Uplift Of Plateau Research Articles

Molecular phylogeny and taxonomy of the genus Nectogale (Mammalia: Eulipotyphla: Soricidae).

The elegant water shrew, Nectogale elegans, is one of the small mammal species most adapted to a semi‐aquatic lifestyle. The taxonomy of the genus Nectogale has received little attention due to difficulties in specimen collection. In this study, we sequenced one mitochondrial and eight nuclear genes to infer the phylogenetic relationship of Nectogale. Phylogenetic analyses revealed two large clades within Nectogale. One clade represented N. elegans, and the other was regarded as N. sikhimensis. The split between N. elegans and N. sikhimensis dated back to the early Pleistocene (2.15 million years ago [Ma]), which might be relevant to the Qinghai‐Tibet Plateau (QTP) uplift. The morphological comparison showed several distinguishing characters within Nectogale: the shape of the mastoids, the first lower unicuspid (a1), and the second upper molar (M2). Overall, the molecular and the morphological evidences supported that the genus Nectogale consists of two valid species: N. elegans and N. sikhimensis.

Assessing Height Variations in Qinghai-Tibet Plateau from Time-Varying Gravity Data and Hydrological Model

Height variations caused by mass change make an important contribution to the tectonic uplift of the Qinghai-Tibet Plateau (QTP). To study the deformation attributable to hydrological loading and real potential tectonic vertical motion, satellite gravity data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) with data from the Global Land Data Assimilation System (GLDAS) and Global Positioning System (GPS) are adopted to estimate height variations in QTP. Based on spherical harmonic function (SHF) and Green’s function (GF), the results show the trend of height variations is unevenly distributed in the spatial domain. The SHF indicated that the rate in the southwest of the QTP is ~1 mm/year, while the northern and eastern show a subtle decreasing trend, which indicates hydrological loading is not the main cause of the uplift observed with GRACE. The maximum annual amplitude of height variations is ~12 mm, reaching the annual maximum around February to March. The average correlation coefficients of SHF, and GF height variations with GPS heights are 0.70 and 0.82, respectively. Based on cross wavelet transform, it is concluded that there are annual signals between the height variations derived from GPS with GRACE (-FO) and GLDAS. Finally, the tectonic vertical motion in the QTP is given by removing the effect of hydrological loading, which shows most GPS stations are uplifted at a rate of 0.06 mm/year–1.97 mm/year.

Reorganization of Asian climate in relation to Tibetan Plateau uplift

Reorganization of Asian climate in relation to Tibetan Plateau uplift

Editorial: Tibetan Plateau uplift and environmental impacts: New progress and perspectives

Editorial: Tibetan Plateau uplift and environmental impacts: New progress and perspectives

Comparative Mitogenomics of Two Sympatric Catfishes of Exostoma (Siluriformes: Sisoridae) from the Lower Yarlung Tsangpo River and Its Application for Phylogenetic Consideration.

The genus Exostoma is a group of stenotopic and rheophilic glyptosternine catfishes distributed in South and Southeast Asia. So far, comprehensive studies on mitogenomics referring to this genus are very scarce. In this study, we first sequenced and annotated the complete mitochondrial genomes of Exostoma tibetanum and Exostoma tenuicaudatum—two sympatric congeners from the lower Yarlung Tsangpo River, Tibet, China. The mitogenomes of both species contained 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, one light-strand origin of replication, and one control region, with lengths of 16,528 bp and 16,533 bp, respectively. The mitogenome architecture, nucleotide composition, and codon usage of protein-coding genes were almost identical between the two Exostoma species, although some estimated parameters varied. Phylogenetic analysis strongly supported the monophyly of Exostoma in the subfamily Glyptosternae, and Exostoma tibetanum had the closest relationship to Exostoma tenuicaudatum. The divergence time estimation demonstrated that these two species diverged approximately 1.51 Ma during the early Pleistocene, which was speculated to be triggered by the river system changes caused by the uplift of the southeastern Tibetan Plateau. Selection pressure analyses indicated that all protein-coding genes of Exostoma species underwent a strong purifying selection, while minority positive sites from NADH dehydrogenase complex genes were detected. These findings are expected to promote our understanding of the molecular phylogeny of the genus Exostoma and provide valuable mitogenomic resources for the subfamily Glyptosternae.

