Haiping Liu

Polyploidy represents a major driver of eukaryotic genome evolution. In vertebrates, premeiotic endoreplication is considered as an important route to polyploidization, yet the molecular basis governing this process remains elusive. Here, we reported that heterozygous mutation of cdk1 in the loach, Misgurnus anguillicaudatus (Teleostei, Cobitidae), triggered premeiotic endoreplication in spermatogonia, resulting in the production of unreduced diploid sperms. Through integrated proteomic and phosphoproteomic profiling, we uncovered that Cdk1 heterozygosity led to widespread dysregulation of the phosphorylation of key proteins in the cell cycle and DNA replication pathways in spermatogonia. Mechanistically, Cdk1 heterozygosity induced increased inhibitory phosphorylation of Cdk2 at tyrosine 15, and accumulated Cdk2/Ccne1 complex directly phosphorylated Fzr1a at threonine 124, inhibiting APC/C ^Fzr1a complex activity. Cdk2 Y15 phosphorylation arrested cells at the G1/S boundary, while Fzr1a phosphorylation-driven APC/C ^Fzr1a inactivation blocked mitotic exit and sustained DNA replication, thereby triggering premeiotic endoreplication. Inhibition of Cdk2 expression in cdk1 ^+/− loach males suppressed this pathway and abolished unreduced sperm formation. Our study elucidates the molecular pathway for unreduced gamete production in fish and establishes Cdk1 as a key guardian of diploidy before meiosis. Furthermore, leveraging this mechanism, we generated triploid and tetraploid loach lines with unreduced sperms, demonstrating a direct bridge between gene function and polyploid breeding. These findings provide a mechanistic framework for understanding polyploidization in vertebrate evolution and offer a targeted strategy for chromosome set manipulation in aquaculture.

Phytoplankton are sensitive indicators of environmental change in high-altitude aquatic ecosystems, but their community responses across river–lake confluence zones remain insufficiently understood. We investigated phytoplankton community characteristics and environmental associations in the Siling Co river–lake continuum. This endorheic system lies above 4500 m, where river inflows, lake-water mixing, and evaporative concentration generate marked hydrochemical gradients. Genus-level cell density and estimated biomass were assessed with 22 environmental variables from 14 sampling events at 10 lake and river sites. We recorded 54 phytoplankton genera, with Bacillariophyta dominant. Lake and River samples overlapped in composition, whereas sampling period accounted for more community variation than water-body type. Major-ion and salinity-related gradients were associated with cell-density community dissimilarity after accounting for water-body type. Cell-density and biomass composition also showed partly distinct associations with pH and SiO₂, and with Cl⁻, respectively. These observations indicate that phytoplankton communities in the Siling Co river–lake confluence zone are more closely associated with sampling-period variation and hydrochemical gradients than with Lake/River habitat classification. These findings provide an initial basis for integrated biological and hydrochemical monitoring.

Schizothoracinae represent an endemic and dominant teleost group in the Qinghai–Xizang Plateau and adjacent regions. Despite their rich species diversity, closely related Schizothoracinae species exhibit remarkable external morphological similarity, which hinders traditional morphological discrimination. In this study, lapillus otoliths from 360 individuals representing 12 Schizothoracinae species collected across major Tibetan water systems were systematically examined. We evaluated and compared the performance of traditional scalar-based shape indices and Elliptic Fourier Analysis (EFA, 60 normalized harmonic coefficients following size-allometry correction) in otolith contour quantification and species identification. Statistical analyses including one-way ANOVA, principal component analysis (PCA), non-linear manifold learning (t-SNE and UMAP), and linear discriminant analysis (LDA) were executed. One-way ANOVA revealed highly significant differences among all 12 species across all shape indices and Fourier coefficients. The overall LDA classification accuracy was 35.3% for the shape index method, whereas EFA achieved a higher overall accuracy of 68.3%, representing a 33.0 percentage point improvement. Under EFA, Schizothorax lhasaensis (93.3%) and Schizothorax nukiangensis (90.0%) demonstrated the highest single-species discrimination success. Interspecific otolith morphological divergence was substantially higher in the riverine genus Schizothorax than in lacustrine genera (Gymnocypris and Schizopygopsis), the latter two of which show extensive morphological overlap consistent with their low genomic differentiation. Fishes of Gymnocypris displayed significantly higher otolith roundness (p < 0.05), which correlates with their adaptation to lacustrine or sluggish water habitats. Our findings demonstrate that EFA effectively captures multi-scale otolith contour harmonics, serving as a valuable morphometric approach for Schizothoracinae species identification and morphological discrimination, although challenges remain for species with incomplete lineage sorting. The morphometric database established herein provides valuable morphological baselines for the conservation and management of endemic QXP fish resources.

