J Syst Evol

• Research Articles •    

Morphological distinctiveness of Ligularia tongolensis and L. cymbulifera is maintained between habitats despite bidirectional and asymmetrical introgression in multiple hybrid zones

Li Hu1,2,3†, Rui Yang1,2,3†, Guo‐Qian Yang4, Gui‐Ling Sun5, and Xun Gong1,2*   

  1. 1 CAS Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China
    2 Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China
    3 University of Chinese Academy of Sciences, Beijing 100049, China
    4 Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China
    5 State Key Laboratory of Cotton Biology, Department of Biology, HPC Center of Bioinformatics Platform, Institute of Plant Stress Biology, Henan University, Kaifeng 475001, Henan, China

    These authors contributed equally to this work.
    *Author for correspondence. E‐mail: gongxun@mail.kib.ac.cn
  • Received:2020-12-31 Accepted:2021-04-27 Online:2021-05-02

Abstract: Natural hybridization is a crucial evolutionary process and a long-standing topic of study in evolutionary biology. Hybrid zones, where two congeneric species interact, can provide insight into the process of natural hybridization, especially with respect to how taxon diversity is maintained. In this study, we used double digest restriction-site associated DNA sequencing technology (ddRAD-seq) to examine genetic structure and estimate introgression in four hybrid zones of Ligularia tongolensis and Ligularia cymbulifera. Our analysis demonstrated that parental species were highly differentiated, whereas pairwise FST between parents and their hybrids was low, indicating that sympatric sites can form hybrid zones. As most F1 hybrid individuals were observed within these zones, our finding also implied the presence of substantial barriers to interbreeding. Furthermore, some individuals that possessed the typical morphology of the parental species belonged to the F1 generation. Genomic clines analysis revealed that a large fraction of single nucleotide polymorphisms (SNPs) deviated from a model of neutral introgression in the four hybrid zones, and most SNPs exhibited selection favoring the L. cymbulifera genotype. Bidirectional but asymmetric introgression was revealed as evident in the four hybrid zones. Habitat differences between the four hybrid zones may affect isolation barriers between both species. Taken together, these findings suggest that where incomplete reproductive barriers allow natural hybridization, the introgression between species generates rich genetic recombination that contributes to the fast adaptation and diversification of the widespread Ligularia in the Hengduan Mountains Region (HMR).

Key words: ddRAD, hybrid zones, Ligularia, natural hybridization, reproductive isolation