Nuclear and plastid phylogenomic analyses provide insights into the reticulate evolution, species delimitation and biogeography of the Sino-Japanese disjunctive Diabelia (Caprifoliaceae)

Understanding biological diversity and the mechanisms of the Sino-Japanese
disjunctions are major challenges in eastern Asia biogeography. The
Sino-Japanese flora has been broadly studied as an ideal model for plant
phylogeography. Diabelia (Caprifoliaceae) is an East Asian genus, with a
disjunctive distribution across the Sino-Japanese region. However,
relationships within Diabelia remain elusive. In this study, we
reconstructed the phylogeny of Diabelia and inferred historical
biogeography and evolutionary patterns based on nuclear and plastid
sequences from target enrichment and genome skimming approaches,
respectively. We found that the main clades within Diabelia were
discordant between nuclear and plastid trees. Both nuclear and plastid
phylogenetic analyses supported five main clades: D. serrata, D.
tetrasepala, D. sanguinea, D. spathulata var. stenophylla and D.
spathulata var. spathulata. Species network analyses revealed that
Diabelia tetrasepala is likely the result of a hybridization event.
Divergence time estimation and ancestral area reconstructions showed that
Diabelia originated in Japan during the early Miocene, with subsequent
vicariance and dispersal events between Japan and Korea, and between Japan
and China. Overall, our results support the division of Diabelia into five
main clades and the recognition of five species in the genus. This
research provides new insights in the species delimitation and speciation
processes of taxonomically complex lineages such as Diabelia.