KEYWORDS
Anthropogenic disturbances, gene flow, Hainan Island, Island
biogeography
1 |
INTRODUCTION
Human activities, which are
regarded as primary threats to biodiversity worldwide, are capable of
disturbing the habitat integrity and, thus, modifying phylogeographic
patterns of naturally distributed species (Young et al., 1996; Aguilar
et al., 2006; Martínez-Ramos et al., 2016). For example, anthropogenic
infrastructures such as expressways, buildings, and expansive farmlands
can interrupt plant pollination and seed dispersal by hindering the
movements and migration of insects and other animals (Honnay &
Jacquemyn, 2007). Fragmentation of natural populations and geographical
isolation of individuals may also lead to increased levels of inbreeding
and genetic drift (Lowe et al., 2015), putting populations at risk of
extinction (Tambarussi et al., 2017; Moraes et al., 2018).
Hainan Island, located in south China, has an area of 35,000
km2 and is a distinctive part of the globally
important Indo-Burma biodiversity hotspot (Myers et al. , 2000),
as it harbors ca. 4800 vascular plants in total with nearly 500
endemics (Francisco-Ortega et al. , 2010a, b; Yang, 2013). Most of
this rich plant diversity (e.g. 80% of the endemic species) are
concentrated in the south-central mountain system of the island
(Francisco-Ortega et al. , 2010a, b). Notably, this area is the
home to the world’s most endangered primate Nomascus hainanusThomas (Long et al., 2021), highlighting its conservation value.
Currently, however, Hainan island is experiencing a rapid economic
development, which is partly based on the construction of large
infrastructures; for example, the local authorities are aiming to build
the world’s biggest free trade port
(www.xinhuanet.com/english/2018-04/13/c_137109243.htm).
The landscapes and vegetation have been severely affected in the past
decades due to the accelerated growth of the human population and
urbanization. For example, the
Daguangba Reservoir on the Changhua River, the second largest river on
the island, was completed in 1994 and formed a sluggish waterbody of
nearly 6 km in width. This huge reservoir located between Mt. E’xian and
Mt. Jianfeng may disrupt the connectivity of the natural vegetation of
these two mountains. Moreover, two expressways were recently built in
Hainan’s biodiversity-rich mountainous regions: Road G9811 (hereafter
referred to as Expressway 1) was completed in 2018 and has a width of 26
m, and Road S10 (hereafter referred to as Expressway 2) was built in
2019 and is 20 m wide
(www.xinhuanet.com/english/2021-04/15/c_139882827.htm).
These anthropogenic constructions lie in the middle part of the
south-central mountains on the island and may affect habitat integrity
and genetic continuity of the rare and endangered plants, which may
further result in the alteration of evolutionary processes, especially
genetic differentiation and the whole plant’s phylogeographical
structure.
The family Gesneriaceae on Hainan Island is notable for its high levels
of species diversity and endemism (Wei, 2010; Ling et al., 2017a, b).
Fourteen genera and 25 species of the family occur on the island,
including one endemic genus and 10 endemic species (Li & Wang, 2005;
Yang, 2013; Ling et al., 2017a, 2020b).Primulina heterotricha(Merr.) Y. Dong & Yin Z. Wang, one of these endemic species, is widely
distributed in the south-central mountains on the island (Ling et al.,
2017a, b). The plant, a short-lived herb (with a generation time of 1–3
years), has zygomorphic tubular flowers that are pollinated by several
insects, particularly Glossamegilla malaccensis Friese andG. yunnanensis Wu of Anthophoridae (Ling, 2017a, b). The fruit
(capsule) is erect with small brown and fusiform-shaped seeds,
suggesting a poor dispersal capability that is likely associated with
water courses (MXR, personal observations). Taking all the
above-mentioned factors into consideration, this species is a good model
system to uncover possible short-term fragmentation effects of the
Daguangba Reservoir and the newly-built expressways on its genetic
differentiation and phylogeographical patterns.
In this study, we addressed the following questions: (1) are the
recently built reservoir and expressways (i.e. artificial barriers)
already influencing the genetic make-up in the Hainan-endemic P.
heterotricha ? and (2) if yes, how are these artificial barriers
affecting the population differentiation and phylogeographical patterns
of the study species? To get insights into these questions, we performed
a population genetics and a phylogeographical study based on samples ofP. heterotricha that were collected in 2016 and 2022 (i.e.,
before and after expressway construction), using conserved and slowly
evolving nuclear and chloroplast DNA sequences.