Local Structural Environment Research Articles

Dispersal traits as benthic invertebrate assemblage drivers in a neotropical large river

Metacommunity theory is a mechanistic framework that explains the interdependence of local factors and regional processes as community drivers. Recent evidence suggests that dispersal mode is a key trait that potentially affects metacommunity dynamics. We analyzed the distribution patterns of benthic macroinvertebrates with different dispersal modes in the Middle Paraná, a neotropical large river. We assessed the relative importance of local environmental conditions and regional spatial structure as assemblage drivers. Aquatic and aerial dispersers presented Clementsian and Gleasonian structures, respectively. For both groups, local environmental conditions influenced community assembly, and spatial structure (overland distances) also affected the distribution of aerial dispersers. Our study highlights that the role of spatial structure as a driver of benthic metacommunities depends on species' dispersal modes. Aerial dispersers responded to regional spatial variables and it is likely that these organisms are also influenced by mass effects. Our results are consistent with current ideas of metacommunity dynamics in large rivers, where dispersal is not considered to limit the distribution of benthic organisms.

(My Microbiome) Would Walk 10,000miles: Maintenance and Turnover of Microbial Communities in Introduced Dung Beetles.

Host-associated microbes facilitate diverse biotic and abiotic interactions between hosts and their environments. Experimental alterations of host-associated microbial communities frequently decrease host fitness, yet much less is known about if and how host-microbiome interactions are altered by natural perturbations, such as introduction events. Here, we begin to assess this question in Onthophagus dung beetles, a species-rich and geographically widely distributed genus whose members rely on vertically transmitted microbiota to support normal development. Specifically, we investigated to what extent microbiome community membership shifts during host introduction events and the relative significance of ancestral associations and novel environmental conditions in the structuring of microbial communities of introduced host species. Our results demonstrate that both evolutionary history and local environmental forces structure the microbial communities of these animals, but that their relative importance is shaped by the specific circumstances that characterize individual introduction events. Furthermore, we identify microbial taxa such as Dysgonomonas that may constitute members of the core Onthophagus microbiome regardless of host population or species, but also Wolbachia which associates with Onthophagus beetles in a species or even population-specific manner. We discuss the implications of our results for our understanding of the evolutionary ecology of symbiosis in dung beetles and beyond.

Effect of V2O5 on crystallization tendency and chemical durability of Mo-bearing aluminoborosilicate glass

AbstactThe effect of V2O5 addition on molybdates crystallization tendency, glass structure and chemical durability of aluminoborosilicate glass belonging to SiO2-B2O3-CaO-Na2O-Al2O3-MoO3 system has been studied. The results confirm that V2O5 addition can effectively suppress the crystallization tendency of powellite and enhance the molybdenum solubility in the glass. The MoO3 solubility limit is found to be 2.8 mol% in the V2O5-containing aluminoborosilicate glass. Raman results reveal that V2O5 addition seems to modify the local structural environment of isolated MoO4 units and increase their chemical disorder in the glass, which is favored for molybdenum incorporation in the glass. The molar volume and glass transition temperature of samples are found to depend on V2O5 content. Product consistency test (PCT) results show that the normalized leaching rates of the V2O5-containing aluminoborosilicate glass maintain at a fairly low level compared with standard borosilicate glassy waste form.

Climate and local environment structure asynchrony and the stability of primary production in grasslands

