Phylogeography Of Hippophae Tibetana Schlecht

The uplift of the Qinghai-Tibetan Plateau (QTP) and Quaternary climate changes are crucial aspects affecting the distribution and evolution of the plateau biota. The uplift of the QTP dramatically changed the topography and climate of Asia and affected the biodiversity of the plateau and its adjacent areas. However, the effects of the uplift on the dispersal, differentiation and adaptation of plants remain a puzzle when the date and process of the uplift cannot be determined with certainty and the impacts of the alternations of Quaternary glacial-intergalcial on plants on the QTP are unknown. To clarify the relationships among plants on the QTP with the plateau uplift and the Quaternary glaciations, the cpDNA trnT-trnF regions of 891 individuals from 37 populations of Hippophae tibetana Schlecht., endemic to the QTP, were sequenced in the present study, as well as individuals of the outgroup species H. rhamnoides subsp. sinensis, H. rhamnoides subsp. yunnanensis, H. rhamnoides subsp. turkestanica, H. gyantsensis, H. neurocarpa, H. neurocarpa subsp. stellatopilosa and H. litangensis. In H. tibetana, a total of 50 h aplotypes were found and a strong phylogeographic structure was revealed. The results show that three main lineages of the present populations of H. tibetana occupy the western, the middle, and the eastern geographical range, respectively, and their divergence time dates back to 3.15 Ma before present. Of 50 h aplotypes,33 are private haplotypes are scattered throughout the present geographical range of H. tibetana. They originated from multiple differentiations in many lineages during a more than 1.0 M a period, strongly suggesting that multiple microrefugia of H. tibetana existed throughout the present geographical range during the last glacial maximum (LGM) and even earlier glaciations. Additionally, the average elevation of present populations is over 4500 m in the west and the equilibrium-line of glaciers in the LGM was 500-300 m lower than present in the major interior part of the plateau suggesting that at most sites in the west, LGM microrefugia of H. tibetana may have been over 4000 m above sea level, the highest of all known plant refugia. Besides, the divergence times among and within the three lineages and their distinct distributions as well as dispersal barriers support the theory of the recent and rapid uplift of the QTP. The rapid uplift of the plateau within the last 3.4 Ma and the associated environmental changes may have affected the dispersal and differentiation of H .tibetana and shaped its phylogeographic structure. Furthermore, using cpDNA trnT-trnF regions and five microsatellite loci, this study investigated the genetic varations of H. tinetana at different elevations along Rongbuk valley, north of Mt. Everest, which is one of the LGM microrefugia, and by integrating geological, glaciological and meteorological information, to study how the low shrub has adapted to the extreme climate fluctuations of the last 25,000 years. Microrefugia are thought to play an important role in the post-glacial colonization of species, and are pertinent to understanding how species might respond to recent and future climate changes. But why species could survive in such microrefugia and how they responded to climate changes in the glacial and post-glacial periods remain unclear. The results show that Rongbuk Valley was a microrefugium of H. tibetana with a long history, and that H. tibetana survived below 4800 m during the LGM and survived the extreme climate fluctuations after the LGM by upward and downward migrations at around～5000 m. Moreover, with the rise of temperature in the last four decades, the upper limit of H. tibetana has shifted at least 30 m upward; surprisingly, these new arrivals did not expand from adjacent areas but from populations near the lower altitudinal limit. Our results demonstrate that not only did mountain slopes play an important part in H. tibetana finding refuges, but that ice and glacial meltwater were also critical for its survival. Combining population history and recent range shifts of this species is important in predicting the fate of this species to future climate changes.