Mass Abundance Research Articles

Life history and production of pelagic mysids and decapods in the Oyashio region, Japan

Pelagic Mysidacea and Decapoda have important roles in marine ecosystems. However, information on their life histories is extremely limited. This study aimed to evaluate the life cycles of pelagic Mysidacea and Decapoda in the Oyashio region, Japan. Production of the four dominant species was estimated by combining body mass (DM) data and abundance data. Mysidacea belonging to 5 species from 5 genera occurred in the study area. Their abundance and biomass ranged between 11.7-50.1 ind. m−2 and 1.2-7.9 g wet mass (WM) m−2, respectively. Six species from 6 genera belonged to Decapoda, and their abundance and biomass ranged between 9.0-17.3 ind. m−2 and 3.0-17.3 g WM m−2, respectively. Based on body length histograms, there were two to four cohorts for the three dominant mysids and one dominant decapod on each sampling date. Life histories of the two numerically dominant mysids (Eucopia australis and Boreomysis californica) followed similar patterns: recruitment of young in May, strong growth from April to June, and a longevity of three years. Life cycles of the two minor species (the mysid Meterythrops microphthalma and the decapod Hymenodora frontalis) were not clear because of their low abundance. The timing of recruitment of the young and the strong juvenile growth for the two dominant mysids corresponds with the season when their prey is abundant. The annual production of the dominant mysid species was 14.0 mg DM m−2 (B. californica) and 191.8 mg DM m−2 (E. australis). Annual production/biomass () ratios ranged between 0.242 (H. frontalis) and 0.643 (M. microphthalma). Compared with other regions, the Oyashio region showed high production and low ratios. The high production in the Oyashio region may be related to the high biomass of these species. Because of the low temperature conditions (3°C), pelagic mysids and decapods in the Oyashio region may have slower growth, longer generation times and lower ratios than in other oceans.

Dynamics of silver nanoparticle formation and agglomeration inside the cavitation bubble after pulsed laser ablation in liquid

The formation of nanoparticles within the laser-induced cavitation bubble is studied in situ using small angle X-ray scattering with high spatiotemporal resolution. Directly after laser ablation, two different particle fractions consisting of compact primary particles of 8-10 nm size and agglomerates of 40-60 nm size are formed. The abundance of these species is strongly influenced by the dynamics of the oscillating cavitation bubble. Primary particle mass is most abundant during maximal expansion of the first bubble and reappears a little weaker in the rebound. In contrast to this, the mass abundance of agglomerates is relatively low in the first bubble but strongly increases during first bubble collapse and following rebound. Although most of the ablated material is trapped inside the bubble and follows its oscillation, a minor fraction of both species could be detected outside the cavitation bubble even before its final collapse.

Cheddar: analysis and visualisation of ecological communities in R

Summary There has been a lack of software available to ecologists for the management, visualisation and analysis of ecological community and food web data. Researchers have been forced to implement their own data formats and software, often from scratch, resulting in duplicated effort and bespoke solutions that are difficult to apply to future analyses and comparative studies. We introduce Cheddar – an R package that provides standard, transparent implementations of a wide range of food web and community‐level analyses and plots, focussing on ecological network data that are augmented with estimates of body mass and/or numerical abundance. The package allows analysis of individual communities, as well as collections of communities, allowing examination of changes in structure through time, across environmental gradients, or due to experimental manipulations. Several commonly analysed food web data sets are included and used in worked examples. This is the first time these important features have been combined in a single package that helps improve research efficiency and serves as a unified framework for future development.

