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Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.4 |
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Author | Topic: Kin Selection & Altruism | |||||||||||||||||||||||
Cal Inactive Member |
Lets see, throwing away perfectly good cellular material, expending energy unrelated to feeding or reproduction, positive benefit?
The amount of material we're talking about is sufficiently negligible that its loss may be regarded as neutral. But I see that I have yet to persuade you that plasmids are best viewed as autonomous entities (examples of selfish DNA, if you will) anyway, and that they capitalize on bacterial cellular machinery to facilitate their own replication. The important thing to remember is that whether it ends up earning its keep or not, the plasmid is an uninvited guest to the cell. If you look only at those horizontal gene transfers that confer an advantage upon the recipient cell (such as antibiotic resistance) it is easy to get confused; why indeed would the donor cell want to do that? The answer, as I've tried to point out, is that it wouldn't; the proper question to ask is: what would be the advantage for the plasmid?
At a minimum the energy would need to be recovered before the organism could proceed to reproduce.
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pink sasquatch Member (Idle past 6044 days) Posts: 1567 Joined: |
Nice post.
The amount of material we're talking about is sufficiently negligible that its loss may be regarded as neutral. Absolutely. The other important issue is that when dealing with transfer and especially plasmids, the donor is not losing genetic resources. A cell may contain a hundred copies of the same plasmid - giving a few away is a small expenditure of resources, and whatever genetic benefit the plasmid may be conferring is kept by the donor. BUT, an important point that I think both you and RAZD have overlooked:
RAZD writes: Lets see, throwing away perfectly good cellular material, expending energy unrelated to feeding or reproduction, positive benefit? Cal writes: If you look only at those horizontal gene transfers that confer an advantage upon the recipient cell (such as antibiotic resistance) it is easy to get confused; why indeed would the donor cell want to do that? The answer, as I've tried to point out, is that it wouldn't A donor cell definitely gets a strong benefit in transferring antibiotic resistance to its friends and neighbors. There are various ways of becoming resistant to antibiotics - but one of the most commonly transferred ways involves passing on genetic info for the production of enzymes that break down the antibiotic. A cell with this mode of resistance produces these enzymes, hopefully (for the cell) in sufficient numbers to reduce the antibiotics to survivable levels in its local area. If said cell is surrounded by other cells all breaking down the antibiotic, then the active antibiotic levels will more likely be brought down to survivable levels for everyone involved. If sufficient numbers of cells are involved, the amount of energy expended producing resistance enzymes drops for all the cells involved, and can eventually go to zero if all the antibiotic is broken down. So is there a benefit to transfer of antibiotic resistance? Increased chance of survival. Reduced energy expenditure. Hell yeah.
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Cal Inactive Member |
If sufficient numbers of cells are involved, the amount of energy expended producing resistance enzymes drops for all the cells involved, and can eventually go to zero if all the antibiotic is broken down.
Good point. But I'll also point out again that not all plasmids do 'earn their keep' by offering (say) antibiotic resistance; some persist despite the fact that they may even be detrimental to the cell. A genome is a battleground.
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pink sasquatch Member (Idle past 6044 days) Posts: 1567 Joined: |
But I'll also point out again that not all plasmids do 'earn their keep' by offering (say) antibiotic resistance; Quite right, but the existence of plasmids whose transfer to other cells directly benefits the donor means that a mechanism of such transfer could have readily evolved, and thus we have no need to invoke altruism.
A genome is a battleground. Plasmids aren't genomic. But evolution is often a case of balancing competing interests. If you see that as a "battleground", so be it. I prefer to see it as exquisite, life-permitting compromise.
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RAZD Member (Idle past 1426 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Quite right, but the existence of plasmids whose transfer to other cells directly benefits the donor means that a mechanism of such transfer could have readily evolved, and thus we have no need to invoke altruism. That just explains why it persists in the population, not why it started. Claiming that altruism only applies to confering a reproductive benefit and then claiming that reproduction of it is evidence that altruism is not necessary for an explanation is circular reasoning. Thus either one or both of these positions is false. The benefit to the whole species is different than the benefit to the individual of the species, and the definition of altruism that has been mentioned here is an individual making a sacrifice of elements of self to some detriment to individual reproduction does so to confer a benefit to the species as a whole. This is a very narrow definition, but using it means that demonstrated benefit to the species as a whole, as done here, does not mean that it is not altruism. Regardless of the 'population' of plasmids within the organism, energy and resources have gone into the production of those plasmids. If this is not directly related to the individuals {fitness for survival or for reproduction} then this is wasted use of energy and resources, as those resources could have been directed to result in earlier reproduction. This message has been edited by RAZD, 12*10*2005 07:44 AM by our ability to understand RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ... to share.
