From glacial refugia to wide distribution range: demographic expansion of Loropetalum chinense (Hamamelidaceae) in Chinese subtropical evergreen broadleaved forest

Abstract

The subtropical evergreen broadleaved forest (STEBF) in China is globally one of the most diverse and biologically important forest systems. There has been a long-term debate whether this region was affected dramatically during Pleistocene glaciation and deglaciation cycles, e.g., in terms of range dimensions and changes in species richness. Here we report a large-scale phylogeographic study, focusing on a widespread and typical constituent species of the Chinese STEBF, Loropetalum chinense (R. Br.) Oliver (Hamamelidaceae). In total, 56 populations spanning the entire distribution range of L. chinense were analyzed. Chloroplast DNA sequence variation and AFLPs as molecular marker systems were used in combination with ecological niche modeling (ENM). ENM indicated that the distribution ranges of L. chinense were contracted remarkably and most populations retreated southward. Thereby, based on ENM, geographical distribution pattern of cpDNA haplotypes, and AFLP genetic clusters, one glacial refuge was inferred in the Nanling Mountains in southern China, and a second glacial refuge was identified in Three Gorges Area and Dabashan Mountains in Chongqing Province, southwestern China. In addition to ENM, with mismatch distribution analysis and Bayesian skyline plots, demographic expansion was inferred to take place about 10.6 kya. The current geographic distribution pattern of genetic variation might be shaped by northward and eastward expansion along Nanling Mountains and Wuyishan Mountains, respectively. Additionally, the two mountain ranges were supposed to act as geographical barriers restricting gene flow between the southern and northern populations. Herewith, we aim to further contribute a case study of the phylogeographic history of this vegetation type, which will help to improve deeper understanding of past vegetation dynamics and floristic evolutionary pathways of the Chinese STEBF.