6 Mar 2009
Jeff Gore
van Oudenaarden group
Department of Physics, MIT
The origin of cooperation is a central challenge to our understanding of evolution. In order for budding yeast to grow on sucrose the sugar must first be broken down, a reaction catalyzed just outside of the cell. We find that the vast majority of the resulting hydrolysis products diffuse away before they can be imported into the cell, thus making sucrose hydrolysis a cooperative behavior. In well-mixed culture we observe coexistence between wildtype cooperator cells and a mutant cheater strain that does not break down sucrose, suggesting that the interaction is what game theorists call the snowdrift game. A simple model of the cooperative interaction incorporating nonlinear benefits explains the origin of this coexistence and sheds light on how cooperative strategies can survive in the presence of cheater strategies.