Understanding the dynamics of co-colonization systems with multiple strains

The high number and diversity of microbial strains circulating in host populations pose challenges to human health and have inspired extensive research on the mechanisms that maintain such biodiversity. While much of the theoretical work focuses on strain-specific and cross-immunity interactions, another less explored mode of pairwise interaction is via altered susceptibilities to co-colonization (co-infection) in hosts already colonized by one strain. Diversity in such interaction coefficients enables 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 gradients modulating stability-complexity regimes in such multi-player endemic systems remain poorly understood.

In this seminar I will present results from an epidemiological study where we analyze mathematically such an interacting system and the eco-evolutionary dynamics that emerge. Adopting a slow-fast dynamic decomposition of the original SIS model, we obtain a model reduction coinciding with a version of the replicator equation from evolutionary game theory. This enables us to highlight the key coexistence principles and the critical shifts in multi-strain dynamics potentiated by mean-field gradients.