Early Eocene A-type (ferroan) rhyolites in southwestern Tibet: A far-field tectonic effect of the India–Eurasia collision

ABSTRACT Eocene igneous rocks along the Gangdese belt in southern Tibetan Plateau are important for understanding the India–Eurasia collision and Tibetan Plateau uplift. These magmatic rocks are widely considered to be related to roll-back or break-off of the Neotethyan slab during northward subduction. However, Eocene rhyolites in the northwestern Gangdese belt (SW Qiangtang margin) do not fit either the rollback or breakoff models. This paper investigates these Early Eocene lavas and compares them with contemporaneous igneous rocks along the Gangdese belt via detailed field observations, petrology, zircon geochronology, zircon Lu–Hf isotopes and whole-rock geochemistry. These felsic lavas form large outcrops in western Tibet and have two zircon U–Pb ages of 54.71 ± 0.14 Ma and 54.74 ± 0.27 Ma. They have high SiO2 and alkali contents, FeO*/MgO, and Ga/Al ratios as well as strongly negative Eu anomalies and slightly positive zircon εHf(t) values (+2.5 to +4.4). Both Ti-in-zircon and Zr saturation thermometers confirm high magmatic temperatures (~900°C). They are ferroan, A-type rhyolites. Furthermore, the distinctive low εHf(t) values imply that these rhyolites are likely partial melting products of the southwestern Qiangtang Terrane. The lithosphere in this region undergone long-term shortening and thickening since 80–95 Ma. Pre-thickened lithosphere may be a prerequisite for the Early Eocene delamination, and the simultaneous inducement is a far-field tectonic effect from the India–Eurasia collision. We suggest that: (1) India collided with Eurasia before 55 Ma and triggered delamination to form the Shiquanhe A-type rhyolites on the southwestern Qiangtang margin thereafter; and (2) tectonic stresses related to India–Eurasia collision during the Eocene were transmitted efficiently over large distances.

Rock slope failure in the Southern Carpathians (Romania): Range-wide inventory and links with long-term mountain landscape evolution

Rock slope failure (RSF) is now widely recognised as a significant contributor to the denudation of mountain ranges. Its spatial incidence can consequently be a valuable indicator of prevailing process domains, tectonic regimes and climatic variations, whether active or past. Here we provide the first systematic inventory of RSF in the Southern Carpathians, a mountain range marginally glaciated during the Pleistocene, cut by valleys up to 1.3 km deep, and displaying low-gradient summit erosion surfaces that suggest late Neogene uplift and incision of an extensive plateau. We discuss the spatial distribution of RSF in terms of process interactions and landscape evolution scenarios. Widespread metamorphic bedrock outcrops are confirmed as highly susceptible to RSF, particularly to large-scale slope deformation, but RSF also occurs on other lithologies as smaller rockslides and avalanches. Substantial spatial densities of RSF cluster around the residual, plateau-like range-top surface rims. We ascribe this to the ‘raised plateau’ features of the mountain range, where its fat, flat massifs engender greater slope stresses than would thin, serrated ones where arêtes and pyramidal peaks are gravitationally more stable. A large minority (42 %) of RSFs are spatially associated with glacial cirques and trough flanks. While these nominally qualify as paraglacial RSFs, glacial erosion may not be the main driver because the majority of RSFs occur along ridgetops and upper hillslopes in previously unglaciated fluvial contexts. Many of them thus qualify as parafluvial RSFs – i.e., occurring within a fluvial catchment but not directly generated by stream undercutting. We introduce the concept of fluvial–parafluvial and periglacial–parafluvial cycles as complementary to the recognised glacial–paraglacial cycle. All three process regimes may have prevailed concurrently or in succession, emphasising that cirque glaciation was probably not a principal agent in shrinking range-top erosion surfaces during the Quaternary. We point to post-orogenic (Neogene) tectonic uplift as the overarching driver of RSF in the Southern Carpathians, with pervasive fluvial incision keeping slopes close to failure thresholds. The role of RSF (extant and in earlier cycles) as a primary agent in perimeter scarp retreat and massif dissection here offers a ‘Transylvanian model’ of global interest whether as a comparator or a contrast for other ranges.