AbstractAimClimate variability threatens to destabilize production in many ecosystems. Asynchronous species dynamics may buffer against such variability when a decrease in performance by some species is offset by an increase in performance of others. However, high climatic variability can eliminate species through stochastic extinctions or cause similar stress responses among species that reduce buffering. Local conditions, such as soil nutrients, can also alter production stability directly or by influencing asynchrony. We test these hypotheses using a globally distributed sampling experiment.LocationGrasslands in North America, Europe and Australia.Time periodAnnual surveys over 5 year intervals occurring between 2007 and 2014.Major taxa studiedHerbaceous plants.MethodsWe sampled annually the per species cover and aboveground community biomass [net primary productivity (NPP)], plus soil chemical properties, in 29 grasslands. We tested how soil conditions, combined with variability in precipitation and temperature, affect species richness, asynchrony and temporal stability of primary productivity. We used bivariate relationships and structural equation modelling to examine proximate and ultimate relationships.ResultsClimate variability strongly predicted asynchrony, whereas NPP stability was more related to soil conditions. Species richness was structured by both climate variability and soils and, in turn, increased asynchrony. Variability in temperature and precipitation caused a unimodal asynchrony response, with asynchrony being lowest at low and high climate variability. Climate impacted stability indirectly, through its effect on asynchrony, with stability increasing at higher asynchrony owing to lower inter‐annual variability in NPP. Soil conditions had no detectable effect on asynchrony but increased stability by increasing the mean NPP, especially when soil organic matter was high.Main conclusionsWe found globally consistent evidence that climate modulates species asynchrony but that the direct effect on stability is low relative to local soil conditions. Nonetheless, our observed unimodal responses to variability in temperature and precipitation suggest asynchrony thresholds, beyond which there are detectable destabilizing impacts of climate on primary productivity.

Do local environmental factors structure the trophic niche of the splash tetra, Copella arnoldi? A test in an Amazonian stream system

ABSTRACT Environmental variation affects the availability of spatial and trophic resources in Amazonian streams and may be important factors structuring the diet of fishes. We analyzed the diet composition and trophic niche breadth of the lebiasinid splash tetra, Copella arnoldi, aiming to evaluate how environmental variation in Amazonian streams affects the species’ trophic niche. Fish were captured and environmental factors were recorded in 20 streams in the Caxiuanã National Forest, in the eastern Amazon, in November 2010. We made a semi-quantitative analysis of stomach contents of 200 individuals. Copella arnoldi exhibited an omnivorous diet composed mainly of detritus and allochthonous invertebrates. Environmental variation (stream width, stream depth, canopy cover and flow) did not affect the diet composition or trophic niche breadth of the species, possibly due to the regional integrity of the forest within the boundaries of the protected area. Riparian cover probably minimizes the effect of the small-scale variations in food resources, thus leading to a locally homogeneous diet composition in the splash tetra C. arnoldi.

Does Greater Transparency Discipline the Loan Loss Provisioning of Privately Held Banks?

We investigate the relationship between the transparency of loan loss provision disclosures and the provisioning practices of privately held banks. We study a unique change in disclosure regulation under German banking law which introduces mandatory disclosures of loan loss provisions. Using proprietary data provided by the national supervisor, we are able to observe provisioning practices before and after disclosure becomes mandatory. Our findings suggest that bank managers use loan loss provisions to a lesser extent for income smoothing once they are required to disclose their accounting choice. At the same time, provisions become more informative about future loan losses. The change comes in the absence of capital market pressure and highlights the role of depositors and public pressure in the monitoring of bank managers. We exploit cross-sectional variation and show that the change is associated with differences in the local information environment and banks' funding structure.

Neural-Network-Based Path Collective Variables for Enhanced Sampling of Phase Transformations.

The investigation of the microscopic processes underlying structural phase transformations in solids is extremely challenging for both simulation and experiment. Atomistic simulations of solid-solid phase transitions require extensive sampling of the corresponding high-dimensional and often rugged energy landscape. Here, we propose a rigorous construction of a 1D path collective variable that is used in combination with enhanced sampling techniques for efficient exploration of the transformation mechanisms. The path collective variable is defined in a space spanned by global classifiers that are derived from local structural units. A reliable identification of the local structural environments is achieved by employing a neural-network-based classification scheme. The proposed path collective variable is generally applicable and enables the investigation of both transformation mechanisms and kinetics.

Operando Insight into the Correlation between the Structure and Composition of CuZn Nanoparticles and Their Selectivity for the Electrochemical CO2 Reduction.

