Abundance Gradients Research Articles

Probing the role of the C2F domain of otoferlin.

Afferent synapses of cochlear inner hair cells (IHCs) employ a unique molecular machinery. Otoferlin is a key player in this machinery, and its genetic defects cause human auditory synaptopathy. We employed site-directed mutagenesis in mice to investigate the role of Ca2+ binding to the C2F domain of otoferlin. Substituting two aspartate residues of the C2F top loops, which are thought to coordinate Ca2+-ions, by alanines (OtofD1841/1842A) abolished Ca2+-influx-triggered IHC exocytosis and synchronous signaling in the auditory pathway despite substantial expression (~60%) of the mutant otoferlin in the basolateral IHC pole. Ca2+ influx of IHCs and their resting membrane capacitance, reflecting IHC size, as well as the number of IHC synapses were maintained. The mutant otoferlin showed a strong apex-to-base abundance gradient in IHCs, suggesting impaired protein targeting. Our results indicate a role of the C2F domain in otoferlin targeting and of Ca2+ binding by the C2F domain for IHC exocytosis and hearing.

2D chemical evolution models

Context. According to observations and numerical simulations, the Milky Way could exhibit several spiral-arm modes of various pattern speeds, with the slower patterns located at larger galactocentric distances. Aims. Our aim is to quantify the effects of the spiral arms on the azimuthal variations in the chemical abundances of oxygen and iron and for the first time of neutron-capture elements (europium and barium) in the Galactic disc. We assume a model based on multiple spiral-arm modes with different pattern speeds. The resulting model is an updated version of previous 2D chemical evolution models. Methods. We apply new analytical prescriptions for the spiral arms in a 2D Galactic disc chemical evolution model, exploring the possibility that the spiral structure is formed by the overlap of chunks with different pattern speeds and spatial extent. Results. The predicted azimuthal variations in abundance gradients are dependent on the considered chemical element. Elements synthesised on short timescales (i.e. oxygen and europium in this study) exhibit larger abundance fluctuations. Moreover, for progenitors with short lifetimes, the chemical elements returned to the ISM perfectly trace the star formation perturbed by the passage of the spiral arms. The map of the star formation rate (SFR) predicted by our chemical evolution model with multiple patterns of spiral arms presents arcs and arms compatible with those revealed by multiple tracers (young upper-main sequence stars, Cepheids, and the distribution of stars with low radial actions). Finally, our model predictions are in good agreement with the azimuthal variations that emerged from the analysis of Gaia DR3 GSP-Spec [M/H] abundance ratios, if at most recent times the pattern speeds match the Galactic rotational curve at all radii. Conclusions. We provide an updated version of a 2D chemical evolution model capable of tracing the azimuthal density variations created by the presence of multiple spiral patterns. We show that elements synthesised on short timescales exhibit larger abundance fluctuations.

Metagenomic analysis reveals distinct changes in the gut microbiome of obese Chinese children

BackgroundThe prevalence of obese children in China is increasing, which poses a great challenge to public health. Gut microbes play an important role in human gut health, and changes in gut status are closely related to obesity. However, how gut microbes contribute to obesity in children remains unclear. In our study, we performed shotgun metagenomic sequencing of feces from 23 obese children, 8 overweight children and 22 control children in Chengdu, Sichuan, China.ResultsWe observed a distinct difference in the gut microbiome of obese children and that of controls. Compared with the controls, bacterial pathogen Campylobacter rectus was significantly more abundant in obese children. In addition, functional annotation of microbial genes revealed that there might be gut inflammation in obese children. The guts of overweight children might belong to the transition state between obese and control children due to a gradient in relative abundance of differentially abundant species. Finally, we compared the gut metagenomes of obese Chinese children and obese Mexican children and found that Trichuris trichiura was significantly more abundant in the guts of obese Mexican children.ConclusionsOur results contribute to understanding the changes in the species and function of intestinal microbes in obese Chinese children.

