Surfing during population expansions promotes genetic revolutions and structuration.

Recent studies have shown that low-frequency alleles can sometimes surf on the wave of advance of a population range expansion, reaching high frequencies and spreading over large areas. Using microbial populations, Hallatschek and colleagues have provided the first experimental evidence of surfing during spatial expansions. They also show that the newly colonized area should become structured into sectors of low genetic diversity separated by sharp allele frequency gradients, increasing the global genetic differentiation of the population. These experimental results can be easily reproduced in silico and they should apply to a wide variety of higher organisms. They also suggest that a single range expansion can create very complex patterns at neutral loci, mimicking adaptive processes and resembling postglacial segregation of clades from distinct refuge areas.