Plateau archives of lithosphere dynamics, cryosphere and paleoclimate: The formation of Cretaceous desert basins in east Asia

Southeastern Eurasia is a global window to the Cretaceous paleoclimate and lithosphere coupling. China contains one of the most complete and complex sedimentary records of Mesozoic desert basins on planet Earth. In this study, we perform the spatio-temporal tracking of 96 Cretaceous palaeoclimate indicators during 79 Myr which reveal that the plateau paleoclimate archives from East Asia resulted from an Early to Mid-Cretaceous ocean–atmosphere coupling and a shift to a preponderant role of Late Cretaceous lithosphere dynamics and tectonic forcing on high-altitude depositional systems linked to the subduction margins of the Tethys and Paleo-Pacific realms beneath the Eurasian plate. The crustal response to tectonic processes linked with the spatio-temporal evolution of the Tethyan and Paleo-Pacific margins defined the configuration of major sedimentary basins on this region. The significant increase and decrease in the number of active sedimentary basins that occur during the Cretaceous, from 16 in the Early Cretaceous, to 28 in the Mid-Cretaceous, and a decreasing to 20 sedimentary basins in the Late Cretaceous, is a direct response of lithospheric dynamics associated with the two main subduction zones (Tethys and Pacific domains). A shift in subduction style from an Early Cretaceous Paleo-Pacific Plate slab roll back to a Late Cretaceous flat-slab mode might have triggered regional plateau uplift, blocked intraplate volcanism, thus enhancing the denudation and sediment availability, and created wind corridors that led to the construction and accumulation of extensive Late Cretaceous aeolian sandy deserts (ergs) that covered Mid-Cretaceous plateau salars. At the same time, plateau uplift associated with crustal thickening following terrane assembly in the Tethyan margin triggered altitudinal cryospheric processes in sandy desert systems. Evidence of an active Cretaceous cryosphere in China include Valanginian-Hauterivian glacial debris flows, Early Aptian geochemical signature of melt waters from extensive ice sheets, and Cenomanian–Turonian ice-rafted debris (IRD). These cryospheric indicators suggest an already uplifted plateau in southeastern Eurasia during the Cretaceous, and the marked correlation between cold plateau paleoclimate archives and marine records suggests a strong ocean-atmosphere coupling during Early and Mid-Cretaceous cold snaps. We thus conclude that lithospheric tectonics during Cretaceous played a fundamental role in triggering high-altitude basin desertification and spatio-temporal plateau paleohydrology variability in the Cretaceous of south-eastern Eurasia.

New Insights Into the Backbone Phylogeny and Character Evolution of Corydalis (Papaveraceae) Based on Plastome Data.

A robust backbone phylogeny is fundamental for developing a stable classification and is instructive for further research. However, it was still not available for Corydalis DC., a species-rich (> 500 species), ecologically and medically important, but taxonomically notoriously difficult genus. Here, we constructed backbone phylogeny and estimated the divergence of Corydalis based on the plastome data from 39 Corydalis species (32 newly sequenced), which represent ca. 80% of sections and series across this genus. Our phylogenetic analyses recovered six fully supported main clades (I–VI) and provided full support for the majority of lineages within Corydalis. Section Archaeocapnos was unexpectedly turned out to be sister to the rest of the subg. Corydalis s. l. (clades IV–VI), thus treating as a distinct clade (clade III) to render all the main clades monophyletic. Additionally, some unusual plastome structural rearrangements were constantly detected within Corydalis and were proven to be lineage-specific in this study, which, in turn, provided further support to our phylogeny. A segment containing five genes (trnV-UAC–rbcL) in the plastome's LSC region was either normally located downstream of the ndhC gene in clade I species or translocated downstream of the atpH gene in clade II species or translocated to downstream of the trnK-UUU gene in clade III–VI species. The unique large inversion (ca. 50 kb) in the plastome LSC region of clade III species, representing an intermediate stage of the above translocation in clades IV–VI, firmly supported clade III as a distinct and early diverged clade within this large lineage (clades III–VI). Our phylogeny contradicted substantially with the morphology-based taxonomy, rejected the treatment of tuberous species as an independent evolutionary group, and proved that some commonly used diagnostic characters (e.g., root and rhizome) were results of convergent evolution, suggestive of unreliability in Corydalis. We dated the origin of crown Corydalis to the early Eocene (crown age 49.08 Ma) and revealed possible explosive radiation around 25 Ma, coinciding with the drastic uplift of the Qinghai-Tibetan Plateau in Oligocene and Miocene. This study provided the most reliable and robust backbone phylogeny of Corydalis to date and shed some new insights on the evolution of Corydalis.