Quantifying Abundance and Mapping Distribution of Loggerhead Turtles in the Mediterranean Sea Using Aerial Surveys: Implications for Conservation

In the Mediterranean, incidental captures in fishing gear contribute to the high mortality of loggerhead turtles (Caretta caretta). Understanding the effects of bycatch is complex and requires robust knowledge of baseline population parameters such as abundance and density, as well as an understanding of animals’ distribution in relation to commercial fishing efforts. Based on data collected during multi-species line transect aerial surveys conducted between 2009 and 2017, we present density and abundance estimates, corrected for availability bias, for a large sector of the central Mediterranean, discuss temporal and spatial patterns and provide Potential Biological Removal (PBR) values for the monitored areas. Sightings data were also used to evaluate the spatial and temporal usage areas. Strong latitudinal and longitudinal gradients in density, abundance and area usage emerged from the analysis, with turtles occurring in higher numbers in the deeper pelagic waters of the Tunisian Plateau, the Ionian Sea and the Gulf of Taranto, irrespective of the season. PBR values derived from this study are likely unsustainable. This paper investigates the implications of commercial fisheries for Mediterranean loggerhead turtles across an area rarely included in sea turtle monitoring and has the potential to be relevant towards informed management and conservation of this species and highlights the necessity of international collaborative efforts in the region.

Assemblage Structure of Ichthyoplankton Communities in the Southern Adriatic Sea (Eastern Mediterranean).

Studies based on fish early life stages can provide information on spawning grounds and nursery areas, helping to determine the implications for stock biomass fluctuations of recruitment variability. This study describes the composition, abundance, spatial distribution and differences in day/night vertical distribution of ichthyoplankton in the southern Adriatic Sea. Samples were collected within the framework of the COCONET project (Towards COast to COast NETworks of marine protected areas) from 9 to 18 May 2013 by the R/V Urania, using the electronic multinet EZ-NET BIONESS (Bedford Institute of Oceanography Net Environmental Sampling System). A total of 20 species, belonging to 20 genera and 13 families, were identified. Of the collected larvae, 74.3% were meso- or bathypelagic species, 24.7% were epipelagic and 0.9% were demersal. The community was dominated by Gonostomatidae, followed by Engraulidae, Myctophidae and Photychthaidae. The most abundant species was Cyclothone braueri (45.6%), followed by Engraulis encrasicolus, Ceratoscopelus maderensis, Cyclothone pygmaea, Vinciguerria attenuata and Myctophum punctatum. An inshore/offshore increasing gradient in biodiversity and abundance was observed. Different weighted mean depths (WMDs) were observed for larvae and juveniles. No diel vertical migrations were observed. The high abundance of meso- or bathypelagic species in the upper 100 m confirms the epipelagic zone as an important environment for the development of the larval stages of these fish.

Response of soil bacteria on habitat-specialization and abundance gradient to different afforestation types

Studies involving response of subgroups of soil microorganisms to forest change, especially comparative studies on habitat-specialization and abundance gradient were still lack. In this study, we analyzed the response of soil bacterial diversity and structure to afforestation types and its relationship to environment of Fanggan ecological restoration area under the classification of subgroups by habitat-specialization and abundance gradient based on abundance ratio respectively. The results were: (1) On the habitat-specialization gradient, the variation of OTUs species number and abundance was consistent and positively correlated with habitat-specialization; on the abundance gradient, the variation was opposite and OTUs species number was negatively correlated with abundance gradient; (2) The distribution frequency of each subgroup on both gradients was the highest in broad-leaved forests, but the abundance was the opposite. The distribution frequency of the same stand showed no difference among habitat-specialization subgroups, but the abundant subgroup in broad-leaved forests was the highest among the abundance subgroups; (3) α-diversity was positively correlated with habitat-specialization but negatively with abundance, with the highest mostly in broad-leaved and mixed forests; (4) Community structure among stands on habitat-specialization gradient showed no significant difference, but that of rare subgroup between broad-leaved forests and other stands significantly differed. Plant diversity and vegetation composition correlated stronger with community structure than spatial distance and soil physicochemical properties on both gradients. Our results provided a new perspective for revealing the effects of afforestation types on soil bacteria from the comparison of habitat specialization and abundance gradient.

