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Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 4:03 pm UTC
by Odd_nonposter
via Wired Science
Spoiler:
Image
An evolutionary transition that took several billion years to occur in nature has happened in a laboratory, and it needed just 60 days.

Under artificial pressure to become larger, single-celled yeast became multicellular creatures. That crucial step is responsible for life’s progression beyond algae and bacteria, and while the latest work doesn’t duplicate prehistoric transitions, it could help reveal the principles guiding them.

“This is actually simple. It doesn’t need mystical complexity or a lot of the things that people have hypothesized — special genes, a huge genome, very unnatural conditions,” said evolutionary biologist Michael Travisano of the University of Minnesota, co-author of a study Jan. 17 in the Proceedings of the National Academy of Sciences.

In the new study, researchers led by Travisano and William Ratcliff grew brewer’s yeast, a common single-celled organism, in flasks of nutrient-rich broth.

Once per day they shook the flasks, removed yeast that most rapidly settled to the bottom, and used it to start new cultures. Free-floating yeast were left behind, while yeast that gathered in heavy, fast-falling clumps survived to reproduce.

Within just a few weeks, individual yeast cells still retained their singular identities, but clumped together easily. At the end of two months, the clumps were a permanent arrangement. Each strain had evolved to be truly multicellular, displaying all the tendencies associated with “higher” forms of life: a division of labor between specialized cells, juvenile and adult life stages, and multicellular offspring.

“Multicellularity is the ultimate in cooperation,” said Travisano, who wants to understand how cooperation emerges in selfishly competing organisms. “Multiple cells make make up an individual that cooperates for the benefit of the whole. Sometimes cells give up their ability to reproduce for the benefit of close kin.”

Since the late 1990s, experimental evolution studies have attempted to induce multicellularity in laboratory settings. While some fascinating entities have evolved — Richard Lenski’s kaleidoscopically adapting E. coli, Paul Rainey’s visible-to-the-naked-eye bacterial biofilms — true multicellularity remained elusive.

According to Travisano, too much emphasis was placed on identifying some genetic essence of complexity. The new study suggests that environmental conditions are paramount: Give single-celled organisms reason to go multicellular, and they will.

Apart from insights into complexity’s origins, the findings could have implications for researchers in other fields. While multicellularity would have a hard time emerging now in nature, where existing animals have a competitive advantage, the underlying lesson of rapid, radical evolution is universal.

“That idea of easy transformability changes your perspective,” said Travisano. “I’m certain that rapid evolution occurs. We just don’t know to look for it.”

Targeted breeding of single-celled organisms into complex, multicellular forms could also become a biotechnological production technique.

“If you want to have some organism that makes ethanol or a novel compound, then — apart from using genetic engineering — you could do selection experiments” to shape their evolution, Travisano said. “What we’re doing right here, engineering via artificial selection, is something we’ve done for centuries with animals and agriculture.”


Apparently, this is different enough from normal yeast flocculation that they can now be considered multicellular organisms.

Err... yay? Evolution dissent discredited? Thoughts, anyone?

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 4:06 pm UTC
by mike-l
Cool! Of course this will do little to dissuade dissenters, but very cool nonetheless.

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 4:11 pm UTC
by Angua
Just keep it away from the napalm.

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 4:45 pm UTC
by sourmìlk
I'm pretty sure evolutionary dissent has already been thoroughly discredited. Still, I think it's awesome that this was figured out. I remember reading about a lot of complex mechanisms that are supposed to be required for multicellular life, like large protein chains connecting all of the cells or something. Is this not necessary now, or am I misunderstanding something?

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 5:05 pm UTC
by Angua
Crude multicellular life probably doesn't need that much in the way of matrix, and can get away with some protein anchors to help cluster cells together, which are probably not that far removed from existing glyoproteins that are already found on the surface of the cells, which would allow them to interact for transfer of genetic information even in their single-celled form.

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 5:18 pm UTC
by bigglesworth
Huh. Apparently apoptosis has been seen in the yeast colonies before they separate from each other.

http://www.bti.umn.edu/gateway/assets/img/gateway_page5.pdf

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 5:55 pm UTC
by Steax
Angua wrote:Just keep it away from the napalm.


It's fine, why do you think we stocked up on Heads and Shoulders?

I wonder if they can get the organisms to compete against each other, potentially obtaining newer and better forms...

(EDIT: By 'compete', I mean 'destroy each other to obtain something'.)

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 5:57 pm UTC
by Diadem
bigglesworth wrote:Huh. Apparently apoptosis has been seen in the yeast colonies before they separate from each other.

http://www.bti.umn.edu/gateway/assets/img/gateway_page5.pdf

That ... is awesome. Being able to reproduce multicellular life is a pretty big thing, but apoptosis too? Very interesting.

Steax wrote:I wonder if they can get the organisms to compete against each other, potentially obtaining newer and better forms...

What do you think they are doing?

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 6:30 pm UTC
by Heisenberg
I'm skeptical. 60 days?

