3.4 | Geographical barrier, isolation by distance, mismatch distribution analysis, and neutrality detection
By calculating Monmonier’s maximum difference using the program BARRIER, we found three obvious geographic barriers using nrDNA and cpDNA separately. For the 2016 samples, the first barrier using nrDNA (supported by 99% of F ST matrices) separated QX from WZ and XA, thus partially corresponding to Expressway 2 (Figure 4a). The second barrier (66% support) separated the NW group from the other populations, thus fitting well the Daguangba Reservoir and Expressway 1. Finally, the third barrier (33% support) was found between populations XA and WZ (Figure 4a). For the 2022 samples, the first barrier (99% support) separated the JF population from the rest (i.e., the Daguangba Reservoir plus a section of Expressway 1) (Figure 4b). Part of the second (66% support) and third (33% support) barriers could also be assigned to some sections of expressways 1 and 2, respectively (Figure 4b).