Biogeographic divides in East Asia delineated by the three-step landforms of China and the East China Sea: insights from phylogeographical breaks of Kerria japonica

Aim: East Asia exhibits complex geomorphological and climatic characteristics. The aim of this study is to test whether the biogeographic divides present along the so-called three-step landforms of China and the East China Sea (ECS), and provide insight into the evolution the East Asian Flora (EAF) with respect to Hengduan Mountains, Central China and East China.

Location: East Asia

Taxon: Kerria japonica, a deciduous shrub distributed in subtropical mixed evergreen and deciduous broadleaved forests of East Asia.

Methods: Three chloroplast DNA (cpDNA) regions and 15 nuclear microsatellite (nSSR) loci were sequenced/genotyped in 576/450 individuals. We performed phylogeographical analyses to assess genetic structure, historical gene flow and demographic history. Climate factors were examined to identify their effects on the phylogeographical breaks. Time-calibrated phylogenetic trees and ancestral range reconstruction were used to infer biogeographic history. Potential habitats at present and in the past (LIG, LGM) were identified using ecological niche modelling (ENM).

Results: Distinct phylogeographical breaks were found along the ECS and the edges of the three-step landforms of China. Low historical gene flow and significant climatic differences were detected in each pair of adjacent regions. Compared with the quite stable distribution range on the Chinese mainland, Japanese populations had experienced obvious northward expansion after the LGM in response to Quaternary climate change.

Main conclusions: K. japonica has a complex biogeographic history, with a Mid-Miocene origin in North America and subsequent migration into East Asia via the Bering land bridge. The onset of intra-specific diversification was probably associated with the Asian monsoon intensifications, while the CJK land bridge facilitated the formation of the Japan lineage (6.78 Ma). The spatiotemporal population differentiation in Chinese mainland demonstrates the significant role of biogeographic divides delineated by three-step landforms of China; and provides clues to help understand the floristic regionalization and evolutionary history of plant diversity in East Asia, especially with respect to the Hengduan Mountains, Central China and East China.