Temperature acclimation in hot-spring snakes and the convergence of cold response

Animals have evolved sophisticated temperature-sensing systems and mechanisms to detect and respond to ambient temperature changes. As a relict species endemic to the Qinghai-Tibet Plateau, hot-spring snake (Thermophis baileyi) survived the dramatic changes in climate that occurred during plateau uplift and ice ages, providing an excellent opportunity to explore the evolution of temperature sensation in ectotherms. Based on distributional information and behavioral experiments, we found that T. baileyi prefer hot-spring habitats and respond more quickly to warmth than other two snakes, suggesting that T. baileyi may evolve an efficient thermal-sensing system. Using high-quality chromosome-level assembly and comparative genomic analysis, we identified cold acclimation genes experiencing convergent acceleration in high-altitude lineages. We also discovered significant evolutionary changes in thermosensation- and thermoregulation-related genes, including the transient receptor potential (TRP) channels. Among these genes, TRPA1 exhibited three species-specific amino acid replacements, which differed from those found in infrared imaging snakes, implying different temperature-sensing molecular strategies. Based on laser-heating experiments, the T. baileyi-specific mutations in TRPA1 resulted in an increase in heat-induced opening probability and thermal sensitivity of the ion channels under the same degree of temperature stimulation, which may help the organism respond to temperature changes more quickly. These results provide insight into the genetic mechanisms underpinning the evolution of temperature-sensing strategies in ectotherms as well as genetic evidence of temperature acclimation in this group.

Phylogeography of Chinese cereal cyst nematodes sheds lights on their origin and dispersal.

Reconstructing the dispersal routes of pathogens can help identify the key drivers of their evolution and provides a basis for disease control. The cereal cyst nematode Heterodera avenae is one of the major nematode pests on cereals that can cause 10%–90% crop yield losses worldwide. Through extensive sampling on wheat and grasses, the Chinese population of H. avenae is widely identified in virtually all wheat growing regions in China, with H1 being the predominant haplotype. The monoculture of wheat in north China might have been the key driver for the prevalence of H1 population, which should date no earlier than the Han Dynasty (202 BCE–220 CE). Molecular phylogenetic and biogeographic analyses of Chinese H. avenae suggest a Pleistocene northwest China origin and an ancestral host of grasses. We assume that the prosperity of Heterodera in this region is a result of their preference for cooler climate and various grass hosts, which only appeared after the uplift of Qinghai‐Tibetan Plateau and aridification of Inner Asia. Nematode samples from the current and historical floodplains show a significant role of the Yellow River in the distribution of Chinese H. avenae. Whereas mechanical harvesters that operate on an inter‐provincial basis suggest the importance in the transmission of this species in eastern China in recent times. This study highlights the role of environmental change, river dynamics, and anthropogenic factors in the origin and long‐distance dissemination of pathogens.

