Grow or Go? Studying fitness of cell populations using a mathematical model

In nature, no organism lives in an isolated environment. Competition between different organisms is a fact of life, and we are familiar with the famous phrase “Survival of the fittest’’ as the principle behind natural selection. But what factors decide whether one organism is more fit than another? Similar questions can be asked about cell populations. For a long time ``evolutionary fitness’’ was thought to be simply determined by the rate at which an organism (or cell) reproduced. Recent studies have, however, questioned this view, and have suggested fast migration and invasion as a competing mechanism to fast reproduction. It has been observed that many types of cells and organisms favor either growth and proliferation, or rapid and distant migration. This is referred to as the grow or go hypothesis. We test this hypothesis using a computer simulation of populations of two types of cells, modeled as active, interacting particles. The two cell types have different self-propulsion speeds, and different rates of proliferation and death. The simulation assumes that the faster cells divide at slower rates and have shorter life spans. We investigate the migration and phase separation in this system and look to see which population is more successful in reaching the periphery.