Evolutionary step from single cell to multicellular organism demonstrated

[billvon]

Pretty cool:

===========================
Multicellular Life Evolves in Lab

January 18, 2012

More than 500 million years ago, single-celled organisms on the Earth’s surface began forming multicellular clusters that ultimately became plants and animals. Just how that happened is a question that has eluded evolutionary biologists.

But scientists in the Univ. of Minnesota’s College of Biological Sciences have replicated that key step in the laboratory using natural selection and common brewer’s yeast, which are single-celled organisms. The yeast “evolved” into multicellular clusters that work together cooperatively, reproduce and adapt to their environment – in essence, precursors to life on Earth as it is today.
================================


http://www.laboratoryequipment.com/...-Recreate-Vital-Evolutionary-Step-011812.aspx

 

[Aqueous Id]

Pretty cool:

cool indeed.

They seem to be signalling across cell membranes. The centrifuge imposed a force, created a gradient for density, and impacted osmosis. So there must be some even cooler underlying science, just in that aspect alone.

At some point there is signalling anyway. Somehow certain cells are specializing themselves for apoptosis for the good of the community.

Specialization is cool in itself, too, as it leads to the invention of sexual reproduction, and stem cells come to mind. The algae Volvox is of interest. (It may have diverged around 200 MYA.)

Naysayers and fans alike may enjoy reading:
Triassic origin and early radiation of multicellular volvocine algae.

 

[wellwisher]

The idea of the first multicellular expression, being a loose grouping of cells came to me twenty years ago. It took science two decades to catch up.

From this simple state, evolution will then make use of potential gradients to help differentiate different parts of the grouping. For example, a loose grouping of plant cells could make use the potential gradient created by sun and soil (dark). This creates different parameters at each end for cell differentiations. The next experiment would be to create a gradient around the synthetic cell mass.

As a practical test of potential gradients in action, start with a group of identical seedlings, so the DNA is fixed for all or at least tight. Next, alter the gradient between light and soil, for each seedling, by altering the light and the composition of the soil.

Next, note that although all the cells have the same DNA, the different gradients will induce different expressions in the DNA, from strong and vigorous to weak and spindly. You then ask someone who knows genetics, which of these genes will have natural selection. If they point to the best plant, say, the weak has the same genetics too. The stock answer does not always think anything else is possible.

If we did this again, the best gradient will have selective advantage, even with all the seedlings having the same DNA. Evolution does not even go there since it does not think beyond the dogma.

 

[Aqueous Id]

The idea of the first multicellular expression, being a loose grouping of cells came to me twenty years ago.

Volvox is the template:

It's a spherical colony of identical flagellate monocytes, that employ signalling and then differentiate. They are possibly very close to the dawn of sexual reproduction. Differentiation unleashes this huge capability - the merging of DNA from two sources. It would open an exploding scenario for altering the way natural selection unfolds. It probably ushered in the Cambrian bloom.

It took science two decades to catch up.

Considering Leeuwenhoek first reported observations of Volvox in 1700, you might actually be a three centuries behind the curve.

From this simple state, evolution will then make use of potential gradients... & etc...

I don't think evolution makes use of anything. I think natural selection is the observed rule, that operates on mutation. Aside from that, I'm not able to subscribe to your ideas, because I don't see the evidence for them. It would help if you'd furnish some references.

Evolution does not even go there since it does not think beyond the dogma.

Evolution is the observed phenomenon, not an ideology or thinking pattern that engages dogma. If anything, dogma is usually associated with unfounded ideas. Giving cites to shore up your position would mitigate what appears to me to be a dogmatic stance that you are taking.

By the way, I agree that the cell membrane is taking on a new role in the colonial forms, since signaling is required. So they're transporting chemicals in and out of their membranes. Furthermore, the reason for signalling at all seems to have originated in intracellular basal activities like sending messenger RNA to the organelles. You might want to consider whether the first strand to leach out of one cell into another happened to start this ball rolling.

 

[Pandaemoni]

The reason I remain skeptical is that yeast itself evolved from a multicellular ancestor, and so it may have been relatively easy for it to adapt itself into a quasi-multicellular structure than it would be for other unicellular life. It took life on Earth, so far we can tell, more than 3 billion years to discover the key to multicellular existence.

If it were as easy to establish as this experiment suggests, I wonder why the trait only evolved about 500 million years ago (or, rather—since it's possible that multicellular life could have developed earlier, but died out—why there is no evidence of multicellular life existing on Earth prior to the Cambrian Explosion).

I would like to see their experiment repeated with a different lifeform (and ideally a range of different unicellular life forms) to rule out the possibility that latent traits present in yeast from its multicellular ancestors aren't skewing the results.

 

[wellwisher]

If you compare ten single cells to ten dependent cells, the first have more degrees of freedom since they need to take care of all business alone and can't depend on division of labor to take care of part of their needs. The net effect is the ten connected cells represent a loss of entropy relative to ten independent cells.