Bimetallic CuZn catalysts have been recently proposed as alternatives in order to achieve selectivity control during the electrochemical reduction of CO2 (CO2RR). However, fundamental understanding of the underlying reaction mechanism and parameters determining the CO2RR performance is still missing. In this study, we have employed size-controlled (∼5 nm) Cu100–xZnx nanoparticles (NPs) supported on carbon to investigate the correlation between their structure and composition and catalytic performance. By tuning the concentration of Zn, a drastic increase in CH4 selectivity [∼70% Faradaic efficiency (F.E.)] could be achieved for Zn contents from 10 to 50, which was accompanied by a suppression of the H2 production. Samples containing a higher Zn concentration displayed significantly lower CH4 production and an abrupt switch in the selectivity to CO. Lack of metal leaching was observed based on quasi in situ X-ray photoelectron spectroscopy (XPS). Operando X-ray absorption fine structure (XAFS) spectroscopy measurements revealed that the alloying of Cu atoms with Zn atoms takes place under reaction conditions and plays a determining role in the product selectivity. Time-dependent XAFS analysis showed that the local structure and chemical environment around the Cu atoms continuously evolve during CO2RR for several hours. In particular, cationic Zn species initially present were found to get reduced as the reaction proceeded, leading to the formation of a CuZn alloy (brass). The evolution of the Cu–Zn interaction with time during CO2RR was found to be responsible for the change in the selectivity from CH4 over Cu-ZnO NPs to CO over CuZn alloy NPs. This study highlights the importance of having access to in depth information on the interplay between the different atomic species in bimetallic NP electrocatalysts under operando reaction conditions in order to understand and ultimately tune their reactivity.

Deciphering Molecular Virulence Mechanism of Mycobacterium tuberculosis Dop isopeptidase Based on Its Sequence-Structure-Function Linkage.

The pupylation pathway marks proteins for prokaryotic ubiquitin-like protein (Pup)-proteasomal degradation and survival strategy of mycobacteria inside of the host macrophages. Deamidase of Pup (Dop) plays a central role in the pupylation pathway. It is still a matter of investigation to know the function of Dop in virulence of mycobacterial lineage. Hence, the present study was intended to describe the sequence-structure-function-virulence link of Dop for understanding the molecular virulence mechanism of Mycobacterium tuberculosis H37Rv (Mtb). Phylogenetic analysis of this study indicated that Dop has extensively diverged across the proteasome-harboring bacteria. The functional part of Dop was converged across the pathogenic mycobacterial lineage. The genome-wide analysis pointed out that the pupylation gene locus was identical to each other, but its genome neighborhood differed from species to species. Molecular modeling and dynamic studies proved that the predicted structure of Mtb Dop was energetically stable and low conformational freedom. Moreover, evolutionary constraints in Mtb Dop were intensively analyzed for inferring its sequence-structure-function relationships for the full virulence of Mtb. It indicated that evolutionary optimization was extensively required to stabilize its local structural environment at the side chains of mutable residues. The sequence-structure-function-virulence link of Dop might have retained in Mtb by reordering hydrophobic and hydrogen bonding patterns in the local structural environment. Thus, the results of our study provide a quest to understand the molecular virulence and pathogenesis mechanisms of Mtb during the infection process.

Intrinsic and extrinsic drivers of intraspecific variation in seed dispersal are diverse and pervasive.

There is growing realization that intraspecific variation in seed dispersal can have important ecological and evolutionary consequences. However, we do not have a good understanding of the drivers or causes of intraspecific variation in dispersal, how strong an effect these drivers have, and how widespread they are across dispersal modes. As a first step to developing a better understanding, we present a broad, but not exhaustive, review of what is known about the drivers of intraspecific variation in seed dispersal, and what remains uncertain. We start by decomposing ‘drivers of intraspecific variation in seed dispersal’ into intrinsic drivers (i.e. variation in traits of individual plants) and extrinsic drivers (i.e. variation in ecological context). For intrinsic traits, we further decompose intraspecific variation into variation among individuals and variation of trait values within individuals. We then review our understanding of the major intrinsic and extrinsic drivers of intraspecific variation in seed dispersal, with an emphasis on variation among individuals. Crop size is the best-supported and best-understood intrinsic driver of variation across dispersal modes; overall, more seeds are dispersed as more seeds are produced, even in cases where per seed dispersal rates decline. Fruit/seed size is the second most widely studied intrinsic driver, and is also relevant to a broad range of seed dispersal modes. Remaining intrinsic drivers are poorly understood, and range from effects that are probably widespread, such as plant height, to drivers that are most likely sporadic, such as fruit or seed colour polymorphism. Primary extrinsic drivers of variation in seed dispersal include local environmental conditions and habitat structure. Finally, we present a selection of outstanding questions as a starting point to advance our understanding of individual variation in seed dispersal.

