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Bacteria evolving complex traits in lab conditions!

 
 
Reply Tue 10 Jun, 2008 03:18 pm
Ripped from slashdot:


[URL=http://www.newscientist.com/channel/life/dn14094-bacteria-make-major-evolutionary-shift-in-the-lab.html]newscientist.com[/url] wrote:
A major evolutionary innovation has unfurled right in front of researchers' eyes. It's the first time evolution has been caught in the act of making such a rare and complex new trait.

And because the species in question is a bacterium, scientists have been able to replay history to show how this evolutionary novelty grew from the accumulation of unpredictable, chance events.

Twenty years ago, evolutionary biologist Richard Lenski of Michigan State University in East Lansing, US, took a single Escherichia coli bacterium and used its descendants to found 12 laboratory populations.

The 12 have been growing ever since, gradually accumulating mutations and evolving for more than 44,000 generations, while Lenski watches what happens.
Profound change

Mostly, the patterns Lenski saw were similar in each separate population. All 12 evolved larger cells, for example, as well as faster growth rates on the glucose they were fed, and lower peak population densities.

But sometime around the 31,500th generation, something dramatic happened in just one of the populations - the bacteria suddenly acquired the ability to metabolise citrate, a second nutrient in their culture medium that E. coli normally cannot use.

Indeed, the inability to use citrate is one of the traits by which bacteriologists distinguish E. coli from other species. The citrate-using mutants increased in population size and diversity.

"It's the most profound change we have seen during the experiment. This was clearly something quite different for them, and it's outside what was normally considered the bounds of E. coli as a species, which makes it especially interesting," says Lenski.
Rare mutation?

By this time, Lenski calculated, enough bacterial cells had lived and died that all simple mutations must already have occurred several times over.

That meant the "citrate-plus" trait must have been something special - either it was a single mutation of an unusually improbable sort, a rare chromosome inversion, say, or else gaining the ability to use citrate required the accumulation of several mutations in sequence.

To find out which, Lenski turned to his freezer, where he had saved samples of each population every 500 generations. These allowed him to replay history from any starting point he chose, by reviving the bacteria and letting evolution "replay" again.

Would the same population evolve Cit+ again, he wondered, or would any of the 12 be equally likely to hit the jackpot?
Evidence of evolution

The replays showed that even when he looked at trillions of cells, only the original population re-evolved Cit+ - and only when he started the replay from generation 20,000 or greater. Something, he concluded, must have happened around generation 20,000 that laid the groundwork for Cit+ to later evolve.

Lenski and his colleagues are now working to identify just what that earlier change was, and how it made the Cit+ mutation possible more than 10,000 generations later.

In the meantime, the experiment stands as proof that evolution does not always lead to the best possible outcome. Instead, a chance event can sometimes open evolutionary doors for one population that remain forever closed to other populations with different histories.

Lenski's experiment is also yet another poke in the eye for anti-evolutionists, notes Jerry Coyne, an evolutionary biologist at the University of Chicago. "The thing I like most is it says you can get these complex traits evolving by a combination of unlikely events," he says. "That's just what creationists say can't happen."
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Type: Discussion • Score: 1 • Views: 1,073 • Replies: 19
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Wolf ODonnell
 
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Reply Tue 10 Jun, 2008 03:33 pm
What I don't understand is Lenski's attempt to replay evolution. You can't replay evolution, as evolution has no set direction.

Still, 31,500 generations for a bacteria to mutate a new trait. Good thing the Earth's billions of years old, otherwise we'd never have evolved anything.
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Vengoropatubus
 
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Reply Tue 10 Jun, 2008 11:26 pm
Certainly evolution isn't a thing with a set direction, but it does have a general direction, that is, towards lifeforms that can compete and reproduce better, and I think part of what this experiment might have been hoping to establish is how narrow or broad that tendency is.
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Dr Huff
 
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Reply Wed 11 Jun, 2008 12:36 am
Wolf_ODonnell wrote:
What I don't understand is Lenski's attempt to replay evolution. You can't replay evolution, as evolution has no set direction.

Evolution isn't a done deal it's a continuing enterprise, so there is no "replaying" going on.
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spendius
 
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Reply Wed 11 Jun, 2008 05:57 pm
Any self-respecting organism evolving in lab. conditions would show different traits than one evolving in Nature unless lab. conditions are natural under the exigencies of the Naturalistic Fallacy.

That they might be "complex" is a mere matter of social cachet. "Complex" is generally associated with high intelligence and thus the right to a larger salary.

Every silly phucker knows that.
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farmerman
 
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Reply Wed 11 Jun, 2008 06:04 pm
Wolf, I see your point when I reread the article. MHO says that the writer of the article misspoke. Its a writers word choice, not Lenski's.



Our "friendi" has recently gotten bet over the head with his new favorite phrase. So hes not denying himself every opportunity to trot it out.


You go girl.
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spendius
 
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Reply Wed 11 Jun, 2008 06:23 pm
You go sit on the khazi with your frock up yourself you silly person.
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farmerman
 
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Reply Thu 12 Jun, 2008 05:08 am
I had to go to the urban dictionary to look up khazi. Is that a UK slang word? I have never heard it before you alter kocker.
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spendius
 
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Reply Thu 12 Jun, 2008 05:52 am
It is not my fault or responsibility that I have reached a time of life when my experience is long and eclectic enough to have discovered that chasing after the female of the species, of any age, is not only a fool's errand but usually, 99.9999rec %, extremely embarrassing in any number of ways one of which is an affront to dignity.
0 Replies
 
Quincy
 
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Reply Thu 12 Jun, 2008 11:00 am
So the population that had already evolved this special trait was the only population that could, um, evolve it again? And it took 12 populations 31500 generations? Is that a long or a short time?

