Metabolic pathway expression and relative phenotypic frequencies during evolution in the AB environment. (A) Emergence of the XOR phenotype in a mixed (A &B) population evolving in the XOR environment. Phenotypes of the fittest organisms of the population are shown for the first 500 epochs of simulation. Without HGT (left panel) cells with initial phenotypes A and B (orange and green plots, respectively) are the fittest for the first 150 epochs; afterwards cells mutate to intermediate phenotypes (black plots) and finally an XOR-like phenotype emerges (red plots). Emergence of the intermediate and final phenotype occurs sooner if networks of type A and B are combined in one organism by HGT (right panel). Time profile of nutrient abundance is shown for comparison with phenotype profiles on the top of each panel in blue. (B) Emergence of an XOR phenotype in a population composed as a 1:1 mixture of cells with A and B phenotype without (left panel) and with (right panel) HGT in 400 epoch intervals. Frequencies of A, B, and XOR phenotypes are shown in red, blue, and grey respectively; percentage of cells with no distinct phenotype is shown in black. Statistics is collected over 64 experiments.