One way to see this is to look at the human body, The white blood cells have our DNA and exist as independent cells with motion and semi-consciousness. They need to take care of all their business alone, requiring more complexity than a dependent cell that has a single important task.

Another example can be done with humans. If we had ten people who are self efficient and ten people who can only exist as a group, the ten self sufficient can each do all the tasks of all ten people in the group. This is not true the other way around.

Multicellular was the logical result of the fact that life lowers entropy in terms of its chemical configurations.

 

[wlminex]

. . .just skimmed this thread for now . . . more detailed read later . . . so, humans evolved from a planet-wide (in oceans) yeast infection? . . .
boy, that explains a lot! (<-- humor here!)

 

[Aqueous Id]

If you compare ten single cells to ten dependent cells, the first have more degrees of freedom since they need to take care of all business alone and can't depend on division of labor to take care of part of their needs.

So two things have to happen: (1) a mutation and (2) an ambient pressure that selects for that mutation. I think we can just get by on the idea that there will be many random mutations over a sufficient time, and that you can multiply that by the population count to get a metric for total number of mutations.

It remains to be seen what the stress is that selects for intracellular signaling. In the case of yeast I wondered if it might be to optimize the collection of nutrients. In the case of Volvox, it's an alagae. The monocytes are flagellated and have chloroplasts, so their ancestral DNA gives them a light-activated motor.

Yet in the sphere-shaped colonial form, a "front" of the sphere gets chosen, the ones in "front" become differentiated to sense light only, and the ones in "back" differentiate to wag their flagella only. What drove that specific type of selection? I can speculate as to what drove them to join in a sphere, since it is structurally strong, minimal in cost, and contains the largest volume for the smallest surface area. An investigation into selection pressure that caused this takes this specific result and searches for a pressure that selects for this. Or finds something I missed, and searches for its cause. Maybe there is something that's getting trapped inside the sphere. In their modern form, the hollow inside of the sphere is where they carry their "eggs", which is really crazy, because this need for differentiation shows an immediate connection to the differentiation between egg and sperm.

And then, for differentiation to occur, there has to be signaling. So that, the motility, and the choloroplasts, seem to jointly constitute the prerequisite for adopting a spherical colony.

One way to see this is to look at the human body, The white blood cells have our DNA and exist as independent cells with motion and semi-consciousness.

By "semi-consciousness" I infer you don't mean sentience, but that you are making reference to the way they seem to attack pathogens like assassins.

They need to take care of all their business alone, requiring more complexity than a dependent cell that has a single important task.

All they need is food and (for algae) light, nothing more.

Another example can be done with humans. If we had ten people who are self efficient and ten people who can only exist as a group, the ten self sufficient can each do all the tasks of all ten people in the group. This is not true the other way around.

Ten people in a chain walking up and down the aisles of a grocery store, picking what ever they want to eat or drink as they pass the goods, will live forever (in an idealized model). There is no pressure for them to cooperate. The environment must change to impose a pressure to encourage (select for) cooperation. Obviously, a few years into this, as the food supply diminishes, there's going to be pressure on the individuals to change their behavior. Some will die if they do not, and those that live will give birth to replacements who tend to have the genetic capacity to modify their behavior to survive. Food seems to be the principal cause for primordial selection, but obviously all the conditions of the ambient must play a role.

Multicellular was the logical result of the fact that life lowers entropy in terms of its chemical configurations.

But there had to be a selection process, otherwise nothing evolves.

 

[Aqueous Id]

humans evolved from a planet-wide (in oceans) yeast infection?

Surprise. Look what I found:

Multicellular animals, which evolved about 700 to 1,000 myr ago, contain many of the genes found in yeast. Important for the evolution of multicellular animals were new pathways for intercellular signaling that regulated more complex physiological responses...(etc).​

Here's the article:
Xenobiotics and the Evolution of Multicellular Animals: Emergence and Diversification of Ligand-Activated Transcription Factors

 

[Hercules Rockefeller]

Moderator note: matthew809’s posts (and associated replies) have been moved to a thread in the appropriate sub-forum. matthew809 is free to contribute to B&G threads again once he has actually learnt something about biology and evolution.

 

[wellwisher]

But there had to be a selection process, otherwise nothing evolves.

But what is the nature of this selection process which places a limit on all the options implicit of higher complexity=entropy?

Let me create a hypothetical situation to answer this. Say the earth was super huge and nature was very cooperative, such that every genetic mutation, which ever occurred on the earth during evolution, had room and resources to survive. There is no need for survival of the fittest, because everything is selected by nature since we have tons of room and resources. The amount of entropy would be at a maximum. The system would be very complex and would require a lot of information to model. That is the baseline led by the randomness in the DNA fully integrated.

If we compare this to the actual, natural selection reduced this baseline complexity down to a tiny fraction of the theoretical entropy maximum. This loss of baseline entropy has to do with the efficiency in terms of work cycles. In work cycles, entropy is connected to inefficiencies. Natural selection takes away all the inefficient critters, lowering this baseline complexity=entropy based on random DNA changes.

