Testing effects of post glacial population structure
Compared to the estimation of divergence time, the fixation indexF ST is more sensitive to gene flow among populations, where paired populations experiencing gene flow are expected to have lower F ST values (in a 0 to 1 scale). Therefore, if gene flow occurred across drainage basins after populations recolonized high elevation areas (i.e. across mountain ridges), we expect to see little to no discrepancy in comparisons of populations from the same or different watersheds. For the same set of population pairs of the best model in the TMRCA analysis, we calculated the means of Weir & Cockerham’s F ST in VCFtools version 0.1.17 (Weir & Cockerham 1984, Danecek et al., 2011) using thesemi-filtered dataset . Similar to the TMRCA, the ANCOVA was used to test whether population pairs from different drainages show higherF ST, with geographic distance between paired populations as a covariate.