Multicellular Life Evolves In Months, In a Lab

ananyo writes "The origin of multicellular life, one of the most important developments in Earth's history, could have occurred with surprising speed, U.S. researchers have shown. In the lab, a single-celled yeast (Saccharomyces cerevisiae) took less than 60 days to evolve into many-celled clusters that behaved as individuals. The clusters even developed a primitive division of labor, with some cells dying so that others could grow and reproduce. Multicellular life has evolved independently at least 25 times, but these transitions are so ancient that they have been hard to study. The researchers wanted to see if they could evolve multicellularity in a single-celled organism, using gravity as the selective pressure. In a tube of liquid, clusters of yeast cells settle at the bottom more quickly than single cells. By culturing only the cells that sank, they selected for those that stick together. After many rounds of selection over 60 days, the yeast had evolved into 'snowflakes' comprising dozens of cells."

Comments

Not so sure about this.

[Anonymous Coward]

This is likely just re-emergence of previously evolved and currently dormant behavior.

Re:Not so sure about this.

[syousef]

This. I'd mod informative if I could.

Slashdot moderation simply hasn't evolved to the point where you can.

Re:Not so sure about this.

[Anonymous Coward]

Also mentioned in tfa. The scientist says that he plans to do an experiment with organisms without multicellular ancestors.

Re:Not so sure about this.

[Anonymous Coward]

This was on RichardDawkins.net back in June, and in the version of the article linked there, there were these telling paragraphs:

Sceptics, however, point out that many yeast strains naturally form colonies, and that their ancestors were multicellular tens or hundreds of millions of years ago. As a result, they may have retained some evolved mechanisms for cell adhesion and programmed cell death, effectively stacking the deck in favour of Ratcliff's experiment.

"I bet that yeast, having once been multicellular, never lost it completely," says Neil Blackstone, an evolutionary biologist at Northern Illinois University in DeKalb. "I don't think if you took something that had never been multicellular you would get it so quickly."

Re:Not so sure about this.

[syousef]

Apparently the group has become self aware!

Nuke from orbit. It's the only way to be sure!

Here's the actual article

[damn_registrars]

Experimental evolution of multicellularity

And PNAS has it listed as open access, which means you should be able to download the full text regardless of your subscriber (or non-subscriber) status. Just click the Full Text link.

I've always wondered...

[Beeftopia]

Do the mechanisms which originally created life still occur? Or is "The Genesis Event" so rare that it was a one-time occurrence billions of years ago?

Re:I've always wondered...

[Samantha Wright]

That's a big question! We currently believe that the circumstances that created life were pretty harsh in some respects and extremely mild in others. There are a number of different ideas floating around, including the proverbial primordial soup, clouds of space dust (panspermia), and a boiling puddle of fat. Most likely, the conditions that were on Earth billions of years ago (a hot boiling hell with a mostly hydrogen atmosphere, amongst other things) contributed substantially to the factors that led to life's rise.

Re:I've always wondered...

[tchuladdiass]

Now a related question -- is there any evidence (for or against) that life originated more than once on earth? Is the prevailing theory that a single reproducing organism came into being, from which all others were derived, or is it more likely that multiple instances of life happened over the course of time, and they all happen to take the same form? If this is the case, then it lends credence to life existing elsewhere in the universe, with much similarity to what we know. However, if it is unlikely for more than one independent instance of life to be similar, then we should be observing various non-related life types here on earth (i.e., some carbon based, some silicon based, etc).

Re:I've always wondered...

[Samantha Wright]

This has indeed been pondered! We're pretty sure that all life that presently exists all comes from one root, however. If there ever were alternative life-starting events, they didn't survive. The reason for this is that all extant organisms share a number of completely arbitrary decisions called chirality (if you know any physics, that's left-handed vs. right-handed molecular symmetry.) Chirality is completely random in the chemical reactions that produce amino acids and nucleotides, but absolutely fixed, in the same way, in every living organism we've studied. A number of environmental tests have been conducted specifically to look for organisms of contrary chirality, but we haven't found anything yet.

