Rib oyster neurons–an evolutionary pathway dead end

Who would have thought that the most controversial creature on earth is the tiny, but so charming rib-eye clam?

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It has been argued for many years whether these animals or more primitive sponges are the most ancient multicellular animals on Earth. It turns out that in order to be the oldest multicellular evolutionary animal alive today, one would have to appear extremely sensitive and present a significant level of internal complexity. Rib oysters won that particular race for priority, which I’ve described in these pages.

A few days ago, an older article came to my attention, but I’m sorry I wasn’t aware of it before, in which it talked about the evolutionary antiquity of the beautiful water rib oyster. They are erroneously discussed in school next to cnidarians (in which there are many sea anemones, corals, cherries and hydras, better known to us as jellyfish), although they are de facto predators.

However, as is usual in those cases where appearances deceive us as to the classification of creatures, genome analyses, that is, relationships studied by their traces in the DNA of the genetic material of many organisms, have proved useful. It turns out that deep observations of the neurons of the rib clams indicate that they may have arisen entirely independently of the rest of the neurons, remaining in service today only in this species of invertebrate and no one else in the world. We call such situations the dead end of development.

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Just because a path is a dead end doesn’t mean it’s inefficient, unwise, or otherwise flawed – there are plenty of examples of this in nature. For example, the extraordinary immune systems of lampreys and hagfish, which together make up a subgroup of vertebrates—and in that sense our rather close relatives—evolved in a common ancestor, and then, when the entire group of their descendants was restricted to two living ones. requests, they are just in it and it works really well.

Just because we have a different one doesn’t necessarily mean it’s much better. Let’s remember that what is good enough under certain conditions continues to evolve, not just the best. What wins the race is what is able to adapt as widely as possible, not what has achieved the highest specialization.

It’s the same with the eye of a cephalopod or any other arthropod – they don’t have much in common with our eyes. Outside of these groups of invertebrates, none use the evolutionary solutions that were developed there, and yet it’s hard to say that these eyes are worse than ours. Moreover, the eye of such an octopus is structurally similar to ours, but it does not have any meaning for the development of these organs – they are not related to each other, but similar. This is called similes.

Here, therefore, we touch on the main question to which rib clams seem to give a positive answer, and which caused quite a stir in the scientific community in 2015: did neurons evolve twice? As described then, also in the popular version on the pages of BussinesInsider.com, neuroscientist Leonid Moroz, then of the Whitney Laboratory for Marine Biosciences in St. Augustine of Florida, author of one of the available complete genome sequences of cnidarians published in 2013, noted that their neurons are not visible. Doesn’t mean it doesn’t exist. This would be impossible, because ribbed clams are not only excited (unicellular protists, such as the well-known gem that swims toward light or the sole that swims towards food, can do this), but also coordinate the movement of their tentacles and the pulsation of their iridescent cilia.

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They can’t be seen in microscope slides because the “dyees” that scientists normally use to study these cells simply didn’t work. It was necessary to choose their anatomy and arrangement differently. For example, they did not have serotonin or any other evolutionarily ancient neurotransmitter…. This is ambiguous, because if the neurons of all animals were associated cells, the antibodies could not be fooled. If the immunosuppressant is not working properly, something is wrong. Perhaps oyster neurons look alike to our neurons, do similar things, but have no common origin whatsoever, and so have different proteins in their membranes, and their biochemical components are slightly different?

Since the ribbed clam is the oldest evolutionarily multicellular animal living today (Precambrian, from the time when our planet was like a snowball, so it was covered with glaciers, i.e. 700 million years old), the antiquity and uniqueness of its neurons Don’t miss the point. Sponges, having adopted an ancient, no less active way of life, secondarily have no nerve cells, because who needs nervous sensitivity when it sits in the place of such a fungus and drops food itself into its mouth? So there is not a lot of material for deep comparisons. No energy is spent on what is not needed. An avid hunter for food, the rib-eye clam has been honing its neural intelligence for thousands of years.