Exploring the Sun’s birth radius and the distribution of planet building blocks in the Milky Way galaxy: a multizone Galactic chemical evolution approach

ABSTRACT We explore the influence of the Milky Way galaxy’s chemical evolution on the formation, structure, and habitability of the Solar system. Using a multizone Galactic chemical evolution (GCE) model, we successfully reproduce key observational constraints, including the age–metallicity ([Fe/H]) relation, metallicity distribution functions, abundance gradients, and [X/Fe] ratio trends for critical elements involved in planetary mineralogy, including C, O, Mg, and Si. Our GCE model suggests that the Sun formed in the inner Galactic disc, Rbirth,⊙ ≈ 5 kpc. We also combined a stoichiometric model with the GCE model to examine the temporal evolution and spatial distribution of planet building blocks within the Milky Way galaxy, revealing trends in the condensed mass fraction (fcond), iron-to-silicon mass fraction (firon), and water mass fraction (fwater) over time and towards the inner Galactic disc regions. Specifically, our model predicts a higher fcond in the protoplanetary disc within the inner regions of the Milky Way galaxy, as well as an increased firon and a decreased fwater in the inner regions. Based on these findings, we discuss the potential impact of the Sun’s birth location on the overall structure and habitability of the Solar system.

The individual abundance distributions of disc stars across birth radii in GALAH

ABSTRACT Individual abundances in the Milky Way disc record stellar birth properties [e.g. age, birth radius (Rbirth)], and capture the diversity of the star-forming environments over time. Assuming an analytical relationship between ([Fe/H], [α/Fe]), and Rbirth, we examine the distributions of individual abundances [X/Fe] of elements C, O, Mg, Si, Ca (α), Al (odd-z), Mn (iron-peak), Y, and Ba (neutron-capture) for stars in the Milky Way. We want to understand how these elements might differentiate environments across the disc. We assign tracks of Rbirth in the [α/Fe] versus [Fe/H] plane as informed by expectations from simulations for ∼59 000 GALAH stars in the solar neighborhood (R ∼ 7−9 kpc) which also have inferred ages. Our formalism for Rbirth shows that older stars (∼10 Gyrs) have an Rbirth distribution with smaller mean values (i.e. $\bar{R}_{\mbox{birth}} \sim 5\pm 0.8$ kpc) compared to younger stars (∼6 Gyrs; $\bar{R}_{\mbox{birth}} \sim 10\pm 1.5$ kpc), for a given [Fe/H], consistent with inside–out growth. The α-, odd-z, and iron-peak element abundances decrease as a function of Rbirth, whereas the neutron-capture abundances increase. The Rbirth–[Fe/H] gradient we measure is steeper compared to the present-day gradient (−0.066 dex kpc−1 versus −0.058 dex kpc−1), which we also find true for Rbirth–[X/Fe] gradients. These results (i) showcase the feasibility of relating the birth radius of stars to their element abundances, (ii) demonstrate that the Milky Way abundance gradients across Rbirth have evolved to be shallower over time, and (iii) offer an observational comparison to element abundance distributions in hydrodynamical simulations.

