Body size determines total reproductive-energy output. Most theories assume reproductive output is a fixed proportion of size, with respect to mass, but formal macroecological tests are lacking. ...Management based on that assumption risks underestimating the contribution of larger mothers to replenishment, hindering sustainable harvesting. We test this assumption in marine fishes with a phylogenetically controlled meta-analysis of the intraspecific mass scaling of reproductive-energy output. We show that larger mothers reproduce disproportionately more than smaller mothers in not only fecundity but also total reproductive energy. Our results reset much of the theory on how reproduction scales with size and suggest that larger mothers contribute disproportionately to population replenishment. Global change and overharvesting cause fish sizes to decline; our results provide quantitative estimates of how these declines affect fisheries and ecosystem-level productivity.
The development of synthetic chemistry since the early 1900s owes much to the service of organolithium reagents. Brilliant bases (e.g., deprotonating C–H bonds), nucleophiles (e.g., adding to ...unsaturated molecules), and transfer agents (e.g., delivering ligands to other metals), these versatile virtuosi and to a lesser extent the organic derivatives of the other common alkali metals sodium and potassium have proved indispensable in both academia and technology. Today these monometallic compounds are still utilized widely in synthetic campaigns, but in recent years they have been joined by an assortment of bimetallic formulations that also contain an alkali metal but in company with another metal. These bimetallic formulations often exhibit unique chemistry that can be interpreted in terms of synergistic effects, for which the alkali metal is essential, though it is often the second metal that performs the synthetic transformation. Here, this “alkali-metal-mediated” chemistry is surveyed focusing mainly on bimetallic formulations containing two alkali metals or an alkali metal paired with magnesium, calcium, zinc, aluminum, or gallium. In this International Year of the Periodic Table (IYPT), we ponder whether a Pairiodic Table of Element Pairs will emerge in the future.
Sub-daily ensemble rainfall forecasts that are bias free and reliably quantify forecast uncertainty are critical for flood and short-term ensemble streamflow forecasting. Post-processing of rainfall ...predictions from numerical weather prediction models is typically required to provide rainfall forecasts with these properties. In this paper, a new approach to generate ensemble rainfall forecasts by post-processing raw numerical weather prediction (NWP) rainfall predictions is introduced. The approach uses a simplified version of the Bayesian joint probability modelling approach to produce forecast probability distributions for individual locations and forecast lead times. Ensemble forecasts with appropriate spatial and temporal correlations are then generated by linking samples from the forecast probability distributions using the Schaake shuffle. The new approach is evaluated by applying it to post-process predictions from the ACCESS-R numerical weather prediction model at rain gauge locations in the Ovens catchment in southern Australia. The joint distribution of NWP predicted and observed rainfall is shown to be well described by the assumed log-sinh transformed bivariate normal distribution. Ensemble forecasts produced using the approach are shown to be more skilful than the raw NWP predictions both for individual forecast lead times and for cumulative totals throughout all forecast lead times. Skill increases result from the correction of not only the mean bias, but also biases conditional on the magnitude of the NWP rainfall prediction. The post-processed forecast ensembles are demonstrated to successfully discriminate between events and non-events for both small and large rainfall occurrences, and reliably quantify the forecast uncertainty. Future work will assess the efficacy of the post-processing method for a wider range of climatic conditions and also investigate the benefits of using post-processed rainfall forecasts for flood and short-term streamflow forecasting.
A description is given of a sequence of events which would have led to the appearance of the organic compounds and living cells present on Earth, one of which is human cells. The evolutionary events ...involved are proposed as having taken place in phosphate ion-dominated aqueous pools formed in regions associated with volcanoes. The mechanism involved the unique molecular structure variations and chemical properties of polyphosphoric acid and compounds of this acid producing urea as the first organic compound formed on Earth and derivatives of urea giving rise to DNA and RNA. The occurrence of the process in present times is considered possible.
Epigenetic modifications are heritable changes in gene expression not encoded by the DNA sequence. In the past decade, great strides have been made in characterizing epigenetic changes during normal ...development and in disease states like cancer. However, the epigenetic landscape has grown increasingly complicated, encompassing DNA methylation, the histone code, noncoding RNA, and nucleosome positioning, along with DNA sequence. As a stable repressive mark, DNA methylation, catalyzed by the DNA methyltransferases (DNMTs), is regarded as a key player in epigenetic silencing of transcription. DNA methylation may coordinately regulate the chromatin status via the interaction of DNMTs with other modifications and with components of the machinery mediating those marks. In this review, we will comprehensively examine the current understanding of the connections between DNA methylation and other epigenetic marks and discuss molecular mechanisms of transcriptional repression in development and in carcinogenesis.
