Spirogyra is just a set of cells connected to each other; it has no leaves, roots, etc... It even doesn't have multiple layers of cells like Hydra. So what is evolutionary advantage for Spirogyra cells to connect to each other? Why not to live separately like Chlorella?

P.S. I think this question is different from this one: Why do some bad traits evolve, and good ones don't? The reason is that I don't see that connecting cells to each other is "bad trait". If anyone can argument that such connecting is obviously "bad trait", they are welcome to write it in comments or in answer.

I think it is obvious that been multicell is advantage, but the advantage primarily is ability for organism to combine cells of different types that perform some specific tasks better that 'universal' cell of single cell organism. So, there are no question what is advantage to be multicell for apple tree. But spirogyra looks like something unusual for me. It has multicellularity (in my understanding it is actually very ancient organism), but what is advantage of this trait?

We can of course imagine that multicellularity is "bad trait" here, and that organisms similar to spirogyra became just "evolution raw material" like dinosaurs became ancestors of birds. But this idea doesn't look correct for me, I think we have to dig deeper here. We see that colonies of similar cells are widespread and spirogyra is not the only such organism. We have also Volvox, and Cladophora is more complex but shares the same idea. So, such organisms are too widespread to be "evolutionary error" in my opinion.

From comments I can see 2 ideas:

  1. It is more complex to eat such organism.
  2. Such organisms can attach to the substrate.

These ideas may be correct. BTW what is advantage to attach to the substrate? Many even single-sell species can do that (for example, Vorticella).

  • $\begingroup$ Well, the hairs catch onto objects well, might be harder for predators to eat. $\endgroup$ Apr 30, 2022 at 5:42
  • $\begingroup$ well to start it is harder to eat a long strand of cell than a singe cell. $\endgroup$
    – John
    Apr 30, 2022 at 15:50
  • $\begingroup$ Does this answer your question? Why do some bad traits evolve, and good ones don't? $\endgroup$
    – tyersome
    May 2, 2022 at 0:30
  • $\begingroup$ @tyersome I have no idea whether it is good or bad to be multicellular, so the link may or may not be the correct answer. I thought about that last days when I shew Spirogyra in microscope to my children, so I asked may be there is obvious answer that biologists know; I am computer programmer myself. $\endgroup$
    – Vitalii
    May 2, 2022 at 6:23
  • $\begingroup$ If you have "no idea whether it is good or bad", then why did you ask what the "advantage" is? If there some subtle distinction you are trying to make can you please clarify. ——— One of the problems with this type of question is that they assume that there must currently be an advantage and ignore the huge influence of contingency of evolution. You may find this, introduction to evolutionary theory from UC Berkeley to be of interest. $\endgroup$
    – tyersome
    May 5, 2022 at 21:22


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