Dispersal and Distribution of Thermophilic Endospores in Deep-Sea Ecosystems

The distance-decay relationship is a central concept in biogeography and spatial biodiversity, describing how two distinct entities decrease in similarity as the distance between them increases. The decay of community similarity with geographical distance is driven by multiple factors, such as gene drift, environmental selection, and the accumulation of mutations over time. While the distance-decay relationship has been recognized for several decades, there are certain circumstances where the biogeographical patterns of certain species and communities cannot be predicted by this relationship. The example addressed in this project is the case of thermophilic endospore-forming bacteria found in permanently cold deep ocean sediments. Thermophilic endospores (thermospores) are routinely found on the deep ocean floor, a permanently cold environment that does not support their metabolic activity (Hubert et al. 2009). Thermospores are metabolically dormant states developed by some thermophilic bacteria having optimal growth temperatures between 40°C and 70°C. There is evidence that these heat-loving bacteria originate from the deep subsurface and are transported upward to the deep ocean via geological features of the oceanic crust including geofluid fluxes in high-temperature axial systems and natural hydrocarbon seeps (Gittins et al. 2022). Due to the ability of endospores to stay viable for thousands of years and resist a wide range of physicochemical stressors, they can disperse over long distances while remaining unaffected by changing factors such as selection, drift, or mutation (Gittins et al. 2022; Fig. 1). Consequently, these thermospores have the potential to challenge the distance-decay relationship and exhibit unique biogeographical patterns. This work quantifies endospores in sediment cores at and around hydrocarbon seeps using cores from deep-sea Scotian Slope sediments. Given the challenge of quantifying specific groups of endospores (e.g., thermophiles but not mesophiles), high-temperature germination assays that allow tracking of an exponential increase in signal as spores in marine sediment samples germinate and grow can be used. Distinct exponential increases can be attributed to different populations of germinated thermospores in the post-germination growth phase and are being monitored through measurements of sulfate reduction rates (using radiolabelled 35SO4), strain-specific quantitative PCR (qPCR), and fluorescence in-situ hybridization (FISH) (Rezende et al. 2017). These measurements revealed growth dynamics enabling an estimation of the initial cell numbers using exponential functions. These approaches are being applied to samples obtained via push coring using a remotely operated vehicle at different distances from deep sea hydrocarbon seeps, to test for the presence of abundance gradients of different thermospores. Current results already show a difference in thermospore abundance between sites at different distances from the seep. Quantitative tracking of the dispersal of thermospores by oceanic currents in the deep sea provides an excellent opportunity to investigate their distribution and potential to colonize more remote habitats, improving the understanding of microbial biodiversity and biogeography on our planet. By investigating thermospores and their interactions with the geophysical features of the deep sea and deep subsurface, this study aims to challenge the canonical idea that speciation occurs with distance and presents new perspectives on the theme of microbial biogeography. The evidence supporting the subsurface origin of thermophilic endospores, along with the proposed model for their dispersal and distribution, will contribute toward improving an integrated understanding of ecology and geology and their intersection in the microbial realm.

Diel vertical migration of copepods in the tropical and subtropical Atlantic Ocean

The vertical distribution of the zooplankton community was analyzed from the surface to 800 m depth in the tropical-subtropical Atlantic Ocean in a transect of 12 stations during day and nighttime from Brazilian waters (10°S) to the Canary Islands (27°N). A depth stratified opening-closing 1 m2 mouth MOCNESS was used and 8 layers analyzed. Besides this net, the epipelagic layer (0–200 m) was sampled for microzooplankton (53 µm Calvet net) and mesozooplankton (200 µm WP2 net) communities. An increasing gradient of mesozooplankton abundance was observed from the oligotrophic waters off Brazil to the oceanic upwelling off Northwest Africa. Copepods were always the most abundant group (86 %) and 241 species identified, although only 60 were >1 %. Smaller species predominated and Oncaea was the dominant group (18 %) followed by Clausocalanus (14 %) with C. furcatus dominating. Paracalanus and Oithona were also quite abundant (12 and 9 % respectively). Small copepods such as C. furcatus and Euchaeta marina predominated in the oligotrophic waters while Calanus helgolandicus, Calanoides carinatus, Temora stylifera, Paracalanus parvus, and Pleuromamma robusta dominated in the upwelling area. In the epipelagic layer large copepods (e.g., Rhincalanus, Pleuromamma, Euchirella, and Metridia) were numerous during nighttime and in the mesopelagic zone during day were quantitatively less abundant. The vertical distribution of the dominant copepods (>1 %) showed multiple diel patterns but at least five were distinguished and their dominant taxa defined: (1) Species living in the twilight zone with slight up and down motion. (2) Species dominating the epipelagic layers with weak vertical movements. (3) Strong migrants living in the mesopelagic zone during day and moving upward towards the surface or (4) migrating to the subsurface layer at nighttime, and (5) those organisms characterizing the oceanic upwelling where the calanoids predominated (e.g., C. helgolandicus and C. carinatus). Our findings highlight the complexity in the diel vertical migration patterns of copepods in the tropical-subtropical Atlantic Ocean and the relevant role of the deep-sea copepods and their diel vertical migration. These results could be used as baseline information for low latitudes of the Atlantic Ocean in future studies of the biological carbon pump.

