Non-random Distribution Research Articles

Water mass-driven multiple ecological effects determine the biodiversity and community assembly of microbial flagellates in subtropic-tropic marginal seas of China

Marine microbial flagellates form an important part of marine ecosystems, and play an essential role in maintaining ecosystem functions. However, the underlying biogeographic processes and ecological effects that shape marine microbial flagellate communities (MFCs) on the geographical scale (∼2000 km) remain unclear, especially how their composition is related to movements of water masses. In this study, high-throughput sequencing of 18S rRNA genes was conducted to survey two size-fractioned groups (0.8–2.0 μm for pico-sized and 2.0–20 μm for nano-sized groups) of MFCs in three subtropic-tropic marginal seas of China. In addition, the impacts of environmental factors, spatial factors, and water masses on MFCs were explored and compared across different spatiotemporal conditions. The results demonstrate non-random biogeographic distributions of MFCs in the studied area. These distributions were affected by several ecological processes, such as environmental selection, dispersal limitation, neutral process, and interactions within communities. These processes were driven by complex water masses that formed on a geographical scale. Notably, environmental heterogeneity was identified as the principal determinant of MFCs in each sea area. However, the importance of spatial factors increased with the spatial scale, which weakened biotic interactions within the community on a geographical scale. This effect was more apparent in nano-sized MFCs, indicating stronger dispersal limitation because of their larger cells and weaker dispersal ability. In summary, this study expands the available knowledge on the dynamic biogeographic patterns of MFCs associated with water masses on a geographical scale where strong spatial and environmental gradients exist.

Single-cell imaging of α and β cell metabolic response to glucose in living human Langerhans islets

Here we use a combination of two-photon Fluorescence Lifetime Imaging Microscopy (FLIM) of NAD(P)H free/bound ratio in living HIs with post-fixation, immunofluorescence-based, cell-type identification. FLIM allowed to measure variations in the NAD(P)H free/bound ratio induced by glucose; immunofluorescence data allowed to identify single α and β cells; finally, matching of the two datasets allowed to assign metabolic shifts to cell identity. 312 α and 654 β cells from a cohort of 4 healthy donors, 15 total islets, were measured. Both α and β cells display a wide spectrum of responses, towards either an increase or a decrease in NAD(P)H free/bound ratio. Yet, if single-cell data are averaged according to the respective donor and correlated to donor insulin secretion power, a non-random distribution of metabolic shifts emerges: robust average responses of both α and β cells towards an increase of enzyme-bound NAD(P)H belong to the donor with the lowest insulin-secretion power; by contrast, discordant responses, with α cells shifting towards an increase of free NAD(P)H and β cells towards an increase of enzyme-bound NAD(P)H, correspond to the donor with the highest insulin-secretion power. Overall, data reveal neat anti-correlation of tissue metabolic responses with respect to tissue insulin secretion power.

Modeling the power of acoustic monitoring to predict bat fatalities at wind turbines

AbstractLarge numbers of bats are killed at wind turbines worldwide. To formulate mitigation measures such as curtailment, recent approaches relate the acoustic activity of bats around reference turbines to casualties to extrapolate fatality rates at turbines where only acoustic surveys are conducted. Here, we modeled how sensitive this approach is when spatial distributions of bats vary within the rotor‐swept zone, and when the coverage of acoustic monitoring deteriorates, for example, with increasing turbine size. The predictive power of acoustic surveys was high for uniform or random distributions of bats. A concentration of bat passes around the nacelle or at the lower portion of the risk zone caused an overestimation of bat activity when ultrasonic microphones were pointed downwards at the nacelle. Conversely, a concentration of bat passes at the edge or at the top portion of the risk zone caused an underestimation of bat activity. These effects increased as the coverage of the acoustic monitoring decreased. Extrapolated fatality rates may not necessarily match with real conditions without knowledge of the spatial distribution of bats, particularly when the risk zone is poorly covered by acoustic monitoring, when spatial distributions are skewed and when turbines are large or frequencies of echolocating bats high. We argue that the predictive power of acoustic surveys is sufficiently strong for nonrandom or nonuniform distributions when validated by carcass searches and by complementary studies on the spatial distribution of bats at turbines.