According to traditional evolutionary biology, neurons only evolved once, hundreds of millions of years ago at the beginning of animal multicellularity. But Dr. Moroz agreed and tried to show that this could happen twice. Once in the rib ancestors of clams, and again in the creatures that gave rise to cnidarians and all subsequent animals, including chordates, that is, us and all our cousins ​​from scalpels to chimpanzees.

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Of course, such an opinion can be criticized by the so-called peasant of common sense. However, nature, which has developed “in our ability to calculate from the first equations on paper, what is the temperature inside a star 100 light years away from us” (as a physicist from the University of Warsaw, Professor Krzysztof Messner) does not care much about our peasant mind and follows its own path .

Thus, critics have argued that “neurons are the most complex type of cell in existence, capable of capturing information, performing calculations, and making decisions. Because they are so complex, they are unlikely to evolve twice.”

The specialization of neurons from cells that were not neurons is a remarkable event in animal evolution. Not only are they quick to excite, but they are also capable of communicating in a variety of ways and pre-engineered to create cohesive and often very complex IT networks. This allows you to receive, transmit and process information using precise chemical and electrical language.

Whether it is the rib oyster, whose nervous system is essentially not centralized, or the octopus, which is able to decipher the mouthful of appetite, where it is centralized (even in each individual arm), or finally, our brain, which is capable of counting, if it is trained to do so , that’s the temperature inside a distant star, though it’s not really needed for anything – the power of the nervous system lies in its network. This means that not only neurons must evolve twice, but also their delicate and complex networks.

As the neuroscientists conclude, “This level of complexity requires an unlikely confluence of evolutionary events. Mechanisms must be developed that not only physically connect cells but also enable them to transmit and interpret signals.”

So, according to Dr. Moroz’s version of the evolutionary tree, the common ancestor of all animals did not have nerve cells. When the rib clams diverged, they developed their own neurons and networks. Then the ancestors of sponges and the so-called Placozoa (type Placozoa, slightly resembling the shape of ancient Ediacaran leaves dikonia – both without the nervous system known today.

The original neurons then evolved a second time in the common ancestor of cnidarians (they have radial symmetry) and bilateral symmetry animals to which we all belong as we stand here. This formed the basis of the nervous system found in all of their descendants.

Other scientists believe that the common ancestor of all animals had a simple nervous system, which the sponge lost secondarily when it settled. And the rib clams and the rest of the animal world in the common developmental branch to which our ancestors belonged built on these proton neurons in two very different ways, leading to the development of more complex nervous systems. Basically, today it is impossible to say who is right in this matter.

Why are these kinds of examples of evolution not going straight, “as God commanded,” but in various dead ends, usually coming from genetic analyses, because evolution has left its indelible mark, important? They undermine the long-held and misguided notion that evolution, which generates complexity, is constantly moving forward. Confuse evolution with progress, especially not so much since the days of Darwin, as the crude Marxism applied in communist systems (educational too) taught as part of the “WKP(b) short history course”. Evolution has nothing to do with progress. Rather, with evolution, and even understood as change rather than striving for perfection.

Finding oyster rib is a challenge. Their basic biology is still shrouded in mystery, and their bodies are so fragile that they break off when grasped. They are also difficult to grow in the laboratory; How do experiments on these animals?

They hunt thanks to their sticky tentacles, because unlike jellyfish, they are tasteless. Their genome also launches them off the tree of life to a more recent common ancestor with sponges, and not with the rest of the animals living today. Furthermore, there is evidence strongly suggesting that riboi evolved faster than other ancient animal groups, which means that their genetic sequence changed at a higher rate.

If we think we can learn all about biology by just studying ourselves, or perhaps mice, when research on ourselves is unethical, we are more than wrong. We are not alone here, and biodiversity is not only the richness of the present, but also the richness of the past, recorded in the ancient genomes of representatives of ancient groups of organisms that still live today.

Do you burn a library of ancient manuscripts, or do you think this is barbaric? So what if they don’t have any knowledge left that we can use, since there is history recorded there? Destroying the habitats of organisms that are evolutionarily far from us is exactly the same. It’s like: do we destroy or do we consider it barbaric?

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# Neurons


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