The evolution of fitness during range expansions in multiple dimensions

We efficiently simulate range expansions of populations, by using our set of computer programs, on a laterally connected lattice in 1D, 2D (on a strip, and on a disk) and 3D (in a cylinder, and in a sphere). We employ a model with finite genome regions, each containing infinite sites, for a population of diploid individuals. Using the programs, we generate tens of simulation replicates to analyse the temporal evolution of mean fitness of individuals on the expansion front. We explore the model over different conditions, compare normalisation methods for fitness, and explore the case of radial (sphere) and axial (cylinder) expansions in 3D, which might apply in the analysis of the behaviour of viruses/bacteria inside a host, in the prediction of expansions of marine species in ocean environments, and even in scenarios of interstellar space colonization. In 3D expansions, we find complex spatial fluctuations in deme-average fitness values, different from those in radial 2D expansions. In axial 3D (cylinder) expansions, we determine that the highest-valued deme-average fitness lies along the axis of the expansion. We also find the fluctuation patterns of fitness in 3D cylinder expansions, similar to those previously seen in radial expansions in 2D. In radial 2D (disk) expansions, we find that the fitness of a population undergoing multiple mutations shows a smooth combination of binary segregation pictures against each of those mutations. We confirm the accumulation of deleterious mutations -- a phenomenon known as expansion load -- in all scenarios above. ### Competing Interest Statement The authors have declared no competing interest.