Multisite spectroscopic seismic study of the β Cep star V2052 Ophiuchi: inhibition of mixing by its magnetic field

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic β Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f1 = 7.148 46 d−1) and by rotational modulation (Prot = 3.638 833 d). Two non-radial low-amplitude modes (f2 = 7.756 03 d−1 and f3 = 6.823 08 d−1) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign and known in the literature. Using the photometric constraints on the degrees ℓ of the pulsation modes, we show that both f2 and f3 are prograde modes with (ℓ, m) = (4, 2) or (4, 3). These results allowed us to deduce ranges for the mass (M ∈ [8.2, 9.6] M⊙) and central hydrogen abundance (Xc ∈ [0.25, 0.32]) of V2052 Oph, to identify the radial orders n1 = 1, n2 = −3 and n3 = −2, and to derive an equatorial rotation velocity veq ∈ [71, 75] km s−1. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (αov ∈ [0, 0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic β Cep star θ Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior.

Exceptional Late Pliocene microvertebrate diversity in northwestern Argentina reveals a marked small mammal turnover

Despite a century of paleontological work in Neogene sequences of northwestern Argentina there is still much to learn about the biotic diversity in this area during Pliocene times. We report a rich microvertebrate assemblage recovered from Late Pliocene deposits of Uquía Formation, Jujuy Province, northernmost Argentina. Taxa represented in the studied sample include members of Bufonidae (Amphibia: Anura), Iguanoidea (Reptilia: Squamata), Passeriformes (Aves), Argyrolagidae, Didelphidae, Caviidae, Ctenomyidae, Octodontidae, and Cricetidae (Mammalia). Taphonomic attributes indicate that the bone concentration was produced by owls. The remains were disposed highly concentrated suggesting that the assemblage would have been generated in a short lapse, indicating a low time-averaging, retaining the main ecological signals of the past living community. The studied assemblage is noteworthy because it encompasses at least five new genera of cricetid rodents, illustrating the oldest record in northwestern Argentina for this diverse family of mammals. In spite of clear taxonomic differences at specific and generic levels, the structure of the assemblage is ecologically comparable to modern small mammal communities in terms of body mass distribution, trophic structure and abundance, with a dominance of cricetids over marsupials and caviomorph rodents. Striking differences in taxonomic composition between the Uquian assemblage and the coeval record from central Argentina indicate biogeographical distinctions since the Late Pliocene. The new Uquian cricetids show that the early divergence times for phyllotine genera proposed by several authors cannot be supported. The dominance of phyllotines in the assemblage as well as the record of Microcavia and an octodontid allow inferring arid or semiarid paleoenvironment conditions, in a more or less open habitat. The studied assemblage reflects a noteworthy faunal turnover, which implies the establishment of cricetid rodents as the dominant group in the small mammal communities. This faunal change can be associated to increasing aridity during Late Pliocene worldwide.

Rapid Screening for 67 Drugs and Metabolites in Serum or Plasma by Accurate-Mass LC-TOF-MS

Sixty-seven drugs and metabolites were detected in serum or plasma using a fast (7.5 min) liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) method. This method was developed as a blood drug screen, with emphasis on the detection of common drugs of abuse and drugs used to manage chronic pain. Qualitative drug detection may identify a drug exposure, assure patient adherence with prescribed therapy and document abstinence from non-prescribed medications. Compound identification is based on chromatographic retention time, mass, isotope spacing and isotope abundance. Data analysis software (Agilent) generates a compound score based on how well these observed criteria matched theoretical and empirical values. The method was validated using fortified samples and 299 residual patient specimens (920 positive results). All results were confirmed by gas chromatography-MS or LC-tandem MS. The accuracy of positive results (samples meeting all qualitative criteria for retention time, mass and compound score) was >90% for drugs and/or metabolites, except for two benzodiazepines. There were 35 false positive results (seven compounds, 3.8%) that could be distinguished by retention time and/or absence of metabolites. The most frequent was 6-acetylmorphine in the absence of morphine. The LC-TOF-MS targeted screening method presented represents a sensitive and specific technology for drug screening of serum or plasma.

