do. It is obviously a step toward complete multicellularity and illustrates how big the Cambrian gap really is. Note the comment about coding. It must exist in the tiny DNA in this animals.