Is this a true organism or are these just single cells behaving weirdly? Does this behavior persist after removal from the adverse conditions, or does the "organism" split up into its original cells who go on their merry way? How do they reproduce? Are there genetic differences between the single celled ancestors and the multi-celled descendants?

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 8:47 pm UTC
by jareds
Heisenberg wrote:Is this a true organism or are these just single cells behaving weirdly?

The line between unicellular and multicellular organisms is not a bright one. See slime mold. That said, I'm not sure how this compares and I'd be interested if someone with relevant expertise can compare this experimental organism to slime mold.

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 8:58 pm UTC
by JudeMorrigan
Here's the link to the full article:

http://www.pnas.org/content/early/2012/ ... l.pdf+html

It's interesting stuff. I'll note that they specifically state that the snowflake-phenotype yeast do NOT arise from floc-type aggregation and are phenotypically stable. It also addresses their reproduction.

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 10:15 pm UTC
by bigglesworth
I tried to find that article and failed :lol:

Yeah, it seemed quite conclusive that they did actually reproduce rather than randomly sloughing parts of the mass.

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 10:21 pm UTC
by Jave D
This is pretty amazing stuff.

Re: Multicellular Life Evolves in Laboratory

Posted: Wed Jan 18, 2012 11:55 pm UTC
by PossibleSloth
I love articles like this. Evolutionary biology is fascinating. I hope they continue this experiment to see if the yeast develop more complex cellular differentiation.

Re: Multicellular Life Evolves in Laboratory

Posted: Thu Jan 19, 2012 12:20 am UTC
by big boss
Heisenberg wrote:I'm skeptical. 60 days?
Does this behavior persist after removal from the adverse conditions, or does the "organism" split up into its original cells who go on their merry way? How do they reproduce?


I'm most curious about this, but didn't see anything about it in the articles.

Re: Multicellular Life Evolves in Laboratory

Posted: Thu Jan 19, 2012 1:09 am UTC
by Steax
Diadem wrote:
Steax wrote:I wonder if they can get the organisms to compete against each other, potentially obtaining newer and better forms...

What do you think they are doing?


I think they're enforcing natural selection by only taking the heaviest of each generation, and passing it on to the next iteration. I want to see them have to destroy each other over food, since that should invoke an effort to not just "get bigger" but also "get faster" or "get stronger" or something like that.

Re: Multicellular Life Evolves in Laboratory

Posted: Thu Jan 19, 2012 1:19 am UTC
by sourmìlk
Also, there's nothing like the sight of combat to the death.

Re: Multicellular Life Evolves in Laboratory

Posted: Thu Jan 19, 2012 10:02 am UTC
by Zamfir
Steax wrote:
I think they're enforcing natural selection by only taking the heaviest of each generation, and passing it on to the next iteration. I want to see them have to destroy each other over food, since that should invoke an effort to not just "get bigger" but also "get faster" or "get stronger" or something like that.

Eventually, you'll end up with efficient killing machines like these
Image

Re: Multicellular Life Evolves in Laboratory

Posted: Thu Jan 19, 2012 10:24 am UTC
by yurell
The message I'm getting is:
This image can't be displayed for the moment!
Please go to www.gifbin.com to see it.

Re: Multicellular Life Evolves in Laboratory

Posted: Thu Jan 19, 2012 10:48 am UTC
by Zamfir
Crap, it worked fine half an hour ago. Also a bit off-topic, so I received righteous punishment.

Re: Multicellular Life Evolves in Laboratory

Posted: Thu Jan 19, 2012 2:35 pm UTC
by Dauric
Steax wrote:
Diadem wrote:
Steax wrote:I wonder if they can get the organisms to compete against each other, potentially obtaining newer and better forms...

What do you think they are doing?


I think they're enforcing natural selection by only taking the heaviest of each generation, and passing it on to the next iteration. I want to see them have to destroy each other over food, since that should invoke an effort to not just "get bigger" but also "get faster" or "get stronger" or something like that.


And now I have images in my head of a squishy-biological "Robot Wars", a big arena and teams of scientists pouring their monster-blobs in to compete in obstacle courses and task challenges leading up to the final "Eat or be Eaten" final confrontation.

Re: Multicellular Life Evolves in Laboratory

Posted: Sat Jan 21, 2012 12:12 am UTC
by PossibleSloth
big boss wrote:
Heisenberg wrote:I'm skeptical. 60 days?
Does this behavior persist after removal from the adverse conditions, or does the "organism" split up into its original cells who go on their merry way? How do they reproduce?


I'm most curious about this, but didn't see anything about it in the articles.


The "adverse condition" is just the artificial selection of centrifuging and taking samples. The yeast were out of the adverse conditions while under the microscope, where they continued to reproduce as multicellular organisms for at least the two or three generations shown in the video. I'd guess that, given enough time they would eventually return to single cells once the selection pressure is removed, but that would just be another round of evolution.

Steax wrote:
Diadem wrote:
Steax wrote:I wonder if they can get the organisms to compete against each other, potentially obtaining newer and better forms...

What do you think they are doing?


