Just imagine you are a typical bacterium minding your own business (and a bit that of your neighbours as well) and just eating your way around some host. The place is not that great but you can make ends meet just by showing a bit of civility and expecting the same from the other bacteria. So as a good citizen of bacteriopolis you secrete molecules that cost only a little bit to produce but that can be used by your neighbours to coordinate the behaviour of the entire colony in a way that makes everybody better off.
So what would you think if you find that some of your neighbours are freeriders that save themselves all the effort to produce those molecules relying instead on the ones you work hard to synthetise? Not very happy I guess!
It is entirely reasonable on the other hand, to expect that the host might have a different opinion and if you are one of the mice used by Stuart West at Edinburgh’s University and briefly described in this article, you might hope for as many cheats as possible in the population of bacteria. That is because this research has shown that a colony of cheaters in a mice is indeed a less virulent colony, which increases the life expectancy of the mice when compared to those in which the population is made of cooperators only. Interestingly (very interestingly I may add), when the mice were infected with mixtures of cheaters and cooperators the results were still similar to those in which the population is made only of cheaters. That would imply that one would only need to add a certain number of cheaters in an existing colony of cooperators to obtain similarly disrupting results.
Now, there’s also a good deal of cooperation and competition going on in cancer (you might want to take a look at an older post on that “here:”http://cancerevo.blogspot.com/2007/02/axelrod-et-al-evolution-of-cooperation.html) so this could potentially have an impact on therapies designed to minimise the aggressiveness of a growing tumour.
Mullard, A. (2009). Cheating bacteria could treat infections Nature DOI: 10.1038/news.2009.47
Interesting stuff, David. Some thoughts…
1) The idea that overall group fitness is greater when everyone is cooperating seems to follow as an emergent macro property from the (micro-)economic concept of comparative advantage
2) In looking at somatic cell populations, cancerous or “normal”, it behooves us to remember that behavior of individual cells must be seen in the context of an extremely cooperative pre-existing background. That is, the base rate of cooperation between any two cells in a multicellular organism is extremely high compared to independent single-celled organism in the wild or even colonies of cells. Thus, when viewed from a relative standpoint, cancer cells might be seen as cooperating with one another even if all they are actually doing is disrupting cooperation between normal cells. You could even quantify disruptive cooperation if you determined what the base rate of normal cellular cooperation is.
Hi Rafe,
Many thanks for your comment and for your comparison with economics but also for the reminder that cancer cells are just healthy cells that have started a process of transformation in which cooperation with healthy cells gradually leads to competition with healthy cells (and potentially cooperation between cancer ones). I think the main challange here is to move from suspecting that cooperation plays a big role in driving cancer evolution to proper measurements of what this cooperation adds to the tumour and the mechanism by which it works (and maybe be disrupted).