No, These Researchers Did Not See a Single-Celled Organism Evolve Into A Multicellular Organism!

A green algae in a predator-free environment (far left) and other environments with predators. (click for credit)

A student sent me an article from Science Alert, asking me about its rather bold claim:

Scientists Have Witnessed a Single-Celled Algae Evolve Into a Multicellular Organism…Most of us know that at some point in our evolutionary history around 600 million years ago, single-celled organisms evolved into more complex multicellular life. But knowing that happened and actually seeing it happen in real-time in front of you is an entirely different matter altogether. And that’s exactly what researchers from the George Institute of Technology and University of Montana have witnessed – and captured in the breathtaking, time-lapse footage below.

Over the course of my scientific career, I have learned that many science journalists are terrible at science and not much better at journalism, so I did what I always do when I read about science in the popular press: I found the scientific article upon which it was based. Not surprisingly, the study didn’t do what the article claims. It did find one interesting result, however.

The study examined the behavior of a green algae in the species charmingly named Chlamydomonas reinhardtii. In the wild, these algae exist as individual, single-celled organisms. In the lab, the researchers exposed some of them to a natural predator (Paramecium tetraurelia) and found that the algae would come together and form colonies, since that made them less likely to be eaten by the predator. In other words, several individual single-celled organisms would “team up” to gain protection from the predator.

This is not surprising, and it is not a new result. Indeed, other researchers noted this behavior four years ago. Interestingly enough, they found that the algae didn’t even need to be in the same species to “team up.” They also saw that when the predator was removed, the algae went back to their single-celled form. Technically, this is called facultative multicellularity, and it is seen in many single-celled organisms. They prefer to live life as individuals, but when they have to, they come together to help one another out.

Here is where the new study is different. When they removed the predator, the cells stayed together. They even reproduced together. Indeed, the researchers report that even though the predator was removed four years ago, the cells have stayed in groups and reproduced in groups. As a result, they say they have produced an obligate multicellular form of the organism: one that stays together even when it could split into individual cells again.

I am skeptical that this is the case. Most likely, there is no selective advantage to these algae reverting back to their single-celled form in this artificial environment, so it doesn’t happen. Instead, the algae continue to behave the way they were behaving when the predator was present. I would suspect that if these organisms were put in the wild (or even a more freely-changing artificial environment), they would revert back to single-celled organisms when that produced an advantage over the group form.

However, let’s give the researchers the benefit of the doubt. Let’s say that even in the wild, this group of algae stays a group and is therefore truly an obligate multicellular form of the algae. Does this tell us anything about the origin of multicellularity? No. All it shows is that single-celled organisms which already tend to clump together in groups when the need arises will sometimes stay in groups, even when the initial reason for the formation of the group is gone. While this is interesting, it tells us nothing about how multicellular life might have formed. It might tell us how colonies of single-celled organisms (which exist in abundance today) formed, but that is all.

Multicellular organisms are not just colonies of single-celled organisms. Multicellular organisms have cells that split the tasks of the organism and communicate with one another to make sure all the tasks are being performed and being performed properly. That is a lot different from a colony of single-celled life forms that all do the same thing but just group together because there is strength in numbers.

If evolution in the flagellate-to-philosopher sense is true, there must have been a transition between single-celled organisms (or colonies of single-celled organisms) and multicellular organisms. It would require the evolution of cellular specialization, sophisticated cellular communication, and many other genetic innovations, none of which are needed to explain the results of this study. Thus, while this study is interesting in the sense that it might have produced a stable colonial version of a single-celled organism, it tells us nothing about how multicellular organisms formed.

13 Comments

  1. Dr. GS Hurd says:

    Ratcliff and his research team have been working with yeast as a model organism for some years now. These are good, but not the only experimental, or natural examples of how multicellylar organisms evolved;

    Ratcliff, W.C., Denison, R.F., Borrello, M. and Travisano, M., 2012. Experimental evolution of multicellularity. Proceedings of the National Academy of Sciences, 109(5), pp.1595-1600.

    Ratcliff, W.C., Herron, M.D., Howell, K., Pentz, J.T., Rosenzweig, F. and Travisano, M., 2013. Experimental evolution of an alternating uni-and multicellular life cycle in Chlamydomonas reinhardtii. Nature communications, 4, p.2742.

    Bacteria can respond to environmental change and develop cell specialization as well;

    Claessen, D., Rozen, D.E., Kuipers, O.P., Søgaard-Andersen, L. and Van Wezel, G.P., 2014. Bacterial solutions to multicellularity: a tale of biofilms, filaments and fruiting bodies. Nature Reviews Microbiology, 12(2), p.115.

    The classic examples are the amoebae Dictylostelium discoideum.
    Strassmann, J.E. and Queller, D.C., 2011. Evolution of cooperation and control of cheating in a social microbe. Proceedings of the National Academy of Sciences, 108(Supplement 2), pp.10855-10862.

