Dataset Information

The Tanggula Mountains enhance population divergence in Carex moorcroftii: a dominant sedge on the Qinghai-Tibetan Plateau.

ABSTRACT: High-altitude mountains are often geographic barriers to gene flow and play important roles in shaping population divergence. The central Qinghai-Tibetan Plateau (QTP) stands the location of the Tanggula Mountains (TM). We use the TM as a case, using Carex moorcroftii, a dominant species on the QTP to test the effects of geographic barriers on plant population divergence. We sampled 18?C. moorcroftii populations along a north-south transect crossing the TM to investigate the correlations of genetic variation and morphological traits with climate variables. The results showed this species holds high genetic diversity (He?=?0.58) and the surveyed populations can be genetically clustered into two groups: populations from the north face of TM, and the other from the south. Gene flow between populations within groups is higher than those between groups. The traits, number and mass of seeds, mass of root and infructescence significantly varied among populations. Mantel-tests detected a weak but significantly positive correlation between genetic and geographic (R2?=?0.107, p?=?0.032) and climatic distance (R2?=?0.162, p?=?0.005), indicating both isolation by distance and isolation by environment. These findings together suggest high-altitude mountains of TM interrupt habitat continuity, result in distinct climatic conditions on both sides, increasing population divergence of plant species.

SUBMITTER: Liu W

PROVIDER: S-EPMC5807306 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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The Tanggula Mountains enhance population divergence in Carex moorcroftii: a dominant sedge on the Qinghai-Tibetan Plateau.

Liu Wensheng W Zhao Yao Y Qi Danhui D You Jianling J Zhou Yin Y Song Zhiping Z

Scientific reports 20180209 1

High-altitude mountains are often geographic barriers to gene flow and play important roles in shaping population divergence. The central Qinghai-Tibetan Plateau (QTP) stands the location of the Tanggula Mountains (TM). We use the TM as a case, using Carex moorcroftii, a dominant species on the QTP to test the effects of geographic barriers on plant population divergence. We sampled 18 C. moorcroftii populations along a north-south transect crossing the TM to investigate the correlations of gene ...[more]

PMID: 29426823

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Project description:Several previous studies have shown that some morphologically distinctive, small genera of vascular plants that are endemic to the Qinghai-Tibetan Plateau and adjacent Hengduan Mountains appear to have unexpected and complex phylogenetic relationships with their putative sisters, which are typically more widespread and more species rich. In particular, the endemic genera may form one or more poorly resolved paraphyletic clades within the sister group despite distinctive morphology. Plausible explanations for this evolutionary and biogeographic pattern include extreme habitat specialization and hybridization. One genus consistent with this pattern is Nomocharis Franchet. Nomocharis comprises 7-15 species bearing showy-flowers that are endemic to the H-D Mountains. Nomocharis has long been treated as sister to Lilium L., which is comprised of more than 120 species distributed throughout the temperate Northern Hemisphere. Although Nomocharis appears morphologically distinctive, recent molecular studies have shown that it is nested within Lilium, from which is exhibits very little sequence divergence. In this study, we have used a dated molecular phylogenetic framework to gain insight into the timing of morphological and ecological divergence in Lilium-Nomocharis and to preliminarily explore possible hybridization events. We accomplished our objectives using dated phylogenies reconstructed from nuclear internal transcribed spacers (ITS) and six chloroplast markers.Our phylogenetic reconstruction revealed several Lilium species nested within a clade of Nomocharis, which evolved ca. 12 million years ago and is itself nested within the rest of Lilium. Flat/open and horizon oriented flowers are ancestral in Nomocharis. Species of Lilium nested within Nomocharis diverged from Nomocharis ca. 6.5 million years ago. These Lilium evolved recurved and campanifolium flowers as well as the nodding habit by at least 3.5 million years ago. Nomocharis and the nested Lilium species had relatively low elevation ancestors (<1000 m) and underwent diversification into new, higher elevational habitats 3.5 and 5.5 million years ago, respectively. Our phylogeny reveals signatures of hybridization including incongruence between the plastid and nuclear gene trees, geographic clustering of the maternal (i.e., plastid) lineages, and divergence ages of the nuclear gene trees consistent with speciation and secondary contact, respectively.The timing of speciation and ecological and morphological evolutionary events in Nomocharis are temporally consistent with uplift in the Qinghai-Tibetan Plateau and of the Hengduan Mountains 7 and 3-4 million years ago, respectively. Thus, we speculate that the mountain building may have provided new habitats that led to specialization of morphological and ecological features in Nomocharis and the nested Lilium along ecological gradients. Additionally, we suspect that the mountain building may have led to secondary contact events that enabled hybridization in Lilium-Nomocharis. Both the habitat specialization and hybridization have probably played a role in generating the striking morphological differences between Lilium and Nomocharis.

