Demographic history
To elucidate the evolutionary events generating the current genetic structure, we simulated and tested five scenarios using DIYABC. The observed data set is located in the middle of simulation priors and a combination of posterior parameters using PCA, indicating a good model fit (Fig. S4). Among the tested scenarios, scenario 5 (s5; an admixed origin of the Central population) is the most supported based on the highest logistic regression estimate of posterior probability, with no overlap of the 95% confidence interval with other scenarios (P = 0.312, 95% CI 0.286-0.337; Table S10). In this scenario, divergence of the Southern and Northern populations (td) occurred 813 years ago (95% CI 257-5010), with the Central population being generated 208 years ago (95% CI 40.6-969) from interbreeding between the Northern and Southern populations. All estimated parameters are provided in Table S10.
From the demographic histories inferred from VarEff, all three populations showed a steady decline in effective population sizes over the last 500 years, followed by an accelerated and steep drop in population size around 150-300 years ago, highlighting the time when the populations underwent genetic bottlenecks (Fig. S5).