Spatial patterns of genetic variation generated by different forms of dispersal during range expansion

We examined the impact of three forms of dispersal, stepping-stone, normal and leptokurtic, on spatial genetic structure of expanding populations using computer simulations. When dispersal beyond neighbouring demes is allowed, rare long-distance migration leads to the establishment of pocket populations in advance of the main invasion front and results in spatial clustering of genotypes which persists for hundreds of generations. Patchiness is more pronounced when dispersal is leptokurtic as is the case in many animal and plant species. These results are of particular interest because population genetic parameters such as gene flow and effective population size are commonly estimated using gene frequency divergence information assuming equilibrium conditions and island models. We show how the three forms of dispersal during colonization bring about contrasting population genetic structures and how this affects estimates of gene flow. The implications for experimental studies of the spatial dimension of population genetic structure are discussed.