Toxin-Producing Ostreopsis cf. ovata are Likely to Bloom Undetected along Coastal Areas

Mass appearances of the toxic dinoflagellate genus Ostreopsis are known to cause dangerous respiratory symptoms in humans exposed to aerosols. The outbreaks can appear in shallow marine waters of temperate regions around the globe. We followed a massive bloom event on a public beach on the northern Adriatic coast near Rovinj, Croatia. We identified the responsible species and the produced toxins as well as the dynamics of the event with respect to environmental conditions. Ostreopsis cf. ovata appeared in masses from September through October 2010 on a public beach near Rovinj, Croatia but stayed undetected by public health organizations. Respiratory symptoms were observed whenever humans were exposed to substrate samples containing large numbers of Ostreopsis cells. During the mass abundance of O. cf. ovata also exposure to the aerosols on the beach evoked respiratory symptoms in humans. Our measurements showed high cell abundances and high toxin contents with a stable relative contribution of putative Palytoxin and Ovatoxins a-e. Artificial beach structures proved to dramatically reduce settling of the observed Ostreopsis biofilm. Blooms like those reported herein have a high potential to happen undetected with a high potential of affecting the health of coastal human populations. Increased monitoring efforts are therefore required to understand the ecology and toxicology of those bloom events and reduce their negative impact on coastal populations.

Ecology and Distribution of the Isopod Genus Idotea in the Baltic Sea: Key Species in a Changing Environment

AbstractMarine isopods of the genus Idotea [I. balthica (Pallas, 1772), I. chelipes (Pallas, 1766), and I. granulosa Rathke, 1843] are common meso-grazers that enter deep into the Baltic Sea and here appear to live at their physiological limit, determined by salinity and temperature tolerance. We review available data on distribution and community ecology to assess the functional role of Idoteain the Baltic Sea and how global change may affect essential ecological interactions. Data from the last 150 years suggest an on-going shift southward for I. chelipes and I. granulosa that may be caused by a changing climate. Several studies report local extinctions and mass abundances, which may be caused by a changing food web from over-fishing and eutrophication. The three species of Idotea have clear habitat segregation in the Baltic Sea, where salinity, temperature and vegetation are the main dimensions. Idotea spp. have a central role as grazers and in communities dominated by the perennial macrophytes Fucus spp. and Zostera marina and attain impressive feeding rates on a range of epiphytes/filamentous algae (top-down effect). Idotea can have both a direct negative grazing effect on macrophytes but also an indirect positive effect by removing epiphytes. The relative role of nutritional value and chemical defence for food preference is yet unclear for Idotea. Baltic idoteids are also important prey for several fish (bottom-up effect) and fish predation may have increased following overfishing of piscivorous fish. It is concluded that Idotea is a key taxon in the Baltic Sea food web, where guilds often contain few dominant species. Changes in population dynamics of Idotea, as a function of human generated global change, may have large-scale consequences for ecosystem functions in a future Baltic Sea, e.g. the extent of vegetation cover in the coastal zone.

Characterization and Inventory of PCDD/F Emissions from the Ceramic Industry in China

The ceramic industry is considered to be a potential source of dioxins (polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), considering the widespread distribution of dioxins in kaolinitic clays. Nevertheless, studies on the emission of dioxins from the ceramic industry are still very scarce. In this study, raw clays and stack gases from six typical ceramic plants in China were collected and analyzed to estimate the emission of dioxins from the ceramic industry. Dioxin profiles in raw clays were characterized by the domination of the congener octachlorodibenzo-p-dioxin (OCDD), and the contents of other congeners declined with the decreasing degree of chlorination. During the ceramic firing process, a considerable amount (16.5-25.1 wt % of the initial quantity in raw clays) of the dioxins was not destroyed and was released to the atmosphere. Dechlorination of OCDD generated a broad distribution within the PCDD congeners including a variety of non-2,3,7,8-substituted ones with the mass abundance of 0.4-3.6%. Based on the mean concentrations measured in this study, the inventory of PCDD/Fs from the manufacturing of ceramics on the Chinese scale was estimated to be 7.94 kg/year; the corresponding value on the I-TEQ basis is 133.6 g I-TEQ/year. This accounts for about 1.34% (I-TEQ basis) of the total emission of dioxins to the environment in China. The results suggest that the ceramic industry is a significant source of dioxins in the environment.

