Phenotypic Heterogeneity and the Evolution of Bacterial Life Cycles
Fig 1
The model structure consists of two parts: ecology and development. Ecology: cells can express two phenotypes, non-sticky cells or sticky cells. The sticky and non-sticky cells occur in one of two niches: the liquid or the surface. Cells in liquid are well mixed. Cells on the surface are placed on hexagonal grid and can only stay on the surface when being sticky or directly surrounded by sticky cell. Cells can migrate from the liquid to the surface and vice versa. Migration to the surface is only possible when being sticky or when a cell is directly surrounded by sticky cell on the surface. Development: three differentiation strategies are examined in the model: (1) pure strategy, (2) probabilistic strategy, (3) decision-making strategy. In the pure strategy, cells only express one phenotype and can switch via mutations. In the probabilistic strategy, cells have a probability P to differentiate. In the decision-making strategy, cells can differentiate in response to the environment. Cells sense two environmental cues: the niche in which they occur (N) and the fraction of surrounding sticky cells (i.e. stickiness, S). Cells differentiate when the sum of regulatory input, weighted by connection weights (W1 and W2), exceeds the activation threshold (θ).