Magnetic properties and photoluminescence of thulium-doped calcium aluminosilicate glasses

We report on the optical and magnetic properties of Tm2O3-doped calcium aluminosilicate glasses with dopant concentrations of up to 7 mol%. These materials provide a rare case in which high magnetic susceptibility, low Faraday rotation, Tm3+-related infrared photoluminescence and the ability to produce optical fibers are combined. From emission intensity and decay curves of the 3H4→3F4 and 3F4→3H6 transitions, we find cross-relaxation already for 0.5 mol% of Tm2O3 doping, indicating notable Tm2O3 clustering. This facilitates antiferromagnetic interaction and results in high magnetic susceptibility. Substitution of Al2O3 by Tm2O3 induces a more asymmetric local structural environment around Tm3+ species and enhances the diamagnetic contribution to Faraday rotation as opposed to the other rare-earth ions.

Bioinspired Approaches for Autonomous Small-Object Detection and Avoidance

Small-object detection and avoidance in unknown environments is a significant challenge to overcome for small autonomous vehicles that are generally highly agile and restricted in payload and computational processing power. Typical machine-vision and range measurement-based solutions suffer either from restricted fields-of-view or significant computational complexity and are, hence, not easily portable to small platforms. In order to overcome these drawbacks, in this paper, two novel bioinspired approaches are proposed to extract information about small-field objects contained in planar optic flow. The first approach, which is analogous to the small-field extraction process hypothesized to occur in the lobula plate of the fly visual system, is based on the Fourier residual analysis of instantaneous optic flow. Alternatively, the flow-of-flow method is the engineering analogue of the small-field extraction process thought to occur in the fruit-fly's medulla, and extracts high-frequency content of optic flow by means of an elementary motion detector array. Both approaches extract instantaneous relative range and bearing of small-field obstacles from planar optic flow in a local environment characterized by small and wide-field obstacles, which is then combined with an artificial potential function-based low-order steering control law. The proposed sensing and control scheme is experimentally validated with a quadrotor vehicle that is able to effectively navigate an unknown environment laden with small-field clutter. This bioinspired approach is computationally efficient, which renders extraction of vehicle velocity and local environment structure superfluous, and thus, serves as a robust, reflexive solution to the problem of small-object detection, and avoidance for small autonomous robots.

Local Environment Structure in Positively Charged Porous Ionic Polymers for Ultrafast Removal of Sulfonamide Antibiotics

Selectivity and efficiency are always the most difficult challenges for adsorption technology, especially for the removal of trace amounts of antibiotics from an aqueous system. We employed the str...

Photoluminescence and Structural Characterization of RE‐Doped Sodium Aluminosilicate Oxyfluoride Glass and Nanocrystalline Glass‐Ceramics as a Function of γ‐Irradiation Dose

Dy3+ and Eu3+‐doped oxyfluoride glass and glass nanocomposites are subjected to low and high dose of γ‐irradiation, i.e., 100 Gy and 1 kGy, respectively. The photoluminescence spectra show changes in electric to magnetic dipole ratios signifying variations in local structural environment. Glass‐ceramics depict the tendency of crystallization or the ordering of structure with increasing γ‐irradiation dose. The results are further supported with X‐ray diffraction and scanning electron microscopy (SEM) measurements. The formation of nanometer size fluoride particles in the pristine glass and glass‐ceramics after γ‐irradiation has been observed from SEM studies. Fourier transform infrared (FTIR) study reveals the restructuring of aluminosilicate network under γ‐irradiation.

