Evolution of strategies in a spatial IPD game with a number of different representation schemes

We examine the evolution of strategies for a spatial IPD (Iterated Prisoner´s Dilemma) game, which are encoded using different representation schemes. Each agent at a cell in a two-dimensional grid-world has its own representation scheme for encoding its strategy. In general, strategies with different representation schemes cannot be recombined. Thus a population of agents can be viewed as a mixture of different species (i.e., an ecology with different species). When the size of a neighborhood structure is small and/or the number of representation schemes is large, it is likely that some agents have no neighbors with the same representation scheme. We discuss the handling of those agents because they cannot generate their new strategies through recombination. In computational experiments, we use four types of strings (i.e., four representation schemes). Agents in our spatial IPD game are randomly divided into four groups of the same size. One string type is assigned to each group. Recombination is performed between strings of neighboring agents with the same string type. With respect to the IPD game, we compare two settings with each other. In one setting, the IPD game is played between any pair of neighboring agents regardless of their string types. In the other setting, it is played only between neighboring agents with the same string type. Using these two settings, we examine the effect of the IPD game between agents with different representation schemes on strategy evolution. We also examine the effect of the number of different representation schemes in a population (i.e., the number of species) on strategy evolution.