The Host-Pathogen Game: an evolutionary approach to biological competitions

We introduce a model called Host-Pathogen game for studying biological competitions. Notably, we focus on the invasive dynamics of external agents, like bacteria, within a host organism. The former are mapped to a population of defectors, that aim to spread in the extracellular medium of the latter. In turn, the host organism is composed of cells mapped to a population of cooperators, that aim to remove pathogens. The cooperative behavior of cells allows to support the living functions of the whole organism, since each one provides an unitary amount of energy. When one or more bacteria are spatially close to a cell, the latter may use a fraction of its energy to remove them. On the other hand, when a bacterium survives an attack, it absorbs the received energy, becoming stronger and more resistant to further attacks. In addition, since bacteria play as defectors, they aim only to increase their wealth, without supporting their own kind. As in many living organisms, the host temperature plays a relevant role in host-pathogen equilibria. In particular, cooperators succeed when bacteria are completely removed, while the opposite outcome entails the host undergoes a deep invasive process, like a blood poisoning. Results of numerical simulations show that the dynamics of the proposed model allow to reach a variety of equilibria. Here it is worth noting that, on a quality level, the achieved outcomes describe some real scenarios, that can be observed in living systems. To conclude, we deem that our model might open the way to further developments, based on evolutionary game theory, for studying several complex biological