Satellite image texture for the assessment of tropical anuran communities

AbstractThe relationship between environmental heterogeneity and biodiversity represents a cornerstone of ecological research. While environmental descriptors over large extents usually have medium‐to‐low spatial resolution, in situ measures provide accurate information for limited areas, and a gap remains in providing remote descriptors that represent local environmental structure. Texture from satellite images can represent fine‐scale heterogeneity over wide spatial coverage, but to date, it has mostly been used to predict general aspects of species diversity, such as richness. Here, we assess the utility of image textures from high‐resolution satellite images (RapidEye 3A) and in situ variables to predict differences in the composition of anuran communities in a tropical savanna (Cerrado) of Brazil. While in situ measures accounted for compositional differences in the whole community, two measures of image textures were associated only with the variation of species within the Hylidae family (adj. R² = 0.16 and 0.14). Comparatively, image textures predicted ~2/3 of the variation explained by in situ measures (adj. R² = 0.23). When both approaches were combined, a greater compositional variation was achieved (adj. R² = 0.28), with 1/5 of it shared by both in situ and textures, and 1/5 attributed solely to texture. Our findings suggest that image texture can complement the assessment of environmental heterogeneity acting on the assembly of local anuran communities. This approach can be valuable for explicitly including spatial heterogeneity in biological assessments over broad spatial extents, especially for biological groups strongly filtered by environmental conditions.Abstract in Portuguese is available with online material.

Probing Jahn-Teller distortions in Mn(acac)3 through paramagnetic interactions in solid-state MAS NMR

The structural and electronic properties of solid coordination compounds are of great interest in a wide variety of applications. The sensitivity of solid-state NMR to local structural environments in the presence of a transition metal with unpaired spins is demonstrated through 13C and 1H MAS NMR spectra of tris(acetylacetonato)manganese (III), Mn(acac)3. The spectral assignment is established using a combination of density-functional theory and experimental NMR methods. An analysis of the spin-density distribution throughout the ligands as probed by NMR provides an understanding of the molecular electronic structure. The paramagnetic interaction enhances the spectral resolution and offers the possibility of using these spectra as structural fingerprints. The unique character of Mn(acac)3 to manifest various degrees of Jahn-Teller distortions allows for a discussion of the relation between the electron occupancy, crystal structure, and 13C NMR peak shifts.

(Invited) Structural Design Via Group Energy Materials for High-Efficient Photoelectrochemical Hydrogen Evolution Reaction

Photoelectrochemical hydrogen evolution reaction (HER) and electrochemical reduction of carbon dioxide (CO2RR) to chemical fuels have the potential to relieve the energy problem. The performance of these devices depends intimately on the properties of their materials. Herein we modify the inorganic sulfide by organic polymer molecules and thus improve the electronic and band structure, optimization the overall hydrogen evolution performance. Meanwhile, earth-abundant first-row (3d) transition-metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials significantly above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxy-hydroxide materials with an atomically homogeneous metal distribution. These gelled FeCoW oxy-hydroxide exhibits the lowest overpotential (191 mV) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation following more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between W, Fe and Co in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER. We also used in operando soft X-ray absorption to quantify the ratio of the Ni4+ and Ni2+ active site, achieved an OER overpotential of only 330 mV under neutral condition, better than novel metal oxide catalyst, IrO2, with ideal stability within 100 h. With the modulating of 3d coordination environment and electronic structure, maximum optimization the energetics of oxygen evolution reaction, we finally achieved the lowest over potential for OER and hence improved the HER efficiency. Furthermore, we engineered the metal sites by using non-metal element and which significantly improved the efficiency of CO2RR to formate.