Spectroscopic age estimates for APOGEE red-giant stars: Precise spatial and kinematic trends with age in the Galactic disc

Over the last few years, many studies have found an empirical relationship between the abundance of a star and its age. Here we estimate spectroscopic stellar ages for 178 825 red-giant stars observed by the APOGEE survey with a median statistical uncertainty of 17%. To this end, we use the supervised machine learning technique XGBoost, trained on a high-quality dataset of 3060 red-giant and red-clump stars with asteroseismic ages observed by both APOGEE and Kepler. After verifying the obtained age estimates with independent catalogues, we investigate some of the classical chemical, positional, and kinematic relationships of the stars as a function of their age. We find a very clear imprint of the outer-disc flare in the age maps and confirm the recently found split in the local age-metallicity relation. We present new and precise measurements of the Galactic radial metallicity gradient in small age bins between 0.5 and 12 Gyr, confirming a steeper metallicity gradient for ∼2 − 5 Gyr old populations and a subsequent flattening for older populations mostly produced by radial migration. In addition, we analyse the dispersion about the abundance gradient as a function of age. We find a clear power-law trend (with an exponent β ≈ 0.15) for this relation, indicating a relatively smooth radial migration history in the Galactic disc over the past 7 − 9 Gyr. Departures from this power law may possibly be related to the Gaia Enceladus merger and passages of the Sagittarius dSph galaxy. Finally, we confirm previous measurements showing a steepening in the age-velocity dispersion relation at around ∼9 Gyr, but now extending it over a large extent of the Galactic disc (5 kpc < RGal < 13 kpc). To establish whether this steepening is the imprint of a Galactic merger event, however, detailed forward modelling work of our data is necessary. Our catalogue of precise stellar ages and the source code to create it are publicly available.

Oxygen, sulfur, and iron radial abundance gradients of classical Cepheids across the Galactic thin disk

Context. Classical Cepheids (CCs) are solid distance indicators and tracers of young stellar populations. Dating back to the beginning of the 20th century, they have been safely adopted to trace the rotation, kinematics, and chemical enrichment history of the Galactic thin disk. Aims. The main aim of this investigation is to provide iron, oxygen, and sulfur abundances for the largest and most homogeneous sample of Galactic CCs analyzed so far (1118 spectra of 356 objects). The current sample, containing 70 CCs for which spectroscopic metal abundances are provided for the first time, covers a wide range in galactocentric distances, pulsation modes, and pulsation periods. Methods. Optical high-resolution spectra with a high signal-to-noise ratio that were collected with different spectrographs were adopted to provide homogeneous estimates of the atmospheric parameters (effective temperature, surface gravity, and microturbulent velocity) that are required to determine the abundance. Individual distances were based either on trigonometric parallaxes by the Gaia Data Release 3 (Gaia DR3) or on distances based on near-infrared period-luminosity relations. Results. We found that iron and α-element radial gradients based on CCs display a well-defined change in the slope for galactocentric distances larger than ~12 kpc. We also found that logarithmic regressions account for the variation in [X/H] abundances from the inner to the outer disk. Radial gradients for the same elements, but based on open clusters covering a wide range in cluster ages, display similar trends. This means that the flattening in the outer disk is an intrinsic feature of the radial gradients because it is independent of age. Empirical evidence indicates that the S radial gradient is steeper than the Fe radial gradient. The difference in the slope is a factor of two in the linear fit (−0.081 vs. −0.041 dex kpc−1) and changes from −1.62 to −0.91 in the logarithmic distance. Moreover, we found that S (explosive nucleosynthesis) is underabundant on average when compared with O (hydrostatic nucleosynthesis). The difference becomes clearer in the metal-poor regime and for the [O/Fe] and [S/Fe] abundance ratios. We performed a detailed comparison with Galactic chemical evolution models and found that a constant star formation efficiency for galactocentric distances larger than 12 kpc accounts for the flattening observed in both iron and α-elements. To further constrain the impact of the predicted S yields for massive stars on radial gradients, we adopted a toy model and found that the flattening in the outermost regions requires a decrease of a factor of four in the current S predictions. Conclusions. CCs are solid beacons for tracing the recent chemical enrichment of young stellar populations. Sulfur photospheric abundances, when compared with other α-elements, have the key advantage of being a volatile element. Therefore, stellar S abundances can be directly compared with nebular sulfur abundances in external galaxies.

