8 research outputs found
The rate of beneficial mutations surfing on the wave of a range expansion
Many theoretical and experimental studies suggest that range expansions can
have severe consequences for the gene pool of the expanding population. Due to
strongly enhanced genetic drift at the advancing frontier, neutral and weakly
deleterious mutations can reach large frequencies in the newly colonized
regions, as if they were surfing the front of the range expansion. These
findings raise the question of how frequently beneficial mutations successfully
surf at shifting range margins, thereby promoting adaptation towards a
range-expansion phenotype. Here, we use individual-based simulations to study
the surfing statistics of recurrent beneficial mutations on wave-like range
expansions in linear habitats. We show that the rate of surfing depends on two
strongly antagonistic factors, the probability of surfing given the spatial
location of a novel mutation and the rate of occurrence of mutations at that
location. The surfing probability strongly increases towards the tip of the
wave. Novel mutations are unlikely to surf unless they enjoy a spatial head
start compared to the bulk of the population. The needed head start is shown to
be proportional to the inverse fitness of the mutant type, and only weakly
dependent on the carrying capacity. The second factor is the mutation
occurrence which strongly decreases towards the tip of the wave. Thus, most
successful mutations arise at an intermediate position in the front of the
wave. We present an analytic theory for the tradeoff between these factors that
allows to predict how frequently substitutions by beneficial mutations occur at
invasion fronts. We find that small amounts of genetic drift increase the
fixation rate of beneficial mutations at the advancing front, and thus could be
important for adaptation during species invasions.Comment: 21 pages, 7 figures; to appear in PLoS Computational Biolog