Abstract
Background: The eastern Sino-Himalayan region of southwest China, as one of the world’s biodiversity hotspots, has undergone dramatic geomorphological and climatic changes during the Late Tertiary/Quaternary. The dry-hot valleys in southwest China is overlapping with the Hengduan Mountains. However, when this endemism was assembled in dry-hot valleys and how the climatic oscillations and/or tectonic movements influence their phylogeographical patterns remained largely unknown. Himalrandia lichiangensis is a shrub of Rubiaceae, endemically distributes in dry-hot valleys of southwest China. By integrating evidences from phylogeography, population dynamic and ecological niche modelling, we are aiming to trace the evolutionary history and explain the origin of biodiversity and endemism in the dry-hot valleys of southwest China. Results: Based on sequencing four chloroplastic non-coding regions (psbM-trnD, trnD-trnT, atpB-rbcL and accD-psaI) and two single-low copy nuclear genes CAMX (Calmodulin) and ITS of 423 individuals from 23 populations, we found high genetic variation mainly existed between the populations (cpDNA: 89.80％, ITS: 84.55％, CAMX: 95.68％). Haplotypes in different river basins showed significant phylogeographical structure. The geographical distribution of haplotypes indicated that there is a high degree of genetic differentiation and this differentiation is associated with altitude discrepancy. BARRIER analysis detects a strong geographic barrier between the Nanpan River and Jinsha River. The MaxEnt result shows that the suitable distribution area was the largest in the LGM. The future climate warming will lead to the niche expansion for H. lichiangensis but will also cause fragmented distribution.Conclusions: Our study highlighted the importance of altitude in explaining the genetic differentiation. The current phylogeographical pattern of H. lichiangensis may be shaped by long-term geographical isolation resulted from the uplifting of Himalaya, which gives rise to the barriers from the Hengduan Mountain or multiple river systems, and the vertical altitude discrepancies that both limited gene flow among regions. The Middle Jinsha River valley is most likely to be a main refuge for H. lichiangensis till now, and the glaciation retreat may account for the high endemism of plants in the dry-hot valleys of southwest China.
Synchronous-Asynchronous Encounter Probability Analysis of High-Low Runoff for Jinsha River, China, using Copulas*