Re:I've always wondered...

[Michael Woodhams]

In all probability new life (unrelated to current life) cannot evolve on Earth because current life either prevents the required conditions (eating the food before it gets concentrated enough for extremely primitive life to make use of it) or out competing the new life as soon as it arises.

If somehow the Earth were cleansed of all life but otherwise left unaffected, there is no great reason to believe it couldn't re-evolve life. However, as we don't understand the origin of life, there is a possibility that necessary conditions are no longer available - e.g. early life relies critically on the presence of a radioactive nucleotide with half-life of a few hundred million years, present in the early Earth but now decayed.

We find evidence of life in pretty much the oldest rocks on Earth which could contain evidence of life. So in the only instance we can study, life arose about as soon as it possibly could have. This suggests (but does not prove) that given the right conditions, evolution of life is an easy step, rather than one which requires a once-in-a-trillion-years fluke occurance.

However, unicellular life was around for some 2.5 to 3 billion years before multicellular life arose (or at least, multicellular life which left fossil evidence.) This suggests that the step from unicellular to multicellular is hard. Or so I've argued, until this result turned up...

So, we have this result, and the fact that multicellularity has arisen multiple times, and although only in Eukaryotes, it has arisen in very distantly related Eukaryotes (plants vs the fungi/animal clade) suggesting that multicellularity is fairly easy to evolve. So why did it take so long? Perhaps it required a certain level of atmospheric oxygen before multicellular life was viable (plot.)

(I have only tangential professional connection to these topics, so these are merely semi-educated ramblings.)

Re:I've always wondered...

[Samantha Wright]

A few clarifications, and things you might find neat:

1. The nucleus and mitochondria only appear in more complex organisms (eukaryotes.) Simpler ones (prokaryotes: bacteria and archaeons) are just bags with DNA in them. Mitochondria and chloroplasts (and their less well-known cousins, chromoplasts and amyloplasts) actually started out as different kinds of bacteria and just got absorbed into a cell one day. They even have their own DNA, ribosomes, and reproductive cycle.
2. No two species have exactly the same proteins, but their sequences are similar enough that we can infer homology (relatedness) over great distances; often billions of years of separation. That being said, there are some species so isolated and so remote (because all of their relatives have died off) that we have trouble proving homology for—but these species still do more or less the same functions with similarly-shaped proteins.
3. The arsenic-using extremophile was more like arsenic-tolerant. Normally, organisms die when they take up arsenic because it replaces phosphorus with a heavier nucleus that has different binding affinities. However, the organism those researchers discovered was capable of replacing at least some of its phosphorus with arsenic without dying. But yeah, your point is correct! :)
4. It's widely believed now (in an idea called the RNA World hypothesis) that DNA and proteins were invented later. The original "life" was probably a self-replicating RNA molecule. RNA can perform both catalytic functions (like proteins) and information storage functions (like DNA), it's just not as good at them. It still performs many of these functions in the modern cell as well—almost the entire ribosome (the protein making machine) is made out of RNA, and there's a large class of so-called "ribozymes" that can cut and modify other molecules.

Re:I've always wondered...

[Samantha Wright]

Yep. It's called endosymbiotic theory. For a while it was just a crazy idea, but we're pretty sure we know exactly what kind of bacterium it came from (purple and green sulphur bacteria for mitochondria and chloroplasts, respectively.) Another name for it might be "yet another blatant dagger in the back of intelligent design," but genomics is a treasure trove of those on any day.

Re:I've always wondered...

[robotkid]

This has indeed been pondered! We're pretty sure that all life that presently exists all comes from one root, however. If there ever were alternative life-starting events, they didn't survive. The reason for this is that all extant organisms share a number of completely arbitrary decisions called chirality (if you know any physics, that's left-handed vs. right-handed molecular symmetry.) Chirality is completely random in the chemical reactions that produce amino acids and nucleotides, but absolutely fixed, in the same way, in every living organism we've studied. A number of environmental tests have been conducted specifically to look for organisms of contrary chirality, but we haven't found anything yet.