If you don't normalize the complexity, you can call up, down or down, up. When you normalize, direction is not relative to the desired opinion.

Going from single to multicellular reflected gains in efficiency. But since nothing is 100% efficient (perpetual motion), there will be a net gain in entropy=complexity but not as much as with pure random assumptions= 100% inefficient. The cell grouping starr simply do reflect lower entropy=complexity in line with efficiency. The team makes many thing much more efficient. But since nothing is 100% efficient here is will be some entropy=complexity also evolving.

The question becomes where is the source of work cycles which can steal energy from the random assumptions of entropy, so the absolute entropy is less than it would be in a random world? In life, one source are the enzymes. These are nano machines with 80+ % efficiency. With gravity there is also work which is not 100% inefficient so it can steal from entropy.

 

[Aqueous Id]

But what is the nature of this selection process which places a limit on all the options implicit of higher complexity=entropy?

Maybe we should introduce the concept of a niche:

For a species to maintain its population, its individuals must survive and reproduce. Certain combinations of environmental conditions are necessary for individuals of each species to tolerate the physical environment, obtain energy and nutrients, and avoid predators. The total requirements of a species for all resources and physical conditions determine where it can live and how abundant it can be at any one place within its range. These requirements are termed abstractly the ecological niche:.

...all of the physical, chemical and biological conditions required by a species for survival, growth and reproduction. Two further abstractions of this concept are the fundamental niche and the realized niche.

Fundamental niche:

Describes the total range of environmental conditions that are suitable for a species existence without the effects of interspecific competition and predation from other species.​

Realized Niche:

Describes the part of the fundamental niche that a species actually occupies.​

Restated:

A useful extension of the niche concept is the distinction between fundamental and realized niches. The fundamental niche of a species includes the total range of environmental conditions that are suitable for existence without the influence of interspecific competition or predation from other species. The realized niche describes that part of the fundamental niche actually occupied by the species.

Citing:
http://www.physicalgeography.net/fundamentals/9g.html

 

[Aqueous Id]

The reason I remain skeptical is that yeast itself evolved from a multicellular ancestor, and so it may have been relatively easy for it to adapt itself into a quasi-multicellular structure than it would be for other unicellular life. It took life on Earth, so far we can tell, more than 3 billion years to discover the key to multicellular existence.

If it were as easy to establish as this experiment suggests, I wonder why the trait only evolved about 500 million years ago (or, rather—since it's possible that multicellular life could have developed earlier, but died out—why there is no evidence of multicellular life existing on Earth prior to the Cambrian Explosion).

I would like to see their experiment repeated with a different lifeform (and ideally a range of different unicellular life forms) to rule out the possibility that latent traits present in yeast from its multicellular ancestors aren't skewing the results.

I read a misunderstanding in your comment, so I will try to correct it, although I am not a biologist, so you will have to bear with me!

I think it is incorrect to say that the yeast carries a latent multicellular trait in its DNA, and this experiment merely enabled a dormant section of code. I will try to bridge the gap between your understanding and mine.

First we must establish a prerequisite for evolution from monocyte to colonial form. They will need signalling. A packet will have to leave the membrane of one cell and enter the membrane of its neighbor. This requires a systemic change through evolution. But it is built upon a pre-existent system, which is the signaling between cell nucleus and the various organelles in the cytoplasm. As an example, consider protein synthesis:

The gene that codes for a particular protein assembles a messenger RNA strand, which, upon completion, floats into the cytoplasm and eventually attaches to a receptive mitochondrion, which uses the mRNA to assemble the required protein, triplet by triplet. ("codons" of length=3).

That systemic capability, to move assembled strands, utilizes a special molecule known as a nuclear receptor. The presence of the nuclear receptor is a trait that is genetically coded.

Therefore, the cell that exists as a monocyte must utilize a nuclear receptor in order to create a message packet that will serve as the intracellular signalling function.

In a 2006 study, yeast were shown to have evolved the gene that codes for this type of nuclear receptor - but not the DNA that codes for multicellularity itself, as you may think:

Unexpectedly, a similar search of the genome of the yeast Saccharomyces cerevisiae did not find any nuclear receptor genes (Goffeau et al., 1996). Also unexpectedly, a search of the genome of the plant Arabidopsis did not find any nuclear receptor genes (The Arabidopsis Genome Initiative, 2000). This was surprising because nuclear receptors, such as the estrogen receptor (Metzger et al., 1988) and glucocorticoid (Schena and Yamamoto, 1988) receptor, can function nicely when transfected into yeast along with a reporter gene. Similarly, the glucocorticoid receptor can function when transfected into Arabidopsis (Schena et al., 1991). This indicates that the basic machinery for transcriptional activation by nuclear receptors evolved in yeast, even if they do not contain these receptors. These genome analyses indicate that nuclear receptors arose in multicellular animals and suggest that nuclear receptors had an important role in their evolution.

I think they specifically chose yeast in the centrifuge experiment because it is the "missing link" between nuclear receptor evolution for signalling, and multicellularity.