Orbital eccentricity and inclination metronomes in Middle Miocene lacustrine mudstones of Jiuxi Basin, Tibet: Closing an astrochronology time gap and calibrating global cooling events

Reconstructing Cenozoic lacustrine astrochronology is essential for understanding climatic and environmental change around northeastern Tibetan Plateau. Existing models attribute the driving mechanism of regional precipitation and aridification to the Tibetan Plateau uplift and global climate change. However, in northeastern Tibet lacustrine astrochronology has a gap from 17 Ma to 14 Ma. To bridge this gap, we investigate Milankovitch-forced cyclicity of green-red mudstone rhythms deposited during the early Middle Miocene Epoch in Jiuxi Basin. We construct color rank stratigraphic series from lacustrine sedimentary successions, and develop a 3.6 Myr-long astrochronology from 16.0 Ma to 12.4 Ma that partly covers the gap. Time series analysis reveals dominant 405-kyr cycles associated with the long orbital eccentricity cycle, and 173-kyr and 1.2-Myr cycles associated with amplitude modulations of the obliquity cycle. We propose that orbital eccentricity (405-kyr cycle) and inclination (173-kyr cycle) metronomes were recorded as climate-sedimentary threshold responses in the lacustrine setting. The maxima of 173-kyr and 405-kyr cycles correspond to green mudstones during lake expansions, and their minima to red mudstones during lake contractions. Anchoring the astrochronology to modeled orbital eccentricity and inclination metronomes further reveals that the recorded astronomical cycles are in phase with those of the marine archives, and suggests that lake evolution in Jiuxi Basin was paced with Middle Miocene cooling events.

Timing and mechanisms of Tibetan Plateau uplift

Timing and mechanisms of Tibetan Plateau uplift

Subduction Evolution Controlled Himalayan Orogenesis: Implications from 3-D Subduction Modeling

Himalayan orogenesis remains enigmatic in terms of Tibetan Plateau geodynamics originating from the Cenozoic India–Eurasian continental collision. India underthrusts below Tibet to the Yarlung–Tsangpo suture, which has been identified as the northernmost boundary for underplating. However, the way in which the historical evolution of continental subduction induces plateau uplift and the way it controls the variation in uplift between outboard and inboard areas is still unclear. To interpret the evolutionary mechanisms involved in the Himalayan growth history, we constructed different 3-D dynamic models at important stages to address these questions related to the formation of the Himalayas on the basis of paleoenthalpy evidence encoded in fossil leaves from recently documented assemblages in southern Tibet. The results show that (1) the effect of crustal thickening was the predominant factor in the early evolution from the Paleocene to the early Eocene, which resulted in a moderate growth rate. (2) The consecutive slab break-off eastward from the western syntaxis and the associated slab rebound significantly accelerated orogenesis from the late Eocene to the Oligocene. The upwelling asthenospheric flow was a key control of increasing crustal buoyancy, which resulted in the fastest growth of the Himalayas during the early Miocene. (3) Thereafter, the gradually enhanced monsoon and surface erosion during accompanying the increasing mountain height resulted in a slowdown of the orogenic rate, which counterbalanced the buoyant force produced by asthenospheric flow driving continuous Himalayan growth.

The stepwise Indian-Eurasian collision and uplift of the Himalayan-Tibetan plateau drove the diversification of high-elevation Scytodes spiders.

The Cenozoic Indian-Eurasian collision and uplift of the Himalayan-Tibetan Plateau (HTP) are among the most important geological events in the world. They have affected the diversification of regional biota of many taxonomic groups on and around the HTP. However, the exact timing and model of the collision and uplift events and speciation on and around the HTP are still in debate. The Himalayas group of Scytodes spitting spiders (Araneae: Scytodidae) are distributed at high elevations of the HTP and northern Indochina. Here, we reconstruct a dated molecular phylogeny for pan-Himalayan Scytodes spiders, including the Himalayas group, with full geographical sampling of the species from the HTP and Indochina. We test a hypothesis to explain that the rich montane biodiversity of the region is uplift-driven diversification-that orogeny drives rapid in situ speciation of the resident Scytodes lineages. Our findings revealed that the separation of the Himalayas clade from the Myanmar clade took place during the middle Oligocene, reflecting the final collision of India with Eurasia. The deep divergences among three clades (the Himalayas, the Myanmar and the Indochina clades) occurred from the middle Eocene to the middle Oligocene, corresponding to two early uplift events of the HTP. The evolutionary split between the Himalayas + Myanmar and Indochina clades were simultaneous with the rapid lateral extrusion of Indochina by the initial Himalayan uplift around the Eocene. This study highlights the importance of the diversification of dispersal-limited, high-elevation invertebrates as independent lines of evidence to reflect key tectonic events in the Himalayan-Indochina region, supporting the stepwise model for the Indian-Eurasian collision and uplift of HTP.

