From co-colonization interactions to emergent system dynamics in multi-strain systems

The high number and diversity of microbial strains circulating in host populations has inspired extensive research on the mechanisms that maintain biodiversity. While much of this work focuses on strain-specific and cross-immunity interactions, another less explored mode of pairwise interaction is via altered susceptibilities to co-colonization in hosts already colonized by one strain. Diversity in such interaction coefficients enables different strains to create dynamically their niches for growth and persistence, and 'engineer' their common environment. How such a network of interactions with others mediates collective coexistence remains puzzling analytically and computationally difficult to simulate. Furthermore, the factors modulating stability-complexity regimes in such high-dimensional multi-player systems remain poorly understood. In this talk I will present results from two recent studies with my collaborator in Tours, where we analyze such a multi-strain epidemiological system and the eco-evolutionary dynamics that emerge. Applying timescale separation to the original model, we obtain a replicator equation, which enables to highlight the key coexistence principles and the critical shifts in multi-strain dynamics potentiated by mean-field gradients.