There are two points here. As for the single root of life, I saw Carl Woese give a talk on this - see timely PNAS perspective here if you have institutional access: http://www.pnas.org/content/early/2012/01/13/1120749109.short?rss=1
  (he's a giant in evolutionary biology and the one who proved archaea were a separate lineage using ribosomal RNA sequences, thus redefining our understanding of microbiology, so I'm inclined to give large weight to his views)

His view was that some events almost certainly happened to one unique organism, you can do the backwards projection on the endosymbiosis of mitochondria and a very distinct genetic profile emerges from multiple, independent lines of evidence. But when you try and project all the way back to the LUCA (last universal common ancestor of all three kingdoms) the uncertainty becomes so large and some of the contradictions so severe that it is in fact best explained by groups of highly similar (but not identical) universal ancestors over a window of time, not just literally one unique genome at a specific point in time. So he thinks that the "base" of the tree of life ends up being more like a collection of small shrubbery or bushes instead of a singular point of origin. Carrying that thought a bit further, if there were indeed multiple bushes of life at the start it seems probable there were also other bushes that completely vanished without a trace (no fossil record possible).

As for the universal chirality, that speaks to the origin of self-replicating macromolecules that would have preceeded the last universal common ancestor by quite a spell, so we can only speculate what happened based on our knowledge of organic chemistry. NASA funds some rather creative chemists to think about this question to help define what life might be like elsewhere, and last time I saw one of them speak they seemed to be of the opinion that it was probably just a random chance that gave us one hand and not the other and that there were pools of similar chemical species being selectively concentrated by some sort of clay catalyst. But that means it could have occurred multiple times and only one pool resulted in a proto-cell, or multiple proto-cells arose and the rest died off, or maybe all steps really did only happen once, there's absolutely no projection or record to build upon except geological models of what the earth might have been like then.

Genesis

[sakdoctor]

God still holds the copyright for the original genesis event. It should have entered the public domain, but the copyright just keeps getting extended, and extended for billions of years. God keeps raking in the royalties and has no incentive to create new works, which is why you haven't heard anything from him lately.

Relation to yeast

[pgward]

Reading the comments on the physorg page made by intelligent design supporters, I have come to a conclusion. Some of us have not evolved far beyond yeast.

Re:Yeasty "evolution"

[Samantha Wright]

Well, it's not that hard to create a similar environment in the real world, they take too long to get grant money for. Consider, for example, a microbe growing in a hot spring that needs a very high temperature to function properly (like every molecular biologist's friend, Thermus aquaticus.) If that thing floats to the top of the pond, it might get cold and die. Evolutionary pressures such as sink-or-die aren't that implausible.

Think of it this way: a random walk will get to every possible location eventually. If you push it in a certain direction, it'll simply get there sooner. But if it doesn't get there when you do, then there's no chance it'll ever get there on its own. Unless they tampered with the genes of the yeast in question, these results are completely legitimate.

Actually I thought Eukaryotes were the big jump

[wisebabo]

Not to diminish the importance of multi-cellularity (and of this discovery) but wasn't the development of Eukaryotes (cells with Nuclei and other differentiated organelles) the big step needed for complex life? I mean with chloroplasts you get plants and mitochondria (or mitoklorines for you Star Wars fans) you get animals.

With multi-cellularity and prokaryotes you get strombolites (algal mats).

That said, it shows that evolution can happen quite quickly and can overcome some serious obstacles in a short amount of time in a very limited scope (a laboratory workbench). When multiplied by geologic ages and oceans of room is it any wonder that life has evolved in so many fascinating ways?