High throughput quantitation of artesunate and its degradation products by flow injection gradient ratio standard addition mass spectrometry (FI-GRSA-MS)

There is a pressing need to equip post-marketing drug quality surveillance systems with higher throughput and robust analytical tools that can reinforce pharmaceutical quality control to ensure safety of patients and integrity of treatment practices. This manuscript reports the development of a flow injection analysis mass spectrometry-based gradient ratio standard addition (FI-GRSA-MS) method for quantification of artesunate, a common antimalarial active pharmaceutical ingredient in a simple, efficient, accurate, and high throughput manner. Dodecylamine (DDA) was evaluated as an electrospray modifier for improving the sensitivity of the GRSA quantitation method. The linear dynamic range and precision for artesunate quantification were found to be 7 ng to 86 pg artesunate and 2.1%, respectively. When compared to high performance liquid chromatography, results were found to be equivalent at the 95% confidence level. To identify chemical markers of improper drug storage and artesunate degradation, tablets were artificially exposed to heat for time periods ranging between 1 and 12 hours and the degradation products detected were identified via accurate mass and isotopic cluster abundance measurements. Moreover, degradation behavior of artesunate tablets from two different manufacturers under identical degradation conditions was investigated, indicating that tablet formulation plays a significant role in the shelf life of these valuable medicines.

A re-evaluation of the use of branched GDGTs as terrestrial biomarkers: Implications for the BIT Index

This study examines estimates of soil organic matter content (%OMsoil) in marine sediments based on the branched/isoprenoid tetraether (BIT) Index, and suggests a new calculation method based on branched GDGT (brGDGT) concentrations. Four sediment cores were collected in 2008 at the 20m isobath of the Louisiana Continental Shelf. Glycerol dialkyl glycerol tetraether (GDGTs) and cupric oxide (CuO) oxidation products were analyzed down to ∼20cm depth to examine terrestrially-derived organic matter. BIT Indices ranged from 0.50 to 0.03, and correlated poorly with lignin (mg S, V, and C phenols 10g−1 sediment; ∑810) and 3,5-dihydroxybenzoic acid (μg 3,5-Bdg−1 sediment; 3,5:g) concentrations, which ranged from 0.01 to 0.87mgg−1 and 0.00 (below detection limit) to 1.39μgg−1, respectively. By calculating mass normalized core-lipid branched GDGT (brGDGT) and crenarchaeol mass abundances with the assistance of a surrogate standard, it was shown that overall, large variations in sedimentary crenarchaeol concentrations were responsible for vertical distributions of BIT Indices, due to the relatively smaller range of brGDGT concentrations. brGDGT concentrations produced stronger correlations with terrestrial CuO oxidation products than the BIT Index, which correlated strongly with crenarchaeol concentrations. Variations in the BIT Index may therefore reflect changes in the delivery of marine-derived organic matter to sediments in regions with large seasonal or decadal shifts in productivity, such as stratified continental shelves. An in depth look at conversions of the BIT Index to percent soil organic matter using a binary mixing model with a marine BIT value of 0 and a terrestrial BIT value of 1 (%OMsoil=BIT Index*100) used in recent literature reveals that this method results in non-linear mixing of marine and terrestrial end-members, and the shape of the mixing line is based on sedimentary crenarchaeol concentrations. An alternative approach is to use sedimentary brGDGT yields as a OMsoil proxy, rather than normalizing them to crenarchaeol. %OMsoil could then be calculated using brGDGT concentrations in a two end-member mixing model as follows:%OMsoil=([brGDGT]sample*100)/[brGDGT]soil, where [brGDGT]sample and [brGDGT]soil represent the concentrations of branched GDGTs in the given sediment sample and in the average soil end-member, respectively. However, due to the wide range of brGDGT concentrations found in soils both regionally and globally, assigning a terrestrial end-member may not always be possible. While this method may in some instances also be a misrepresentation of %OMsoil in sediments, both estimation methods should be used with regard to their individual strengths and weaknesses.