Atomic-Scale Control of Magnetism at the Titanite-Manganite Interfaces

Complex oxide thin-film heterostructures often exhibit magnetic properties different from those known for bulk constituents. This is due to the altered local structural and electronic environment at the interfaces, which affects the exchange coupling and magnetic ordering. The emergent magnetism at oxide interfaces can be controlled by ferroelectric polarization and has a strong effect on spin-dependent transport properties of oxide heterostructures, including magnetic and ferroelectric tunnel junctions. Here, using prototype La2/3Sr1/3MnO3/BaTiO3 heterostructures, we demonstrate that ferroelectric polarization of BaTiO3 controls the orbital hybridization and magnetism at heterointerfaces. We observe changes in the enhanced orbital occupancy and significant charge redistribution across the heterointerfaces, affecting the spin and orbital magnetic moments of the interfacial Mn and Ti atoms. Importantly, we find that the exchange coupling between Mn and Ti atoms across the interface is tuned by ferroelectric polarization from ferromagnetic to antiferromagnetic. Our findings provide a viable route to electrically control complex magnetic configurations at artificial multiferroic interfaces, taking a step toward low-power spintronics.

Deciphering structure, function and mechanism of Plasmodium IspD homologs from their evolutionary imprints.

Malaria is a life-threatening mosquito-borne blood disease caused by infection with Plasmodium parasites. Anti-malarial drug resistance is a global threat to control and eliminate malaria and therefore, it is very important to discover and evaluate new drug targets. The 2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase (IspD) homolog is a second in vivo target for fosmidomycin within isoprenoid biosynthesis in malarial parasites. In the present study, we have deciphered the sequence-structure-function integrity of IspD homologs based on their evolutionary imprints. The function and catalytic mechanism of them were also intensively studied by using sequence-structure homology, molecular modeling, and docking approach. Results of our study indicated that substrate-binding and dimer interface motifs in their structures were extensively conserved and part of them closely related to eubacterial origins. Amino acid substitutions in their coiled-coil regions found to bring a radical change in secondary structural elements, which in turn may change the local structural environment. Arg or Asp was identified as a catalytic site in plasmodium IspD homologs, contributing a direct role in the cytidylyltransferase activity similar to bacterial IspD. Results of molecular docking studies demonstrated how anti-malarial drugs such as fosmidomycin and FR-900098 have competitively interacted with the substrate-binding site of these homologs. As shown by our analysis, species-specific evolutionary imprints in these homologs determine the sequence-structure-function-virulence integrity and binding site alterations in order to confer anti-malarial drug resistance.

Tyrosine nitration of human ERK1 introduces an intra-hydrogen bond by molecular dynamics simulations

ERK1 is an important kinase in Ras–Raf–MEK signaling. We have recently demonstrated by mass spectrometry that Tyr210 of ERK1 can be nitrated, and the nitration leads to a novel CHIP–dependent ERK1 degradation pathway. This motivated us to investigate the effect of this nitration on local and global structures of human ERK1 by Gaussian calculations and molecular dynamics simulations. Our study shows that the nitration at either the CE1 or the CE2 positions introduces an intra-hydrogen bond between the hydroxyl group and the nitro group of the nitrated Tyr210 of ERK1. Our data indicate that the hydrogen bond between Tyr210 and Glu237 is not stable and the nitration of Tyr210 facilitates its breakage. The previous studies demonstrated that ERK1 can be autophosphorylated at tyrosine residue 204. We next studied the effect of the phosphorylation in combination with the nitration. We found that the nitration of Tyr210 modestly decreases its inter-residue electrostatic interactions, and the phosphorylation of Tyr204 increases its inter-residue electrostatic interactions as expected. In the active state of ERK1, the conserved Lys71 forms a salt bridge with the conserved Glu88 and this salt bridge is essential for the activity of ERK1. Our data demonstrate an additional salt bridge for Glu88 with Arg84, and this salt bridge is unphosphorylation-dependent. The phosphorylation of ERK1 with the nitration at CE2, not at CE1, slightly enhances the K71–E88 salt bridge. Collectively, our simulations have demonstrated formation of a tyrosine nitration–dependent hydrogen bond. Our molecular dynamics simulations in combination with the experimental data on the nitration of Tyr210 of ERK1 indicate that a post-translational modification of a protein can specifically alter local structural environments, and a local structural change could lead to changes of protein functions.