Application of Parallel Factor Analysis (PARAFAC) to the Regional Characterisation of Vineyard Blocks Using Remote Sensing Time Series

Monitoring wine-growing regions and maximising the value of production based on their region/local specificities requires accurate spatial and temporal monitoring. The increasing amount and variability of information from remote sensing data is a potential tool to assess this challenge for the grape and wine industry. This article provides a first insight into the capacity of a multiway analysis method applied to Sentinel-2 time series to assess the value of simultaneously considering spectral and temporal information to highlight site-specific canopy evolution in relation to environmental factors and management practices, which present a large diversity at this regional scale. Parallel Factor Analysis (PARAFAC) was used as an unsupervised technique to recover pure spectra and temporal signatures from multi-way spectral imagery of vineyards in the Languedoc-Roussillon region in the south of France. The model was developed using a time series of Sentinel-2 satellite imagery collected over 4978 vineyard blocks between May 2019 and August 2020. From the Sentinel-2 (spectral and temporal) signal, the PARAFAC analysis allowed the identification of spectral and temporal profiles in the form of pure components, which corresponded to vegetation and soil. The PARAFAC analysis also identified that two of the pure spectra were strongly related to characteristics and dynamics of vineyard cultivation at a regional scale. A conceptual framework was proposed in order to simultaneously consider both vegetation and soil profiles and to summarise the mass of data accordingly. This methodology allowed the computation of a concentration index that characterised how close a field was to a vegetation or a soil profile over the season. The concentration indices were validated for the vegetation and the soil over two growing seasons (2019 and 2020) with geostatistical analysis. A non-random distribution of the concentration index at the regional scale was assumed to highlight a strongly spatially organised phenomenon related to spatially organised environmental factors (soil, climate, training system, etc.). In a second step, spatial patterns of indices were subjected to the expertise of a panel of advisors of the wine industry in order to validate them in relation to vine-growing conditions. Results showed that the introduction of the PARAFAC method opened up the possibility to identify relevant spectro-temporal profiles for vine monitoring purposes.

Elucidation of the O-antigen structure of Escherichia coli O93 and characterization of its biosynthetic genes.

The structure of the O-antigen from the international reference strain Escherichia coli O93:-:H16 has been determined. A nonrandom modal chain-length distribution was observed for the lipopolysaccharide, a pattern which is typical when long O-specific polysaccharides are expressed. By a combination of (i) bioinformatics information on the gene cluster related to O-antigen synthesis including putative function on glycosyl transferases, (ii) the magnitude of NMR coupling constants of anomeric protons, and (iii) unassigned 2D 1H, 13C-HSQC, and 1H,1H-TOCSY NMR spectra it was possible to efficiently elucidate the structure of the carbohydrate polymer in an automated fashion using the computer program CASPER. The polysaccharide also carries O-acetyl groups and their locations were determined by 2D NMR experiments showing that ~½ of the population was 2,6-di-O-acetylated, ~¼ was 2-O-acetylated, whereas ~¼ did not carry O-acetyl group(s) in the 3-O-substituted mannosyl residue of the repeating unit. The structure of the tetrasaccharide repeating unit of the O-antigen is given by: →2)-β-d-Manp-(1→3)-β-d-Manp2Ac6Ac-(1→4)-β-d-GlcpA-(1→3)-α-d-GlcpNAc-(1→, which should also be the biological repeating unit and it shares structural elements with capsular polysaccharides from E. coli K84 and K50. The structure of the acidic O-specific polysaccharide from Cellulophaga baltica strain NN015840T differs to that of the O-antigen from E. coli O93 by lacking the O-acetyl group at O6 of the O-acetylated mannosyl residue.