Size-based food web characteristics govern the response to species extinctions

How ecological communities react to species extinctions is a long-standing yet current question in ecology. The species constituting the basic units of ecosystems interact with each other forming complex networks of trophic relationships and the characteristics of these networks are highly important for the consequences of species extinction. Here we take a more general approach and analyze a broad range of network characteristics and their role in determining food web susceptibility to secondary extinctions. We extend previous studies, that have focused on the consequences of topological and dynamical food web parameters for food web robustness, by also defining network-wide characteristics depending on the relationships between the distribution of species body masses and other species characteristics. We use a bioenergetic dynamical model to simulate realistically structured model food webs that differ in their structural and dynamical properties as well as their size structure. In order to measure food web robustness we calculated the proportion of species going secondarily extinct. A multiple regression analysis was then used to fit a general model relating the proportion of species going secondarily extinct to the measured food web properties. Our results show that there are multiple factors from all three groups of food web characteristics that affect food web robustness. However, we find the most striking effect was related to the body mass–abundance relationship which points to the importance of body mass relationships for food web stability.

Spitzer characterization of dust in an anomalous emission region: the Perseus cloud

Anomalous microwave emission is known to exist in the Perseus cloud. One of the most promising candidates to explain this excess of emission is electric dipole radiation from rapidly rotating very small dust grains, commonly referred to as spinning dust. Photometric data obtained with the Spitzer Space Telescope have been reprocessed and used in conjunction with the dust emission model DUSTEM to characterise the properties of the dust within the cloud. This analysis has allowed us to constrain spatial variations in the strength of the interstellar radiation field ($\chi_\mathrm{ISRF}$), the mass abundances of the PAHs and VSGs relative to the BGs (Y$_\mathrm{PAH}$ and Y$_\mathrm{VSG}$), the column density of hydrogen (N$_\mathrm{H}$) and the equilibrium dust temperature (T$_\mathrm{dust}$). The parameter maps of Y$_\mathrm{PAH}$, Y$_\mathrm{VSG}$ and $\chi_\mathrm{ISRF}$ are the first of their kind to be produced for the Perseus cloud, and we used these maps to investigate the physical conditions in which anomalous emission is observed. We find that in regions of anomalous emission the strength of the ISRF, and consequently the equilibrium temperature of the dust, is enhanced while there is no significant variation in the abundances of the PAHs and the VSGs or the column density of hydrogen. We interpret these results as an indication that the enhancement in $\chi_\mathrm{ISRF}$ might be affecting the properties of the small stochastically heated dust grains resulting in an increase in the spinning dust emission observed at 33 GHz. This is the first time that such an investigation has been performed, and we believe that this type of analysis creates a new perspective in the field of anomalous emission studies, and represents a powerful new tool for constraining spinning dust models.

Constraints on star formation driven galaxy winds from the mass-metallicity relation at z= 0

