Extensive genome-wide phylogenetic discordance is due to incomplete lineage sorting in the rapidly radiated East Asian genus Nekemias (Vitaceae)

Nekemias is a small genus of the grape family, with nine species discontinuously distributed in temperate to subtropical zones of the Northern Hemisphere but mostly in East Asia. Previous phylogenetic studies on Nekemias have mainly based on a few chloroplast markers, and the phylogenetic framework and systematic relationships are still highly contested. We carried out a systematic framework reconstruction of Nekemias and intra-generic reticulate evolutionary analyses based on extensive single-copy nuclear and chloroplast genomic data obtained by the Hyb-Seq approach, combining genome skimming and target enrichment. Both nuclear and chloroplast genomic data strongly support the monophyly of Nekemias with its division into two major lineages from East Asia and North America, respectively. There are strong and extensive topological conflicts among nuclear gene trees and between nuclear and chloroplast topologies within the genus, especially within the East Asian clade. Rapid radiation through predominant incomplete lineage sorting (ILS) throughout the evolutionary history of the East Asian taxa is supported to explain the relatively high species diversity of Nekemias in East Asia. This study highlights the important role of short periods of rapid evolutionary radiations accompanied by ILS as a mechanism for the complex and fast species diversifications in the grape family as well as potentially in many other plant lineages in East Asia and beyond.