Cooperation, Cheating, and the Games that Yeast Play
March Meeting 2010
WASHINGTON, D.C. — Yeast is a convenient "model" organism that scientists can use to test ideas about evolution because they can easily genetically alter yeast in the laboratory and grow large populations of different strains in a matter of days.
Mathematicians who study "game theory" often analyze worldly subjects as complex as macroeconomics or evolution by using simple abstractions that involve multiple players competing for limited resources. Such analyses sometimes attest to a simple, if unfair, rule—that in games, as in life, the best strategy may be to cheat. But according to MIT physicist Jeff Gore, who studies cooperation and cheating in different strains of yeast, sometimes the good guys (or yeast) do win in the end.
Populations of certain strains of yeast will cooperate with each other metabolically by secreting an enzyme called invertase that breaks down the sugar sucrose (which they cannot digest) into the sugar glucose (which they can). In a homogeneous pool of such yeast, each cell benefits from the collective actions of the whole pool.
At first glance cheaters—yeast that do not secrete anything—would seem to have an advantage in this scenario because they would enjoy the glucose while being spared from having to spend any energy producing the enzyme. However, according to experiments Gore and his colleagues published in Nature last year, that's not always the case. In populations of yeast where the number of cooperators is initially small, it is the cooperators that enjoy the distinct advantage because they are always as close to the food source as possible. The majority of the sugar they break down diffuses away from them, but they still have preferential access to some portion of it.
In Portland, Gore will discuss his experiments testing game theories in yeast as well as the results of new experiments probing the degree to which evolutionary adaptations are reversible.
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