We extend a chemical evolution model relating galaxy stellar mass and gas-phase oxygen abundance (the mass-metallicity relation) to explicitly consider the mass-dependence of galaxy gas fractions and outflows. Using empirically derived scalings of galaxy mass with halo virial velocity in conjunction with the most recent observations of z~0 total galaxy cold gas fractions and the mass-metallicity relation, we place stringent global constraints on the magnitude and scaling of the efficiency with which star forming galaxies expel metals. We demonstrate that under the assumptions that metal accretion is negligible and the stellar initial mass function does not vary, efficient outflows are required to reproduce the mass-metallicity relation; without winds, gas-to-stellar mass ratios >~ 0.3 dex higher than observed are needed. Moreover, z=0 gas fractions are low enough that while they have some effect on the magnitude of outflows required, the slope of the gas fraction--stellar mass relation does not strongly affect our conclusions on how the wind efficiencies must scale with galaxy mass. Despite systematic uncertainties in the normalization and slope of the mass-metallicity relation, we show that the metal expulsion efficiency zetaw=(Zw/Zg)etaw (where Zw is the wind metallicitiy and Zg is the interstellar medium metallicity) must be both high and scale steeply with mass. Specifically, we show that zetaw >> 1 and zetaw proportional to vvir^-3 or steeper. In contrast, momentum- or energy-driven outflow models suggest that etaw should scale as vvir^-1 or vvir^-2, respectively, implying that the Zw-Mstar relation should be shallower than the Zg-Mstar relation. [abridged]

Fruit production of strawberry tree (Arbutus unedo L.) in two Spanish forests

Recent studies have emphasized the nutritional interest of the fruits of strawberry tree (Arbutus unedo L.), a species traditionally gathered in the Mediterranean region. Since fruit production in this species has been scarcely studied, we aimed to assess its local fruit supply in terms of fruit mass and fruit abundance. We carried out a 2-year study in two representative sites from continental and temperate regions of Central and Western Spain, respectively. Tree size, tree density and meteorological data were considered. The aged small population at Site 1 yielded 6.42 ± 1.19 kg per tree (46 ± 19 kg ha−1). The young large population from resprouts at Site 2, where forest management practices related to cork extraction have favoured shrubby growth forms, yielded 2.61 ± 0.42 kg per tree (539 ± 60 kg ha−1). Annual differences in fruit production per tree were recorded at Site 1, characterized by a Mediterranean climate with more severe continental traits than those at Site 2. This original data on wild fruit production may contribute to assessing the yield potential of this species for both sustainable use and cultivation purposes.

Modeling nearby FGK Population I stars: A new form of estimating stellar parameters using an optimization approach

Context. Modeling a single star with theoretical stellar evolutionary tracks is a nontrivial problem because of a large number of unknowns compared to the number of observations. A current way of estimating stellar age and mass consists of using interpolations in grids of stellar models and/or isochrones, assuming ad hoc values for the mixing length parameter and the metal-to-helium enrichment, which is normally scaled to the solar values. Aims. We present a new method to model the FGK main-sequence of Population I stars. This method is capable of simultaneously estimating a set of stellar parameters, namely the mass, the age, the helium and metal abundances, the mixing length parameter, and the overshooting. Methods. The proposed method is based on the application of a global optimization algorithm (PSwarm) to solve an optimization problem that in turn consists of finding the values of the stellar parameters that lead to the best possible fit of the given observations. The evaluation of the fitting objective function requires the use of a stellar evolution simulation code, however. Results. The methodology is tested using the Sun and five FGK fictitious stars, and is then adapted to 115 stars with a detailed spectroscopic analysis; half of these are planet-hosting stars. Conclusions. We present and discuss the stellar parameters estimated for each star in the context of previous works.

Long period variables and mass loss in the globular clusters NGC 362 and NGC 2808

The pulsation periods of long period variables (LPVs) depend on their mass and helium abundance as well as on their luminosity and metal abundance. Comparison of the observed periods of LPVs in globular clusters with models is capable of revealing the amount of mass lost on the giant branch and the helium abundance.} {We aim to determine the amount of mass loss that has occurred on the giant branches of the low metallicity globular clusters NGC 362 and NGC 2808. We also aim to see if the LPVs in NGC 2808 can tell us about helium abundance variations in this cluster.} We have used optical monitoring of NGC 362 and NGC 2808 to determine periods for the LPVs in these clusters. We have made linear pulsation models for the pulsating stars in these clusters taking into account variations in mass and helium abundance. Reliable periods have been determined for 11 LPVs in NGC 362 and 15 LPVs in NGC 2808. Comparison of the observed variables with models in the logP - K diagram shows that mass loss of ~0.15-0.2 Msun is required on the first giant branch in these clusters, in agreement with estimates from other methods. In NGC 2808, there is evidence that a high helium abundance of Y~0.4 is required to explain the periods of several of the LPVs. It would be interesting to determine periods for LPVs in other Galactic globular clusters where a helium abundance variation is suspected to see if the completely independent test for a high helium abundance provided by the LPVs can confirm the high helium abundance estimates.