River–lake confluence zones are shaped by inflow hydrology, evaporative concentration, and water mixing, providing natural systems for examining phytoplankton responses to environmental gradients. Here, we investigated Siling Co and adjacent river–lake confluence zones at elevations above 4,500 m. We integrated genus-level phytoplankton cell-density and biomass data with 22 environmental variables from 14 sampling events at 10 sites, including seven Lake and seven River samples. Community diversity, composition, and community–environment associations were evaluated using ordination, permutation tests, correlation analyses, distance-based redundancy analysis, Mantel tests, and multi-method evidence integration. In total, 54 genera were recorded, with Bacillariophyta representing the dominant phylum. Lake and River samples overlapped in community composition, whereas sampling period explained more genus-level variation than water-body type. Major-ion and mineralization gradients were consistently associated with community turnover. pH and SiO₂ were associated with cell-density composition, whereas Cl⁻ was associated with biomass composition. Cyanobacterial relative biomass was positively correlated with total nitrogen and negatively correlated with SO₄²⁻. These findings indicate that phytoplankton community structure in the Siling Co river–lake confluence zone cannot be attributed simply to two discrete habitat types, namely lakes and rivers, and provide a new perspective on community assembly in extremely high-altitude river–lake confluence zones.

Transport density is a pivotal regulatory factor during live fish transport, as it determines the intensity of stress responses and subsequent survival. With increasing demands for artificial propagation, stock enhancement, and scientific research, the frequency of transporting Schizothorax nukiangensis has risen substantially. This study evaluated the effects of different transport densities (100, 150, and 200 kg/m³) after 4 h on water quality, plasma biochemistry, tissue morphology, and transcriptional responses. High-density transport elevated ammonia nitrogen and temperature, reduced pH, and caused mortality in the highest-density group. Gill and liver tissues exhibited progressive structural damage, accompanied by increased plasma ROS, SOD, cortisol, and glucose levels, while IgG, CAT and T-AOC decreased under higher densities. Transcriptomic analyses showed that upregulated DEGs in the gill were primarily enriched in Antigen processing and presentation, whereas innate immune pathways—including RIG-I-like receptor, IL-17, and cytosolic DNA-sensing—were suppressed. This pattern suggests that increasing transport density suppresses innate immune responses, thereby shifting immune regulation toward enhanced adaptive immune activation via antigen processing and presentation. Both gill and liver exhibited pronounced enrichment of lipid metabolism–related pathways—including steroid biosynthesis, fatty acid metabolism, glycerolipid metabolism, and fat digestion and absorption—accompanied by extensive upregulation of these genes. These changes are tightly associated with activation of the PPAR signaling pathway, which facilitates fatty acid transport, degradation, and β-oxidation, thus sustaining energy supply under transport-induced stress. These findings clarify the physiological and molecular mechanisms of transport stress in S. nukiangensis and provide guidance for optimizing short-distance transport strategies.

Climate change and human disturbance threaten freshwater biodiversity, particularly endangered species on the Qinghai‐Xizang Plateau. Oxygymnocypris stewartii , Schizothorax macropogon , and Schizothorax waltoni ( Schizothorax spp. hereafter) are Class II Protected Species in China, indigenous to the Qinghai‐Xizang Plateau, and primarily distributed in the middle and upper Yarlung Zangbo River (MUR). Based on species distribution points, the Maximum Entropy (MaxEnt) model was used to simulate potentially suitable habitats and identify key environmental factors for Schizothorax spp. Ecologically suitable areas were reconstructed using a kernel density estimation (KDE) algorithm that incorporates hydropower plants, and future distribution dynamics were predicted under various climate scenarios. Results indicated that the flow accumulation and the mean temperature of the coldest quarter were the primary environmental factors affecting Schizothorax spp. For Schizothorax spp., the suitable habitat exhibited a non‐monotonic trend: it increased before the 2050s (up to 108.28% at 2050s‐SSP7.0), then turned downward by the 2070s (18.1% at 2070s‐SSP2.6). Moreover, habitat suitability sustained expansion at the upper reaches, with the rate of expansion increasing with the intensification of radiative forcing, and projected an increase in elevation at SSP7.0 and SSP8.5. At the local scale, however, hydropower plants pose a deterministic threat, causing permanent habitat loss of Schizothorax spp. in the middle and lower reaches. Overall, the model predicts that future climate‐driven events may lead to a spatial expansion of potentially suitable habitats for Schizothorax spp. However, due to limitations in hydrological connectivity and the unique characteristics of fish, these high‐altitude habitats face significant constraints. Enhanced conservation efforts in the Saga, Angren, and Miling basins of the MUR are recommended, along with continuous monitoring and early warning of changes in habitat suitability to protect the Schizothoracinae conservation areas.