Figure 4

Results of the modified computer simulations. (a, b) Cells take up nutrients as they grow, creating gradients at the edge of the colony. All colonies demixed into clonal sectors, with the demixing distance (see Materials and methods) increasing with nutrient concentration. (a, c) The background gray intensity represents the concentration of nutrients. Here we show images for four out of the eight nutrient concentrations. (b) Heterozygosity H at different distances from the initial inoculum for different nutrient concentrations. Inset: Demixing distance as a function of nutrients. Both plots show similar results to the experiments: demixing occurs further in space when nutrients are more abundant. (c, d) Nutrient gradients were removed by keeping the concentration of nutrients constant throughout the environment (cells grew without depleting nutrients). (c) With no gradients, the colonies did not form sectors, and (d) their heterozygosity remained high. Note that results from simulations are noisier than the experimental data owing to a much lower number of cells and should not be compared quantitatively.