Growth and form control population dynamics of cellular aggregates*

While the colony morphology reflects the interplay of biophysical processes such as nutrient diffusion, motility, and growth. How these processes control genetic correlations within the population remains an open question. To understand how growth morphology influences evolutionary dynamics, we have developed a numerical model of two-dimensional colonies in which microbes grow by consuming a diffusible nutrient and have a density-dependent motility. We show that this model can reproduce a diverse family of shapes observed in the experiments. Many of these morphologies exhibit a qualitatively different pattern of genetic drift compared to microbial colonies with a moderately rough front, which have been the focus of previous work. We report the scaling exponents for both morphological and genetic quantities for each of the growth regime. Most importantly, we show the consequences of the transition from pulled to pushed expansions in two-dimensional models with nutrient diffusion.