Multilevel selection in multitype populations

Multilevel selection has important implications for understanding the origin, ecology, and evolution of host-associated microbiomes. Selection on the host-level can have a substantial impact on the evolution of microbial lineages, favoring microbes that are beneficial to the host. However, previous research has focused on the evolution of interactions among only two types. We alter this perspective by examining the role of multilevel selection in shaping the interaction dynamics of a population with many microbial types-a case of particular relevance for microbiomes. We ask how multilevel selection influences the selection of interactions among various microbial types, whether it promotes microbial diversity within the population, and whether it increases the likelihood of microbial lineages evolving beneficial interactions with their host and other microbes. To address these questions, we simulate a multitype population structured into groups, where individuals interact within groups through an evolutionary game that determines their fitness. We classify pairwise interactions by their dynamical outcomes: dominance, coexistence, or bistability. We find that multilevel selection reshapes interactions dynamics in complex ways, depending on the details of the population structure. We show the impact of the interaction patterns emerging in such a system.