Demographic history
The observed data set in DIYABC was located in the middle of simulation priors and a combination of posterior parameters using PCA, indicating a good fit of the model (Fig. S7). Among the tested scenarios, scenario 5 (s5; an admixed origin of the Central population) was 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 S6). In this scenario, the divergence of the Southern and Northern populations (td) occurred 813 years ago (95% CI: 257-5010 years ago), and the Central population was generated 208 years ago (95% CI 40.6-969) through interbreeding between the Northern and Southern populations. The interbreeding involved more immigrants from the Northern population (60%) than the Southern population (40%; Table 1).
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 a sudden and steep drop in population size approximately 150-300 years ago, indicating that the populations underwent genetic bottlenecks during this period (Fig. S8).