The hyperbenthic environment: A forgotten habitat for plastic pollution

This study investigates the abundances and composition of microplastics (MP) among the shallow layers of a coastal Mediterranean Marine Protected Area (Cabrera MPA), seafloor sediments, hyperbenthic environment, and the water column. The mid waters samples were collected mid-way between the sea surface and the seafloor and hyperbenthic samples at the water layer adjacent to the seafloor. Sampling was carried out on patchiness seafloor of Posidonia oceanica meadows. The seafloor sediments showed a mean abundance of 378,769.20 ± 508,109.11 MPs/m3, three orders of magnitude higher than the hyperbenthic (209.17 ± 117.07 MPs/m3), and the mid waters layer (106.48 ± 107.17 MPs/m3). An increasing vertical gradient in MP abundances, mainly composed of fibers was observed. Fibers were made-up mainly of polystyrene (PS, 25 %), expanded polystyrene (EPS, 18 %) and cellulose acetate (CA, 16 %). The results stress the need to increase efforts to find solutions to mitigate fiber pollution in the marine environment.

Assessing the accuracy of paired and random sampling for quantifying plant–plant interactions in natural communities

AbstractPlant interactions in extreme environments are often inferred from spatial associations and quantified by means of paired sampling. Yet, this method might be confounded by habitat‐sharing effects. Here, we address whether paired and random sampling methods provide similar results at varying levels of environmental heterogeneity. We quantified spatial associations with the two methods at three sites that encompass different micro‐environmental heterogeneity and stress levels: Mediterranean environments in Canary Islands, Spain, and Sardinia, Italy, and a cold alpine environment in Hokkaido, Japan. Then, we simulated plant communities with different levels of species micro‐habitat preferences, environmental heterogeneity, and stress levels. We found that differences in species associations between paired and random sampling were indistinguishable from zero in a homogeneous space. When simulating codispersion over a decreasing abundance gradient, both sampling methods correctly identified facilitation and distinguished it from codispersion. Yet, the pairwise method provided higher facilitation estimates than the random one. At each site, there were strong differences between beneficiary species in their spatial association with nurse species, and associations became more positive with increasing stress in Spain. Most importantly, there were no differences in results yielded by the two methods at any of the different stress levels at the Spanish and Japanese sites. At the Italian site, although micro‐environmental heterogeneity was low, we found weakly significant differences between methods that were unlikely due to habitat‐sharing effects. Thus, the paired sampling method can provide significant insights into net and long‐term effects of plant interactions in spatially conspicuous environments.

