3.3 | Population genetic structure and phylogeographical patterns
The pairwise genetic differentiation (F ST) was low for the nrITS dataset: for the 2016 samples,F ST values ranged from 0 (BW-EX and YJ-EX pairs) to 0.010 (JF-YG and JF-WZ pairs) with a mean of 0.0045; estimates for the 2022 samples ranged from 0 (BW-EX pair) to 0.013 (JF-YG), averaging 0.0054 (Table S1). Regarding the cpDNA dataset,F ST values for 2016 samples ranged from 0.001 (BW-YJ pairs) to 0.020 (JF-EX and JF-YG pairs), with a mean of 0.0098, while values for the 2022 samples ranged from 0.001 (JF-XA pair) to 0.018 (EX-XA, EX-JF, OX-XA, OX-JF, WZ-XA, and WZ-JF pairs), averaging 0.0097 (Table S2). The population that is separated from the rest by the dam (JF) showed the largest pairwise F ST values for both datasets, although for the cpDNA the population XA also showed relatively high levels of genetic divergence (Tables S1, S2). Indeed, mean F ST values between populations belonging to different groups were considerably higher when separated by the dam, i.e. JF (= SW region) vs. NW region, than when separated by expressways (the rest of pairwise values; Tables S3, S4); for nrDNA,F ST-dam[2022] = 0.0113 ± 0.0013 andF ST-dam[2016] = 0.0085 ± 0.001 vs.F ST-expwy[2022] = 0.0075 ± 0.0017 andF ST-expwy[2016] = 0.0062 ± 0.0020; for cpDNA,F ST-dam[2022] = 0.0170 ± 0.0008 andF ST-dam[2016] = 0.0193 ± 0.0010 vs.F ST-expwy[2022] = 0.0110 ± 0.0077 andF ST-expwy[2016] = 0.0122 ± 0.0030. Thus, as also occurred among individual populations, F STvalues among groups of populations increased during the period 2016–2022 only for nrITS.
Based on the ΔK approach,K = 3 was the most likely number of genetic clusters after running the software STRUCTURE (Figures S1a, S1b), both for the 2016 and 2022 datasets of nrDNA. In the K = 3 grouping scheme, one cluster included the BW, YJ, EX, and YG populations, which represent the NW group of populations (Figures 3a, 3b). The SE group of populations (QX and WZ) formed another cluster, while the XA population showed two genetic components (NW and SE, with NW decreasing rapidly its weight from 2016 to 2022). The population JF constituted the third cluster.