Spatiotemporal variations in retrovirus-host interactions among Darwin’s finches

Endogenous retroviruses (ERVs) are inherited remnants of retroviruses that colonized host germline over millions of years, providing a sampling of retroviral diversity across time. Here, we utilize the strength of Darwin’s finches, a system synonymous with evolutionary studies, for investigating ERV history, revealing recent retrovirus-host interactions in natural populations. By mapping ERV variation across all species of Darwin’s finches and comparing with outgroup species, we highlight geographical and historical patterns of retrovirus-host occurrence, utilizing the system for evaluating the extent and timing of retroviral activity in hosts undergoing adaptive radiation and colonization of new environments. We find shared ERVs among all samples indicating retrovirus-host associations pre-dating host speciation, as well as considerable ERV variation across populations of the entire Darwin’s finches’ radiation. Unexpected ERV variation in finch species on different islands suggests historical changes in gene flow and selection. Non-random distribution of ERVs along and between chromosomes, and across finch species, suggests association between ERV accumulation and the rapid speciation of Darwin’s finches.

Investigating the Origin of Mycobacterium chimaera Contamination in Heater-Cooler Units: Integrated Analysis with Fourier Transform Infrared Spectroscopy and Whole-Genome Sequencing.

Mycobacterium chimaera is ubiquitously spread in the environment, including factory and hospital water systems. Invasive cases of M. chimaera infection have been associated with aerosols produced by the use of heater-cooler units (HCU) during cardiac surgery. The aim of this study was to evaluate for the first time the performance of IR-Biotyper system on a large number of M. chimaera isolates collected from longitudinal environmental HCUs samples and water sources from hospitals located in three Italian provinces. In addition, IR-Biotyper results were compared with whole-genome sequencing (WGS) analysis, the reference method for molecular epidemiology, to investigate the origin of M. chimaera contamination of HCUs. From November 2018 to May 2021, 417 water samples from 52 HCUs (Stockert 3T, n = 41 and HCU40, n = 11) and 23 hospital taps (used to fill the HCU tanks) were concentrated, decontaminated, and cultured for M. chimaera. Positive cultures (n = 53) were purified by agar plate subcultures and analyzed by IR-Biotyper platform and Ion Torrent sequencing system. IR-Biotyper spectra results were analyzed using a statistical approach of dimensionality reduction by linear discriminant analysis (LDA), generating three separate clusters of M. chimaera, ascribable to each hospital. Furthermore, the only M. chimaera-positive sample from tap water clustered with the isolates from the HCUs of the same hospital, confirming that the plumbing system could represent the source of HCU contamination and, potentially, of patient infection. According to the genome-based phylogenies and following the classification proposed by van Ingen and collaborators in 2017, three distinct M. chimaera groups appear to have contaminated the HCU water systems: subgroups 1.1, 2.1, and branch 2. Most of the strains isolated from HCUs at the same hospital share a highly similar genetic profile. The nonrandom distribution obtained with WGS and IR-Biotyper leads to the hypothesis that M. chimaera subtypes circulating in the local plumbing colonize HCUs through the absolute filter, in addition with the current hypothesis that contamination occurs at the HCU production site. This opens the possibility that other medical equipment, such as endoscope reprocessing device or hemodialysis systems, could be contaminated by M. chimaera. IMPORTANCE Our manuscript focuses on interventions to reduce waterborne disease transmission, improve sanitation, and control infection. Sanitary water can be contaminated by nontuberculous Mycobacteria, including M. chimaera, a causative agent of invasive infections in immunocompromised patients. We found highly similar genetic and phenotypic profiles of M. chimaera isolated from heater-cooler units (HCU) used during surgery to thermo-regulate patients' body temperature, and from the same hospital tap water. These results lead to the hypothesis that M. chimaera subtypes circulating in the local plumbing colonize HCUs through the absolute filter, adding to the current hypothesis that contamination occurs at the HCU production site. In addition, this opens the possibility that other medical equipment using sanitized water, such as endoscope reprocessing devices or hemodialysis systems, could be contaminated by nontuberculous Mycobacteria, suggesting the need for environmental surveillance and associated control measures.

