Plant recolonization in the Himalaya from the southeastern Qinghai-Tibetan Plateau: Geographical isolation contributed to high population differentiation.

The Himalaya-Hengduan Mountains region (HHM) in the southern and southeastern Qinghai-Tibetan Plateau (QTP) is considered an important reservoir and a differentiation center for temperate and alpine plants in the Cenozoic. To reveal how plants responded to the Quaternary climatic oscillations in the QTP, the phylogeographical histories of a few subalpine and alpine plants have been investigated, but nearly all studies used only uniparentally inherited cytoplasmic DNA markers, and only a couple of them included sampling from the Himalaya. In this study, range-wide genetic variation of the Himalayan hemlock (Tsuga dumosa), an important forest species in the HHM, was surveyed using DNA markers from three genomes. All markers revealed genetic depauperation in the Himalaya and richness in the Hengduan Mountains populations. Surprisingly, population differentiation of this wind-pollinated conifer is very high in all three genomes, with few common and many private nuclear gene alleles. These results, together with fossil evidence, clearly indicate that T. dumosa recolonized the Himalaya from the Hengduan Mountains before the Last Glacial Maximum (LGM), accompanied with strong founder effects, and the influence of the earlier glaciations on demographic histories of the QTP plants could be much stronger than that of the LGM. The strong population differentiation in T. dumosa could be attributed to restricted gene flow caused by the complicated topography in the HHM that formed during the uplift of the QTP, and thus sheds lights on the importance of geographical isolation in the development of high plant species diversity in this biodiversity hotspot.

Cun YZ ，Wang XQ 《-》

Glacial survival east and west of the 'Mekong-Salween Divide' in the Himalaya-Hengduan Mountains region as revealed by AFLPs and cpDNA sequence variation in Sinopodophyllum hexandrum (Berberidaceae).

Molecular phylogeographic studies have recently begun to elucidate how plant species from the Qinghai-Tibetan Plateau (QTP) and adjacent regions responded to the Quaternary climatic oscillations. In this regard, however, far less attention has been paid to the southern and south-eastern declivities of the QTP, i.e. the Himalaya-Hengduan Mountains (HHM) region. Here, we report a survey of amplified fragment length polymorphisms (AFLPs) and chloroplast DNA (cpDNA) sequence variation in the HHM endemic Sinopodophyllum hexandrum, a highly selfing alpine perennial herb with mainly gravity-dispersed berries (105 individuals, 19 localities). We specifically aimed to test a vicariant evolutionary hypothesis across the 'Mekong-Salween Divide', a known biogeographic and phytogeographic boundary of north-to-south trending river valleys separating the East Himalayas and Hengduan Mts. Both cpDNA and AFLPs identified two divergent phylogroups largely congruent with these mountain ranges. There was no genetic depauperation in the more strongly glaciated East Himalayas (AFLPs: H(E)=0.031; cpDNA: h(S)=0.133) compared to the mainly ice-free Hengduan Mts. (AFLPs: H(E)=0.037; cpDNA: h(S)=0.082), while population differentiation was consistently higher in the former region (AFLPs: Φ(ST)=0.522 vs. 0.312; cpDNA: Φ(ST)=0.785 vs. 0.417). Our results suggest that East Himalayan and Hengduan populations of S. hexandrum were once fragmented, persisted in situ during glacials in both areas, and have not merged again, except for a major instance of inter-lineage chloroplast capture identified at the MSD boundary. Our coalescent time estimate for all cpDNA haplotypes (c. 0.37-0.48 mya), together with paleogeological evidence, strongly rejects paleo-drainage formation as a mechanism underlying allopatric fragmentation, whereas mountain glaciers following the ridges of the MSD during glacials (and possible interglacials) could have been responsible. This study thus indicates an important role for mountain glaciers in driving (incipient) allopatric speciation across the MSD in the HHM region by causing vicariant lineage divergence and acting as barriers to post-divergence gene flow.

Li Y ，Zhai SN ，Qiu YX ，Guo YP ，Ge XJ ，Comes HP ... -  《-》

Mitochondrial and chloroplast phylogeography of Picea crassifolia Kom. (Pinaceae) in the Qinghai-Tibetan Plateau and adjacent highlands.

