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.