Phylogenomic insights into the divergent history and hybridization within the East Asian endemic Abelia (Caprifoliaceae)

Background and AimsAbelia (Caprifoliaceae) is a small genus with five species (including one artificial hybrid). The genus has a disjunct distribution across mainland China, Taiwan and the Ryukyu Islands, providing a model system to explore species dispersal mechanisms of the East Asian flora. However, the current phylogenetic relationships within Abelia remain controversial. MethodsIn this study, we reconstructed the phylogenetic relationships within Abelia using nuclear loci generated by target enrichment and the cpDNA from genome skimming. Key ResultsWe found large cytonuclear discordance across the genus. Based on the nuclear and chloroplast phylogenies we proposed to merge A. schumannii into A. macrotera, and A. macrotera var. mairei into A. uniflora. Divergence time estimation, ancestral area reconstruction, and ecological niche modelling (ENM) were used to examine the biogeographic history of Abelia. Our results showed that Abelia originated in Southwest China, and diversification began in the Early Eocene, followed by A. chinensis var. ionandra colonizing Taiwan in the Middle Miocene. The ENM results suggested an expansion of climatically suitable areas during the Last Glacial Maximum and range contraction during the Last Interglacial. Disjunction between the Himalaya-Hengduan Mountain region (HHM) and Taiwan is most likely the consequence of topographic isolation and postglacial contraction. ConclusionsOverall, our results supports that postglacial range contraction together with topographic heterogeneity resulted in the Taiwan and China mainland disjunction. Furthermore, when we using genome data to reconstruct the phylogeny of related species, branch evolution and network evolution should be considered, as well as gene flow in historical periods. This research provide new insights for the speciation process and taxonomy of Abelia.