A first step towards inferring levels of long-distance dispersal during past expansions

Improving the realism of spatially explicit demographic models is important for better inferring the history of past populations and for understanding the genetic bases of adaptation and speciation. One particular type of demographic event to take into account is long-distance dispersal (LDD). The goals of this study are to explore the impact of various levels of LDD on genetic diversity and to show to what extent LDD levels can be correctly inferred from multilocus data sets using an approximate Bayesian computation approach. We therefore incorporated LDD into a 2D stepping stone forward simulation framework coupled to a coalescent backward simulation step to generate genetic diversity at 100 microsatellite markers under various demographic conditions relevant to recent human evolution. Our results confirm that LDD considerably increases genetic diversity within demes and decreases levels of diversity between demes. By controlling the spatial occurrence of LDD, it appears that LDD events occurring during a phase of range expansion into new territories are more important in maintaining genetic diversity than those occurring in the wake of the expansion or when colonization is over. We also show that it is possible to infer whether LDD has occurred during a range expansion, but our results suggest that one can only approximately estimate the extent of LDD based on genetic summary statistics.