3.3 Population genetic structure and differentiation
After LD filtering, 1,545,006 SNPs common to di- and triploids were
selected and used for population structure analysis. The three methods
including PCA, structure analysis and genetic distance analysis all
showed the same patterns of population genetic structure (Figure 3 and
4, and Figure S3). For diploids, two clear genetic clusters were shaped
and consisted of individuals from invasive and native populations,
respectively. The genetic cluster owned by native individuals split into
three subclusters and followed a pattern of geographical separation:
individuals from the mid Yangzte River (SS and ZDL); individuals from
the lower Yangzte River (TH and CL) and Huai River (RR and HZL) and
individuals from the Songhua River (DQ and JPL). For triploids, although
several genetic clusters were observed, the pattern was not related to
the geographical origin, with each cluster containing individuals from
different rivers. The invasive triploids were assigned into different
clusters. Results of PCA for all individuals revealed that both PCA1 and
PCA2 did not clearly separate diploids and triploids, indicating
patterns of population structure were not linked to the ploidy level.
For diploids, highly significant genetic differentiation
(F ST) was detected for all pairwise comparisons
among the invasive population (LL) and three genetic subclusters from
the native range (Table 2). The F ST values
between LL and two source genetic subclusters (i.e., the mid Yangzte
River, the lower Yangzte River and Huai River) were 0.1045 and 0.0926,
respectively, which were both higher than that between the two
subclusters (0.0449). AMOVA analysis revealed that genetic variation
between regions (invasive and source), among populations within regions
and within populations were all significant and accounted for 6.29%,
8.65% and 85.06% of the total variation (P < 0.01),
respectively. For triploids, low F ST values
ranging from 0.0073 to 0.0281 (P > 0.05) were
detected for pairwise comparisons between invasive (LL and CBL) and
source (SC and NX) populations and a relative higherF ST (0.0345) was obtained between the two source
populations (P < 0.01). The variation between regions,
among populations within regions and within populations accounted for
-2.93%, 4.41% and 98.52%, respectively.
Overall, theF ST values between invasive and source
populations were 0.0866 in diploids and 0.0027 in triploids.