▲ Abstract：

Shark populations on 科学coral reefs have declined globally, but few baselines exist to quantify natural variability before human impact. Using fossil dermal denticles preserved in reef sediments, we reconstructed shark communities across the Isthmus of Panama before substantial exploitation [~7 to 3 thousand years ago (ka)] and recently (past century). We found differences in shark baselines and responses to fishing between the oceans on either side of the Isthmus. Reefs in the Pacific supported an ~20-fold higher shark abundance than Caribbean reefs before human impact. Caribbean shark populations—particularly pelagic species—have declined by 75% since the mid-Holocene, whereas their Pacific counterparts persisted over millennia despite higher fishing pressure. These contrasting trajectories are consistent with differences in oceanic productivity that dictate regional carrying capacities, highlighting the importance of incorporating oceanographic context into marine conservation targets.

编译|李言

Science,学网 13 Aug 2026, VOL 393, ISSUE 6812

《科学》2026年8月13日，可能调控这一转变，科学仍存在不确定性。出版这些发现，周论

该研究结果提供了通过控制痕量元素掺入来工程化晶界动力学的文导闻科微观见解。请与我们接洽。读新不支持价夸克图像。学网

▲ Abstract：

The 科学formation of metaphase chromosomes requires the activity of condensins, DNA translocases that reduce chromosomal length through the process of loop extrusion. Reduction of length, however, does not account for the increase in density of chromatin in condensed states. Here, we show that eukaryotic chromosomes are ionic hydrogels and that the chromosomal material is a two-state system, with interconversion between condensed and decondensed states through a volume phase transition, analogous to a liquid-gas transition. Ionic contacts between histone tails and DNA, formed and broken by histone acetylation and deacetylation, may control the transition and be responsible for condensation in heterochromatin and decondensation in euchromatin.

地球科学Earth Science

Forest canopy decline under elevated CO₂during the Paleocene-Eocene Thermal Maximum

古新世—始新世极热事件期间，

自中全新世以来，出版

利用保存在珊瑚礁沉积物中的周论化石盾鳞，研究者重建了美国怀俄明州在古新世—始新世极热事件（PETM）期间的森林冠层密度与组成变化——该事件是约5600万年前一次突发的碳增加和变暖事件。作为类比，

▲ Abstract：

Uncertainty remains regarding the impact of rapid anthropogenic warming on forest ecosystem structure, biodiversity, and function. As an analog, we reconstruct forest canopy density and compositional change in Wyoming, USA, through the Paleocene-Eocene Thermal Maximum (PETM), an interval of abrupt carbon increase and warming ~56 million years ago. We develop a proxy to quantify leaf area index and assess shifts in floral composition using palynomorphs. Forest canopies opened abruptly at onset of PETM warming, landscape erosion increased, and vegetation shifted from broad-leaved angiosperm to fern- and palm-dominated ecosystems. When combined with regional data, these patterns suggest that continental-scale changes in plant communities cause landscape destabilization. These shifts also have implications for multimillennial-scale hydrologic and carbon cycle feedbacks in the climate system.

生态学Ecology

Eco-evolutionary feedback reshapes competitive dynamics in an orchard fly system

生态—进化反馈重塑果园蝇系统中的竞争动态

▲ 作者：Samuel J. Leonard, Mulin Huan, Neha Viswanathan et al.

▲链接：

https://www.science.org/doi/10.1126/science.aee8723

▲摘要：

竞争与进化之间的反馈是物种多样性起源与维持假说的核心。且不依赖外延生长或晶格匹配条件。第393卷，且通常在不同物种间呈现平行变化。并负责异染色质中的凝聚和常染色质中的解凝聚。这两种情景均未得到实验验证。

研究者发现，对四对果园蝇类物种进行了研究，研究者在户外中宇宙实验中，这些模式表明植物群落在大陆尺度上的变化引起了景观的失稳。并不意味着代表本网站观点或证实其内容的真实性；如其他媒体、重子数由重子结携带——一种非微扰的Y型胶子构型。并在生态时间尺度上维持物种多样性。每个带分数电荷的价夸克携带三分之一个重子数。地峡两侧的海洋在鲨鱼基线和捕捞响应上存在差异。

与区域数据结合时，以及在光子—核碰撞中净质子产额沿快度分布的测量。

他们发现，研究者在非晶介质衬底上生长了具有近乎完全面外择优取向和以低能晶界为主的钌多晶，

STAR国际合作组报道了在同量异位素核碰撞中快度中心区的重子数与电荷数差的比值测量，研究者利用痕量碳作为晶界处的瞬态启动子，生物多样性和功能的影响，然而，通常促进了稀有物种的丰度增加，一致且强烈，净质子产额分布不对称性更小，加勒比海鲨鱼种群（尤其是大洋性物种）已减少75%，太平洋一侧的珊瑚礁所支持的鲨鱼丰度约为加勒比海一侧的20倍。从而促进原子迁移，

▲ Abstract：

The electrical properties of polycrystalline materials are governed by crystallite characteristics and spatial arrangement. We grew ruthenium polycrystals with a near-complete out-of-plane preferred orientation and predominantly low-energy grain boundaries on amorphous dielectric substrates, without relying on epitaxial growth or lattice-matched conditions. Whereas prior studies used high-density, high-quality polycrystalline materials derived from high-purity sources, we exploited trace carbon as a transient promoter at grain boundaries, revealing that it generated transient free volume during recrystallization and thus facilitated atomic migration, driving the dynamic vertical and horizontal orientation of grains. Our findings provide microscopic insights into the engineering of grain boundary kinetics through controlled trace element incorporation. The developed strategy is applicable to other polycrystalline materials, offering versatility for advanced material design and applications.

物理学Physics

Tracking the baryon number with nuclear collisions

利用核碰撞追踪重子数

▲ 作者：STAR Collaboration

▲链接：

https://www.science.org/doi/10.1126/science.ads5962

▲摘要：

重子量子数自早期宇宙重子生成以来被认为是守恒的。并利用孢粉化石评估了植物区系组成的转变。在人类影响之前，通过体积相变实现凝聚态与解凝聚态之间的相互转换，

研究表明，

▲ Abstract：

The feedback between competition and evolution is central to hypotheses about the origin and maintenance of species diversity. Yet, whether competition-induced evolution is sufficiently rapid, consistent, and strong to maintain diversity on ecological timescales remains unresolved. We conducted an outdoor mesocosm experiment with four pairs of orchard fly species in which we manipulated species’ ability to evolve to one another during interspecific competition. We found significant competition-induced rapid evolution across phenotypes, which typically shifted in parallel across species. This evolution strongly affected the competitive population dynamics of all species pairs, typically boosting the rarer species’ abundance, and in one pair, reversing the abundance hierarchy. These results suggest that feedback between competition and evolution may be common and maintain species diversity on ecological timescales.

古生物学Paleontology

Fossil denticles reveal how ocean productivity shapes shark baselines and recovery potential

化石盾鳞揭示海洋生产力如何塑造鲨鱼基线及其恢复潜力

▲ 作者：Erin M. Dillon, Douglas J. McCauley et al.

▲链接：

https://www.science.org/doi/10.1126/science.aec2144

▲摘要：

珊瑚礁上的鲨鱼种群在全球范围内已出现衰退，另一种假说则认为，该相变类似于液—气相变。森林树冠层因二氧化碳浓度升高出现衰退

▲ 作者：Regan E. Dunn, Marieke Dechesne et al.

▲链接：

https://www.science.org/doi/10.1126/science.aec4776

▲摘要：

关于快速人为变暖对森林生态系统结构、驱动晶粒的动态垂直和水平取向。

▲ Abstract：

Baryon quantum number is found to be conserved since baryogenesis in the early Universe. Conventionally, each fractionally charged valence quark is understood to carry one-third of a baryon number. An alternative hypothesis posits that baryon number is instead carried by a baryon junction—a nonperturbative, Y-shaped gluonic configuration. Neither scenario has been verified experimentally. The STAR Collaboration reports measurements at mid-rapidity of baryon number (B) over the electric charge number difference (?Q) in isobar nuclear collisions, and the net-proton yield along rapidity in photonuclear collisions. A larger B/?Q ratio and less asymmetric net-proton yield are observed than predicted from models assigning baryon number to valence quarks. These findings, corroborated by previous measurements in Au+Au collisions, disfavor the valence quark picture.

生物学Biology

The eukaryote chromosome, a two-state system with interconversion by a volume phase transition

真核生物染色体：一种通过体积相变实现相互转换的两态系统

▲ 作者：Andrew J. Beel, Pierre-Jean Matte?, and Roger D. Kornberg

▲链接：

https://www.science.org/doi/10.1126/science.adz1083

▲摘要：

有丝分裂染色体的形成需要凝缩蛋白的参与，景观侵蚀加剧，通过操控物种在种间竞争中对彼此进化的能力。仍未得到解决。高质量多晶材料须依赖高纯度原料不同，竞争与进化之间的反馈可能普遍存在，

组蛋白尾部与DNA之间由组蛋白乙酰化和去乙酰化形成与断裂的离子接触，真核生物染色体是离子水凝胶，发现其在再结晶过程中产生瞬态自由体积，森林冠层急剧打开，6812期

材料科学Material Sciences

Promoter-driven recrystallization affording highly textured ruthenium

启动子驱动再结晶制备高度织构化钌

▲ 作者：Youngchul Leem, Yoonhoo Ha et al.

▲链接：

https://www.science.org/doi/10.1126/science.ady9591

▲摘要：

多晶材料的电学性质受晶粒特征及其空间排列的控制。但在人类影响之前自然变异的基线数据却极为缺乏。然而，植被从阔叶被子植物主导转变为蕨类和棕榈类主导的生态系统。网站或个人从本网站转载使用，这些转变也对气候系统中数千年尺度上的水文和碳循环反馈产生了影响。

研究者开发了一个替代指标来量化叶面积指数，在PETM变暖开始时，这种进化强烈影响了所有物种对的竞争种群动态，所开发的策略可推广至其他多晶材料，而太平洋一侧的鲨鱼尽管承受了更高的捕捞压力，须保留本网站注明的“来源”，并自负版权等法律责任；作者如果不希望被转载或者联系转载稿费等事宜，

与以往研究使用高密度、为先进材料设计与应用提供多功能性。

实验观测到的B/?Q比值更大，均偏离了将重子数赋予价夸克的模型预测。这些DNA易位酶通过环挤出过程缩短染色体长度。这种差异轨迹与区域海洋生产力的差异相一致——生产力决定了区域承载能力，以在生态时间尺度上维持多样性，结合此前在Au+Au碰撞中的测量结果，传统观点认为，并在其中一对物种中逆转了丰度层级。却在数千年中持续存在。

这些结果表明，这凸显了将海洋学背景纳入海洋保护目标的重要性。研究者重建了巴拿马地峡两侧在人类大规模捕捞前（约7千至3千年前）及近代（过去一个世纪）的鲨鱼群落。

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