Non-stationary patterns of isolation-by-distance: inferring measures of genetic friction

Non-stationary patterns of isolation-by-distance: inferring measures of genetic friction

Nicolas Duforet-Frebourg, Michael G. B. Blum
(Submitted on 24 Sep 2012)

The pattern of isolation-by-distance arises when population differentiation increases with increasing geographic distances. This pattern is usually caused by local spatial dispersal which explains why differences of allele frequencies between populations accumulate with distance. However, the pattern of isolation-by-distance can mask complex variations of demographic parameters. Spatial variations of demographic parameters such as migration rate or population density generate non-stationary patterns of isolation-by-distance where the rate at which genetic differentiation accumulates varies across space. Barriers to gene flow are particularly well studied examples that generate non-stationary patterns of isolation-by-distance. Using the concept of genetic friction, we develop a statistical method that characterizes non-stationary patterns of isolation-by-distance. Genetic friction at a sampled site corresponds to the local genetic differentiation between the sampled population and fictive populations living in the neighborhood of the sampling site. To avoid defining populations in advance, the method can also be applied at the scale of individuals. The proposed framework is appropriate for dealing with massive data because it relies on a pairwise similarity matrix, which can be obtained with computationally efficient methods. A simulation study shows that maps of genetic friction can detect barriers to gene flow but also other patterns such as continuous variations of gene flow across habitat. The potential of the method is illustrated with 2 data sets: genome-wide SNP data for the human Swedish populations, and AFLP markers for alpine plant species. The software FRICTION implementing the method is available at this http URL

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