I think they're enforcing natural selection by only taking the heaviest of each generation, and passing it on to the next iteration. I want to see them have to destroy each other over food, since that should invoke an effort to not just "get bigger" but also "get faster" or "get stronger" or something like that.


Even if they're not competing for food, they're still competing. Any "organism" that reproduces faster than its neighbors will eventually come to dominate the environment.

Re: Multicellular Life Evolves in Laboratory

Posted: Sat Jan 21, 2012 7:10 am UTC
by psyck0
I'm surprised this is in PNAS and not Science or Nature. Makes me a tiny bit sceptical, although it's not my field to comment.

Re: Multicellular Life Evolves in Laboratory

Posted: Sat Jan 21, 2012 5:54 pm UTC
by qetzal
Having now read the article, I don't think there's any reason to be skeptical of the results. They look pretty solid.

I find it intriguing that the multicellular "snowflake" phenotype appears reproducibly in independently selected cultures, and that it first appears after only ~ 100 generations of selection (see Figure S1 here). That makes me wonder about the genetic basis of this phenotype.

The authors don't describe any genetic analysis in this paper. (They're working on that now; see link below.) However, they do show that the multicellular phenotype is stable even after selection is removed, for at least ~ 250 generations. That would be consistent with multicellularity arising from one or more mutations. On the other hand, it seems surprising that it would arise in only a few hundred generations in 10 out of 10 cultures if it required spontaneous mutations. You could get that if there are lots of different mutations that can give the snowflake phenotype. But the authors seem to show that independent cultures all show a evolution of similar traits in succession. (I.e. first they start to show the snowflake phenotype, then they evolve increased apoptosis as a reproductive mechansism.) That made me wonder if it could be an epigenetic effect, or based on some hypermutable element, or something else that would have a higher probability than de novo single base mutations.

Also, I'm not sure how much this tells us about the initial evolutionary transition from uni- to multicellularity. Especially since the ancestor of Saccharomyces is believed to have been multicellular itself.

I recommend this discussion to those who have further interest. It brings up a number of questions about what's really going on, and what the evolutionary signficance may be. Best of all, it includes some significant comments from the study authors, with hints of what their latest, not-yet-published studies are showing. Great stuff!

Re: Multicellular Life Evolves in Laboratory

Posted: Sat Jan 21, 2012 9:54 pm UTC
by addams
I wonder: Does this stuff have a pet name with the lab staff?

They made a life form. Did they name it?

Will it ever follow them into the bathroom.

A flask of that stuff would be fun. Take it with you where ever you go.

Come on; Fungus! We are going to the park. No. You can not sit in the sun. The other microbes must play in the shade with you.

Maybe they will not compete for food. Maybe, they will, just, hang out. They are in the custody of Scientists. Scientists usually have lots of sugar water lying about.

Re: Multicellular Life Evolves in Laboratory

Posted: Sun Jan 22, 2012 5:20 pm UTC
by Silas
qetzal wrote:Also, I'm not sure how much this tells us about the initial evolutionary transition from uni- to multicellularity. Especially since the ancestor of Saccharomyces is believed to have been multicellular itself.

That was my thought. Isn't it likely that what's happened in these yeast cultures is a reactivation of latent genes (traits? pathways? I'm not fluent in this vocabulary) that lead to multicellular organization? In which case, this would be like feral pigs developing tusks over some generations, not fish developing lungs.

Re: Multicellular Life Evolves in Laboratory

Posted: Sun Jan 22, 2012 7:15 pm UTC
by qetzal
Silas,

At that second link in my previous post, the authors claim that's not the case:

Will Ratcliff wrote:Our yeast are not utilizing ‘latent’ multicellular genes and reverting back to their wild state. The initial evolution of snowflake yeast is the result of mutations that break the normal mitotic reproductive process, preventing daughter cells from being released as they normally would when division is complete. Again, we know from knockout libraries that this phenotype can be a consequence of many different mutations. This is a loss of function, not a gain of function. You could probably evolve a similar phenotype in nearly any microbe (other than bacteria, binary fission is a fundamentally different process). We find that it is actually much harder to go back to unicellularity once snowflake yeast have evolved, because there are many more ways to break something via mutation than fix it. The amazing thing we see is that we rapidly see adaptations to this adaptation. If we select for more rapid settling, snowflake yeast evolve to delay reproduction until the parent is larger, allowing it settle more quickly. We see the evolution of higher rates of apoptosis as a way to regulate the size and number of propagules produced. We show that the transition to multicellularity in yeast is surprisingly easy, and have no reason to suspect it would be any harder in other microbes with a reproductive process similar to yeast.


So if they're correct, the initial appearance of the snowflake phenotype is not some reversion to some latent genetic state. However, it does seem to me that the subsequent rapid adaptations depend on already having suitable genes, proteins, etc. that allow for such adaptation. That's where I think it's hard to know how relevant this is to the initial evolution of multicellularity. E.g., in this case the authors make a big deal of how the snowflakes evolve increased apoptosis rates to optimize their size. But that requires that they already have the capability of apoptosis to begin with. Would that capability have existed prior to the first appearance of multicellularity? I have no idea.