4.2 Genetic differentiation and genetic structure in C.
hainanense
PCA analysis showed that PC1, PC2, and PC3 contributed 10.04%, 6.85%,
and 5.07%, respectively. The principal component analysis’s clustering
results may differ from those of the other group analyses. In PCA, the
Wuzhishan population is genetically distant from other populations and
forms 1 cluster separately. In addition, the cluster structure of
principal component analysis, K-value selection of cluster structure,
and phylogenetic tree analysis of all samples resulted in the same
clusters. The fact that PCA showed the Wuzhishan population as
genetically distant from other populations, forming a separate cluster,
suggests that there may be unique genetic features in this population
that were captured by the PCA. This could indicate that the Wuzhishan
population has experienced different evolutionary pressures, gene flow
patterns, or demographic histories compared to the other populations in
the study. It is also important to note that the PCA clustering results
may differ from other group analyses. This is because PCA is focused on
capturing the maximum amount of variance in the data, while other
methods, such as phylogenetic tree analysis or population structure
analysis using Bayesian clustering approaches (e.g., STRUCTURE), might
focus on different aspects of the data. These other methods may consider
more specific evolutionary models or genetic relationships, leading to
different interpretations of the population structure. Despite the
differences in clustering results between PCA and other group analyses,
the study found that the cluster structure of the PCA, K-value selection
of the cluster structure, and phylogenetic tree analysis all resulted in
the same clusters. This consistency across different analytical methods
provides strong evidence for the observed population structure, lending
credibility to the findings. The PCA results highlight the genetic
distinctiveness of the Wuzhishan population, which may have important
implications for the conservation and management of C.
hainanense . Understanding the factors contributing to the genetic
differentiation between populations can inform targeted conservation
efforts aimed at preserving the unique genetic diversity found in each
population. Further research on the specific genetic differences between
the Wuzhishan population and others, as well as the potential
environmental or ecological factors driving these differences, would
provide valuable insights into the species’ evolutionary history and
inform future conservation strategies.
All supported the division of 6 clusters into two clusters, so it was
reasonable to divide 35 C.
hainanense samples from 6 clusters into two clusters of 1 cluster
(Diaoyu Mountain and Baisha Ridge) and 2 clusters (Wuzhishan, Huishan,
Bawang Ridge, and Tsimshatsui Ridge). This division into two primary
clusters could be a result of various factors, such as historical gene
flow, geographical isolation, or habitat fragmentation. The two clusters
may have experienced different evolutionary pressures, environmental
conditions, or demographic histories that have shaped their genetic
makeup. The consistency of this clustering pattern across multiple
analytical methods (PCA, K-value selection, and phylogenetic tree
analysis) strengthens the evidence for the observed population
structure. This consistent finding implies that the division of the six
populations into two primary clusters is a robust and meaningful
representation of the genetic relationships among these C.
hainanense samples.
Differences in population genetic structure are an important expression
of genetic diversity. A species’ evolutionary potential and ability to
withstand adverse environments depends not only on the level of genetic
variation within the species but also on the genetic structure of the
species (McCauley et al., 2014; Hamrick et al., 2011; Qu et al.,
2004). Our results indicate that
the six populations on Hainan Island are divided into two broad taxa,
consistent with the principal component analysis results. A population’s
genetic differentiation index (Fst) is an important parameter to measure
the degree of genetic differentiation among populations. It can explain
the factors that affect the genetic differentiation of populations (Zhou
et al., 2022). The genetic differentiation coefficient among the
populations showed that the Fst values among the six C.
hainanense populations were between -0.09648-0.076729. There is a
moderate degree of genetic differentiation (0.05 < Fst
< 0.15) between the two populations of Baishaling (BSL) and
Jianfengling (JFL). Furthermore, the genetic differentiation among other
populations is low, and the differentiation is not noticeable (Fst
< 0.05). Therefore, the genetic differentiation among C.
hainanense populations is weak. The existing gene flow may originate
from the genetic exchange between their common ancestor populations and
be brought into other populations by other factors such as human
factors, animal carrying, or geological factors. In addition, the
topography may also affect gene flow in this species. The terrain of
Hainan Island is high in the middle and low in the surrounding areas. It
rises and descends to the periphery step by step. The cascade structure
is prominent, and the terraces, hills, plains, and mountains form a
ring-shaped layered landform (Chen et al., 2022).
The samples taken in this study were from Wuzhishan, Diaoluoshan,
Jianfengling, and their surrounding forests. Geographically, the
Jianfengling and Baishaling populations are far apart
(>100km). However, the genetic distance between the two
populations is relatively small (Fst = 0.076729), possibly due to the
number of sampling populations of C. hainanense being too small.
The population distribution of C. hainanense is relatively
concentrated under the influence of habitat fragmentation, so the
evidence is not sufficient. Therefore, the next step is to expand the
scope of the sampling population for subsequent research and analysis.
Limited sampling: As the study itself points out, the number of sampled
populations of C. hainanense may be too small to accurately
represent the full extent of genetic diversity and differentiation
within the species. Additional sampling from other populations,
particularly those that may be geographically intermediate between
Jianfengling and Baishaling, could help provide a more comprehensive
understanding of the genetic relationships among populations. The small
genetic distance between the Jianfengling and Baishaling populations may
be due to historical gene flow that occurred before the populations
became geographically isolated. Over time, barriers such as geographical
features, habitat fragmentation, or human activity may have restricted
the movement of individuals between populations, but the genetic legacy
of past gene flow could still be apparent in the current populations.C. hainanense may be capable of long-distance seed dispersal
through mechanisms such as wind, water, or animal-mediated dispersal.
Even if the frequency of long-distance dispersal events is low, they can
still contribute to maintaining gene flow between geographically distant
populations and reducing genetic differentiation. Human activities, such
as the movement of seeds or plants for horticulture, agriculture, or
reforestation efforts, may have inadvertently facilitated gene flow
between the Jianfengling and Baishaling populations. This could result
in the observed small genetic distance despite the large geographical
separation between the populations. Small or isolated populations are
more susceptible to founder effects and genetic drift, which can reduce
genetic diversity and lead to increased genetic differentiation between
populations. However, these processes can sometimes produce
counterintuitive patterns, such as closely related populations that are
geographically distant, or vice versa. To better understand the factors
influencing the genetic structure of C. hainanense , further
research is needed. This could include increasing the number of sampled
populations and individuals, examining historical patterns of gene flow,
and investigating potential mechanisms of seed dispersal. Ultimately, a
more comprehensive understanding of the species’ genetic diversity and
population structure can inform conservation strategies and help ensure
the long-term survival of C. hainanense .