From transport in channels to population evolution: how heterogeneities shape dynamics - Arthur Alexandre (EPFL, Switzerland)

In this seminar, I will discuss two problems where effective descriptions capture the essential mechanisms at play: one from hydrodynamics and one from population genetics.

In hydrodynamics, Taylor dispersion describes the enhanced spreading of particles in a fluid due to the combined effects of diffusion and flow. We show how this phenomenon can be understood in tortuous, highly corrugated channels using an effective model that captures the main transport properties, providing insight into flows in porous media.

In population genetics, the gut microbiota presents extensive genetic diversity shaped by its flow-dominated environment. Using a minimal model [2] incorporating flow, diffusion, and microbial growth that we extend to non-neutral mutations, we show how spatial structure and advection influence the fixation of beneficial mutants. This illustrates the interplay between flow, growth, and spatial heterogeneity in shaping microbial evolution.

[1] Alexandre, A., Guérin, T. & Dean, D. S. Effective description of taylor dispersion in strongly corrugated channels. Physical Review E 111, 064124 (2025).

[2] Labavić, D., Loverdo, C. & Bitbol, A.-F. Hydrodynamic flow and concentration gradients in the gut enhance neutral bacterial diversity. Proceedings of the National Academy of Sciences 119, e2108671119 (2022).

Contact: Bahram Houchmandzadeh