Mutation surfing and the evolution of dispersal during range expansions

Abstract

A growing body of empirical evidence demonstrates that at an expanding front, there can be strong selection for greater dispersal propensity, whereas recent theory indicates that mutations occurring towards the front of a spatially expanding population can sometimes ‘surf’ to high frequency and spatial extent. Here, we consider the potential interplay between these two processes: what role may mutation surfing play in determining the course of dispersal evolution and how might dispersal evolution itself influence mutation surfing? Using an individual‐based coupled‐map lattice model, we first run simulations to determine the fate of dispersal mutants that occur at an expanding front. Our results highlight that mutants that have a slightly higher dispersal propensity than the wild type always have a higher survival probability than those mutants with a dispersal propensity lower than, or very similar to, the wild type. However, it is not always the case that mutants with very high dispersal propensity have the greatest survival probability. When dispersal mortality is high, mutants of intermediate dispersal survive most often. Interestingly, the rate of dispersal that ultimately evolves at an expanding front is often substantially higher than that which confers a novel mutant with the greatest probability of survival. Second, we run a model in which we allow dispersal to evolve over the course of a range expansion and ask how the fate of a neutral or nonneutral mutant depends upon when and where during the expansion it arises. These simulations highlight that the success of a neutral mutant depends upon the dispersal genotypes that it is associated with. An important consequence of this is that novel mutants that arise at the front of an expansion, and survive, typically end up being associated with more dispersive genotypes than the wild type. These results offer some new insights into causes and the consequences of dispersal evolution during range expansions, and the methodology we have employed can be readily extended to explore the evolutionary dynamics of other life history characteristics.

Exploring neutral and adaptive processes in expanding populations of gilthead sea bream, Sparus aurata L., in the North-East Atlantic

“…Among the several genetic consequences of range expansion described in Excoffier et al (2009a), the surfing of rare variants on the front of the expansion wave can mimic divergent selection, generating strong F ST values only at few loci (Travis et al, 2007(Travis et al, , 2010Excoffier and Ray, 2008;Hallatschek and Nelson, 2008). BLAST results failed to provide any tangible evidence of functional genes associated with Ad-10 and/or Bld-10.…”

Evolving mutation rate advances the invasion speed of a sexual species

“…Increasing ecological realism in our models [56] can improve the predictability of theoretical phenomena which can then be tested by data from field studies. So far, increased dispersal has been shown to increase invasion speeds [11, 57], affect the fate of neutral mutations [58], as well as the level of local adaptation [59], and local population dynamics [33], and in addition causes strong patterns of spatial disequilibrium [34, 35]. …”

An evolutionary process that assembles phenotypes through space rather than through time

“…Interbreeding at the fast-moving invasion front thus will produce offspring with higher mean dispersal rates (and hence higher extreme maximum values for dispersal-enhancing traits, given additive genetic variance) than was the case in the parental generation. Successive generations evolve faster and faster dispersal by the colocation of such traits (e.g., genes conferring speed, endurance, and high activity levels) within the same individuals, even without new mutations (17). Such mutations may be readily available, however, because they "surf" expanding range fronts where selection against them is ineffective ( [18][19][20].…”