Study of the Human Microbiota Under Physiological Conditions

Profiling the human intestinal environment under physiological conditions involves characterizing the various components and factors in the gut to understand its normal functioning. This profiling can encompass multiple aspects, including the microbiome, host immune response, metabolites, and the physical environment of the intestine. Shalon and colleagues developed an ingestible device that collects samples from multiple regions of the human intestinal tract during normal digestion. The collection of 240 intestinal samples from 15 healthy individuals using the device and subsequent multi-omics analyses identified significant differences between bacteria, phages, host proteins, and metabolites in the intestines versus stool. Certain microbial taxa were differentially enriched, and prophage induction was more prevalent in the intestines than in stool. The host proteome and bile acid profiles varied along the intestines and were highly distinct from those of stool. Correlations between gradients in bile acid concentrations and microbial abundance predicted species that altered the bile acid pool through deconjugation. Furthermore, microbially conjugated bile acid concentrations exhibited amino acid-dependent trends that were not apparent in the stool. Overall, non-invasive, longitudinal profiling of microorganisms, proteins, and bile acids along the intestinal tract under physiological conditions can help elucidate the roles of the gut microbiome and metabolome in human physiology and disease. Nature. 2023 May;617(7961):581-591. doi: 10.1038/s41586-023-05989-7.

Modelling spatial variation in an exploited species across marine reserve boundaries

Abstract An increase in exploited species within marine reserves is often expected to benefit adjacent fished areas through the movement or ‘spill‐over’ of exploited species across reserve boundaries. However, harvest at and near reserve boundaries can also decrease abundances inside reserves, forming ‘edge‐effects’. Spatial analysis of gradients in abundance across reserve boundaries have been used to interpret the extents of edge‐effects and spill‐over. While the shape of these gradients will vary depending on species mobility and fishing intensity on reserve boundaries, they have largely been assumed to be gradual and quantified using continuous modelling strategies. This study shows that continuous modelling strategies can lead to overestimations of spill‐over and edge‐effects by underfitting the rapid transition in abundance that can occur from reserve to fished areas. The abundances of spiny lobster (Jasus edwardsii) across the boundaries of two north‐eastern New Zealand marine reserves were quantified using catch survey data collected over 2 years. Several modelling approaches were used, and the predictive performance of each approach was compared. Abrupt changes in lobster abundances were found across reserve boundaries and were best represented with models that incorporated a stepwise function across boundaries or where data from reserve and fished areas were modelled independently. Despite the mobile nature of this species, we found little evidence of edge‐effects and spill‐over within and adjacent to the surveyed marine reserves, which may reflect the low population status within these reserves. In contrast, standard continuous modelling approaches overestimated the extent of edge‐effects and spill‐over in both marine reserves. Policy implications. This study shows how accurate assessments of edge‐effects and spill‐over can be used to evaluate the effectiveness of existing marine reserves in protecting exploited species. These findings emphasise the importance comparing several different modelling strategies when evaluating edge‐effects and spill‐over to ensure appropriate model fits. Although modelling approaches such as generalised additive models present a simple solution to exploring spatial variation in ecological data, we emphasise the importance of questioning the applicability of such strategies when assessing variation across areas of rapid change such as protected area boundaries.

Unveiling the time evolution of chemical abundances across the Milky Way disc with APOGEE

ABSTRACT Chemical abundances are an essential tool in untangling the Milky Way’s enrichment history. However, the evolution of the interstellar medium abundance gradient with cosmic time is lost as a result of radial mixing processes. For the first time, we quantify the evolution of many observational abundances across the Galactic disc as a function of lookback time and birth radius, $\rm \text{R}_\text{birth}$. Using an empirical approach, we derive $\rm \text{R}_\text{birth}$ estimates for 145 447 APOGEE DR17 red giant disc stars, based solely on their ages and $\rm [Fe/H]$. We explore the detailed evolution of six abundances [Mg, Ca (α), Mn (iron-peak), Al, C (light), Ce (s-process)] across the Milky Way disc using 87 426 APOGEE DR17 red giant stars. We discover that the interstellar medium had three fluctuations in the metallicity gradient ∼9, ∼6, and ∼4 Gyr ago. The first coincides with the end of high-α sequence formation around the time of the Gaia–Sausage–Enceladus disruption, while the others are likely related to passages of the Sagittarius dwarf galaxy. A clear distinction is found between present-day observed radial gradients with age and the evolution with lookback time for both [X/Fe] and [X/H], resulting from the significant flattening and inversion in old populations due to radial migration. We find the $\rm [Fe/H]$–$\rm [\alpha /Fe]$ bimodality is also seen as a separation in the $\rm \text{R}_\text{birth}$–$\rm [X/Fe]$ plane for the light and α-elements. Our results recover the chemical enrichment of the Galactic disc over the past 12 Gyr, providing tight constraints on Galactic disc chemical evolution models.

