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

• Published in: Journal of systematics and evolution : JSE Vol. 60; no. 6; pp. 1319 - 1330
• Main Authors: Hu, Li, Yang, Rui, Yang, Guo‐Qian, Sun, Gui‐Ling, Gong, Xun
• Format: Journal Article
• Language: English
• Published: Beijing Wiley Subscription Services, Inc 01.11.2022
• Subjects: Asymmetry; Biological evolution; Clines; ddRAD; Developmental biology; DNA sequencing; Genetic structure; Genomic analysis; Hybrid zones; Hybridization; Hybrids; Ligularia; Morphology; Mountains; natural hybridization; Nucleotides; Recombination; reproductive isolation; Single-nucleotide polymorphism; Species; Sympatric populations
• ISSN: 1674-4918; 1759-6831
• DOI: 10.1111/jse.12756

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). 1. Geographic distribution of Ligularia tongolensis and Ligularia cymbulifera implies except these four discovered hybrid zones, there should be other recessive hybrid zones. 2. Most F1 hybrid individuals were observed within the four hybrid zones implying the presence of substantial barriers to interbreeding. Some parent species identified as F1 class, this revealed that using morphological characteristics to identify L. tongolensi and L. cymbulifera was not accurate. 3. A large fraction of SNPs deviated from a model of neutral introgression in the four hybrid zones, of which most SNPs exhibited selective preference for L. cymbulifera genotypes. 4. Bidirectional but asymmetric introgression appeared in the four hybrid zones. 5. Natural hybridization with incomplete reproductive isolation may significantly a contribution to the diversification of Ligularia in the HMR.