Re:Actually I thought Eukaryotes were the big jump

[Samantha Wright]

Yeah... But! There are plenty of fancy single-celled eukaryotes that are fantastically dull. Multicellular life is still a pretty neat thing. You just wait; give molecular biology enough time and we'll see experiments that recreate the emergence of eukaryotes, animals, chordates, mammals, primates, hominids, and finally molecular biologists. Just give 'em time.

Yes - sounds like "grant time"

[Moblaster]

I suspect it's not "evolution" at all, but subtly bad science (i.e. a scientist gunning for more grant money). DNA can express in many ways given varying environmental conditions, without the mutations that characterize true evolution -- and artificially forcing genetic drift by selecting for the bottom-clumpers is certainly VERY DIFFERENT from having gravity serve as the "selection pressure."

It's well known DNA can express in many different ways without true evolution. We've come a long way from the theory of Lamarckian evolutionary theory (evolution of acquired characteristics). One is example: exons, which can express differently across generations based on environmental conditions-- without actual change to the DNA.

I'm thinking this great discovery will get pounded upon by other biologists pretty quickly -- and put in its proper place as an interesting science experiment that really does not advance the field much if at all. INTERESTING evolution would be a group of mutations that lead to a multicellular outcome. That's NOT what these guys 1) demonstrated happened (multicellular DNA base-pair-causing mutations) or 2) proved was the actual genetic cause at the molecular-biology level.

Re:Yes - sounds like "grant time"

[airuck]

10 yeast cells clumped together have more mass than 1 yeast cell. Therefore they sink to the bottom of a tube.

Bzzt. Please review the difference between mass and density and the relationship between density and buoyancy.

Re:Yes - sounds like "grant time"

[Eskarel]

The summary is true, but ultimately misleading.

This is evolution, and it did happen in months. What it doesn't account for is getting the clumping gene in the first place, and that the likelihood of getting selection pressures as extreme as the ones in the lab is fairly low.

They've proven that yeast has the capacity to evolve in this way given the right selection pressures, which is interesting. With additional research they may be able to prove that many other single celled life forms have the same capacity, from which we may extrapolate that the gene responsible for this behavior either occurred very early or is a relatively minor mutation.

The "more quickly than we believed" part is probably bogus. They applied extreme selection pressures to this particular colony of yeast and so they got an extreme time scale result the same would happen in any species if you extrapolated for the length of a given generation. You could do the same thing to humans for some arbitrary characteristic.

Re:Yes - sounds like "grant time"

[koekepeer]

IIRC from the times when I used yeast in my PhD research, wild type (that means: not mutated) S. cerevisiae clumps in advanced stationary phase (end of growth curve, nutritional deprivation). Such circumstances happen more often that not in the real life of S. cerevisae: just imagine that in nature it cannot walk to the nearest grapevine and say 'hey lets do some sugar fermentation here'... no it depends on being able to survive in times of drought. ne way it does that is through forming spores, another way of temporarily surviving could be this kind of 'clumping'. So, the 'clumping gene' is already there, it is just expressed in certain circumstances, circumstances easily simulated in a lab situation.

In my mind the argument would revolve around self-organisation versus (old, dormant) organisational information still present in the S. cerevisae genome. I'm bummed I cannot access the original article at the PNAS site, else I could comment on that in a bit more detail.

Re:Yes - sounds like "grant time"

[robotkid]

I suspect it's not "evolution" at all, but subtly bad science (i.e. a scientist gunning for more grant money). DNA can express in many ways given varying environmental conditions, without the mutations that characterize true evolution -- and artificially forcing genetic drift by selecting for the bottom-clumpers is certainly VERY DIFFERENT from having gravity serve as the "selection pressure."

It's well known DNA can express in many different ways without true evolution. We've come a long way from the theory of Lamarckian evolutionary theory (evolution of acquired characteristics). One is example: exons, which can express differently across generations based on environmental conditions-- without actual change to the DNA.

I'm thinking this great discovery will get pounded upon by other biologists pretty quickly -- and put in its proper place as an interesting science experiment that really does not advance the field much if at all. INTERESTING evolution would be a group of mutations that lead to a multicellular outcome. That's NOT what these guys 1) demonstrated happened (multicellular DNA base-pair-causing mutations) or 2) proved was the actual genetic cause at the molecular-biology level.