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Cal Inactive Member |
Plasmids aren't genomic.
Is extrachromosomal extragenomic? It's almost a philosophical question, isn't it? Does an exact count of the number of cells in a human body properly include commensal gut flora?
If you see that as a "battleground", so be it.
Prolly a guy thing.
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RAZD Member (Idle past 1426 days) Posts: 20714 From: the other end of the sidewalk Joined: |
But I see that I have yet to persuade you that plasmids are best viewed as autonomous entities ... So you are saying that plasmids are infections in the host cell? That individual organisms are sum{host DNA + infection DNA}? by our ability to understand RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ... to share.
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Cal Inactive Member |
So you are saying that plasmids are infections in the host cell? That individual organisms are sum{host DNA + infection DNA}?
Yes.
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RAZD Member (Idle past 1426 days) Posts: 20714 From: the other end of the sidewalk Joined: |
So the fitness of an individual organism for {survival\reproduction} depends on random mutation (whether this includes copy errors or not) within the host genes
and infection? Just wondering. by our ability to understand RebelAAmerican.Zen[Deist
... to learn ... to think ... to live ... to laugh ... to share.
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Cal Inactive Member |
So the fitness of an individual organism for {survival\reproduction} depends on random mutation (whether this includes copy errors or not) within the host genes
I'm not sure I understand the question. Can you rephrase it?
and infection? Just wondering.
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pink sasquatch Member (Idle past 6044 days) Posts: 1567 Joined: |
This is a very narrow definition, but using it means that demonstrated benefit to the species as a whole, as done here, does not mean that it is not altruism. Obviously you didn't actually read my explanation of how donor cells benefit from transfer of antibiotic resistance to their neighbors. The specific, individual donor cell is more likely to survive and reproduce, and reduces its own energy expenditure, if it transfers info on how to break down antibiotics to its neighbors. This is the exact opposite of "benefit the species as a whole".
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pink sasquatch Member (Idle past 6044 days) Posts: 1567 Joined: |
Is extrachromosomal extragenomic? It's almost a philosophical question, isn't it? Not really. Why philosophical? Terminology is in place for a reason - extragenomic DNA like plasmids and mitochondrial DNA behaves very differently than the genome itself.
Prolly a guy thing. I lost my penis because I don't think the genome is at "war" with itself!?!!?! ARGhgHHH!?!? My penis!!! [edited: because I forgot who I was responding to for a minute...] This message has been edited by pink sasquatch, 12-10-2005 10:08 AM
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Cal Inactive Member |
So the fitness of an individual organism for {survival\reproduction} depends on random mutation (whether this includes copy errors or not) within the host genes
I would say that since what constitutes an "individual organism" may not be as neat and tidy as one might suppose, the fitness of both 'guest' and 'host' need to be considered both separately and collectively.
and infection?
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Cal Inactive Member |
Why philosophical?
Let me put it this way: how many genomes constitute a human genome? Is the mitochondrial genome properly regarded as part of a human genome, or as a separate 'human genome' -- and does not arriving at an answer to this question involve something closer to philosophy than to biology? It's really mostly about getting things straight in our heads, isn't it?
I lost my penis because I don't think the genome is at "war" with itself!?!!?! LOL. Just testing a hypothesis.
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pink sasquatch Member (Idle past 6044 days) Posts: 1567 Joined: |
Is the mitochondrial genome properly regarded as part of a human genome, or as a separate 'human genome' -- and does not arriving at an answer to this question involve something closer to philosophy than to biology? I don't think we need to invoke philosophy regarding these technical terms. Mitochondrial genomes behave much differently than the genome proper, so a distinction is made in the terminology. Similarly, plasmids in a bacterium behave much differently than the bacterial genome, so a technical distinction is made. If part of the DNA of a plasmid or mitochondrion integrates into the genome, it becomes genomic DNA. It's really much more mechanical, not really philosophical.
Just testing a hypothesis. You're not the first to try to determine if sasquatch coat color is sex-linked...
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