Complex genomic patterns of abasic sites in mammalian DNA revealed by a high-resolution SSiNGLe-AP method

DNA damage plays a critical role in biology and diseases; however, how different types of DNA lesions affect cellular functions is far from clear mostly due to the paucity of high-resolution methods that can map their locations in complex genomes, such as those of mammals. Here, we present the development and validation of SSiNGLe-AP method, which can map a common type of DNA damage, abasic (AP) sites, in a genome-wide and high-resolution manner. We apply this method to six different tissues of mice with different ages and human cancer cell lines. We find a nonrandom distribution of AP sites in the mammalian genome that exhibits dynamic enrichment at specific genomic locations, including single-nucleotide hotspots, and is significantly influenced by gene expression, age and tissue type in particular. Overall, these results suggest that we are only starting to understand the true complexities in the genomic patterns of DNA damage.

Segregated structures induced linear mechanoelectrical responses to low strains for elastomer/CNTs composites

Carbon nanotubes (CNTs)-based polymer composites are great potential as flexible piezoresistive sensors to apply to wearable devices, electronic skins, etc. We herein prepared a type of polymer composites with a segregated structure derived from double-percolating structured polymer composites of two elastomers and CNTs. Expressly, CNTs were composited with two elastomers by melt blending, forming double-percolated structures. The composites with segregated structures were attained after removing the elastomeric phase where CNTs selectively located by solvent extraction, followed by hot compression to eliminate voids. This kind of segregated structure could reduce the percolation threshold of CNTs while maintaining superior stretchability of the elastomeric matrix. Compared to polymer composites with randomly distributed CNTs, the composites with the segregated structure posed nonrandom distribution of CNTs, forming a denser conductive network with the same content. Therefore, the composites exhibited different mechanoelectrical responses from the traditional CNTs-based polymer composites. The composites with the segregated structure showed a higher strain where the relative change of resistance increased significantly. Notably, the composites exhibited a linear (instead of the commonly nonlinear) piezoresistive response with improved sensitivity under low mechanical strains. The practical applications of the as-prepared composites as piezoresistive sensors showed reliable performance in detecting gentle touching, dropping impact, and human body motions.

Pathogenic variants of sphingomyelin synthase SMS2 disrupt lipid landscapes in the secretory pathway.

Sphingomyelin is a dominant sphingolipid in mammalian cells. Its production in the trans-Golgi traps cholesterol synthesized in the ER to promote formation of a sphingomyelin/sterol gradient along the secretory pathway. This gradient marks a fundamental transition in physical membrane properties that help specify organelle identify and function. We previously identified mutations in sphingomyelin synthase SMS2 that cause osteoporosis and skeletal dysplasia. Here, we show that SMS2 variants linked to the most severe bone phenotypes retain full enzymatic activity but fail to leave the ER owing to a defective autonomous ER export signal. Cells harboring pathogenic SMS2 variants accumulate sphingomyelin in the ER and display a disrupted transbilayer sphingomyelin asymmetry. These aberrant sphingomyelin distributions also occur in patient-derived fibroblasts and are accompanied by imbalances in cholesterol organization, glycerophospholipid profiles, and lipid order in the secretory pathway. We postulate that pathogenic SMS2 variants undermine the capacity of osteogenic cells to uphold nonrandom lipid distributions that are critical for their bone forming activity.

Missing Race and Ethnicity Data among COVID-19 Cases in Massachusetts

Infectious disease surveillance frequently lacks complete information on race and ethnicity, making it difficult to identify health inequities. Greater awareness of this issue has occurred due to the COVID-19 pandemic, during which inequities in cases, hospitalizations, and deaths were reported but with evidence of substantial missing demographic details. Although the problem of missing race and ethnicity data in COVID-19 cases has been well documented, neither its spatiotemporal variation nor its particular drivers have been characterized. Using individual-level data on confirmed COVID-19 cases in Massachusetts from March 2020 to February 2021, we show how missing race and ethnicity data: (1) varied over time, appearing to increase sharply during two different periods of rapid case growth; (2) differed substantially between towns, indicating a nonrandom distribution; and (3) was associated significantly with several individual- and town-level characteristics in a mixed-effects regression model, suggesting a combination of personal and infrastructural drivers of missing data that persisted despite state and federal data-collection mandates. We discuss how a variety of factors may contribute to persistent missing data but could potentially be mitigated in future contexts.

