Evolutionary theory including expression mechanism of phenotype: evolutionary significance of the cheater of Dictyostelium discoideum

Dictyostelium discoideum lives as single celled organism when there are a lot of food. When the food depleted, the cells aggregate and make a structure called fruiting body. Fruiting body consists of spore cells and stalk cells. Stalk cells can not produce offspring, so making fruiting body is altruistic behavior. D. discoideum has polymorphism about the ability to make fruiting body. The mutants called cheater tends to become spore when they make fruiting body with wild type cells. Fruiting body of some cheaters can not distinguish from that of wild type. Understanding the existence of the cheater, genes and molecules should be considered. I made simple mathematical model for making fruiting body. By using this simple model, I compare the case the fruiting body is made by a single strain and the case the fruiting body is made by two strains, and discuss the evolutionary significance of the cheater.