Showing papers by "Paul Sabatier University published in 2009"
TL;DR: It is suggested that, similar to the manifold that tree species leaf traits cluster around the 'leaf economics spectrum', a similar 'wood economics spectrum' may be defined.
Abstract: Wood performs several essential functions in plants, including mechanically supporting aboveground tissue, storing water and other resources, and transporting sap. Woody tissues are likely to face physiological, structural and defensive trade-offs. How a plant optimizes among these competing functions can have major ecological implications, which have been under-appreciated by ecologists compared to the focus they have given to leaf function. To draw together our current understanding of wood function, we identify and collate data on the major wood functional traits, including the largest wood density database to date (8412 taxa), mechanical strength measures and anatomical features, as well as clade-specific features such as secondary chemistry. We then show how wood traits are related to one another, highlighting functional trade-offs, and to ecological and demographic plant features (growth form, growth rate, latitude, ecological setting). We suggest that, similar to the manifold that tree species leaf traits cluster around the 'leaf economics spectrum', a similar 'wood economics spectrum' may be defined. We then discuss the biogeography, evolution and biogeochemistry of the spectrum, and conclude by pointing out the major gaps in our current knowledge of wood functional traits.
2,408 citations
TL;DR: The results support the notion that ongoing oscillations shape perception by providing a temporal reference frame for neural codes that rely on precise spike timing, and indicate that the visual detection threshold fluctuates over time along with the phase of ongoing EEG activity.
Abstract: Oscillations are ubiquitous in electrical recordings of brain activity. While the amplitude of ongoing oscillatory activity is known to correlate with various aspects of perception, the influence of oscillatory phase on perception remains unknown. In particular, since phase varies on a much faster timescale than the more sluggish amplitude fluctuations, phase effects could reveal the fine-grained neural mechanisms underlying perception. We presented brief flashes of light at the individual luminance threshold while EEG was recorded. Although the stimulus on each trial was identical, subjects detected approximately half of the flashes (hits) and entirely missed the other half (misses). Phase distributions across trials were compared between hits and misses. We found that shortly before stimulus onset, each of the two distributions exhibited significant phase concentration, but at different phase angles. This effect was strongest in the theta and alpha frequency bands. In this time-frequency range, oscillatory phase accounted for at least 16% of variability in detection performance and allowed the prediction of performance on the single-trial level. This finding indicates that the visual detection threshold fluctuates over time along with the phase of ongoing EEG activity. The results support the notion that ongoing oscillations shape our perception, possibly by providing a temporal reference frame for neural codes that rely on precise spike timing.
1,038 citations
TL;DR: Endocrine and autocrine/paracrine factors cooperate and lead to a fine regulation of lipolysis in adipocytes, which has therapeutic potential in the metabolic disorders frequently associated with obesity and probably in several inborn errors of metabolism.
696 citations
TL;DR: The 2XMM catalogue as mentioned in this paper is the largest ever made at X-ray wavelengths, containing 246 897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191 870 unique sources.
Abstract: Aims. Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods. The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results. The catalogue, the largest ever made at X-ray wavelengths, contains 246 897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191 870 unique sources. The catalogue fields cover a sky area of more than 500 deg(2). The non-overlapping sky area is similar to 360 deg(2) (similar to 1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties
620 citations
TL;DR: The experimental results reveal features of the decision process when pedestrians choose the side on which they evade, and show a side preference that is amplified by mutual interactions.
Abstract: In animal societies as well as in human crowds, many observed collective behaviours result from self-organized processes based on local interactions among individuals. However, models of crowd dynamics are still lacking a systematic individual-level experimental verification, and the local mechanisms underlying the formation of collective patterns are not yet known in detail. We have conducted a set of well-controlled experiments with pedestrians performing simple avoidance tasks in order to determine the laws ruling their behaviour during interactions. The analysis of the large trajectory dataset was used to compute a behavioural map that describes the average change of the direction and speed of a pedestrian for various interaction distances and angles. The experimental results reveal features of the decision process when pedestrians choose the side on which they evade, and show a side preference that is amplified by mutual interactions. The predictions of a binary interaction model based on the above findings were then compared with bidirectional flows of people recorded in a crowded street. Simulations generate two asymmetric lanes with opposite directions of motion, in quantitative agreement with our empirical observations. The knowledge of pedestrian behavioural laws is an important step ahead in the understanding of the underlying dynamics of crowd behaviour and allows for reliable predictions of collective pedestrian movements under natural conditions.
473 citations
TL;DR: A critical review on the coordination chemistry of the metal ions copper and zinc to the amyloid-beta (Abeta) peptide and the affinity of these metal ions towards the peptide, which has been linked to Alzheimer's disease.