The Limiting Spectral Distribution of Large-Dimensional General Information-Plus-Noise-Type Matrices

Let $$ X_{n} $$ be $$ n\times N $$ random complex matrices, and let $$R_{n}$$ and $$T_{n}$$ be non-random complex matrices with dimensions $$n\times N$$ and $$n\times n$$ , respectively. We assume that the entries of $$ X_{n} $$ are normalized independent random variables satisfying the Lindeberg condition, $$ T_{n} $$ are nonnegative definite Hermitian matrices and commutative with $$R_nR_n^*$$ , i.e., $$T_{n}R_{n}R_{n}^{*}= R_{n}R_{n}^{*}T_{n} $$ . The general information-plus-noise-type matrices are defined by $$C_{n}=\frac{1}{N}T_{n}^{\frac{1}{2}} \left( R_{n} +X_{n}\right) \left( R_{n}+X_{n}\right) ^{*}T_{n}^{\frac{1}{2}} $$ . In this paper, we establish the limiting spectral distribution of the large-dimensional general information-plus-noise-type matrices $$C_{n}$$ . Specifically, we show that as n and N tend to infinity proportionally, the empirical distribution of the eigenvalues of $$C_{n}$$ converges weakly to a non-random probability distribution, which is characterized in terms of a system of equations of its Stieltjes transform.

Assessment of the stream invertebrate -diversity along an elevation gradient using a bidimensional null model analysis.

β‐Diversity, commonly defined as the compositional variation among localities that links local diversity (α‐diversity) and regional diversity (γ‐diversity), can arise from two different ecological phenomena, namely the spatial species turnover (i.e., species replacement) and the nestedness of assemblages (i.e., species loss). However, any assessment that does not account for stochasticity in community assembly could be biased and misinform conservation management. In this study, we aimed to provide a better understanding of the overall ecological phenomena underlying stream β‐diversity along elevation gradients and to contribute to the rich debate on null model approaches to identify nonrandom patterns in the distribution of taxa. Based on presence‐absence data of 78 stream invertebrate families from 309 sites located in the Swiss Alpine region, we analyzed the effect size of nonrandom spatial distribution of stream invertebrates on the β‐diversity and its two components (i.e., turnover and nestedness). We used a modeling framework that allows exploring the complete range of existing algorithms used in null model analysis and assessing how distribution patterns vary according to an array of possible ecological assumptions. Overall, the turnover of stream invertebrates and the nestedness of assemblages were significantly lower and higher, respectively, than the ones expected by chance. This pattern increased with elevation, and the consistent trend observed along the altitudinal gradient, even in the most conservative analysis, strengthened our findings. Our study suggests that deterministic distribution of stream invertebrates in the Swiss Alpine region is significantly driven by differential dispersal capacity and environmental stress gradients. As long as the ecological assumptions for constructing the null models and their implications are acknowledged, we believe that they still represent useful tools to measure the effect size of nonrandom spatial distribution of taxa on β‐diversity.

Asymmetry in Galaxy Spin Directions—Analysis of Data from DES and Comparison to Four Other Sky Surveys

The paper shows an analysis of the large-scale distribution of galaxy spin directions of 739,286 galaxies imaged by DES. The distribution of the spin directions of the galaxies exhibits a large-scale dipole axis. Comparison of the location of the dipole axis to a similar analysis with data from SDSS, Pan-STARRS, and DESI Legacy Survey shows that all sky surveys exhibit dipole axes within 52° or less from each other, well within 1σ error, while non-random distribution is unexpected, the findings are consistent across all sky surveys, regardless of the telescope or whether the data were annotated manually or automatically. Possible errors that can lead to the observation are discussed. The paper also discusses previous studies showing opposite conclusions and analyzes the decisions that led to these results. Although the observation is provocative, and further research will be required, the existing evidence justifies considering the contention that galaxy spin directions as observed from Earth are not necessarily randomly distributed. Possible explanations can be related to mature cosmological theories, but also to the internal structure of galaxies.

