Population genetic structure and demographic analyses
The observed F ST values for COI, COII, and Cytb
were 0.781, 0.687, and 0.803, respectively, indicating that regional
populations are genetically isolated. For COI, the estimated migration
rate (Nem, where Ne is the
effective population size and m is the proportion of the
population that migrates in each generation) was 0.07 migrants per
generation (Slatkin, 1987; Slatkin & Barton, 1989). All three genes
showed greater variation among regions (73.25%–75.90%) than within
regions (0%–4.37%) (Table 3 and S4). We detected highF ST in pairwise combinations between regions E,
F, G, and H (Table 4, S5, and S6). For the COI gene, 23 out of 28
pairwise combinations showed significant differentiation, and the
highest pairwise F ST was 0.91731 for the
comparison between region C and region G (Table 4).
Neutrality and population expansion parameters for each gene are
summarized in Tables 5, S7, and S8. For COI, we detected negative
Tajima’s D values for regions A, C, and D, indicating that the
current haplotype diversity resulted from selection on certain
genotypes. Tajima’s D for regions B, E, F, and H was not
statistically significant, indicating neutral evolution. The τ values
that represent the estimated time of expansion were very low in regions
A, B, C and D (min = 0.0 in region B and max = 1.6 in region D),
indicating sudden and recent population growth (Table 5). The τ values
in regions E, F, and H were comparatively high (min = 9.2 in region E
and max = 46.2 in region F), indicating that population growth was
slower than that in regions A–D. The observed mismatch distribution was
used to evaluate the demographic expansion history. The raggedness
indexes for all regions except region E were not significant, suggesting
that the expansion model could not be rejected, except in region E
(Table 5). The analysis of region G, i.e., the USA population, was not
informative because the samples showed no haplotype variation.