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Bacterial swarming, an experimental model for studying morphogenesis and evolution in expanding populations
Bacterial swarming is the ability to collectively spread across surfaces. In Pseudomonas aeruginosa, an opportunistic pathogen, swarming colonies exhibit striking branching patterns. Swarming phenotype requires coordination of various behaviors (quorum sensing, surfactant production, motility) that are precisely regulated. However, how each factor physically controls colony morphogenesis remains unclear.
Moreover, bacteria, with large populations and short generation times, are ideal models for evolution in the lab. I use the swarming phenotype as an experimental tool to study the evolution in expanding populations, where expansion is driven by growth and dispersal. Using the Fisher wave framework, I build a model of invasion in expanding populations. The conditions of invasion are analytically derived. They enable predictions of the direction of evolution in the presence of a trade-off. In particular, I show that a mutant with a lower growth rate can invade the ancestral population, as long as its dispersal rate is sufficiently higher. Invasions by such mutants (slower growth, greater dispersal) are found in microbial communities, cancers, and invasive species.