    1. Jay Wile says:

      Thank you for those references!

  2. Daniel Stern Cardinale says:

    I don’t think this is a reasonable critique of these findings.

    From the original paper:

    “For example, in Fig. 1, an external membrane is visible around both evolved multicellular colonies, indicating that they formed clonally via repeated cell division within the cluster, rather than via aggregation.”

    And later:

    “Conversely, three of the strains isolated from population B2 exist in cell clusters comprised only of direct descendants, as opposed to chimeric aggregations with free-swimming cells. Clusters from strains B2-11, B2-03, and B2-04 grow in tightly associated groups of direct descendants embedded in the maternal cell wall (Fig. 2D; Supplemental Videos 7, 8 and 9, respectively). Development in these isolates is therefore strictly clonal, with important implications for evolvability.”

    The critique in tis post is based on the idea that these multicellular structures formed via aggregation, but the authoers of the original paper make clear that this is not the case, and the supplemental videos show the multicellular structures growing clonally rather than via aggregation.

    I think this piece needs to be updated to reflect that this is the case. Someone reading this post without consulting the actual study would think the authors observed aggregation and nothing more.

    1. Jay Wile says:

      Thanks for your comment, but I will have to disagree with you. Indeed, the quotes you present confirm what I have written. As I state in the article, this study may show how colonies form (assuming the colonial nature continues in a more widely-varying environment), and the quotes you chose from the article specifically refer to the structures as colonies.

      1. Daniel Stern Cardinale says:

        I’m not objecting to the word “colony”. I’m very specifically objecting to the description of this process as “aggregation”. They do not form via aggregation. They’re not “teaming up”. They start as a single cell, divide, but stay together as a unit after division. That’s not aggregation.

        1. Jay Wile says:

          But I don’t use the term “aggregation” at all. I indicate that they reproduce together, and that the authors think they have formed an obligate multicellular form. The cells are, indeed, “teaming up,” but what makes this study interesting, as I indicate, is that the team stays together and even reproduces together. However, I also make the point that this is not a multicellular organism, because it most definitely isn’t. It is a colony.

  3. Daniel Stern Cardinale says:

    Responding to the comment from 1:57pm:

    “In the lab, the researchers exposed some of them to a natural predator (Paramecium tetraurelia) and found that the algae would come together and form colonies”

    The word for this is “aggregation,” but this does not describe the central finding of this paper.

    It does not seem like you are interested in acknowledging this very important difference between what the paper actually describes and how you describe the findings.

    1. Jay Wile says:

      I am describing the paper’s results faithfully. The single-celled organisms come together and form a colony. That’s not the way I understand the definition of aggregation. Aggregation is simply clumping together. That’s why I don’t use the term. The cells are doing more than that. They are forming a colony, as I state in the quote you give and as I have stated in the original post. That is precisely what the authors describe in the paper.

      1. Daniel Stern Cardinale says:

        “The single-celled organisms come together and form a colony.”

        But..I mean…this isn’t what happened. A single cell divided into many, and through that process, they stayed together. It is just not the case that the authors are reporting that they observed multiple independent, free-living organisms associate together to form a colony. The authors say that, right here:

        “For example, in Fig. 1, an external membrane is visible around both evolved multicellular colonies, indicating that they formed clonally via repeated cell division within the cluster, rather than via aggregation.”

        And again here:

        “Conversely, three of the strains isolated from population B2 exist in cell clusters comprised only of direct descendants, as opposed to chimeric aggregations with free-swimming cells.”

        I just don’t know how you’re reading this and getting “several individual single-celled organisms would ‘team up’ “.

        But I’m sure you’re not interesting an changing how you are representing these results, so have the last word. I look forward to the next paper you summarize here.

        1. Jay Wile says:

          Look at Figure 2. The “A” part of the figure shows the ancestral, wild-type life cycle. Parts “B” through “D” show the colonies they observed. What is the difference between A and B-D? They all start out reproducing an association of four cells. In the wild-type, however, the cells split up and go their separate ways. In B-D, they reproduce within the association. So rather than going their separate ways once four cells were formed, the four individuals “teamed up.” Would you rather that I had said “stayed together to team up instead of going their separate ways?” I don’t see how that’s different. After all, I then go on to explain that they stayed together and reproduced together.

          I am happy to alter my text when it is not correct (indeed, I feel obligated to and have done so in past articles), but the text as it is given is correct.

  4. John D says:

    You did neglect to mention the part where the colony was a final contestant in the Publishers Clearing House sweepstakes – whereas none of the single cell organisms received any such notification. That’s gotta count for something!

  5. Manuel says:

    Thank you for this article! I was on a group in FB discussing evolution and intelligent design, and by myself I handled a bunch of them for a while then someone posted that research. I knew there was something “fishy” about it and neither the time or the qualification to analyze it well. I did a research and found your article… silence followed from the followers of evolutionism!

Leave a Reply

Your email address will not be published. Required fields are marked *

 

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: