From the Cover: Phase space transport in the interaction between shocks and plasma turbulence

The interaction of collisionless shocks with fully developed plasma turbulence is numerically investigated. Hybrid kinetic simulations, where a turbulent jet is slammed against an oblique shock, are employed to address the role of upstream turbulence on plasma transport. A technique, using coarse graining of the Vlasov equation, is proposed, showing that the particle transport strongly depends on upstream turbulence properties, such as strength and coherency. These results might be relevant for the understanding of acceleration and heating processes in space plasmas.

A turbulent plasma wind flows from the sun and permeates the heliosphere, encountering several magnetic obstacles, leading to shocks that continuously interact with the incoming complex solar wind—a scenario that becomes a prototype for understanding many other systems characterized by the presence of shocks. Despite decades of research, the interaction of shocks with plasma turbulence and the subsequent energetic particle production still remain poorly understood (1, 2). Shocks are well-known efficient, natural particle accelerators (3) and have been modeled in a number of theories (4–8). Less understood is the interaction of shocks and turbulence that characterizes spectacular high-energy events, as in supernovae explosions propagating through the interstellar turbulent medium, as in the case of coronal mass ejections that stream through the turbulent solar wind, and as for the complex Earth’s bow shock environment. In many of the above examples, oblique shocks are known to generate coherent field-aligned beams (FABs), as observed at Earth’s bow shock (9). FABs are an important source of free energy throughout the interplanetary medium (10). Turbulence-generated coherent structures and waves might interact with the shock discontinuity, in an interplay that is likely to play a pivotal role in particle acceleration and plasma heating (11–13).Turbulence is populated by a variety of structures that can work effectively as particle “traps” and “corridors” that either hinder or enable their motion (14) and represents another crucial source of accelerated particles (15–18). An example of such an energization process has been observed in the patterns of local reconnection that develop in turbulence (19, 20). In order to understand such mechanisms, the transport properties need to be explored in the plasma phase space (21).Due to the difference between the spatial and temporal scales involved in accelerating particles, shocks and turbulence are often considered theoretically in isolation rather than together. However, fundamental studies have suggested that these are inextricably linked: Shocks are likely to propagate in turbulent media, and turbulence is responsible for changing fundamental aspects of shock transitions (22–27). Inspired by these studies, here we quantitatively explore the intimate relation between these two phenomena.     

From the Cover: Solar anti-icing surface with enhanced condensate self-removing at extreme environmental conditions

The inhibition of condensation freezing under extreme conditions (i.e., ultra-low temperature and high humidity) remains a daunting challenge in the field of anti-icing. As water vapor easily condensates or desublimates and melted water refreezes instantly, these cause significant performance decrease of most anti-icing surfaces at such extreme conditions. Herein, inspired by wheat leaves, an effective condensate self-removing solar anti-icing/frosting surface (CR-SAS) is fabricated using ultrafast pulsed laser deposition technology, which exhibits synergistic effects of enhanced condensate self-removal and efficient solar anti-icing. The superblack CR-SAS displays superior anti-reflection and photothermal conversion performance, benefiting from the light trapping effect in the micro/nano hierarchical structures and the thermoplasmonic effect of the iron oxide nanoparticles. Meanwhile, the CR-SAS displays superhydrophobicity to condensed water, which can be instantly shed off from the surface before freezing through self-propelled droplet jumping, thus leading to a continuously refreshed dry area available for sunlight absorption and photothermal conversion. Under one-sun illumination, the CR-SAS can be maintained ice free even under an ambient environment of −50 °C ultra-low temperature and extremely high humidity (ice supersaturation degree of ∼260). The excellent environmental versatility, mechanical durability, and material adaptability make CR-SAS a promising anti-icing candidate for broad practical applications even in harsh environments.

Condensation freezing/frosting on solid surfaces causes severe economic and safety issues. Thus, highly efficient anti-icing/frosting approaches are vital in many engineering applications, ranging from air conditioners to power transmission systems (1–4). Tremendous efforts have been invested into designing active and passive anti-icing surfaces. Active anti-icing strategies including mechanical, chemical, and thermal methods often consume high amounts of energy and require specific facilities for deicing, which limit their practical applications (5, 6). Passive anti-icing surfaces involve strategies to delay and inhibit ice formation, such as hydrated surfaces, lubricant-infused surfaces, bioinspired anti-freezing surfaces, and superhydrophobic surfaces (SHSs) (3, 7–13). Although these passive icephobic materials offer numerous advantages to prevent ice accretion, each comes with its own limitations (14).At extreme environmental conditions where condensation and desublimation are strongly promoted, an optimal passive anti-icing surface should immediately remove condensed water droplets and leave no water for freezing. To prepare such a kind of surface, lots of efforts have been made to study the abilities of SHSs for removing condensed water. However, regular SHSs are incapable of removing microscale condensed water droplets under humid conditions due to the wetting of surface micronanostructures, which leads to the formation of highly pinned Wenzel droplets and the loss of superhydrophobicity (15–17). Tremendous investigations have shown that SHSs with specially designed structures can retain superhydrophobicity to condensed water droplets, and coalesced droplets can be spontaneously removed from the surface via self-propelled jumping (18–20). The self-propelled jumping of condensed droplets is driven by the released surface energy during droplet coalescence after overcoming solid–liquid adhesion (21–25). However, these surfaces inevitably lose their water repellency at low temperatures (i.e., < −15 °C) because of freezing (9, 21, 26). Thus, it is highly desirable to design new anti-icing surfaces that can maintain capability for removing the condensed water at extreme environmental conditions, which is highly important for anti-icing applications in many scenarios (i.e., aircrafts flying through clouds, wind turbines operating in winter, and power transmission facilities working in extremely cold and humid regions) (27).Recently, intensive research efforts have been dedicated to solar anti-icing/frosting surfaces (SASs), which can absorb sunlight efficiently and convert solar energy to heat, thereby delaying or preventing ice formation (28–30). Because of its effective utilization of clean and renewable solar energy, SASs are environmentally friendly and energy efficient. Notably, a number of photothermal conversion materials including carbon materials, conjugated polymers, two-dimensional nanostructural materials, and metallic particles have also been applied as SASs (28, 31–34). Although remarkable improvements have been made, some challenges have yet to be tackled. For instance, most of the reported SASs cannot remove the condensed water effectively, particularly in cold and humid conditions (35, 36). The accumulation of the condensed water would significantly enhance reflectance leading to reduced photothermal efficiency (37) and decreased temperature. As a result, frost formation through the freezing of condensed water (condensation frosting) will prevent sunlight from reaching the SAS, resulting in the complete loss of its photothermal capability: as light harvesting becomes less efficient, the temperature of the SAS decreases, resulting in a vicious compounding cycle of condensation freezing. Moreover, the contaminants on the SAS can also inhibit sunlight absorption (38). Therefore, it is desirable to develop highly photothermal–efficient SASs with the abilities of removing condensed water to maintain high temperature and self-cleaning for avoiding blockage of sunlight by contaminants.Herein, we present a proof-of-concept SAS with synergistically binary effects of enhanced condensate self-removing and efficient solar anti-icing. We fabricated hierarchically structured materials using ultrafast pulsed laser deposition (PLD) technology. Low-effective refractive index and multilayered iron oxide structures endow the material with broadband ultralow reflectance and high solar-to-heat conversation efficiency. The hierarchically structured SHS demonstrated the capability of removing condensates before freezing via self-propelled droplet jumping induced by droplet coalescence and evaporation flux under heating. The sustained shedding of condensed water droplets resulted in a continuously refreshed, dry and clean area available for efficient sunlight absorption and photothermal conversion; the temperature of the condensate self-removing solar anti-icing/frosting surface (CR-SAS) could be constantly maintained above the freezing temperature, which in turn ensured high-performance water repellency. With such synergistic mutual-benefitting effects of condensate self-removal and photothermal heating, under one-sun illumination, the CR-SAS remained ice-free even at an ambient temperature (T_a) of −50 °C and ultra-high humidity with a supersaturation degree (SSD) of ∼260, demonstrating superior anti-icing performances under extremely harsh operating conditions.     

From the Cover: Radiation-induced neoantigens broaden the immunotherapeutic window of cancers with low mutational loads

Immunotherapies are a promising advance in cancer treatment. However, because only a subset of cancer patients benefits from these treatments it is important to find mechanisms that will broaden the responding patient population. Generally, tumors with high mutational burdens have the potential to express greater numbers of mutant neoantigens. As neoantigens can be targets of protective adaptive immunity, highly mutated tumors are more responsive to immunotherapy. Given that external beam radiation 1) is a standard-of-care cancer therapy, 2) induces expression of mutant proteins and potentially mutant neoantigens in treated cells, and 3) has been shown to synergize clinically with immune checkpoint therapy (ICT), we hypothesized that at least one mechanism of this synergy was the generation of de novo mutant neoantigen targets in irradiated cells. Herein, we use Kras^G12D x p53^−/− sarcoma cell lines (KP sarcomas) that we and others have shown to be nearly devoid of mutations, are poorly antigenic, are not controlled by ICT, and do not induce a protective antitumor memory response. However, following one in vitro dose of 4- or 9-Gy irradiation, KP sarcoma cells acquire mutational neoantigens and become sensitive to ICT in vivo in a T cell-dependent manner. We further demonstrate that some of the radiation-induced mutations generate cytotoxic CD8⁺ T cell responses, are protective in a vaccine model, and are sufficient to make the parental KP sarcoma line susceptible to ICT. These results provide a proof of concept that induction of new antigenic targets in irradiated tumor cells represents an additional mechanism explaining the clinical findings of the synergy between radiation and immunotherapy.

Immune checkpoint therapy (ICT) can lead to durable responses in subsets of cancer patients (1–8). On the basis of computational analyses, the patients who most benefit from ICT are those with cancers that have high mutational burden (9–18). For example, patients bearing tumors with high mutational burden caused by environmental exposure (such as ultraviolet-induced melanoma) or deficiencies in DNA repair (such as microsatellite instability-high colorectal cancers) tend to respond well to immunotherapy (18–26). Presumably the sensitivity of such cancers reflects the increased likelihood of formation of immunogenic, tumor-specific mutant neoantigens (27). We and others previously showed that certain tumor-specific neoantigens are major targets of natural and therapeutically induced antitumor responses in both mice and humans (28–41). Therefore, the presence of immunogenic tumor neoantigens is currently thought to contribute to tumor sensitivity to immunotherapy.However, many cancer patients do not respond to ICT, suggesting that their neoantigen burden is either of insufficient magnitude or immunogenicity to function as targets for T cell-dependent antitumor mechanisms. Indeed, there are many tumor types, such as acute myeloid leukemia, estrogen receptor-positive breast, and prostate cancers, that have limited mutational burdens and display low response rates to ICT (9, 13, 42, 43). Additionally, tumor cell clones expressing immunogenic neoantigens that develop during tumor evolution may be eliminated from tumors with high mutational burden by the process of cancer immunoediting, resulting in outgrowth of tumor cell clones with reduced immunogenicity that can then grow progressively in the presence of the unmanipulated immune system (33, 44, 45). Therefore, a process by which tumors with low neoantigen burden can acquire immunogenic mutations has the potential to expand the number of patients able to benefit from ICT.Ionizing radiation has been shown to elicit DNA damage in tumor cells, leading to an increase in overall mutational load (46–52). This damage is thought to occur primarily through generation of reactive oxygen species which induce base pair substitutions by mechanisms involving transitions, transversions, and/or faulty DNA repair (53). Multiple preclinical studies have demonstrated antitumor responses when focal radiation is combined with ICT in tumors that do not respond to ICT alone (54–60) and several clinical studies have demonstrated that human tumor patients have improved responsiveness to ICT following focal radiation (e.g., {"type":"clinical-trial","attrs":{"text":"NCT02303990","term_id":"NCT02303990"}}NCT02303990, {"type":"clinical-trial","attrs":{"text":"NCT02298946","term_id":"NCT02298946"}}NCT02298946, {"type":"clinical-trial","attrs":{"text":"NCT02383212","term_id":"NCT02383212"}}NCT02383212) (61–67). Radiation has been demonstrated to function as an in vivo tumor vaccine by inducing damage-associated molecular patterns (DAMP)-dependent immunogenic cell death (68), inducing DNA damage sensed by pattern recognition receptors (69, 70), enhancing access of immune effector cells to their cognate targets through tumor cell debulking and vasculature changes (71, 72), up-regulating major histocompatibility complex class I (MHC-I) receptors (73), up-regulating cell-surface molecules such as Fas (74), and augmenting tumor antigen cross-presentation by specific subsets of dendritic cells through up-regulation of type I interferon (IFN), which results in increased numbers and action of tumor-specific CD8⁺ T cells (75–77). However, none of these explanations take into account that following irradiation, tumor cells acquire novel mutations that may function as effective tumor neoantigens. In fact, two groups have demonstrated broadening of the T cell repertoire following radiation treatment of mouse 4T1 mammary tumors and B16F10 melanoma tumors (56, 78). Radiation-induced neoantigens may partially explain the broadening of the T cell repertoire reported during noncurative doses of irradiation.Given the above observations, we specifically explored whether one dose of in vitro irradiation could increase the immunogenicity of poorly immunogenic tumor cell lines through mechanisms involving the de novo generation of tumor-specific mutant neoantigens. For this purpose, we used a mouse Kras^G12D x p53^−/− sarcoma cell line as a model system since the R.D.S. and T.J. laboratories have previously shown that these tumor cells express a very limited number of somatic mutations, are essentially devoid of mutational neoantigens, and are nonimmunogenic and grow progressively in syngeneic wild-type (WT) mice either following treatment with control antibody or the combination of anti–PD-1/anti–CTLA-4 (34, 41). We find that treating these cell lines with noncurative doses of irradiation induces expression of somatic mutations, some of which function as neoantigens and render the sarcoma cells susceptible to ICT in vivo. These data support the concept that an additional mechanism underlying the synergy between radiation therapy and immunotherapy is that the former induces immunogenic mutations in tumors that now function as targets for the latter.     

Rapidly deployable and morphable 3D mesostructures with applications in multimodal biomedical devices

Structures that significantly and rapidly change their shapes and sizes upon external stimuli have widespread applications in a diversity of areas. The ability to miniaturize these deployable and morphable structures is essential for applications in fields that require high-spatial resolution or minimal invasiveness, such as biomechanics sensing, surgery, and biopsy. Despite intensive studies on the actuation mechanisms and material/structure strategies, it remains challenging to realize deployable and morphable structures in high-performance inorganic materials at small scales (e.g., several millimeters, comparable to the feature size of many biological tissues). The difficulty in integrating actuation materials increases as the size scales down, and many types of actuation forces become too small compared to the structure rigidity at millimeter scales. Here, we present schemes of electromagnetic actuation and design strategies to overcome this challenge, by exploiting the mechanics-guided three-dimensional (3D) assembly to enable integration of current-carrying metallic or magnetic films into millimeter-scale structures that generate controlled Lorentz forces or magnetic forces under an external magnetic field. Tailored designs guided by quantitative modeling and developed scaling laws allow formation of low-rigidity 3D architectures that deform significantly, reversibly, and rapidly by remotely controlled electromagnetic actuation. Reconfigurable mesostructures with multiple stable states can be also achieved, in which distinct 3D configurations are maintained after removal of the magnetic field. Demonstration of a functional device that combines the deep and shallow sensing for simultaneous measurements of thermal conductivities in bilayer films suggests the promising potential of the proposed strategy toward multimodal sensing of biomedical signals.

Deployable and morphable structures capable of changing their sizes and shapes significantly are essential in engineering (e.g., aerocrafts) and daily life (e.g., tents, umbrellas, and folding fans) (1, 2). Miniaturizing such structures to be comparable to the small scale in natural and/or human-engineered living systems such as arteries (1∼10 mm) (3), early-stage lesions (4), and organoids (∼1 mm) (5), and in minimally invasive surgeries (4) could broaden their applications in biomedical, healthcare, and electronic devices (6, 7). Recent advances in manufacture, fabrication, and assembly techniques enable the use of materials that respond to irradiation (8–12), magnetic field (13–21), electric field (22–27), electromagnetic field (28, 29), heat (17, 30–36), chemicals (37, 38), and pressures (39, 40) to remotely actuate large structural deformations (41–47). For example, the three-dimensional (3D) printing technique of programmed ferromagnetic domains developed by Kim et al. (13) realized the fast transformation between complex 3D configurations using magnetic field. By programming the magnetic configurations of nanomagnets, the micromachines developed by Cui et al. (19) could be transformed among multiple configurations. Mao et al. (28) presented soft electromagnetic actuators driven by Lorentz forces to fold two-dimensional (2D) precursors into various 3D shapes in spatially varying magnetic field. The silicon-lithium alloying reaction was exploited by Xia et al. (38) to drive the transformation of silicon-coated microlattices whose deformed shapes could be locked via plastic deformations.Despite the significant progress, most of the existing strategies are demonstrated only at relatively large sizes (>1 cm), while the ability to scale the deployable and morphable structures down to small sizes, such as millimeter and submillimeter scales, is crucial for many applications, such as the minimally invasive surgery and the sensing of early-stage lesion. With the reduction of the structural size, the integration of actuation components with 3D structures becomes more challenging, and many types of actuation forces, especially those (e.g., Lorentz forces and magnetic forces) that can be controlled remotely, decrease significantly compared to the structural rigidity. Therefore, the strategies that work effectively at relatively large sizes (>1 cm) may not be applicable at millimeter and submillimeter scales. In particular, the following two aspects are worthy of further exploration. On one hand, while a few different strategies have been developed to lock the deformed shape after removing the external stimuli, such as those based on plastic deformations (38, 48), shape-memory effects (49–52), and multistable structures (53–61), none is without limitations. For example, plastic deformations could reduce the durability of 3D architectures, and the prolonged period of phase transition in the shape-memory effect limits the speed of the reconfiguration (49–51). For specially engineered 2D patterns, the mechanics-guided, deterministic 3D assembly through the use of diverse release paths of biaxial prestrain allowed the transformation of assembled structures among multiple stable states (53–55), but applying a mechanical force to the underlying elastomeric substrate in situ is difficult. Incorporating dielectric elastomers that deform under an applied electric field as the assembly platform allows the formation of reconfigurable 3D mesostructures but requires high voltages and patterned electrodes (62, 63). Other strategies including the bistable Kresling patterns in response to the distributed magnetic actuation (15) were demonstrated at relatively large scales (>1 cm). A rapid, robust, and reversible shape reconfiguration at a small scale requires an actuation source that can be easily controlled, as well as a tailored design of low-rigidity structures. On the other hand, many deployable and morphable structures adopted intrinsically soft materials, such as elastomers (modulus ≤ 10 MPa) (64), which limits their applications in microelectronics and biomedical devices. This is because the inorganic functional materials (e.g., metals, silicons, and piezoelectric ceramics) often have large moduli (≥50 GPa) and may not be directly incorporated into those soft structures, due to the incompatibility of the fabrication technique and the increased structural rigidity. Three-dimensional structures made of intrinsically hard functional materials have been previously reported by our group (65–68), but active, large deformations are not accessible, due to the large rigidity and/or the lack of actuation components.Here, based on the mechanics-guided, deterministic 3D assembly (69–82), we introduce schemes of electromagnetic actuation and strategic structural designs to overcome the above limitations. The 3D assembly technique enables the integration of actuation components such as current-carrying metals (66) and magnetic materials (71) into small-scale 3D architectures to generate driving forces with portable magnets, as well as functional components ranging from silicons (67, 68), commercial chips (83–86), to piezoelectric ceramics/polymers (65, 87, 88). The design of low-rigidity structures guided by the finite element analysis (FEA) allows access to large deformations driven by those forces that are otherwise too small for conventional structures (89) at small sizes (e.g., <5 mm). The proposed strategies enable the assembly of millimeter-scale structures of various geometric configurations with submillimeter-scale feature sizes (e.g., ribbon width), ranging from 3D serpentines, kirigami patterns, to pop-up books that can switch rapidly and reversibly among multiple stables states. In particular, combined computational and experimental studies allow the formation of millimeter-scale deployable structures that can rapidly change their sizes by approximately one order of amplitude, which are unachievable previously. Furthermore, we demonstrate a functional device for detection of the thermal conductivities of a bilayer material, which can be actively switched between the deep and shallow sensing modes.     

Evolutionary relationships between drought-related traits and climate shape large hydraulic safety margins in western North American oaks

Quantitative knowledge of xylem physical tolerance limits to dehydration is essential to understanding plant drought tolerance but is lacking in many long-vessel angiosperms. We examine the hypothesis that a fundamental association between sustained xylem water transport and downstream tissue function should select for xylem that avoids embolism in long-vessel trees by quantifying xylem capacity to withstand air entry of western North American oaks (Quercus spp.). Optical visualization showed that 50% of embolism occurs at water potentials below −2.7 MPa in all 19 species, and −6.6 MPa in the most resistant species. By mapping the evolution of xylem vulnerability to embolism onto a fossil-dated phylogeny of the western North American oaks, we found large differences between clades (sections) while closely related species within each clade vary little in their capacity to withstand air entry. Phylogenetic conservatism in xylem physical tolerance, together with a significant correlation between species distributions along rainfall gradients and their dehydration tolerance, suggests that closely related species occupy similar climatic niches and that species'' geographic ranges may have shifted along aridity gradients in accordance with their physical tolerance. Such trends, coupled with evolutionary associations between capacity to withstand xylem embolism and other hydraulic-related traits, yield wide margins of safety against embolism in oaks from diverse habitats. Evolved responses of the vascular system to aridity support the embolism avoidance hypothesis and reveal the importance of quantifying plant capacity to withstand xylem embolism for understanding function and biogeography of some of the Northern Hemisphere’s most ecologically and economically important plants.

Increased rates of drought-induced tree mortality at global scales (1–3) and associated alteration of the land water cycle (4) underscore the timely importance of understanding dynamic plant vascular function during dehydration in order to improve predictions of the composition, productivity, and resilience of woodland and forest communities under future climate conditions (5). Of importance in this regard is elucidating the capacity of the xylem to withstand hydraulic failure as plants desiccate during drought events. Water lost from the internal sites of evaporation within leaf mesophyll—a necessary consequence of a plant’s need to maintain rapid gas exchange in leaves for photosynthesis—places the water column in the internal xylem tissue under tension (6) (i.e., negative pressure). This remarkable biophysical process that passively draws moisture up from the hydrated soil through the xylem (6) accounts for ∼61% of global land evapotranspiration and returns ∼39% of incident precipitation to the atmosphere (7). However, as soil moisture declines during dry periods plants are increasingly unable to replenish the moisture lost from leaves through evapotranspiration (6), making the xylem water column vulnerable to air entry that causes desiccation (i.e., embolisms) (8–10). By reducing the capacity of the xylem to transport water effectively, embolisms isolate downstream tissues (e.g., leaf mesophyll) from water sources in the soil, rendering these tissues susceptible to dehydration and leading to loss of whole-plant function (11, 12) and ultimately plant mortality (5, 13). If, under future climate change scenarios, increasingly common and severe drought events cause dominant plants to embolize more frequently, the potential consequences for global ecosystem function are enormous, including decreased terrestrial productivity, a reduced terrestrial carbon sink, and preferential partitioning of energy fluxes at the land surface into sensible rather than latent heat flux.Given the importance of quantifying losses of hydraulically mediated whole-plant function and providing accurate predictions of forest productivity and demography under future drought scenarios (14), it is imperative to have a robust, quantitative understanding of the physical tolerance limits of species to dehydration. Such limits can be quantified from the relationship between xylem water potential and loss of xylem function (so-called xylem vulnerability curves). Species are typically compared by the xylem water potential value at which 50% loss of hydraulic conductance occurs (P₅₀) (15), although other reference points may be used in specific physiological contexts, for example, P₁₂, P₈₈, or P₁₀₀ (5, 16). Studies conducted over three decades have revealed that the hydraulic systems of terrestrial plants as diverse as diffuse porous angiosperms (17) and mosses (18) can withstand low water potentials (less than −1.5 MPa). In conifers, most species have P₅₀ values below (i.e., more negative than) −2 MPa [∼97% of 96 species in a meta-analysis (15)] and water potentials below the P₅₀ threshold have been quantitatively linked to whole-plant mortality under experimentally imposed conditions of water limitation (19). Interspecific variation in P₅₀ among conifer species has also been shown to limit the dry end of species distributions along aridity gradients (19–22), as well as being correlated with several other functional, structural, and anatomical traits (20, 22–25).However, xylem vulnerability to cavitation does not solely determine drought tolerance in woody trees (5, 23, 26). The probability of reaching the critical water potential threshold and the length of time it takes for this to occur are determined by the interaction of several associated physiological and morphological traits (e.g., leaf habit, stomatal closure, minimum cuticular conductance) (5, 23, 26) in relation to the climate and habitat occupied by the species. Consequently, evolutionary relationships between P₅₀ and other traits related to water use may yet unify multiple facets of plant form and function (24–27) and produce distinct drought tolerance strategies (28). Understanding how xylem capacity to withstand embolism is integrated with other plant traits is therefore critical for testing ecological and evolutionary hypotheses concerning the diversity of physiological function found in woody plant species.In this study, we use the recently developed optical method (29, 30) to examine thresholds of hydraulic failure in long vessel [i.e., maximum vessel length >1 m (31)] species of oaks (Quercus, Fagaceae) to evaluate the hypothesis that avoiding xylem embolism is a key component of drought tolerance in one of the Northern Hemisphere’s most ecologically and economically important angiosperm genera (32). Much uncertainty surrounds the capacity of plants with long vessels to withstand embolism formation and propagation (31, 33, 34) because of methodological difficulties of studying xylem under tension or potential methodological artifacts related to specific techniques for assessing xylem vulnerability to embolism [reviewed extensively by previous authors (33)]. However, recent advances in quantifying the capacity of xylem to withstand air entry and propagation using noninvasive optical techniques, such as X-ray microcomputed tomography (micro-CT) (35, 36) and the optical vulnerability (OV) method (29–31, 34), offer the potential to resolve critical, longstanding issues in plant ecophysiology (31, 34). Although it is not currently feasible to use synchrotron-based micro-CT for the routine study of xylem embolisms in intact plants, many species can be efficiently sampled using the OV method (29, 31), facilitating studies in comparative physiology (31). We asked three related questions: 1) What is the interspecific range in capacity to withstand xylem embolism in Quercus of western North America? 2) Are quantitative thresholds of water transport failure in the xylem associated with species geographic distributions on aridity gradients? 3) Does capacity to withstand xylem embolism form part of a whole-plant physiological strategy (i.e., a combination of mechanistically linked responses and characteristics) that leads to embolism avoidance during periods of water deficit? Since variation in traits may be better understood by comparing closely related species in an explicit phylogenetic context (37, 38), sample species were selected from four sections of Quercus, including three clades of western North American oaks and the phylogenetically isolate species Quercus sadleriana. Species relationships, for purposes of analysis, follow a recently published fossil-dated phylogeny of the North American oaks (39).     

From the Cover: People have shaped most of terrestrial nature for at least 12,000 years

Archaeological and paleoecological evidence shows that by 10,000 BCE, all human societies employed varying degrees of ecologically transformative land use practices, including burning, hunting, species propagation, domestication, cultivation, and others that have left long-term legacies across the terrestrial biosphere. Yet, a lingering paradigm among natural scientists, conservationists, and policymakers is that human transformation of terrestrial nature is mostly recent and inherently destructive. Here, we use the most up-to-date, spatially explicit global reconstruction of historical human populations and land use to show that this paradigm is likely wrong. Even 12,000 y ago, nearly three quarters of Earth’s land was inhabited and therefore shaped by human societies, including more than 95% of temperate and 90% of tropical woodlands. Lands now characterized as “natural,” “intact,” and “wild” generally exhibit long histories of use, as do protected areas and Indigenous lands, and current global patterns of vertebrate species richness and key biodiversity areas are more strongly associated with past patterns of land use than with present ones in regional landscapes now characterized as natural. The current biodiversity crisis can seldom be explained by the loss of uninhabited wildlands, resulting instead from the appropriation, colonization, and intensifying use of the biodiverse cultural landscapes long shaped and sustained by prior societies. Recognizing this deep cultural connection with biodiversity will therefore be essential to resolve the crisis.

Multiple studies confirm that ecosystems across most of the terrestrial biosphere, from 75 to 95% of its area, have now been reshaped to some degree by human societies (1 –3). With a few exceptions (e.g., refs. 4 –8), this global anthropogenic transformation of terrestrial nature has been described by natural scientists as mostly recent: the product of the industrial era (9 –13). This is partly because previous global reconstructions of early populations and land use systematically ignored these earlier transformations (1, 5, 14) and partly due to the conservation community’s focus on recent industrial changes (2, 3, 9, 15). There has also been a history of natural scientists and conservation practitioners interpreting terrestrial ecosystems as uninfluenced by long-sustained interactions with human societies, ignoring prior histories of land use, especially by Indigenous societies (16 –18). While this paradigm has increasingly been questioned with respect to long-term global changes in climate (19), fire regimes (20), and biodiversity (7, 8, 21), it continues to have real-world consequences, including failed policies of fire suppression, wildlife management, and ecological restoration, as well as the repression and removal of Indigenous peoples from traditional lands and waters and the erasure of their extensive knowledge of effective ecosystem management practices, thereby undermining their sovereignty over these ecosystems (17, 22 –24).Here, we examine contemporary global patterns of biodiversity and conservation in relation to the spatial history of human populations and land use over the past 12,000 y. Specifically, we use spatially explicit global datasets to visualize histories of human use in areas identified as biodiversity-rich and high-priority for conservation, including those specifically labeled as more “natural” or “wild,” and test the degree to which global patterns of land use and population at different times are associated statistically with contemporary global patterns of high biodiversity value and vertebrate species richness and threat within areas prioritized for conservation. Through this examination, we assess the early and sustained global significance of cultural landscapes as a basis for better understanding and conserving terrestrial nature.Anthropological, archaeological, and paleoecological evidence indicate that, at least since the start of the current interglacial interval 11,600 y ago, all human societies were interacting with biota and environments in ways that shaped evolutionary dynamics, ecosystems, and landscapes (25 –28). We use the term transformations to describe system-level changes in the social-ecological systems shaped by these interactions, including their initial formation by human inhabitation and the adoption of cultural practices leading to changes in ecosystem state, sensu 5, 27. While the focus is often on negative outcomes relating to these interactions, including extinctions of island endemics (29) and megafauna (21, 30, 31) with cascading ecological consequences (32), there is increasing evidence that human cultural practices can also produce sustained ecological benefits through practices that expand habitat for other species (33, 34), enhance plant diversity (17, 34 –37), increase hunting sustainability (38), provide important ecological functions like seed dispersal (39), and improve soil nutrient availability (40, 41).Hunter-gatherers, early farmers, and pastoralists often shared regional landscapes, which they shaped through a wide array of low-intensity subsistence practices, including hunting, transhumance, residential mobility, long- and short-fallow cultivation, polycropping, and tree-fallowing that created diverse, dynamic, and productive mosaics of lands and novel ecological communities in varying states of ecological succession and cultural modification (34, 37, 42). In many regions, these diverse cultural landscape mosaics were sustained for millennia (17, 24, 25, 27, 33, 34, 37, 43 –45), contrasting sharply with the more homogenous and continuously used landscapes of larger-scale agricultural societies employing annual tillage, irrigation, continuous grazing, and the extractive and colonial use of land, labor, and other resources to support elites (1, 5, 44). The emergence and spread of increasingly globalized and industrial societies only accelerated this trend toward today''s ever more intensively used and homogeneous cultural landscapes shaped by global supply chains, mechanization, chemical nutrients and pest control, leading to ecologically simplified habitats and biotic homogenization through species transported around the world intentionally and unintentionally (1, 44, 46).     

Chemokine CCL5 promotes robust optic nerve regeneration and mediates many of the effects of CNTF gene therapy

Ciliary neurotrophic factor (CNTF) is a leading therapeutic candidate for several ocular diseases and induces optic nerve regeneration in animal models. Paradoxically, however, although CNTF gene therapy promotes extensive regeneration, recombinant CNTF (rCNTF) has little effect. Because intraocular viral vectors induce inflammation, and because CNTF is an immune modulator, we investigated whether CNTF gene therapy acts indirectly through other immune mediators. The beneficial effects of CNTF gene therapy remained unchanged after deleting CNTF receptor alpha (CNTFRα) in retinal ganglion cells (RGCs), the projection neurons of the retina, but were diminished by depleting neutrophils or by genetically suppressing monocyte infiltration. CNTF gene therapy increased expression of C-C motif chemokine ligand 5 (CCL5) in immune cells and retinal glia, and recombinant CCL5 induced extensive axon regeneration. Conversely, CRISPR-mediated knockdown of the cognate receptor (CCR5) in RGCs or treating wild-type mice with a CCR5 antagonist repressed the effects of CNTF gene therapy. Thus, CCL5 is a previously unrecognized, potent activator of optic nerve regeneration and mediates many of the effects of CNTF gene therapy.

Like most pathways in the mature central nervous system (CNS), the optic nerve cannot regenerate once damaged due in part to cell-extrinsic suppressors of axon growth (1, 2) and the low intrinsic growth capacity of adult retinal ganglion cells (RGCs), the projection neurons of the eye (3–5). Consequently, traumatic or ischemic optic nerve injury or degenerative diseases such as glaucoma lead to irreversible visual losses. Experimentally, some degree of regeneration can be induced by intraocular inflammation or growth factors expressed by inflammatory cells (6–10), altering the cell-intrinsic growth potential of RGCs (3–5), enhancing physiological activity (11, 12), chelating free zinc (13, 14), and other manipulations (15–19). However, the extent of regeneration achieved to date remains modest, underlining the need for more effective therapies.Ciliary neurotrophic factor (CNTF) is a leading therapeutic candidate for glaucoma and other ocular diseases (20–23). Activation of the downstream signal transduction cascade requires CNTF to bind to CNTF receptor-α (CNTFRα) (24), which leads to recruitment of glycoprotein 130 (gp130) and leukemia inhibitory factor receptor-β (LIFRβ) to form a tripartite receptor complex (25). CNTFRα anchors to the plasma membrane through a glycosylphosphatidylinositol linkage (26) and can be released and become soluble through phospholipase C-mediated cleavage (27). CNTF has been reported to activate STAT3 phosphorylation in retinal neurons, including RGCs, and to promote survival, but it is unknown whether these effects are mediated by direct action of CNTF on RGCs via CNTFRα (28). Our previous studies showed that CNTF promotes axon outgrowth from neonate RGCs in culture (29) but fails to do so in cultured mature RGCs (8) or in vivo (6). Although some studies report that recombinant CNTF (rCNTF) can promote optic nerve regeneration (20, 30, 31), others find little or no effect unless SOCS3 (suppressor of cytokine signaling-3), an inhibitor of the Jak-STAT pathway, is deleted in RGCs (5, 6, 32). In contrast, multiple studies show that adeno-associated virus (AAV)-mediated expression of CNTF in RGCs induces strong regeneration (33–40). The basis for the discrepant effects of rCNTF and CNTF gene therapy is unknown but is of considerable interest in view of the many promising clinical and preclinical outcomes obtained with CNTF to date.Because intravitreal virus injections induce inflammation (41), we investigated the possibility that CNTF, a known immune modulator (42–44), might act by elevating expression of other immune-derived factors. We report here that the beneficial effects of CNTF gene therapy in fact require immune system activation and elevation of C-C motif chemokine ligand 5 (CCL5). Depletion of neutrophils, global knockout (KO) or RGC-selective deletion of the CCL5 receptor CCR5, or a CCR5 antagonist all suppress the effects of CNTF gene therapy, whereas recombinant CCL5 (rCCL5) promotes axon regeneration and increases RGC survival. These studies point to CCL5 as a potent monotherapy for optic nerve regeneration and to the possibility that other applications of CNTF and other forms of gene therapy might similarly act indirectly through other factors.     

Underpotential lithium plating on graphite anodes caused by temperature heterogeneity

Rechargeability and operational safety of commercial lithium (Li)-ion batteries demand further improvement. Plating of metallic Li on graphite anodes is a critical reason for Li-ion battery capacity decay and short circuit. It is generally believed that Li plating is caused by the slow kinetics of graphite intercalation, but in this paper, we demonstrate that thermodynamics also serves a crucial role. We show that a nonuniform temperature distribution within the battery can make local plating of Li above 0 V vs. Li⁰/Li⁺ (room temperature) thermodynamically favorable. This phenomenon is caused by temperature-dependent shifts of the equilibrium potential of Li⁰/Li⁺. Supported by simulation results, we confirm the likelihood of this failure mechanism during commercial Li-ion battery operation, including both slow and fast charging conditions. This work furthers the understanding of nonuniform Li plating and will inspire future studies to prolong the cycling lifetime of Li-ion batteries.

Lithium (Li)-ion batteries with graphite anodes and Li metal oxide cathodes are the dominant commercial battery chemistry for electric vehicles (EVs) (1). However, their cycle lifetime and operational stability still demand further improvements (2–5). During long-term cycling, Li-ion batteries undergo irreversible capacity decay due to decreased utilization of anode/cathode active materials, metallic Li plating, electrolyte dry-out, impedance build-up, or excessive heat generation (6–9). Some of these issues also lead to battery shorting and thermal runaway (10, 11). To enable mass adoption of EVs, increasing efforts have been made to realize the fast charging of Li-ion batteries (12). Under this condition, all of the detrimental factors mentioned above are aggravated (6, 7, 13), further compromising the battery cycling life and safety. As a result, a clear understanding of the failure mechanisms of Li-ion batteries is crucial for their future development.Plating of metallic Li on graphite anodes is a major cause of the capacity decay of Li-ion batteries (6, 7, 12, 14–17). Significant amounts of solid electrolyte interphase (SEI) and dead Li form and remain inactive, leading to an accelerated loss of Li inventory. It is generally believed that the slow kinetics of Li ion intercalation into graphite causes metallic Li plating (14). Three-electrode measurements (18–25) showed that the potential of graphite anodes shifted negatively under increased charging rates and finally dropped below 0 V vs. Li⁰/Li⁺, reaching Li-plating conditions. However, Li-plating phenomenon on graphite anodes is still not fully understood. Firstly, the actual onset potential of Li plating is still unclear, which is not necessarily below 0 V vs. Li⁰/Li⁺ (18). Furthermore, few studies explained why Li plated on graphite in spatially inhomogeneous patterns (7, 14, 17). Most importantly, in some reports, Li plates even under a moderate charging rate below 1.5 C (6, 7). Under these conditions, three-electrode measurements indicate that the anode potential does not drop below 0 V vs. Li⁰/Li⁺ (18). Kinetic arguments alone are not sufficient to resolve these problems, so we hypothesize that previously neglected thermodynamic factors may also play crucial roles in Li plating.It is well-known that the equilibrium electrode potential of a redox reaction shifts with temperature (26–35). Exothermic reactions and joule heating during cycling raise the temperature of batteries (10), which can also build up an internal temperature gradient. Simulations (7, 36–42) and experimental studies (41, 43–49) showed intensified heating under increased cycling rates, and temperature differences of 2 K to nearly 30 K within the batteries (10). This spatial variation in temperature leads to a heterogeneous distribution of the equilibrium potential for both Li plating and graphite intercalation on the anode, which could make Li plating thermodynamically favorable at certain locations.In this paper, we discover that temperature heterogeneities within Li-ion batteries can cause Li plating by shifting its equilibrium electrode potential. We first introduce a method to quantify the temperature dependence of the equilibrium potential for both Li plating and graphite intercalation. Then, we correlate the shift of the equilibrium potential to Li plating using a Li-graphite coin cell with an intentionally created heterogeneous temperature distribution and explain the observation with thermal and electrochemical simulations. Finally, the effects under fast charging conditions are examined. The data explicitly show that metallic Li can plate above 0 V vs. Li⁰/Li⁺ (room temperature) on a graphite anode. The temperature dependence of the equilibrium potential likely participates in the capacity decay of commercial Li-ion batteries, which can be increasingly severe during fast charging conditions. This research brings insights into a key failure mechanism of Li-ion batteries, highlights the importance of maintaining homogeneous temperature within batteries, and will inspire future development of Li-ion batteries with improved safety and cycle lifetime.     

An isolated water droplet in the aqueous solution of a supramolecular tetrahedral cage

Water under nanoconfinement at ambient conditions has exhibited low-dimensional ice formation and liquid–solid phase transitions, but with structural and dynamical signatures that map onto known regions of water’s phase diagram. Using terahertz (THz) absorption spectroscopy and ab initio molecular dynamics, we have investigated the ambient water confined in a supramolecular tetrahedral assembly, and determined that a dynamically distinct network of 9 ± 1 water molecules is present within the nanocavity of the host. The low-frequency absorption spectrum and theoretical analysis of the water in the Ga₄L₆¹²⁻ host demonstrate that the structure and dynamics of the encapsulated droplet is distinct from any known phase of water. A further inference is that the release of the highly unusual encapsulated water droplet creates a strong thermodynamic driver for the high-affinity binding of guests in aqueous solution for the Ga₄L₆¹²⁻ supramolecular construct.

Supramolecular capsules create internal cavities that are thought to act like enzyme active sites (1). As aqueous enzymes provide inspiration for the design of supramolecular catalysts, one of the goals of supramolecular chemistry is the creation of synthetic “receptors” that have both a high affinity and a high selectivity for the binding of guests in water (2, 3). The Ga₄L₆¹²⁻ tetrahedral assembly formulated by Raymond and coworkers represents an excellent example of a water-soluble supramolecular cage that has provided host interactions that promotes guest encapsulation. Using steric interactions and electrostatic charge to chemically position the substrate while shielding the reaction from solvent, this host has been shown to provide enhanced reaction rates that approach the performance of natural biocatalysts (4–10). Moreover, aqueous solvation of the substrate, host, and encapsulated solvent also play an important role in the whole catalytic cycle. In particular, the driving forces that release water from the nanocage host to favor the direct binding with the substrate is thought to be a critical factor in successful catalysis, but is challenging to probe directly (7, 8, 11–14).In both natural and artificial nanometer-sized environments, confined water displays uniquely modified structure and dynamics with respect to the bulk liquid (15–18). Recently, these modified properties were also found to have significant implications for the mechanism and energetics of reactions taking place in confined water with respect to those observed in bulk aqueous solution (19–21). In a pioneering study on supramolecular assemblies, Cram and collaborators (22) concluded that the interior of those cages is a “new and unique phase of matter” for the incarcerated guests. In more recent studies, it was postulated that, similar to graphitic and zeolite nanopores (23, 24), confined water within supramolecular host cavities is organized in stable small clusters [(H₂O)_n, with n = 8 to 19] that are different from gas phase water clusters (25). In these studies, the hydrogen-bonded water clusters were reported to be mostly ice- or clathrate-like by X-ray and neutron diffraction in the solid state at both ambient and cryogenic temperatures (26–32). However, to the best of our knowledge, such investigations have not characterized the Ga₄L₆¹²⁻ supramolecular tetrahedral assembly in the liquid state near room temperature and pressure, where the [Ga₄L₆]¹²⁻ capsule can perform catalytic reactions (6, 8, 9).Here, we use terahertz (THz) absorption spectroscopy and ab initio molecular dynamics (AIMD) to characterize low-frequency vibrations and structural organization of water in the nanoconfined environment. THz is ideally suited to probe the intermolecular collective dynamics of the water hydrogen bond (HB) network with extremely high sensitivity, as illustrated for different phases of water (33–38), and for aqueous solutions of salts, osmolytes, alcohols, and amino acids (36, 39–42). The THz spectra of the water inside the nanocage has been quantitatively reproduced with AIMD, allowing us to confidently characterize the water network in the cage in order to provide a more complete dynamical, structural, and thermodynamic picture. We have determined that the spectroscopic signature of the confined water in the nanocage is a dynamically arrested state whose structure bears none of the features of water at any alternate thermodynamic state point such as pressurized liquid or ice. Our experimental and theoretical study provides insight into the role played by encapsulated water in supramolecular catalysis, creating a low entropy and low enthalpy water droplet readily displaced by a catalytic substrate.     

Cholinergic suppression of hippocampal sharp-wave ripples impairs working memory

Learning and memory are assumed to be supported by mechanisms that involve cholinergic transmission and hippocampal theta. Using G protein–coupled receptor-activation–based acetylcholine sensor (GRAB_ACh3.0) with a fiber-photometric fluorescence readout in mice, we found that cholinergic signaling in the hippocampus increased in parallel with theta/gamma power during walking and REM sleep, while ACh3.0 signal reached a minimum during hippocampal sharp-wave ripples (SPW-R). Unexpectedly, memory performance was impaired in a hippocampus-dependent spontaneous alternation task by selective optogenetic stimulation of medial septal cholinergic neurons when the stimulation was applied in the delay area but not in the central (choice) arm of the maze. Parallel with the decreased performance, optogenetic stimulation decreased the incidence of SPW-Rs. These findings suggest that septo–hippocampal interactions play a task-phase–dependent dual role in the maintenance of memory performance, including not only theta mechanisms but also SPW-Rs.

The neurotransmitter acetylcholine is thought to be critical for hippocampus-dependent declarative memories (1, 2). Reduction in cholinergic neurotransmission, either in Alzheimer’s disease or in experiments with cholinergic antagonists, such as scopolamine, impairs memory function (3–8). Acetylcholine may bring about its beneficial effects on memory encoding by enhancing theta rhythm oscillations, decreasing recurrent excitation, and increasing synaptic plasticity (9–11). Conversely, drugs which activate cholinergic receptors enhance learning and, therefore, are a neuropharmacological target for the treatment of memory deficits in Alzheimer’s disease (5, 12, 13).The contribution of cholinergic mechanisms in the acquisition of long-term memories and the role of the hippocampal–entorhinal–cortical interactions are well supported by experimental data (5, 12, 13). In addition, working memory or “short-term” memory is also supported by the hippocampal–entorhinal–prefrontal cortex (14–16). Working memory in humans is postulated to be a conscious process to “keep things in mind” transiently (16). In rodents, matching to sample task, spontaneous alternation between reward locations, and the radial maze task have been suggested to function as a homolog of working memory [“working memory like” (17)].Cholinergic activity is a critical requirement for working memory (18, 19) and for sustaining theta oscillations (10, 20–22). In support of this contention, theta–gamma coupling and gamma power are significantly higher in the choice arm of the maze, compared with those in the side arms where working memory is no longer needed for correct performance (23–26). It has long been hypothesized that working memory is maintained by persistent firing of neurons, which keep the presented items in a transient store in the prefrontal cortex and hippocampal–entorhinal system (27–31), although the exact mechanisms are debated (32–37). An alternative hypothesis holds that items of working memory are stored in theta-nested gamma cycles (38). Common in these models of working memory is the need for an active, cholinergic system–dependent mechanism (39–41). However, in spontaneous alternation tasks, the animals are not moving continuously during the delay, and theta oscillations are not sustained either. During the immobility epochs, theta is replaced by intermittent sharp-wave ripples (SPW-R), yet memory performance does not deteriorate. On the contrary, artificial blockade of SPW-Rs can impair memory performance (42, 43), and prolongation of SPW-Rs improves performance (44). Under the cholinergic hypothesis of working memory, such a result is unexpected.To address the relationship between cholinergic/theta versus SPW-R mechanism in spontaneous alternation, we used a G protein–coupled receptor-activation–based acetylcholine sensor (GRAB_ACh3.0) (45) to monitor acetylcholine (ACh) activity during memory performance in mice. In addition, we optogenetically enhanced cholinergic tone, which suppresses SPW-Rs by a different mechanism than electrically or optogenetically induced silencing of neurons in the hippocampus (43, 44). We show that cholinergic signaling in the hippocampus increases in parallel with theta power/score during walking and rapid eye movement (REM) sleep and reaches a transient minimum during SPW-Rs. Selective optogenetic stimulation of medial septal cholinergic neurons decreased the incidence of SPW-Rs during non-REM sleep (46–48), as well as during the delay epoch of a working memory task and impaired memory performance. These findings demonstrate that memory performance is supported by complementary theta and SPW-R mechanisms.     

CAP1 binds and activates adenylyl cyclase in mammalian cells

CAP1 (Cyclase-Associated Protein 1) is highly conserved in evolution. Originally identified in yeast as a bifunctional protein involved in Ras-adenylyl cyclase and F-actin dynamics regulation, the adenylyl cyclase component seems to be lost in mammalian cells. Prompted by our recent identification of the Ras-like small GTPase Rap1 as a GTP-independent but geranylgeranyl-specific partner for CAP1, we hypothesized that CAP1-Rap1, similar to CAP-Ras-cyclase in yeast, might play a critical role in cAMP dynamics in mammalian cells. In this study, we report that CAP1 binds and activates mammalian adenylyl cyclase in vitro, modulates cAMP in live cells in a Rap1-dependent manner, and affects cAMP-dependent proliferation. Utilizing deletion and mutagenesis approaches, we mapped the interaction of CAP1-cyclase with CAP’s N-terminal domain involving critical leucine residues in the conserved RLE motifs and adenylyl cyclase’s conserved catalytic loops (e.g., C1a and/or C2a). When combined with a FRET-based cAMP sensor, CAP1 overexpression–knockdown strategies, and the use of constitutively active and negative regulators of Rap1, our studies highlight a critical role for CAP1-Rap1 in adenylyl cyclase regulation in live cells. Similarly, we show that CAP1 modulation significantly affected cAMP-mediated proliferation in an RLE motif–dependent manner. The combined study indicates that CAP1-cyclase-Rap1 represents a regulatory unit in cAMP dynamics and biology. Since Rap1 is an established downstream effector of cAMP, we advance the hypothesis that CAP1-cyclase-Rap1 represents a positive feedback loop that might be involved in cAMP microdomain establishment and localized signaling.

CAP/srv2 was originally identified in yeast biochemically as an adenylyl cyclase–associated protein (1) and genetically as a suppressor of the hyperactive Ras2-V19 allele (2). CAP/srv2-deficient yeast cells are unresponsive to active Ras2, and adenylyl cyclase activity is no longer regulated by Ras2 in these cells (1, 2), indicating the involvement of CAP/srv2 in the Ras/cyclase pathway. However, some mutant CAP/srv2 alleles presented phenotypes not observed in strains with impaired Ras/cyclase pathway (1–3), indicating the existence of Ras/cyclase-independent functions downstream of CAP/srv2. These two phenotype groups, that is, Ras/cyclase-linked and Ras/cyclase-independent, could be suppressed by expression of an N-terminal half and a C-terminal half of CAP/srv2, respectively (4). Subsequent studies showed that the C-terminal half of CAP/srv2 was able to bind monomeric G-actin (5–8) and other actin regulators establishing a role in F-actin dynamics (9–16). Thus, CAP/srv2 is a bifunctional protein with an N-terminal domain involved in Ras/cyclase regulation and a C-terminal domain involved with F-actin dynamics regulation (16–18).CAP1 is structurally conserved in all eukaryotes (18–22); however, their functions are not. Expression of the closely related Schizosaccharomyces pombe cap or mammalian CAP1 in yeast can only suppress the phenotypes associated with deletion of CAP/srv2’s C-terminal but not its N-terminal domain (19, 20, 22), suggesting that only the F-actin dynamics function was conserved while the Ras/cyclase regulation diverged early on in evolution (16–18). CAP/srv2’s N-terminal 1 to 36 domain was sufficient for cyclase binding in yeast involving a conserved RLE motif with predicted coiled-coil folding (23). Interestingly, this domain is also involved in CAP1 oligomerization both in yeast and mammalian cells (24–26), where it purifies as a high-molecular complex of ∼600 kDa consistent with a 1:1 stoichiometric CAP1-actin hexameric organization (12, 25, 27, 28). Importantly, removal of this domain disrupted CAP1 oligomerization, reduced F-actin turnover in vitro and caused defects in cell growth, cell morphology, and F-actin organization in vivo (24, 29). However, whether the conserved RLE motif in mammalian CAP1 interacts with other coiled-coil–containing proteins is for the moment unknown.Ras2-mediated cyclase regulation in yeast requires its farnesylation (30–32). However, the lipid target involved was not identified in the original studies. We have recently shown that mammalian CAP1 interacts with the small GTPase Rap1. The interaction involves Rap1’s C-terminal hypervariable region (HVR) and its lipid moiety in a geranylgeranyl-specific manner; that is, neither the closely related Ras1 nor engineered farnesylated Rap1 interacted with CAP1 (33). Thus, we raised the question whether CAP1-Rap1, similar to CAP/srv2-Ras2 in yeast, plays a role in cAMP dynamics in mammalian cells.In this study, we report that CAP1 binds to and activates mammalian adenylyl cyclase in vitro. The interaction involves CAP1’s conserved RLE motifs and cyclase’s conserved catalytic subdomains (e.g., C1a and/or C2a). Most importantly, we show that both CAP1 and Rap1 modulate cAMP dynamics in live cells and are critical players in cAMP-dependent proliferation.     

From the Cover: A Middle Eocene lowland humid subtropical “Shangri-La” ecosystem in central Tibet

Tibet’s ancient topography and its role in climatic and biotic evolution remain speculative due to a paucity of quantitative surface-height measurements through time and space, and sparse fossil records. However, newly discovered fossils from a present elevation of ∼4,850 m in central Tibet improve substantially our knowledge of the ancient Tibetan environment. The 70 plant fossil taxa so far recovered include the first occurrences of several modern Asian lineages and represent a Middle Eocene (∼47 Mya) humid subtropical ecosystem. The fossils not only record the diverse composition of the ancient Tibetan biota, but also allow us to constrain the Middle Eocene land surface height in central Tibet to ∼1,500 ± 900 m, and quantify the prevailing thermal and hydrological regime. This “Shangri-La”–like ecosystem experienced monsoon seasonality with a mean annual temperature of ∼19 °C, and frosts were rare. It contained few Gondwanan taxa, yet was compositionally similar to contemporaneous floras in both North America and Europe. Our discovery quantifies a key part of Tibetan Paleogene topography and climate, and highlights the importance of Tibet in regard to the origin of modern Asian plant species and the evolution of global biodiversity.

The Tibetan Plateau, once thought of as entirely the product of the India–Eurasia collision, is known to have had significant complex relief before the arrival of India early in the Paleogene (1–3). This large region, spanning ∼2.5 million km², is an amalgam of tectonic terranes that impacted Asia long before India’s arrival (4, 5), with each accretion contributing orographic heterogeneity that likely impacted climate in complex ways. During the Paleogene, the Tibetan landscape comprised a high (>4 km) Gangdese mountain range along the southern margin of the Lhasa terrane (2), against which the Himalaya would later rise (6), and a Tanghula upland on the more northerly Qiangtang terrane (7). Separating the Lhasa and Qiangtang blocks is the east–west trending Banggong-Nujiang Suture (BNS), which today hosts several sedimentary basins (e.g., Bangor, Nyima, and Lunpola) where >4 km of Cenozoic sediments have accumulated (8). Although these sediments record the climatic and biotic evolution of central Tibet, their remoteness means fossil collections have been hitherto limited. Recently, we discovered a highly diverse fossil assemblage in the Bangor Basin. These fossils characterize a luxuriant seasonally wet and warm Shangri-La forest that once occupied a deep central Tibetan valley along the BNS, and provide a unique opportunity for understanding the evolutionary history of Asian biodiversity, as well as for quantifying the paleoenvironment of central Tibet.^*Details of the topographic evolution of Tibet are still unclear despite decades of investigation (4, 5). Isotopic compositions of carbonates recovered from sediments in some parts of central Tibet have been interpreted in terms of high (>4 km) Paleogene elevations and aridity (9, 10), but those same successions have yielded isolated mammal (11), fish (12), plant (13–18), and biomarker remains (19) more indicative of a low (≤3-km) humid environment, but how low is poorly quantified. Given the complex assembly of Tibet, it is difficult to explain how a plateau might have formed so early and then remained as a surface of low relief during subsequent compression from India (20). Recent evidence from a climate model-mediated interpretation of palm fossils constrains the BNS elevation to below 2.3 km in the Late Paleogene (16), but more precise paleoelevation estimates are required. Further fossil discoveries, especially from earlier in the BNS sedimentary records, would document better the evolution of the Tibetan biota, as well as informing our understanding of the elevation and climate in an area that now occupies the center of the Tibetan Plateau.Our work shows that the BNS hosted a diverse subtropical ecosystem at ∼47 Ma, and this means the area must have been both low and humid. The diversity of the fossil flora allows us to 1) document floristic links to other parts of the Northern Hemisphere, 2) characterize the prevailing paleoclimate, and 3) quantify the elevation at which the vegetation grew. We propose that the “high and dry” central Tibet inferred from some isotope paleoaltimetry (9, 10) reflects a “phantom” elevated paleosurface (20) because fractionation over the bounding mountains allowed only isotopically light moist air to enter the valley, giving a false indication of a high elevation (21).     

From the Cover: Exploitative leaders incite intergroup warfare in a social mammal

Collective conflicts among humans are widespread, although often highly destructive. A classic explanation for the prevalence of such warfare in some human societies is leadership by self-serving individuals that reap the benefits of conflict while other members of society pay the costs. Here, we show that leadership of this kind can also explain the evolution of collective violence in certain animal societies. We first extend the classic hawk−dove model of the evolution of animal aggression to consider cases in which a subset of individuals within each group may initiate fights in which all group members become involved. We show that leadership of this kind, when combined with inequalities in the payoffs of fighting, can lead to the evolution of severe intergroup aggression, with negative consequences for population mean fitness. We test our model using long-term data from wild banded mongooses, a species characterized by frequent intergroup conflicts that have very different fitness consequences for male and female group members. The data show that aggressive encounters between groups are initiated by females, who gain fitness benefits from mating with extragroup males in the midst of battle, whereas the costs of fighting are borne chiefly by males. In line with the model predictions, the result is unusually severe levels of intergroup violence. Our findings suggest that the decoupling of leaders from the costs that they incite amplifies the destructive nature of intergroup conflict.

