1 Introduction
The conservation of biodiversity is crucial for sustaining the stability
and resilience of ecosystems. Genetic diversity constitutes a pivotal
element in the long-term persistence of species, particularly for those
facing extinction risks. Chieniodendron hainanense represents a
rare and imperiled plant species characterized by extremely small
populations (WPESP) and is endemic to the fragmented habitats of Hainan,
China. Owing to the adverse consequences of habitat fragmentation, the
genetic diversity of C. hainanense populations warrants
significant attention in conservation initiatives. Comprehending the
genetic architecture and diversity of these populations enables the
development of suitable management approaches and facilitates species
restoration efforts.
The genetic structure and diversity of a species play critical roles in
their ability to withstand adverse environments and evolve over time.
Studying the genetic makeup of wild plants with extremely small
populations can provide insights into their evolutionary history,
population dynamics, and response to environmental changes, enabling the
development of effective conservation strategies (Yang et al., 2018;
Zhang et al., 2021). Such research is also essential for advancing DNA
sequencing technology and conservation biology (Windig et al., 2010).
Habitat fragmentation and overuse of resources have greatly impacted
species’ genetic diversity, survival, adaptability, and biodiversity (Su
et al., 2020). Habitat fragmentation reduces genetic diversity by
isolating populations and restricting gene exchange, leading to an
increase in genetic drift and inbreeding depression (Bijlsma et al.,
2012; Wang et al., 2022). The reduced genetic diversity weakens the
ability of species to adapt to environmental changes and increases the
risk of species extinction (Luquet et al., 2012). Habitat fragmentation
also reduces the number of plant populations, increases spatial
isolation, and hinders the maintenance of population genetic diversity
by disrupting dispersal, gene exchange, and inter-species interactions
(Aguilar et al., 2008).
Wild plants with extremely small populations (WPESP) are endangered
species under national key protection and require urgent rescue efforts.
Their population sizes are smaller than the minimum viable and are
usually distributed in a narrow area, making them highly vulnerable to
extinction (Zang, 2020; Jain et al., 2013). The Chinese government has
launched the National Project Plan for the Rescue and Protection of Wild
Plants in Extremely Small Populations (2011-2015) to protect 120 WPESP
species, most of which are endemic to China and have significant
ecological, scientific, cultural, and economic value (Ma et al., 2013;
Yang et al., 2020). The loss of biological and genetic values of WPESP
due to their extinction can have significant adverse effects on human
society and the ecosystem (Zhang et al., 2018). Therefore, it is crucial
to prioritize research on WPESP conservation in current biodiversity
conservation studies in China.
Chieniodendron hainanense is a second-class national key protected wild
plant and a unique member of the Annonaceae family Chieniodendron genus
in China. The species is an evergreen tree that grows up to 16 m tall
with a DBH of about 50 cm, and its distribution is limited to the
Guangxi Zhuang Autonomous Region and some areas of Hainan Province.
Habitat fragmentation due to human activities such as logging has
drastically reduced the distribution area of C. hainanense, and the wild
resources of its population are scarce. Field surveys have shown that
the existing populations of C. hainanense are mainly distributed in nine
primary forest areas dominated by fragmented secondary rainforests in
Hainan, with many original populations already disappeared (Jiang et
al., 2021). The species has poor self-renewal ability and is highly
sensitive to external disturbances, making its wild resources already
endangered. Although some research reports have focused on the
population structure, dynamic characteristics, leaf morphology, petal
nodules development, and functional biochemical activities of C.
hainanense, very few studies have investigated its endangerment
mechanisms at the molecular level. To develop targeted and comprehensive
conservation strategies, it is necessary to understand the causes of its
endangerment, including its genetic diversity, and related components
(Sork et al., 2006).
In this investigation, our objective is to evaluate the genetic
diversity and population structure of C. hainanense across its
fragmented habitats in Hainan, utilizing genotyping-by-sequencing (GBS)
and single nucleotide polymorphism (SNP) techniques. Through the
analysis of 35 specimens from six discrete cohort groups, we will
scrutinize patterns of genetic variation, differentiation, and
inbreeding both within and among the populations. The outcomes of this
research will yield valuable insights into the conservation status and
management of C. hainanense, promoting the formulation of efficacious
strategies for the preservation and restoration of this critically
endangered species. Additionally, our findings will augment the
understanding of the wider implications of habitat fragmentation on
genetic diversity in plant populations and inform conservation endeavors
for other threatened plant species inhabiting fragmented ecosystems.