Two Distinct Amyloid β-Protein (Aβ) Assembly Pathways Leading to Oligomers and Fibrils Identified by Combined Fluorescence Correlation Spectroscopy, Morphology, and Toxicity Analyses

Nonfibrillar assemblies of amyloid β-protein (Aβ) are considered to play primary roles in Alzheimer disease (AD). Elucidating the assembly pathways of these specific aggregates is essential for understanding disease pathogenesis and developing knowledge-based therapies. However, these assemblies cannot be monitored in vivo, and there has been no reliable in vitro monitoring method at low protein concentration. We have developed a highly sensitive in vitro monitoring method using fluorescence correlation spectroscopy (FCS) combined with transmission electron microscopy (TEM) and toxicity assays. Using Aβ labeled at the N terminus or Lys(16), we uncovered two distinct assembly pathways. One leads to highly toxic 10-15-nm spherical Aβ assemblies, termed amylospheroids (ASPDs). The other leads to fibrils. The first step in ASPD formation is trimerization. ASPDs of ∼330 kDa in mass form from these trimers after 5 h of slow rotation. Up to at least 24 h, ASPDs remain the dominant structures in assembly reactions. Neurotoxicity studies reveal that the most toxic ASPDs are ∼128 kDa (∼32-mers). In contrast, fibrillogenesis begins with dimer formation and then proceeds to formation of 15-40-nm spherical intermediates, from which fibrils originate after 15 h. Unlike ASPD formation, the Lys(16)-labeled peptide disturbed fibril formation because the Aβ(16-20) region is critical for this final step. These differences in the assembly pathways clearly indicated that ASPDs are not fibril precursors. The method we have developed should facilitate identifying Aβ assembly steps at which inhibition may be beneficial.

Active ulcerative colitis is associated with altered fatty acid precursor availability for the eicosanoid synthetic pathway

IntroductionThe polyunsaturated fatty acids (PUFA) arachidonic acid (AA), eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA) are generated from dietary essential fatty acids linoleic acid (LA) and α-linolenic...

Body mass–abundance relationships are robust to cascading effects in marine food webs

Body mass has been shown to scale negatively with abundance in a wide range of habitats and ecosystems. It is believed that this relationship has important consequences for the distribution and maintenance of energy in natural communities. Some studies have shown that the relationship between body mass and abundance may be robust to major food web perturbations, fuelling the belief that natural processes may preserve the slope of this relationship and the associated cycling of energy and nutrients. Here, we use data from a long‐term experimental food web manipulation to examine this issue in a semi‐natural environment. Similar communities were developed in large experimental mesocosms over a six month period. Some of the mesocosms were then subjected to species removals, based on the mean strength of their trophic interactions in the communities. In treatments where the strongest interactors were removed, a community‐level trophic cascade occurred. The biomass density of invertebrates increased dramatically in these communities, which led to a suppression of primary production. In spite of these widespread changes in ecosystem functioning, the slope of the relationship between body mass and abundance remained unchanged. This was the case whether average species body mass and abundance or individual organism size spectra were considered. An examination of changes in species composition before and after the experimental manipulations revealed an important mechanism for maintaining the body mass–abundance relationship. The manipulated communities all had a higher species turnover than the intact communities, with the highest turnover in communities that experienced cascading effects. As some species increased in body mass and abundance, new species filled the available size–abundance niches that were created. This maintained the overall body mass–abundance relationship and provided a stabilising structure to these experimental communities.