Anyway, I doubt this will change any IDers mind. The ones I know argue that evolution may be true for bacteria, insects and farm animals, but not for humans.
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spendius
 
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Reply Thu 12 Jun, 2008 01:38 pm
It's pointless arguing with such ideas Quincy.
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aperson
 
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Reply Sat 14 Jun, 2008 02:31 am
This may sound stupid, but organisms with a faster life cycle evolve faster, right? And as organisms evolve and gain complexity, their life cycle slows down, right? So if these two statements are correct, is it not true that the rate of evolution slows down as a creature evolves?

f'(e) = 1 / e

Or something along those lines...
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yitwail
 
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Reply Sat 14 Jun, 2008 04:49 am
aperson,

evolution only changes traits; it doesn't necessarily add complexity. parasites, for instance, usually lack traits that their free-living relatives have, because they rely on the host to provide food instead of having to hunt for it.

i also don't think it necessarily the case that simpler organisms evolve faster than complex organisms. precisely how you compare complexity of unrelated species is unclear, but i suppose size would be a measure. then certainly cockroaches are simpler than elephants, but elephants have evolved much more recently from other species than cockroaches, if the fossil record is reliable.
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aperson
 
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Reply Mon 16 Jun, 2008 10:08 pm
Yea OK, but I would say as a general rule, the faster the life cycle the more opportunity for mutation, and therefore the faster evolution goes. Evolution of elephants compared to cockroaches may be due to changes in their habitats, which are limited. Cockroaches, on the other hand, have huge tolerance and can occupy a huge variety of environments. If something changes in their environment, I suspect evolution would be less critical, as they could just move. Elephants don't have that option. For them it is truly evolve or die.
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yitwail
 
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Reply Mon 16 Jun, 2008 11:30 pm
well, agree with you that mutation rates are probably higher in simpler organisms, not just because of shorter life cycles, but because complex organisms have better DNA repair mechanisms that prevent mutations. still, it's not that simple...another factor is sexual reproduction, which allows 2 different alleles for a single gene in one individual. the classic example of this is Sickle-cell trait; when an individual has one sickle-cell allele and one normal one, she has resistance to malaria, but an individual with 2 sickle-cell alleles develops sickle-cell anemia. a trait like sickle-cell cannot develop in organisms that reproduce asexually.
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aperson
 
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Reply Tue 17 Jun, 2008 02:35 am
Ah true, true. I had not thought about that. While this is evolution, though, no new mutations are being added; old ones are being filtered out. I wonder, which is better, sexual, slow reproduction, or asexual, fast reproduction. There's probably a continuum. It would be interesting to see which organisms evolve the fastest.

I have always thought, do organisms evolve to evolve faster? You say complex organisms have DNA repair systems. This is, I assume, because most mutations are harmful, but stopping mutation altogether would stop evolution, and the species would eventually die out. On the other hand, too many mutations would create an unstable community, right? Is there a balance?
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yitwail
 
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Reply Tue 17 Jun, 2008 03:26 pm
there probably is/are optimal tradeoff(s) between mutation & stability, but we need an expert in population genetics to explain it to us. Stephen Gould's punctuated equilibria suggests that speciation is more likely to occur in small isolated populations, but if a population is *too* small it's in danger of inbreeding. Confused
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aperson
 
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Reply Wed 18 Jun, 2008 03:00 pm
Well that happens quite often in humans. Confused In one particular area, all the children are born with an extra finger on each hand. Most are amputated at birth, but one man made a living as a pianist!
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Wolf ODonnell
 
  1  
Reply Wed 18 Jun, 2008 03:07 pm
aperson wrote:
I have always thought, do organisms evolve to evolve faster? You say complex organisms have DNA repair systems. This is, I assume, because most mutations are harmful, but stopping mutation altogether would stop evolution, and the species would eventually die out. On the other hand, too many mutations would create an unstable community, right? Is there a balance?


I'd say there is a balance and that is probably a result of the fact that our DNA copying mechanisms aren't perfect.

New Scientist wrote:
Of our 14 known DNA polymerases, just four are highly accurate, making about one error for every million bases of DNA. The rest are sloppier, with some erring as often as 1 base per 100 copied.

Source: Claire Ainsworth and Michael Le Page. New Scientist 195.2616 (August 11, 2007): p36
(4).


I'm unsure of how accurate our DNA repair mechanisms are, but the sloppiness of the DNA copying mechanisms could more than make up for the repair (in mutation terms, anyway).
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spendius
 
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Reply Wed 18 Jun, 2008 05:17 pm
ap wrote-

Quote:
This may sound stupid, but organisms with a faster life cycle evolve faster, right? And as organisms evolve and gain complexity, their life cycle slows down, right? So if these two statements are correct, is it not true that the rate of evolution slows down as a creature evolves?


That's brilliant. I wish I had thought of that.

When you get to the upper colon ap give us a report so we can consider whether it is a worthwhile mission. If some spin-doctoring is necessary to present it to the public persuasively so be it.
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