Humans are capable of astonishing feats of altruism and cooperation (1–3), but, at the same time, of violent and destructive conflicts (4–8). A key factor contributing to the latter may be that wars are often waged at the behest of leaders who do not share fully in the immediate risks of conflict, and stand to gain benefits in terms of resources and status that are not enjoyed by the majority of combatants (4, 9–11). Could such “warmongering” be a feature of animal conflicts too? Only recently have models of animal aggression begun to explore the impact of inequalities among combatants in collective conflict (12, 13), and the usual assumption of existing theory is that individuals who initiate intergroup conflicts also contribute most to group conflict effort and thereby confer fitness benefits on the rest of their group (a positive or “heroic” model of leadership) (14–17). Here, we explore the more sinister possibility that those who initiate conflict may actually harm their fellows in pursuit of their own interests by exposing them to the risks of conflict while contributing little to fighting themselves (a negative or “exploitative” model of leadership).     

Conditions and extent of volatile loss from the Moon during formation of the Procellarum basin

Rocks from the lunar interior are depleted in moderately volatile elements (MVEs) compared to terrestrial rocks. Most MVEs are also enriched in their heavier isotopes compared to those in terrestrial rocks. Such elemental depletion and heavy isotope enrichments have been attributed to liquid–vapor exchange and vapor loss from the protolunar disk, incomplete accretion of MVEs during condensation of the Moon, and degassing of MVEs during lunar magma ocean crystallization. New Monte Carlo simulation results suggest that the lunar MVE depletion is consistent with evaporative loss at 1,670 ± 129 K and an oxygen fugacity +2.3 ± 2.1 log units above the fayalite-magnetite-quartz buffer. Here, we propose that these chemical and isotopic features could have resulted from the formation of the putative Procellarum basin early in the Moon’s history, during which nearside magma ocean melts would have been exposed at the surface, allowing equilibration with any primitive atmosphere together with MVE loss and isotopic fractionation.

Returned samples of basaltic rocks from the Moon provided evidence decades ago that the Moon is depleted in volatile elements compared to the Earth (1), with lunar basalt abundances of moderately volatile elements (MVEs) being ∼1/5 that of terrestrial basalt abundances for alkali elements and ∼1/40 for other MVE, such as Zn, Ag, In, and Cd (2). The theme of lunar volatiles thus seemed settled. Yet, the unambiguous detection in 2008 of lunar indigenous hydrogen and other volatile elements, such as F, Cl, and S in pyroclastic glasses (3), heralded a new era of research into lunar volatiles, overturning the decades-old paradigm of a bone-dry Moon (e.g., refs. 4 and 5). Here, we define volatile elements as those with 50% condensation temperatures below these of the major rock-forming elements Fe, Mg, and Si (6). This paradigm shift was accompanied by new measurements of volatile stable isotope compositions (e.g., H, C, N, Cl, K, Cr, Cu, Zn, Ga, Rb, and Sn) in a wealth of bulk lunar samples (7–18) and in the mineral phases and melt inclusions they host (19–28). These studies have shown that the stable isotope compositions of most MVEs (e.g., K, Zn, Ga, and Rb) are enriched in their heavier isotopes with respect to the bulk silicate Earth (BSE) (9, 11, 13–15, 17). Such heavy isotope enrichment is associated with elemental depletion, which has been variously attributed to liquid–vapor exchange and vapor loss from the protolunar disk (17, 18), incomplete accretion of MVEs during condensation of the Moon (13, 29, 30), and degassing of these elements during lunar magma ocean crystallization (9, 11, 14, 15, 25, 31). Almost all these hypotheses have typically assumed that the MVE depletions and associated MVE isotope fractionations are relevant to the whole Moon. However, our lunar sample collections are biased, as all Apollo and Luna returned samples come from the lunar nearside from within or around the anomalous Procellarum KREEP Terrane (PKT) region (e.g., ref. 32), where KREEP stands for enriched in K, REEs, and P. Barnes et al. (26) proposed that the heavy Cl isotope signature measured in KREEP-rich Apollo samples resulted from metal-chloride degassing from late-stage lunar magma ocean melts in response to a large crust-breaching impact event, spatially associated with the PKT region, which facilitated exposure of these late-stage melts to the lunar surface. Here, we further investigate whether a localized impact event could have been responsible for the general MVE depletion and heavy MVE isotope enrichment measured in lunar samples.     

Tropospheric carbonyl sulfide mass balance based on direct measurements of sulfur isotopes

Robust estimates for the rates and trends in terrestrial gross primary production (GPP; plant CO₂ uptake) are needed. Carbonyl sulfide (COS) is the major long-lived sulfur-bearing gas in the atmosphere and a promising proxy for GPP. Large uncertainties in estimating the relative magnitude of the COS sources and sinks limit this approach. Sulfur isotope measurements (³⁴S/³²S; δ³⁴S) have been suggested as a useful tool to constrain COS sources. Yet such measurements are currently scarce for the atmosphere and absent for the marine source and the plant sink, which are two main fluxes. Here we present sulfur isotopes measurements of marine and atmospheric COS, and of plant-uptake fractionation experiments. These measurements resulted in a complete data-based tropospheric COS isotopic mass balance, which allows improved partition of the sources. We found an isotopic (δ³⁴S ± SE) value of 13.9 ± 0.1‰ for the troposphere, with an isotopic seasonal cycle driven by plant uptake. This seasonality agrees with a fractionation of −1.9 ± 0.3‰ which we measured in plant-chamber experiments. Air samples with strong anthropogenic influence indicated an anthropogenic COS isotopic value of 8 ± 1‰. Samples of seawater-equilibrated-air indicate that the marine COS source has an isotopic value of 14.7 ± 1‰. Using our data-based mass balance, we constrained the relative contribution of the two main tropospheric COS sources resulting in 40 ± 17% for the anthropogenic source and 60 ± 20% for the oceanic source. This constraint is important for a better understanding of the global COS budget and its improved use for GPP determination.

The Earth system is going through rapid changes as the climate warms and CO₂ level rises. This rise in CO₂ is mitigated by plant uptake; hence, it is important to estimate global and regional photosynthesis rates and trends (1). Yet, robust tools for investigating these processes at a large scale are scarce (2). Recent studies suggest that carbonyl sulfide (COS) could provide an improved constraint on terrestrial photosynthesis (gross primary production, GPP) (2–12). COS is the major long-lived sulfur-bearing gas in the atmosphere and the main supplier of sulfur to the stratospheric sulfate aerosol layer (13), which exerts a cooling effect on the Earth’s surface and regulates stratospheric ozone chemistry (14).During terrestrial photosynthesis, COS diffuses into leaf stomata and is consumed by photosynthetic enzymes in a similar manner to CO₂ (3–5). Contrary to CO₂, COS undergoes rapid and irreversible hydrolysis mainly by the enzyme carbonic-anhydrase (6, 7). Thus, COS can be used as a proxy for the one-way flux of CO₂ removal from the atmosphere by terrestrial photosynthesis (2, 8–11). However, the large uncertainties in estimating the COS sources weaken this approach (10–12, 15). Tropospheric COS has two main sources: the oceans and anthropogenic emissions, and one main sink–terrestrial plant uptake (8, 10–13). Smaller sources include biomass burning, soil emissions, wetlands, volcanoes, and smaller sinks include OH destruction, stratospheric destruction, and soil uptake (12). The largest source of COS to the atmosphere is the ocean, both as direct COS emission, and as indirect carbon disulfide (CS₂) and dimethylsulfide (DMS) emissions that are rapidly oxidized to COS (10, 16–20). Recent studies suggest oceanic COS emissions are in the range of 200–4,000 GgS/y (19–22). The second major COS source is the anthropogenic source, which is dominated by indirect emissions derived from CS₂ oxidation, mainly from the use of CS₂ as an industrial solvent. Direct emissions of COS are mainly derived from coal and fuel combustion (17, 23, 24). Recent studies suggest that anthropogenic emissions are in the range of 150–585 GgS/y (23, 24). The terrestrial plant uptake is estimated to be in the range of 400–1,360 GgS/y (11). Measurements of sulfur isotope ratios (δ³⁴S) in COS may be used to track COS sources and thus reduce the uncertainties in their flux estimations (15, 25–27). However, the isotopic mass balance approach works best if the COS end members are directly measured and have a significantly different isotopic signature. Previous δ³⁴S measurements of atmospheric COS are scarce and there have been no direct measurements of two important components: the δ³⁴S of oceanic COS emissions, and the isotopic fractionation of COS during plant uptake (15, 25–27). In contrast to previous studies that used assessments for these isotopic values, our aim was to directly measure the isotopic values of these missing components, and to determine the tropospheric COS δ³⁴S variability over space and time.