Fig. 1. Overview of the model and experimental setup.

a Host and symbiont each consist of a genome (with discrete beads representing genes and binding sites), a gene regulatory network and a cell cycle. Holobionts (disks) live in space and comprise one host (black square) and one or more symbionts (purple circles) that compete for nutrients. For both the host and symbiont, a division event (blue arrow) and a death event (blurred shape) are shown. Lattice site colors depict nutrient abundance for an influx of n_influx = 30. b Two in silico evolution experiments with endosymbiosis were performed (green and purple boxes): one starting with primitive cells on a nutrient gradient and one starting with pre-evolved prokaryotes from our previous work²⁹. Simulation time and grid sizes are shown for each experiment; colors depict nutrient abundance.