Resource competition and social conflict in experimental populations of yeast

Understanding the conditions that promote the maintenance of cooperation is a classic problem in evolutionary biology(1-5). The essence of this dilemma is captured by the 'tragedy of the commons' 6: how can a group of individuals that exploit resources in a cooperative manner resist invasion by 'cheaters' who selfishly use common resources to maximize their individual reproduction at the expense of the group(7,8)? Here, we investigate this conflict through experimental competitions between isogenic cheater and cooperator strains of yeast with alternative pathways of glucose metabolism(9), and by using mathematical models of microbial biochemistry(10). We show that both coexistence and competitive exclusion are possible outcomes of this conflict, depending on the spatial and temporal structure of the environment. Both of these outcomes are driven by trade-offs between the rate and efficiency of conversion of resources into offspring that are mediated by metabolic intermediates.