Motility induced patterning in range expansions

Range expansions, i.e., the invasion and colonization of space by growing populations of organisms, play a key role in the spread of genetic diversity in spatially extended environments. While most studies of microbial range expansions focus on nondirected diffusive transport as the primary mode of dispersal, microorganisms such as flagellated bacteria are capable of active modes of transport through directed swimming, quorum sensing, chemotaxis etc. How does active motility, which tends to produce radial as opposed to azimthual genotype segregation, affect the frontier expansion of a colony of dividing cells? What are the genetic consequences of active patterning on spatial range expansions when motility is strong? By using numerical simulations and analysis of a continuum model, we demonstrate activity induces finite wavelength patterns that can strongly affect colony expansion for both pulled and pushed waves. We also explore the genetic consequences of these phenomena in populations of antagonistically competing strains and highlight the competition between a genetic line tension and active forces in deciding the evolutionary fate of such mixtures.