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

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]

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...

[dwye]

More likely, it occurred once, and the first species ate the primordial soup until conditions (mainly nutrient density, I expect) dropped below the level that allowed abiogenesis to repeat. All that is required is that the expected time between abiogenesis events is longer than the time for first life to reproduce and spread throughout the world (or at least that part where the event could reoccur), and you have just one life event per planet (at least for most planets - statistically at least a few times the events must occur too frequently for only one type to dominate).

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.

Re:Yeasty "evolution"

[pgward]

Once again, great successes hailed while ignoring the elephant in the room: the researchers cheated by selecting out certain ones (those that sank to the bottom.) in TRUE life-by-incremental-changes, every event is random, including which cells are selected out of the tube to prosper.

False.

The purpose of this "selection" was simply to simulate a larger environment. If this occurred in a big place relative to the size of the yeast, let's call this imaginary place the ocean, it is highly likely the yeast wouldn't be contained to a test tube. It would disperse on its own. Selecting certain ones and continuing to examine them is the same as zooming in and following the large ones in the ocean you'd like to examine. The centrifuge is not meant for culling, selective breeding or to "intelligently design evolution in yeast".

N.B. I have no idea about the atmospheric requirements for this experiment as I skipped that part of the original article. For all I know the bigger place could have been a rock, a lake, a cloud or an iceberg. The argument is based upon the false implication that yeast only exists in constrained environments.

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"

[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

Already common knowledge among brewers

[Just Brew It!]

I brew (and judge) beer... different strains of brewers yeast already have widely varying behaviors with regards to how they settle out. Yeast with "low flocculation" tend to remain in suspension for weeks, consuming more of the sugars (drier, more alcoholic beer); yeast with "high flocculation" tend to clump together and settle after a few days, leaving more residual sugar (sweeter/heavier beer). This is widely known already in the brewing community. These strains have evolved over the years to suit the preferences and procedures of individual breweries. So all these guys have really done is to repeat in a controlled environment the same selective breeding that brewers have been doing (whether they understood it or not) for centuries.

Take a look here; if you click through to each individual strain of yeast, you'll see that there's a spec for flocculation (tendency to clump) and attenuation (tendency to consume sugars); there's a pretty good (though not perfect) inverse correlation between the two.

The only thing really novel here is the claim that these yeast clumps somehow represent a first step towards multi-cellular life. Interesting, but -- while I'm not dismissing it out-of-hand -- I'm definitely taking it with a pinch of salt.