Genetic differentiation, structure, Barrier and Niche
consistency detection
The AMOVA analysis based on cpDNA data and five low-copy nuclear genes
showed that genetic differentiation between the two species was
significant (F ST > 0.25) (Table 3).
Genetic variation partitions revealed by different genes were
inconsistent. cpDNA data showed that more percentage of variations were
partitioned among populations within a species; four nuclear genes
(PHYP , AC5 , PPRC and SAMS ) showed that more
percentage of variations were partitioned among species; nuclear geneAAT showed that more percentage of variations were partitioned
within species. The microsatellite data showed that there was more
percentage of variation within species, and the genetic differentiation
between the two speceis was relatively low (Tables 3). The STRUCTURE
result showed that the optimal number of clusters across all individuals
based on the 16 microsatellite loci was two (Figure 3a). One cluster was
composed of the four populations of C. bifida , while the other
cluster was constituted by the seven populations of C.
micholitzii . When K = 3 or 4, C. micholitzii was divided into
two or three clusters. The two-dimensional PCoA analysis (Figure 3b)
showed the same result with the STRUCTURE analysis. The Barrier analysis
showed that there was only one major genetic boundary with a 95% mean
bootstrap value separated the two species, coinciding with the RRFZ
(Figure 3c).
The AUC scores, for C. bifida and C. micholitzii , were
0.866 and 0.888 respectively, indicating the credibility of ENMs’
simulations. Niche identity tests showed that the observed niche
overlaps were significantly lower than the null distribution of niche
overlaps (P < 0.001) both for I and D, suggesting that
niches of C. bifida and C. micholitzii were dissimilar
(Figure 4), although we should consider that niche identity tests can be
seriously biased by the environmental discrepancies that exist in the
areas where the two species do not overlap (Warren et al., 2010).