The disjunct distribution of forests in the Qinghai-Tibetan Plateau (QTP) and adjacent Helan Shan and Daqing Shan highlands provides an excellent model to examine vegetation shifts, glacial refugia and gene flow of key species in this complex landscape region in response to past climatic oscillations and human disturbance. In this study, we examined maternally inherited mitochondrial DNA (nad1 intron b/c and nad5 intron 1) and paternally inherited chloroplast DNA (trnC-trnD) sequence variation within a dominant forest species, Picea crassifolia Kom. We recovered nine mitotypes and two chlorotypes in a survey of 442 individuals from 32 populations sampled throughout the species' range. Significant mitochondrial DNA population subdivision was detected (G(ST) = 0.512; N(ST) = 0.679), suggesting low levels of recurrent gene flow through seeds among populations and significant phylogeographical structure (N(ST) > GST, P < 0.05). Plateau haplotypes differed in sequence from those in the adjacent highlands, suggesting a long period of allopatric fragmentation between the species in the two regions and the presence of independent refugia in each region during Quaternary glaciations. On the QTP platform, all but one of the disjunct populations surveyed were fixed for the same mitotype, while most populations at the plateau edge contained more than one haplotype with the mitotype that was fixed in plateau platform populations always present at high frequency. This distribution pattern suggests that present-day disjunct populations on the QTP platform experienced a common recolonization history. The same phylogeographical pattern, however, was not detected for paternally inherited chloroplast DNA haplotypes. Two chlorotypes were distributed throughout the range of the species with little geographical population differentiation (G(ST) = N(ST) = 0.093). This provides evidence for highly efficient pollen-mediated gene flow among isolated forest patches, both within and between the QTP and adjacent highland populations. A lack of isolation to pollen-mediated gene flow between forests on the QTP and adjacent highlands is surprising given that the Tengger Desert has been a geographical barrier between these two regions for approximately the last 1.8 million years.

Meng L ，Yang R ，Abbott RJ ，Miehe G ，Hu T ，Liu J ... -  《MOLECULAR ECOLOGY》

Chloroplast phylogeny and phylogeography of Stellera chamaejasme on the Qinghai-Tibet Plateau and in adjacent regions.

Historic events such as the uplift of Qinghai-Tibet Plateau (Q-T Plateau) and climatic oscillations in the Quaternary period greatly affected the evolution and modern distribution of Sino-Tibetan flora. Stellera chamaejasme, a perennial herb with flower color polymorphism that is distributed from the mountainous southeastern Q-T Plateau (Hengduan Mountains, H-D Mountains) to the vast platform of the Q-T Plateau and the adjacent plain of northern China, provides an excellent model to explore the effects of historic events on the origination and variation of species. In this study, we conducted a phylogenetic and phylogeographical study using three chloroplast sequences (trnT-L, trnL-F and rpL16) in 26 populations of S. chamaejasme and 12 outgroups from the Thymeleaceae. Phylogenetic analysis and molecular clock estimation revealed that the monophyletic origin of S. chamaejasme occurred ca. 6.5892 Ma, which is consistent with the radical environment changes caused by the rapid uplift of the Q-T Plateau ca. 7 Ma. Intra-specific differentiation of S. chamaejasme is estimated to have occurred after ca. 2.1 Ma. Twelve haplotypes were revealed from combined trnL-F and rpL16 sequences. High genetic diversity (h(T)=0.834) and population differentiation (N(ST)=0.997 and G(ST)=0.982) imply restricted gene flow among populations and significant geographical or environmental isolation. All populations from the vast plain of northern China were dominated by one haplotype (H1), and the same haplotype was fixed in most populations from the high elevation platform of the western and northern Q-T Plateau. In contrast, the majority of the haplotypes were found in the relatively narrow area of the H-D Mountains, in the southeastern distribution of S. chamaejasme. The contrasting haplotype distribution patterns suggested that the H-D Mountains were either a refugium for S. chamaejasme during the Quaternary climatic oscillations or a diversification center of this species. The present wide distribution of this species on the Q-T Plateau platform and in northern China is likely to have resulted from a rapid post-glacial population expansion from the southeastern refugium involving founder effects, facilitated by the adjacent geographic range with a similar grassland habitat.

Zhang YH ，Volis S ，Sun H 《-》

Phylogeographic structure of Hippophae tibetana (Elaeagnaceae) highlights the highest microrefugia and the rapid uplift of the Qinghai-Tibetan Plateau.

Wang H ，Laqiong ，Sun K ，Lu F ，Wang Y ，Song Z ，Wu Q ，Chen J ，Zhang W ... -  《-》