Tajima's D is a method of addressing the frequencies of variant sites, based on the expectation that under neutrality, different estimates of expected diversity (θ) should be equal. Tajima’s D tests for a skew in the frequency spectrum by comparing two estimates of θ – the number of segregating sites (S), and pairwise nucleotide diversity (π) [32]. Extreme positive values can indicate either balancing selection or population subdivision, and extreme negative values can indicate positive selection or population growth [33]. If the same skew is detected across the genome, the effect is likely due to demography, whereas if the skew is localized to a few loci, selection is more likely to be occurring.
