The fate of beneficial and deleterious mutations in range expansions driven by long-range dispersal

Range expansions are common in nature, and can take such forms as an invasive species colonizing a new habitat or a virus spreading from host to host during a pandemic. Range expansions can leave behind signals that mimic local adaptation via founder events either at the expansion frontier in populations with only short-range dispersal or due to recurrent seeding of satellite outbreaks away from the core population when individuals are capable of long-range dispersal. In this simulation study, we introduce a fitness-affecting mutation in one individual during range expansions driven by long-range dispersal in order to learn about when "survival of the fittest" actually holds in these populations replete with founder events, or if the founder events generally cause "survival of the luckiest" dynamics to win out. We observed how the distribution of possible outcomes depends on when the mutation was introduced, the fitness effect of the mutation, the dispersal distance distribution, and the local carrying capacity. We find that the expected mutation frequency at the end of expansions and the probability that the mutation is still contributing to the population at long times depend strongly on when the mutation was introduced, highlighting the importance of proximity to the initial population bottleneck in determining the fate of mutations that appear in expanding populations. We also show that the dispersal distance distribution plays an important role, with broader distributions leading to a greater probability of mutation success at long times but narrower distributions leading to the highest frequencies in mutations that surf.