Paleoclimate implications of Quaternary river sediments in Yibin area, Sichuan Basin, China

Yibin area is located in the southwestern margin of Sichuan Basin of upper Yangtze River basin, close to the southeastern boundary of the Qinghai-Tibetan Plateau. The paleoclimatic characteristics recorded by Quaternary river sediments in this area can display the impact of uplift of the Qinghai-Tibetan Plateau on paleoclimate change of Sichuan Basin. In this paper, the macro-characteristics, clay minerals and the diagnosis geochemical elements characteristics of the sediments of terraces and floodplain were used as climatic proxies to explore the evolutionary process of the Quaternary paleoclimatic change in the study area. Key findings can be shown as follows: 1) warm and humid paleoclimate occurred during the Middle Pleistocene and the early Late Pleistocene (730–90 ka), shown by the high values of Al2O3, Fe2O3, Rb/Sr, chemical index of alteration (CIA, 82–97), illite chemical index (ICI, >0.5), kaolinite and the low values of Na2O, K2O, MgO, K2O/Al2O3, (CaO + Na2O)/Al2O3, illite, smectite, chlorite from the brown or brownish-red sediments of the terraces T5 to T3. 2) The reversal values of these geochemical and clay mineral proxies (e.g., values of CIA between 50 and 64) derived from grey and greyish-yellow sediments in terrace T2 and floodplain denote the dry and cold paleoclimate, emerging in the middle-late Late Pleistocene (50 ka), corresponding to the Baiyu glacial period of the Qinghai-Tibetan Plateau. Comparing the paleoclimatic evolutionary characteristics in Yibin area with those of the Three Gorges area of northeastern margin of Sichuan Basin from previous researches, this paper considers that during the Gonghe tectonic movement (0.15 Ma), the uplift of the Qinghai-Tibetan Plateau and its southeastern boundary intensified the Plateau winter monsoon and caused the southwesterly withdrawal of the Indian monsoon from Sichuan Basin. Consequently, the warm and humid paleoclimate at the northeastern and southwestern margins of the Basin had successively become dry and cold in the early and middle-late periods of the Late Pleistocene.

Does Large‐Scale Crustal Flow Shape the Eastern Margin of the Tibetan Plateau? Insights From Episodic Magmatism of Gongga‐Zheduo Granitic Massif

The mechanisms driving crustal deformation and uplift of orogenic plateaus are fundamental to continental tectonics. Large‐scale crustal flow has been hypothesized to occur in eastern Tibet, but it remains controversial due to a lack of geologic evidence. Geochemical and isotopic data from Cenozoic igneous rocks in the eastern Tibet‐Gongga‐Zheduo intrusive massif, provide a way to test this model. Modeling results suggest that Cenozoic magmas originated at depths of ∼30–40 km, the depth that crustal flow has been postulated to occur at. Detailed isotopic analyses indicate that the igneous rocks are derived from partial melting of the local Songpan‐Ganzi crust, arguing against a long‐distance crustal flow. Episodic magmatism during the Cenozoic showing a repeated shifting of magmatic sources can be correlated with crustal uplift. The continued indentation of the Indian Block and upwelling of the asthenosphere contribute to the crustal deformation, magmatism, and uplift.

