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Dictyostelium is a slime mold which is well known for having a single cell free living phase and other some conditions (e.g. when food is scarce) for forming communal piles of cells called 'slugs' which migrate as a proto animal. Eventually the slug can turn into a fruiting body with a stem and a nodule of spore forming cells at the top. The spores can then be carried off by the air and seed dicty further away.

Apart from being amazed at the seeming ability to form amoebic, animal, plant and seed like forms, there must be a lot decision making happening at the formation of the stalk and fruiting node at the top.

So my question is: what is the current thought about how cells compete in the mexican hat and stalk formation to be at the top of the pile? Its pretty altruistic of the cells in the stalk to do this - some web pages say they die, is that right? Links to references after 2007 or so would be appreciated unless it's all been decided.

By analogy its always been pretty altruistic of 99% of our bodies to let our gonads reproduce, but we are (approximately) homogeneous genetically. In the wild is slug formation heterogeneous? How does genetic diversity influence slug and fruiting body formation?

dictystelium forming fruiting bodies

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Yes we're homogeneous genetically and each (well OK, most at any rate) of our individual cells reproduces, just not sexually. I am not sure altruism enters into it for bona fide multicellular organisms. Perhaps we could say the same of dicty? Do the stalk cells also replicate in order to grow the stalk? –  terdon Feb 11 '13 at 0:32
    
That is the theory, but in practice, I think its stickier than that - there is some heterogeneity in the cells of the body. I doubt there would be any mysterious force that would cause a conflict in the organism if the germline contained a code for some significant genome changes in some of the organs of the developed body. If there were an advantage to it, it would persist.... –  shigeta Feb 11 '13 at 2:41

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Joan Strassman's work is probably the route to go for this.

The short of your answer is that several things mediate who ends up where in the slug:

Cheaters are limited from exploiting other clones by high relatedness, kin discrimination, pleiotropy, noble resistance, and lottery-like role assignment.

Here's the most relevant paper:

Strassmann, J. E., & Queller, D. C. (2011). Evolution of cooperation and control of cheating in a social microbe. Proceedings of the National Academy of Sciences, 108(Supplement 2), 10855-10862. [pdf]

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thanks @Atticus29 Let me take a look and see if this is clear.. –  shigeta Feb 10 '13 at 18:07
    
The answer appears to be 'not very selfish' as over 90% of slugs found in the wild were all closely related. Is that right? –  shigeta Feb 12 '13 at 18:54
    
The answer to your original question, "So my question is: what is the current thought about how cells compete in the mexican hat and stalk formation to be at the top of the pile? Its pretty altruistic of the cells in the stalk to do this - some web pages say they die, is that right?" is that the assignment to the spore part is by lottery. It is very altruistic (in the sense that individuals die in the stalk). As you point out, it seems pretty common for individuals to be very closely related (although chimerism seems possible). –  Atticus29 Feb 12 '13 at 22:57
    
well its not really altruistic if they are all closely related. I think the fraction of others are being selfish, but that ratio they find is usually similar to the amount of selfishness allowed in such systems in the simple simulations I know. you have got your checkmark sir. –  shigeta Feb 13 '13 at 4:07

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