Opisthopappus
Landscape
SNP
Gene exchange

Introduction

Landscape ecology is an interdisciplinary scientific discipline that focuses on spatial pattern and heterogeneity, and specifically their characterization and description over time, their causes and consequences (Francis et al., 2022; Wu, 2013). By using ecosystem principles and system methods, landscape ecology mainly focuses on landscape structure and function, landscape dynamic change and interaction mechanism, landscape spatial pattern, structure optimization, rational utilization and protection, and human management (Jiang and Li, 2021; Li et al., 2021a). In recent years, more researches have been conducted on land use, human experience and ecosystem services (Hersperger et al., 2021; Lester et al., 2021; Song et al., 2017). Nevertheless, with the constant climate changes and increasing human activities, the landscape configuration of different regions is continuously changing (Aylward et al., 2020; Wang et al., 2021c). This change could affect the ecological and evolutionary processes of organisms, and even ecosystems. During these processes, the organisms begin to respond the habitat change caused by the landscape changes and gradually adapt to and evolve in the changed landscapes (Fisher et al., 2021; Wang et al., 2021b).
Landscape changes can result in the appearance or disappearance of dispersal corridors for species or populations. Landscape factors would affect population connectivity by correlating gene exchange. The patterns of dispersal and gene exchange are key components shaping population or species genetic structure and variation model over small and large spatiotemporal scales (Polato et al., 2017). However, less is known about the ecological role of migration or gene exchange. Landscape-genetic approaches can infer landscape effects on dispersal and migration by examining relationships between genetic differentiation and landscape conditions among sampling locations (Anderson et al., 2010; Savary et al., 2021).
Landscape genetics has been a constantly growing field that combines population genetics, landscape ecology, and spatial analytical techniques to quantify the effects of landscape on micro-evolutionary processes. Recent studies have shown that about 80 % researches in landscape genetics were focused on animals. In comparison, there were only about 14.5 % reaearches were on plants, possibly because the mechanism of plant pollen and seed propagation makes the study of gene exchange at plant landscape-scale more complex than animals (Song et al., 2017). However, the plant landscape genetic research is essential for biodiversity because it can provide a powerful tool for protecting important ecosystems, managing vegetation protection units, and charactering the local adaptation and the evolution of species (De Kort et al., 2021).
Taihang Mountains (N34°34’-40°43’, E110°14’-114°33’) is a vital mountain range and geographical boundary in northern China, one of the second and third stepped boundaries of China’s terrain, which stretches about 400km from northeast to southwest (Shoubao et al., 2019; Wu, 2020). The terrains of the Taihang Mountains are higher in the north and lower in the south, and composed of a variety of rocks, cliffs, and many rivers, which formed various and unique landscapes in the Taihang Mountains. In Taihang Mountains, there are more than 1,290 wild species, of which 34 species were listed as a national priority protection species, and 23 species were rare and endangered plants. Thus, this mountain has already been regarded as one ideal research site for many ecological researchers (Wang, 2020). Nevertheless, most of the researches currently paid attention to the geology, geomorphology, and culture on the Taihang Mountains. There are few reports about the impact of the landscape features on the plants in this area.
Opisthopappus genus only lives on the Taihang Mountains cliffs, presenting excellent ecological, medicinal, and economic values. Unfortunately, the individual number of this genus is decreasing mainly due to artificial harvesting and has been listed as China’s national II-protected plants. It contains two species: Opisopappustaihangensis and O. longilobus . O. taihangensismainly distributes in the south of the Taihang Mountains, covering Henan and Shanxi provinces. O. longilobus mainly grows at northern of the Taihang Mountains, including the border of Hebei province and Shanxi Province (Wang et al., 2022).
Our wild investigation found that the shortest distance between O. taihangensis and O. longilobus is only about 25 km in the central areas of Taihang Mountains. However, the two species showed not only morphologically but also genetically differences. The morphological difference is mainly manifested in the leaves, whereas the morphologies of flowers show little difference. According to the previous studies, the populations of the two species could be clearly separated into two groups with distinct genetic differentiation, which might be the consequence of Opisthopappus ’s long-term adaptation to the environment of Taihang Mountains(Lin et al., 2013). However, how do the unique landscape features of Taihang Mountains affect the dispersal/ migration and differentiation of the two species? In addition, the geographical and geomorphic topological structure caused by mountain uplift often provides pathways for connectivity, gene exchange, and expansion or contraction of species’ populations in its distribution ranges (Hou et al., 2020). Previous studies found that there was a limited gene exchange/flow between O. taihangensis and O. longilobus (Ye et al., 2021). What landscape factors would prevent gene exchange/flow between these two species, abiotic environmental factors, biotic environmental factors, or conbimation of these factors? Is the gene exchange pattern between Opisthopappus species a interplay of landscape changes and species? These questions are still unanswered.
In this study, we combined the reduced representation genome data and landscape characteristics of Taihang Mountains to analyze the genetic characteristics of O. taihangensis and O. longilobus , to reveal the potential gene exchange pattern among these two species, and to analyze the effects of landscape factors and then explore the possible interplay of landscape - species. The results would guide scientific protection and utilization of Opisthopappus species and play a theoretical clue for studying other species in the Taihang Mountains.

Materials and Methods

2.1 Materials collection

The fieldwork had been approved by the Chinese government and implemented following the People’s Republic of China laws. Each participant had a letter of introduction from the College of Life Sciences, Shanxi Normal University. The samples in this study were taken along the Taihang Mountains from August to October and mainly covered the distribution ranges of Opisthopappus species. The elevation, longitude, and latitude information of each site were recorded by GPS and shown in Table 1(Papadopulos et al., 2014).