Project description:BackgroundAlthough allopatric speciation is viewed as the most common way in which species originate, allopatric divergence among a group of closely related species has rarely been examined at the population level through phylogeographic analysis. Here we report such a case study on eight putative cypress (Cupressus) species, which each have a mainly allopatric distribution in the Qinghai-Tibetan Plateau (QTP) and adjacent regions. The analysis involved sequencing three plastid DNA fragments (trnD-trnT, trnS-trnG and trnL-trnF) in 371 individuals sampled from populations at 66 localities.ResultsBoth phylogenetic and network analyses showed that most DNA haplotypes recovered or haplotype-clustered lineages resolved were largely species-specific. Across all species, significant phylogeographic structure (N(ST) > G(ST), P < 0.05) implied a high correlation between haplotypes/lineages and geographic distribution. Two species, C. duclouxiana and C. chengiana, which are distributed in the eastern QTP region, contained more haplotypes and higher diversity than five species with restricted distributions in the western highlands of the QTP. The remaining species, C. funebris, is widely cultivated and contained very little cpDNA diversity.ConclusionsIt is concluded that the formation of high mountain barriers separating deep valleys in the QTP and adjacent regions caused by various uplifts of the plateau since the early Miocene most likely promoted allopatric divergence in Cupressus by restricting gene flow and fixing local, species-specific haplotypes in geographically isolated populations. The low levels of intraspecific diversity present in most species might stem from population bottlenecks brought about by recurrent periods of unfavorable climate and more recently by the negative impacts of human activities on species' distributions. Our findings shed new light on the importance of geographical isolation caused by the uplift of the QTP on the development of high plant species diversity in the QTP biodiversity hotspot.

Project description:Background and aimsHosting several global biodiversity hotspots, the region of the Qinghai-Tibetan Plateau (QTP) is exceptionally species-rich and harbours a remarkable level of endemism. Yet, despite a growing number of studies, factors fostering divergence, speciation and ultimately diversity remain poorly understood for QTP alpine plants. This is particularly the case for the role of hybridization. Here, we explored the evolutionary history of three closely related Gentiana endemic species, and tested whether our results supported the mountain geo-biodiversity hypothesis (MGH).MethodsWe genotyped 69 populations across the QTP with one chloroplast marker and 12 nuclear microsatellite loci. We performed phylogeographical analysis, Bayesian clustering, approximate Bayesian computation and principal components analysis to explore their genetic relationship and evolutionary history. In addition, we modelled their distribution under different climates.Key resultsEach species was composed of two geographically distinct clades, corresponding to the south-eastern and north-western parts of their distribution. Thus Gentiana veitchiorum and G. lawrencei var. farreri, which diverged recently, appear to have shared at least refugia in the past, from which their range expanded later on. Indeed, climatic niche modelling showed that both species went through continuous expansion from the Last Interglacial Maximum to the present day. Moreover, we have evidence of hybridization in the northwest clade of G. lawrencei var. farreri, which probably occurred in the refugium located on the plateau platform. Furthermore, phylogenetic and population genetic analyses suggested that G. dolichocalyx should be a geographically limited distinct species with low genetic differentiation from G. lawrencei var. farreri.ConclusionsClimatic fluctuations in the region of the QTP have played an important role in shaping the current genetic structure of G. lawrencei var. farreri and G. veitchiorum. We argue that a species pump effect did occur prior to the Last Interglacial Maximum, thus lending support to the MGH. However, our results do depart from expectations as suggested in the MGH for more recent distribution range and hybridization dynamics.

Dataset Information

The Tanggula Mountains enhance population divergence in Carex moorcroftii: a dominant sedge on the Qinghai-Tibetan Plateau.

Publications

The Tanggula Mountains enhance population divergence in Carex moorcroftii: a dominant sedge on the Qinghai-Tibetan Plateau.

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