Below the Mesophotic Baldwin, C C; Tornabene, L; Robertson, D R
Scientific reports,
03/2018, Letnik:
8, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Mesophotic coral ecosystems, which occur at depths of ~40 to 150 m, have received recent scientific attention as potential refugia for organisms inhabiting deteriorating shallow reefs. These ...ecosystems merit research in their own right, as they harbor both depth-generalist species and a distinctive reef-fish fauna. Reef ecosystems just below the mesophotic are globally underexplored, and the scant recent literature that mentions them often suggests that mesophotic ecosystems transition directly into those of the deep sea. Through submersible-based surveys in the Caribbean Sea, we amassed the most extensive database to date on reef-fish diversity between ~40 and 309 m at any single tropical location. Our data reveal a unique reef-fish assemblage living between ~130 and 309 m that, while taxonomically distinct from shallower faunas, shares strong evolutionary affinities with them. Lacking an existing name for this reef-faunal zone immediately below the mesophotic but above the deep aphotic, we propose "rariphotic." Together with the "altiphotic," proposed here for the shallowest reef-faunal zone, and the mesophotic, the rariphotic is part of a depth continuum of discrete faunal zones of tropical reef fishes, and perhaps of reef ecosystems in general, all of which warrant further study in light of global declines of shallow reefs.
DNA methylation is a crucial epigenetic modification of the genome that is involved in regulating many cellular processes. These include embryonic development, transcription, chromatin structure, X ...chromosome inactivation, genomic imprinting and chromosome stability. Consistent with these important roles, a growing number of human diseases have been found to be associated with aberrant DNA methylation. The study of these diseases has provided new and fundamental insights into the roles that DNA methylation and other epigenetic modifications have in development and normal cellular homeostasis.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Most synthetic chemists will have at some point utilized a sterically demanding secondary amide (R2N−). The three most important examples, lithium 1,1,1,3,3,3‐hexamethyldisilazide (LiHMDS), lithium ...diisopropylamide (LiDA), and lithium 2,2,6,6‐tetramethylpiperidide (LiTMP)—the “utility amides”—have long been indispensible particularly for lithiation (Li‐H exchange) reactions. Like organolithium compounds, they exhibit aggregation phenomena and strong Lewis acidity, and thus appear in distinct forms depending on the solvents employed. The structural chemistry of these compounds as well as their sodium and potassium congeners are described in the absence or in the presence of the most synthetically significant donor solvents tetrahydrofuran (THF) and N,N,N’,N’‐tetramethylethylenediamine (TMEDA) or closely related solvents. Examples of hetero‐alkali‐metal amides, an increasingly important composition because of the recent escalation of interest in mixed‐metal synergic effects, are also included.
Essential utilities: The Li, Na, and K salts of 1,1,1,3,3,3‐hexamethyldisilazide (HMDS, red), diisopropylamide (DA, green), and 2,2,6,6‐tetramethylpiperidide (TMP, blue) constitute one of the most synthetically important classes of compounds. In this Review, these bulky secondary amides are considered collectively, and their effectiveness as reagents discussed on the basis of their solution behavior and solid‐state structures.
We examine simultaneous X-ray and UV light curves from multi-epoch 8 d XMM–Newton observations of the narrow line Seyfert 1 galaxy 1H 0707–495. The simultaneous observations reveal that both X-ray ...and UV emission are variable and that the amplitude of the X-ray variations is significantly greater than that of the UV variations in both epochs. Using a discrete correlation function the X-ray and UV light curves were examined for correlation on time-scales up to 7 d. Low-significance (∼95 per cent confidence) correlations with the UV leading the X-ray variations are observed. The lack of a significant correlation between the UV and X-ray bands seems consistent with the X-ray source being centrally compact and dominated by light bending close to the black hole. In addition, multiband X-ray light curves were examined for correlations on similar time-scales. Highly significant (>99.9 per cent confidence) correlations were observed at zero lag consistent with previous studies of this active galactic nucleus.
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