On the origin of the Galactic thin and thick discs, their abundance gradients and the diagnostic potential of their abundance ratios

ABSTRACT Using a semi-analytical model of the evolution of the Milky Way, we show how secular evolution can create distinct overdensities in the phase space of various properties (e.g. age versus metallicity or abundance ratios versus age) corresponding to the thin and thick discs. In particular, we show how key properties of the Solar vicinity can be obtained by secular evolution, with no need for external or special events, like galaxy mergers or paucity in star formation. This concerns the long established double-branch behaviour of [alpha/Fe] versus metallicity and the recently found non-monotonic evolution of the stellar abundance gradient, evaluated at the birth radii of stars. We extend the discussion to other abundance ratios and we suggest a classification scheme, based on the nature of the corresponding yields (primary versus secondary or odd elements) and on the lifetimes of their sources (short-lived versus long-lived ones). The latter property is critical in determining the single- or double- branch behaviour of an elementary abundance ratio in the Solar neighbourhood. We underline the high diagnostic potential of this finding, which can help to separate clearly elements with sources evolving on different time-scales and help determining the site of e.g. the r-process(es). We define the ‘abundance distance’ between the thin and thick disc sequences as an important element for such a separation. We also show how the inside-out evolution of the Milky Way disc leads rather to a single-branch behaviour in other disc regions.

Profiling the human intestinal environment under physiological conditions

The spatiotemporal structure of the human microbiome1,2, proteome3 and metabolome4,5 reflects and determines regional intestinal physiology and may have implications for disease6. Yet, little is known about the distribution of microorganisms, their environment and their biochemical activity in the gut because of reliance on stool samples and limited access to only some regions of the gut using endoscopy in fasting or sedated individuals7. To address these deficiencies, we developed an ingestible device that collects samples from multiple regions of the human intestinal tract during normal digestion. Collection of 240 intestinal samples from 15 healthy individuals using the device and subsequent multi-omics analyses identified significant differences between bacteria, phages, host proteins and metabolites in the intestines versus stool. Certain microbial taxa were differentially enriched and prophage induction was more prevalent in the intestines than in stool. The host proteome and bile acid profiles varied along the intestines and were highly distinct from those of stool. Correlations between gradients in bile acid concentrations and microbial abundance predicted species that altered the bile acid pool through deconjugation. Furthermore, microbially conjugated bile acid concentrations exhibited amino acid-dependent trends that were not apparent in stool. Overall, non-invasive, longitudinal profiling of microorganisms, proteins and bile acids along the intestinal tract under physiological conditions can help elucidate the roles of the gut microbiome and metabolome in human physiology and disease.

The Behavior of Bp He-weak Stars in the Far-UV—Paper 5: HD 142301

The analysis of eigthteen spectra of the B8 He-weak Si star HD 142301 recorded by the SWP camera on board the International Ultraviolet Explorer reveals large variations of the far-ultraviolet spectral energy distribution over a time interval of 14 yr and 5 months. Variations are present shortwards of 1700 Å which can be partly attributed to variations of lines and continuum of Si ii. Other lines due to C ii and Si iii also contribute to the opacity in this range too. The variations suggest that silicon is not distributed in a uniform manner over the surface and that the horizontal gradients of the silicon abundance are probably large.