"Multilevel selection models for microbiomes"de Azevedo-Lopes, AmandaThe study of multilevel selection within host-associated microbiomes has important implications for understanding the origin and evolution of these complex associations. To date, our understanding of the various levels influencing selection on microbial communities remains incomplete. The higher level of selection provided to the microbiome by the host has a substantial impact on the evolution of microbial lineages, favoring interactions beneficial on the higher level [1,2,3]. At the individual level, microbial lineages within each host are subject to selection favoring individuals with higher reproduction rates. Conversely, the health status and reproductive success of hosts may be enhanced depending on their microbiome, thereby increasing the chances of proliferation for the microbiome. The typical theoretical model contains two types of individuals: cooperators and defectors. Defectors tend to dominate over cooperators at the individual level, whereas groups composed entirely of cooperators have an advantage at the group level. This scenario illustrates how selection can operate in opposite directions across different levels - cooperation is beneficial at a higher level, but can be detrimental for an individual at a lower level. While previous research [1,2,3] has investigated the effects of higher-level selection, it has predominantly focused on the evolution of interactions among only two types. We expand this perspective by examining the potential role of multilevel selection in shaping the dynamics of host-microbiome interactions, particularly when considering a diverse population of microbial types. We seek to understand how multilevel selection influences the selection of interactions among various microbial types, whether it promotes higher 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 structure a population of individuals into groups, where individuals interact through an evolutionary game that determines their fitness. Individuals immigrate from an environmental pool, reflecting an influx of microbial types. Within the groups, individuals are subject to birth and death as well as group division and extinction. Group sizes are constrained and when a group reaches a certain size, it either splits into two and another group is removed or a random individual from the group dies, such that the maximal group size is not exceeded. Through this process, multilevel selection is triggered by individual reproduction and constraints imposed by population structure. We show the impact on the interaction patterns emerging in such a system. [1] A. Traulsen and M. A. Nowak, “Evolution of cooperation by multilevel selection,” Proceedings of the National Academy of Sciences, vol. 103, pp. 10952–10955, July 2006. [2] S. van Vliet and M. Doebeli, “The role of multilevel selection in host microbiome evolution,” Proceedings of the National Academy of Sciences, vol. 116, pp. 20591–20597, Oct. 2019. [3] D. B. Cooney, S. A. Levin, Y. Mori, and J. B. Plotkin, “Evolutionary dynamics within and among competing groups,” Proceedings of the National Academy of Sciences, vol. 120, p. e2216186120, May 2023. |
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