Spatial differences in Casuarina equisetifolia L. endophyte community structure

PurposeCasuarina equisetifolia, a fast-growing, abundant tree species on the southeastern coast of China, plays an important role in protecting the coastal environment, but the ecological processes that govern microbiome assembly and within-plant microorganism transmission are poorly known.MethodsIn this paper, we used ITS and 16S amplification techniques to study the diversity of fungal and bacterial endophytes in critical plant parts of this species: seeds, branchlets, and roots. Additionally, we examined the litter of this species to understand the process of branchlets from birth to litter.ResultWe uncovered a non-random distribution of endophyte diversity in which branchlets had the greatest and seeds had the lowest endophytic fungal diversity. In contrast, litter endophytic bacteria had the highest diversity, and branchlets had the lowest diversity. As for fungi, a large part of the seed microbiome was transmitted to the phyllosphere, while a large part of the bacterial microbiome in the seed was transmitted to the root.ConclusionOur study provides comprehensive evidence on diversity, potential sources, and transmission pathways for non-crop microbiome assembly and has implications for the management and manipulation of the non-crop microbiome in the future.

Detection and Spatiotemporal Analysis of In-vitro 3D Migratory Triple-Negative Breast Cancer Cells.

The invasion of cancer cells into the surrounding tissues is one of the hallmarks of cancer. However, a precise quantitative understanding of the spatiotemporal patterns of cancer cell migration and invasion still remains elusive. A promising approach to investigate these patterns are 3D cell cultures, which provide more realistic models of cancer growth compared to conventional 2D monolayers. Quantifying the spatial distribution of cells in these 3D cultures yields great promise for understanding the spatiotemporal progression of cancer. In the present study, we present an image processing and segmentation pipeline for the detection of 3D GFP-fluorescent triple-negative breast cancer cell nuclei, and we perform quantitative analysis of the formed spatial patterns and their temporal evolution. The performance of the proposed pipeline was evaluated using experimental 3D cell culture data, and was found to be comparable to manual segmentation, outperforming four alternative automated methods. The spatiotemporal statistical analysis of the detected distributions of nuclei revealed transient, non-random spatial distributions that consisted of clustered patterns across a wide range of neighbourhood distances, as well as dispersion for larger distances. Overall, the implementation of the proposed framework revealed the spatial organization of cellular nuclei with improved accuracy, providing insights into the 3 dimensional inter-cellular organization and its progression through time.

Horses wait for more and better rewards in a delay of gratification paradigm.

Self-control, defined as the ability to forgo immediate satisfaction in favor of better pay-offs in the future, has been extensively studied, revealing enormous variation between and within species. Horses are interesting in this regard because as a grazing species they are expected to show low self-control whereas its social complexity might be linked to high self-control abilities. Additionally, self-control may be a key factor in training and/or coping with potentially stressful husbandry conditions. We assessed horses’ self-control abilities in a simplified delay of gratification test that can be easily implemented in a farm setting. In Experiment 1, we gave horses (N = 52) the choice between an immediately available low-quality reward and a delayed high-quality reward that could only be obtained if the horse refrained from consuming the immediate reward. Different experimenters (N = 30) that underwent prior training in the procedures, tested horses in two test phases either with their eyes visible or invisible (sunglasses). Twenty horses waited up to the maximum delay stage of 60 s while all horses performed worse in the second test phase. In Experiment 2, we improved the test procedure (i.e., one experimenter, refined criterion for success), and tested 30 additional horses in a quality and quantity condition (one reward vs. delayed bigger reward). Two horses successfully waited for 60 s (quality: N = 1, quantity: N = 1). Horses tolerated higher delays, if they were first tested in the quantity condition. Furthermore, horses that were fed hay ad libitum, instead of in a restricted manner, reached higher delays. Coping behaviors (e.g., looking away, head movements, pawing, and increasing distance to reward) facilitated waiting success and horses were able to anticipate the upcoming delay duration as indicated by non-random distributions of giving-up times. We found no correlations between owner-assessed traits (e.g., trainability and patience) and individual performance in the test. These results suggest that horses are able to exert self-control in a delay of gratification paradigm similar to other domesticated species. Our simplified paradigm could be used to gather large scale data, e.g., to investigate the role of self-control in trainability or success in equestrian sports.

Spatial Variations and Determinants of Anemia among Under-five Children in Nepal, DHS (2006-2016).

