Abstract
Abstract: Natural hybridization is a common key evolutionary process and
a long-standing topic in the plant taxon. Hybrid zones, where two
closely related species interact, can provide an avenue to insight the
process, illuminating the maintenance of the taxon diversity. Incomplete
isolation barriers between Ligularia species generally form
hybrid zones. In this study, we used the double digest restriction-site
associated DNA sequencing technology (ddRAD-seq) to examine genetic
structure and estimate introgression in four newly discovered hybrid
zones between L. tongolensis and L. cymbulifera. Our
results showed high differentiation between parental species, whereas
pairwise FST between parents and their hybrids
was low, further corroborating sympatric site form hybrid zones.
Moreover, most F1 hybrid individuals were observed within the four
hybrid zones implying the presence of substantial barriers to
interbreeding. An analysis of genomic clines indicated that a large
fraction of loci deviated from a model of neutral introgression in the
four hybrid zones, of which most loci exhibited selection favouring
L. cymbulifera genotypes. Our analysis demonstrated bidirectional
but asymmetric introgression appearing in the four hybrid zones. The
different habitats among four hybrid zones may affect isolation barriers
between both species. Natural hybridization with post-zygotic isolation
barriers may significantly contribute to the diversification of
Ligularia in the HMR.