Feedback between topography and lithosphere–asthenosphere dynamics beneath the Yerer‐Tulu Wellel volcano‐tectonic lineament: Insights from apatite thermochronology and basalt geochemistry

Ethiopian topography is dominated by an ~2‐km high plateau that underwent uplift and incision after or during the Cenozoic Flood Basalt event in the Early Oligocene; however, the timing and drivers of plateau dynamics are poorly constrained. We constrain the onset and causal mechanism of plateau uplift using thermochronologic and basaltic geochemical techniques. We performed low‐temperature apatite fission track and (U–Th)/He thermochronologic dating on three Neoproterozoic basement rocks from the Yerer‐Tullu Wellel volcano‐tectonic lineament, directly west of Addis Ababa. Thermal models based on these results suggest this part of the plateau underwent slight heating in the Oligocene through Late Miocene, followed by rapid and recent cooling until the present day. To determine the nature of these Cenozoic thermal events, we compiled and reinterpreted a suite of partially published basaltic geochemical data. These geochemical data suggest this part of the plateau is underlain by a metasomatized and pyroxenite‐rich lower lithosphere that began to drip into the asthenosphere in the Miocene. Fault‐facilitated release of the lithospheric drip in the Late Cenozoic encouraged basin inversion, driving rapid cooling and incision within the last 5 Ma. Our study suggests that a direct coupling between lithospheric removal and topographic response highlights significant plateau formation around the Yerer‐Tullu Wellel volcano‐tectonic lineament zone within the Pliocene.

Plastid and mitochondrial phylogenomics reveal correlated substitution rate variation in Koenigia (Polygonoideae, Polygonaceae) and a reduced plastome for Koenigia delicatula including loss of all ndh genes

Koenigia, a genus proposed by Linnaeus, has a contentious taxonomic history. In particular, relationships among species and the circumscription of the genus relative to Aconogonon remain uncertain. To explore phylogenetic relationships of Koenigia with other members of tribe Persicarieae and to establish the timing of major evolutionary diversification events, genome skimming of organellar sequences was used to assemble plastomes and mitochondrial genes from 15 individuals representing 13 species. Most Persicarieae plastomes exhibit a conserved structure and content relative to other flowering plants. However, Koenigia delicatula has lost functional copies of all ndh genes and the intron from atpF. In addition, the rpl32 gene was relocated in the K. delicatula plastome, which likely occurred via overlapping inversions or differential expansion and contraction of the inverted repeat. The highly supported but conflicting relationships between plastome and mitochondrial trees and among gene trees complicates the circumscription of Koenigia, which could be caused by rapid diversification within a short period. Moreover, the plastome and mitochondrial trees revealed correlated variation in substitution rates among Persicarieae species, suggesting a shared underlying mechanism promoting evolutionary rate variation in both organellar genomes. The divergence of dwarf K. delicatula from other Koenigia species may be associated with the well-known Eocene Thermal Maximum 2 or Early Eocene Climatic Optimum event, while diversification of the core-Koenigia clade associates with the Mid-Miocene Climatic Optimum and the uplift of Qinghai-Tibetan Plateau and adjacent areas.

Integrative taxonomy on the rare sky-island Ligidium species from southwest China (Isopoda, Oniscidea, Ligiidae)

BackgroundThe sky-island Ligidium species fauna in southwest China is poorly known. Before this study, six of the seven sky-island species of the genus were known to be endemic to southwest China. In morphology, Ligidium species are often difficult to identify, and an appraisal of integrative taxonomy is needed.ResultsWe integrated morphology and molecular analyses to delimit Ligidium species. Molecular species delimitation based on distance- and evolutionary models recovered seven-candidate lineages from five gene markers (COI, 12S rRNA, 18S rRNA, 28S rRNA and NAK). We also estimated that the species divergences of sky-island Ligidium in southwest China started in late Eocene (40.97 Mya) to middle Miocene (15.19 Mya).Four new species (L. duospinatum Li, sp. nov., L. acuminatum Li, sp. nov., L. rotundum Li, sp. nov. and L. tridentatum Li, sp. nov.) are described. Morphological confusion among L. denticulatum Shen, 1949, L. inerme Nunomura & Xie, 2000 and L. sichuanense Nunomura, 2002 is clarified by integrative taxonomy.ConclusionThis work confirms that an integrative approach to Ligidium taxonomy is fundamental for objective classification, and deduced the uplift of Qinghai-Tibetan Plateau in the late Eocene and middle Miocene as one of the principal reasons for the species divergences of sky-island Ligidium in southwest China. We also inferred that sky-island mountains have a huge reserve of higher Ligidium species diversity.