Anemia among under-five children is the major health problem in Nepal. The lack of nutritional supplementation and lack of healthcare facilities are influential factors of anemia. Thus, the main objective of this study is to explore spatial variations and determinants of anemia among under-five children in Nepal. Nepal Demographic and Health Survey (NDHS) data from 2006 to 2016 were used in this study, which includes: household and individual-level data of 8555 under-five children, whose anemia was measured. In addition, a total of 260 (2006), 281 (2011), and 383 DHS clusters (2016) were taken in consideration for spatial analysis. The overall prevalence of anemia was 48.9%, 46.4%, and 52.2% in 2006, 2011, and 2016 respectively. The spatial analysis revealed a nonrandom spatial distribution, where statistically significant hotspots and coldspots were detected in different parts of the country. The results also identified mother’s age, mother’s educational level, socioeconomic status of household, number of under-5 children, household size, birth weight, underweight, stunting, diarrhea, and fever as associated factors of anemia among under-5 children. These findings may provide assistance to concerned health officials in adopting anemia-related programs and policies to address the anemia problems that plague Nepalese children under the age of five.

Gas generation and intramolecular isotope study in laboratory pyrolysis of the Springfield coal from the Illinois Basin

Position-specific (PS) isotopes of propane have been proposed as a potential geochemical tool to decipher various geological processes (e.g., thermal cracking, biodegradation, H exchange) in natural reservoirs. The limited studies have been conducted on the PS isotopes of propane from the pyrolysis gases from marine shales, and natural gases sourced from lacustrine and marine kerogens, but little is known on gases produced from the humic kerogen. This study investigated the PS δ13C of propane in the closed-system pyrolysis of the Springfield coal, Illinois Basin, Indiana, at 310 to 470 °C (Easy %Ro: 0.76 to 3.07). The C kinetic isotope effect (KIE) of CH4 produced in both this study and previous low-temperature pyrolysis of the same coal indicates the cleavage of CO bonds is the main generation pathway at the early kerogen cracking stage, followed by the breakdown of alkyl groups. At the wet-gas cracking stage, C3H8 production from thermally stable compounds has a significant influence on the bulk and position-specific C KIE in the pyrolysis of marine Woodford kerogen and Springfield coal. According to the PS δ13C of propane, the central site is likely more enriched in 13C and the δ13C of the terminal site is relatively heterogeneous within the propyl group attached to different functional groups of the gas-prone kerogen. Our findings based on the pyrolysis experiments and natural gas samples indicate thermal cracking and biodegradation appear to alter the δ13Ccen values more significantly than the δ13Cter values of propane. The larger magnitude of ΔCc-t in the kMC simulations (Peterson et al., 2018) compared with those from the marine shale and coal possibly implies the non-random distributions of 13C of propane precursors in the kerogens. As a new dimension of intramolecular isotopic information of propane, the PS δ13C values can contribute to fingerprinting the gas origins and identifying the various geological processes (e.g., kerogen cracking, wet-gas cracking, microbial activities) in sedimentary basins.

Phylogenetic structure and diversity among herpetofaunal communities along a successional gradient of a tropical dry forest in Mexico

The tropical dry forest (TDF) is one of the most biodiverse ecosystems on earth, but also one of the most threatened. Therefore, it is critical to understand the processes that control community assembly and generate diversity during succession. We surveyed 15 herpetofaunal communities from a chronosequence of succession plots and tested whether phylogenetic structure (nonrandom distribution of species with respect to phylogeny) and phylogenetic diversity (incorporation of phylogenetic differences between species to measure biodiversity) differed among seasons and succession stages of the TDF in western Mexico. Phylogenetic structure and diversity of both groups showed temporal shifts. Our data suggest a role of environmental filtering in the first succession stages: during the rainy season in amphibians, allowing the coexistence of closely related species in water ponds, while for reptiles during the dry season, where higher exposure to solar radiation and humidity loss predominate in pastures. The more distantly related species in primary and secondary forests in later succession stages may predict ecosystem stability assuring the sufficient ecological strategies in a community to achieve the persistence of the ecosystem under changing conditions. Our results strengthen the arguments for promoting the conservation and managing of secondary forests under recovery to maintain phylogenetic diversity.