How Evolution Modifies the Variability of Range Expansion.

Eco-evolutionary theory suggests that rapid evolution can accelerate range expansion speed. In addition to average speed, recent experimental studies reveal that evolution can also influence the amount of variability across replicates of spreading populations, but in contrasting ways. Here we develop a predictive framework, drawing on ideas from population genetics and spread theory, to understand when, why, and in what direction evolution will modify the variability of range expansion. Our framework revolves around the balance of variance-generating (drift) and variance-reducing (selective) evolutionary processes, and factors that may tip this balance, including population size at the leading edge and mating system. We suggest hypotheses to clarify contrasting experimental results and highlight a way forward for studying eco-evolutionary dynamics of range expansion.