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I have already posted this on chat but haven't got any response. A recent question on group selection stimulated me to ask this here.

QUESTIONS: Why should bacteria conjugate? If we consider that a bacterium is another bacterium's rival (in terms of obtaining resources) why should a bacterium "share" it's antibiotic resistance gene, for example, with another bacterium? I can think of 2 reasons. One is group selection, and the other is "Gene Selection". Group selection has been highly criticized in recent years, and individual selection has dominated thinking, but here my support goes for gene selection rather than individual selection.

Gene selection seems to me the easier explanation over individual selection. Even if we consider the fact that a colony is made from divisions of single cells and the cells are extremely similar and also that conjugation is more probable between cells of a colony, we should also consider that conjugation can happen between very different bacterial species.

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I would love to discuss this in chat with anyone interested as I think this question is more of a question to be discussed. –  biogirl Nov 29 '13 at 10:35
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Does it make any difference, for the purpose of your question, if we speak of bacterial conjugaison or of any sexual reproduction? Isn't you question rather something like "Why would sex evolve?" Such question would require a very long answer that presents many different models! –  Remi.b Nov 29 '13 at 12:18
    
@Remi.b The biggest difference between conjugation and sexual reproduction is - that there is no reproduction of an organism in conjugation. I don't understand why you think the questions are same. I don't want to know the advantages of having " recombination " events in life of an organism. Here, I want to know whether this is an example of selection at individual level or at gene level ? –  biogirl Nov 29 '13 at 15:29
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As I understand it: In order to answer to your question, one should think about the Muller's ratchet, the advantage of recombination for the group, how a selfish gene causing recombination might spread, about the speed of adaptation, effect on genetic variance, resistance to parasites, DNA repair, libertine bubble theory, etc… –  Remi.b Nov 29 '13 at 15:44
    
It is roughly the same hypotheses than for recombination through sexual reproduction. But it does not mean I find your question uninteresting. I just wanted to say that there are certainly lots of different models to compare and that you might find your answer in the standard discussions about evolution of sexual reproduction. I might be mistaken though! –  Remi.b Nov 29 '13 at 15:45
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Interesting Question (glad the "group selection" post got you thinking!)

Me and two friends thought about your question during our Biology BSc at ICL (in fact we also thought about an even more puzzling phenomenon called "bacterial transformation" which is like conjugation, but they incorporate genes from dead bacteria!!) our first year course convener recognized our answers as "most likely candidates" so here they are:

1. Stress-induced Experimentation Hypothesis

The likelihood of conjugation/transformation occurring may change for a bacterial population as a whole depending on how stressed it is (or perhaps how unfamiliar the environment is?). Stress signals could cause the population to be more "risky" and take up the DNA from surrounding living/dead bacteria and incorporate it with its own genome: "the hell, we're out of options.. lets transform into something that resembles the indigenous species of this strange ecosystem!". Indeed Bacteria have memory (see: chemotaxis) this means that perhaps they can be able to tell whether they have been receiving more stress now as opposed to before, meaning they can "trial and error" with various genes that have been imported within their plasmids! — "Let's try this gene, oh wait... I'm dying, hmm let's kill off this plasmid and take some more genes!".

In reply to this my course convener said:

"ah yes, a switch from asexual to sexual reproduction occurs in many organisms under stress. The genes that cause the sex/transformation to occur may gain a net benefit from recombination with genes taken from other organisms/the environment."

2. Diversity Plagarism Hypothesis

If we look at the entire population of conjugating bacteria as a single competitive unit itself (e.g. like a tissue is a coordinated group of specialized cells) that can compete with other populations of bacteria who cannot conjugate the conjugating population will "win". This is because a conjugating population will always have much higher phenotypical diversity as it can mix traits between the individuals. This means a conjugating population is much more efficient at undergoing natural selection for beneficial traits or trait combinations.

Think of natural selection (coupled with mutation) as an inventor... something that helps you invent much "fitter bacteria" is the ability to pull things apart from this bacterium and that bacterium and glue them together, this is essentially what conjugation/transformation does!! it allows you to pull bits from this bacterium and stick it to bits from that bacterium to get a "super-bacterium". It's like open source technology (free to share) as opposed to patented technology!! Conjugation is immediately a good thing because it means you can "steal" cool technology from living/dead bacteria and incorporate it into your population's gene pool!

Hope this was helpful!

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I think I said in the comment prety much the same thing as the last para but with a slightly different perspective. –  biogirl Nov 30 '13 at 12:19
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Awesome, well I have to say I know quite little about the mechanisms and mechanics of the conjugation process. But it would be interesting to know whether conjugation is "consensual". At least for transformation it is clear that there is no need for "compelling", the bacterium merely steals the DNA from the "corpse". A really interesting alternative answer is that the genes themselves are selfish genetic elements that can express some mechanism that allows them to infiltrate the bacterial genome. –  hello_there_andy Nov 30 '13 at 12:36
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Check out the Homing Endonuclease Genes (HEGs) bit.ly/puyHda - HEGs literally make cuts in DNA and insert themselves into the genome. –  hello_there_andy Nov 30 '13 at 12:37
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Oh yes..I think The alternative will definitely be advocated by Dawkins. And yes, I thought of that too and I have written that in the question and in the comments. (It isn't an original idea as I have read the selfish gene !) –  biogirl Nov 30 '13 at 12:42
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The other link seems pretty cool ! And i understand that it is difficult to prove that the other bacteria "compells" the 1st one. But thinking wild things is my hobby :) –  biogirl Nov 30 '13 at 12:43
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