IAAMBP (I am a molecular biophysicist) and I actually just finished discussing this article at work before seeing it on /. The parent post is an odd mix of insightful comments and flamebait so I'll respond to the former. BTW the actual research article itself is free for everyone to read, thanks to the authors shelling out an extra 1K$ to allow public access. I'll link it below:

http://www.pnas.org/content/early/2012/01/10/1115323109.full.pdf+html

If you would prefer having to pay 10-30$ for the privilege of reading what your tax dollars already paid for instead of this commie "open access" stuff, please call your congressman and tell him/her to support HR bill 3699.

To contextualize this work: the path that led from single-celled eukaryotes to multicellular organisms is one of those $64,000 questions in evolutionary biology, that weird crossover from outright competition to coordinated teamwork. The advantages of being multicellular really pay off for big, complex organisms, but why on earth would it have been advantageous for a small group of a few dozen cells? This paper does not answer the question by any stretch, but it does provide a few interesting, unexpected clues. Most groups asking this question focus on Volvocine algae, which evolved multicellularity so recently such that you can compare them side by side with their nearly identical single-celled cousins in the very same pond. But these are not the most convenient organisms to work with; they have a very complicated life cycle, and have a monster-sized genome for their diminutive size (~140 million bases) and doing genetics on such beasties is still quite difficult and tedious.

Yeast, on the other hand, are really easy to work with and are actually pretty boring in most respects; ~12 million base pairs which have all been sequenced many times over. You can actually custom order them with any gene you want deleted just to see what happens, it's that well characterized. So the observation that artificially selecting for clusters in boring yeast leads to weird snowflake-shape colonies with something that resembles "programmed cell death" in higher organisms is completely unexpected an novel. "Programmed cell death" literally means that the colony has found a way to promote what's good for the colony over what's good for the individual, even though these are only 60 days removed from being a pretty ordinary yeast.

Is this how it happened billions of years ago? Probably not, this is just boring yeast after all, and I can't think of a scenario where sinking to the bottom is a life-or-death advantage. In the case of the algae, it would in fact be suicidal to sink beyond where the

Re:Yes - sounds like "grant time"

[RDW]

I'm betting they chose yeast because now they can get the interesting ones sequenced for a few thousand each, which is completely feasible even with a very modest grant compared to what it would cost for algae (or anything that isn't yeast or e. coli really).

Just skimmed through the paper and was almost surprised to see they haven't done the sequencing (yet?) - identifying the presumed mutations would have made this study much more interesting. A 12 Mb genome doesn't need much NGS capacity! Until then, I don't think we can rule out epigenetic inheritance, which has previously been demonstrated in yeast.

Re:Yes - sounds like "grant time"

[GauteL]

First. Thank you for a very interesting post which provides insight that is still understandable by those of us who are not molecular biophysicists. This is not always easy to do.

I may now be able to provide some insight into Slashdot's science discussions, which you may or may not have discovered yet....

A good scientist (which I'm sure you are) will read new research with an open mind combined with healthy scepticism. He/she won't automatically discard papers due to confirmation bias, and they won't shout "CORRELATION DOES NOT EQUAL CAUSATION" every single time they read reporting of a paper which suggests some correlation, because they realise that demonstrating correlation is often a necessary first step towards establishing causation and as such it is still novel and useful to publish papers that suggests correlation.

Slashdot, however, is home to some brilliant scientists who are completely drowned out by the masses of cynical, semi-clever "know-it-alls" who love to demonstrate their cleverness by shooting down any new research, often without bothering to read it first. They will shout "bad science" at the top of their lungs as a knee-jerk reaction to any perceived short coming, even if this short coming is just a limitation in scope of a paper or simply just ignorance on their own part. If the paper doesn't fully answer every possible question, it is worthless.