Re: One celled organisms acting as a swarm?
- From: Lorentz <drosen0000@xxxxxxxxx>
- Date: Mon, 13 Oct 2008 12:58:30 -0400 (EDT)
On Sep 24, 1:18=A0pm, Joachim Pimiskern <JoachimPimisk...@xxxxxx> wrote:
dterr...@xxxxxxxxxxx schrieb:
Another feat is the Pseudomonas quinolone signal. If timesI think a gene centric model is probably an easier way to look
get hard for the bacteria, they emit a chemical signal
named quinolone. Upon receiving this signal, some bacteria
commit suicide, setting free their DNA which is cannibalized
by the still living ones. This kind of bacterial sex enables
them to increase their diversity.
at this process. The bacterial cells are not the level of selection
that provides the clearest explanation. For example, there is no
differential benefit to those bacterial cells that commit suicide. The
cells that commit suicide benefit all sorts of bacteria, not just the
species that emits quinolone. Since bacteria of a different species
are "enemies" of the bacteria that emit quinolone, it seems risky to
commit suicide in terms of survival of the quinolone emitting species.
So an "group selection model" may not be clear. Perhaps the following
gene centric model may be clearer.
Think of the bacterial cells that emit the quinolone as
vehicles for several different genes. The cells are like ships that
carry the genes from place to place, and the genes like sailors. When
times are good, it doesn't take many sailors to run the ship.
The quinolone is more like a "hiring sailors" sign. There is a
network of genes in the bacterial cell that I will call the quinolone
network. When times are bad, this network switches on one gene that
tells the ribosomes to make quinolone. So I hypothesize their are also
suicide genes in the quinolone network that recognize the presence of
quinolone outside the cell.
The bacteria are not "committing suicide" to free their DNA for
other individuals. Rather, some of the genes in the bacterial cells
are ejecting from their vehicles (the cells). If other cells are
emitting quinolone, it means times must really be bad. The environment
must be getting bad for these bacteria. Similar genes in other
bacteria are directing their vehicles (their cells) to pick up the
survivors.
As far as the genes in the suicide cell are concerned, the other
bacteria are rescue vehicles. The quinolone indicates that the nearby
bacteria aren't just going to digest the genes for energy.
Furthermore, the environment in the rescue vehicle is comfortable for
quinolone network genes. So the network genes may have a better chance
of surviving in a cell with other quinolone network genes than by
staying in one with a shortage of other genes.
Some of the genes will be picked up and incorporated into the
new vehicle. Furthermore, the cells that pick up the survivors get new
genes to work on their vehicle. The other gene may have a means of
fighting the hostile environment, or the other gene may increase the
risk of the vehicle being destroyed. However, there is a third
possibility. The new gene may be just a gene that helps emit quinolone
(i.e., part of the quinolone network). In which case, the quinolone
genes have helped one of their own.
The gene centric and the social selection descriptions may be on
some fundamental level equivalent. When trying to analyze how a social
behavior first evolves, I think the gene centric view is clearer. You
can't talk about a "swarm" acting together until the swarm behavior is
already in place. Then, group selection may be a clearer way of
describing the further evolution of the swarm behavior.
.
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