Abstract: In the present perspective, we give a critical review on the coordination chemistry of the metal ions copper and zinc to the amyloid-β (Aβ) peptide; such complexes have been linked to Alzheimer's disease. We focus on two main issues: the identification of the coordination sphere of the Cu(II) and Zn(II) ions and the affinity of these metal ions towards the peptide. With the aim to come up with as few as possible valuable structural models and binding affinity values, we critically review the divergent propositions reported in the literature and take into account the experimental differences and the limits of the methods used in the published studies. We propose that: (i) the conditional dissociation constant of the Cu(Aβ) complexes lies in the range of 10 pM to 100 nM, with a preference for the region between 100 pM to 1 nM. (ii) Two most likely coordination modes for the predominant form of the Cu(Aβ) complexes at physiological pH can be retained, both being 3N1O distorted square planar. In the first model, the Cu(II) ion is coordinated by the Nτ atoms of the three His residues and the carboxylate of the Asp1. In the second model, both the N-terminus and the carboxylate functions of Asp1 are ligated together with the Nτ of His6 and of His13 (or His14). An equilibrium between these two forms at room temperature, and a preferentially freezing out of the second one would explain most of the divergences in the published results (in particular, between those obtained by EPR and NMR). (iii) The apparent dissociation constants of Zn(Aβ) in various buffers are in the range of 1 to 20 μM (a 10 times lower conditional dissociation constant can be estimated. (iv) For the Zn(II) coordination, the implication of the three His and the Asp1 residues is consensual. The Asp1 can be coordinated by the carboxylate and/or the N-terminus functions. Additional ligands are possible, such as Glu11 or H2O.
457 citations
TL;DR: The current standing of the research in this area of drug vectors is presented, and focus on two main families, namely matrix systems and vesicles.
Abstract: The increasing need for drug delivery systems that improve specificity and activity and at the same time reduce toxicity to ensure maximum treatment safety has led to the development of a great variety of drug vectors. Carriers based on soft matter have particularly interesting characteristics. Herein we present the current standing of the research in this area, and focus on two main families, namely matrix systems and vesicles. We outline the structure, properties, and potential applications of these vectors, and discuss their main advantages and drawbacks in their synthesis.
392 citations
TL;DR: It is shown that the HP1 homolog Rhino is required for nuage organization, transposon silencing, and ping-pong amplification of piRNAs, and appears to promote transcription of dual-strand clusters, leading to production ofPiRNAs that drive the ping- pong amplification cycle.
391 citations
TL;DR: Glomerular filtration rate can be predicted with a consistent relationship from early prematurity to adulthood and offers a clinically useful definition of renal function in children and young adults that is independent of the predictable changes associated with age and size.
Abstract: This study pools published data to describe the increase in glomerular filtration rate (GFR) from very premature neonates to young adults. The data comprises measured GFR (using polyfructose, 51Cr-EDTA, mannitol or iohexol) from eight studies (n = 923) and involved very premature neonates (22 weeks postmenstrual age) to adulthood (31 years). A nonlinear mixed effects approach (NONMEM) was used to examine the influences of size and maturation on renal function. Size was the primary covariate, and GFR was standardized for a body weight of 70 kg using an allometric power model. Postmenstrual age (PMA) was a better descriptor of maturational changes than postnatal age (PNA). A sigmoid hyperbolic model described the nonlinear relationship between GFR maturation and PMA. Assuming an allometric coefficient of 3/4, the fully mature (adult) GFR is predicted to be 121.2 mL/min per 70 kg [95% confidence interval (CI) 117–125]. Half of the adult value is reached at 47.7 post-menstrual weeks (95%CI 45.1–50.5), with a Hill coefficient of 3.40 (95%CI 3.03–3.80). At 1-year postnatal age, the GFR is predicted to be 90% of the adult GFR. Glomerular filtration rate can be predicted with a consistent relationship from early prematurity to adulthood. We propose that this offers a clinically useful definition of renal function in children and young adults that is independent of the predictable changes associated with age and size.
390 citations
TL;DR: The evidence on why tuberulosis notification is twice as high in men as in women in most countries is reviewed.
Abstract: The authors have declared that no competing interests exist.
The authors did not receive specific funding for this work. The ON laboratory is supported by the Centre National de la Recherche Scientifique (CNRS), the Fondation pour la Recherche Medicale (FRM), the Agence Nationale de la Recherche (ANR), and the European Union. The LQM laboratory is supported by the Institut Pasteur, CNRS, FRM and ANR. The funders had no role in decision to publish or preparation of the manuscript.
Provenance: Commissioned, externally peer reviewed.
343 citations
TL;DR: The Mediterranean climate and its variability depend on global-scale climate patterns and the teleconnections between the climate of the Mediterranean area and the global climatic system are discussed in this article.
TL;DR: Some of the key success factors and challenges for the HBSC study as it attempts to maximise its scientific output and channels the research findings into health improvement for young people are considered.
Abstract: This paper traces the history of the HBSC study from its origins in the early 1980’s to the present day describing how it was first conceptualised scientifically and how this influenced issues of study design. The challenges of managing a cross-national study are explained as are changes and adaptations over time with growth of the study from 3 to over forty country members. The key partnership with the World Health Organisation and its benefits are presented. With developments in scientific management and theoretical perspectives, HBSC has made a substantial contribution to the area of youth health. The last decade has seen increased dissemination to policy makers and evidence that scientific information arising from the study has influenced strategic policy development and practical health improvement programmes. This paper considers some of the key success factors and challenges for the study as it attempts to maximise its scientific output and channels the research findings into health improvement for young people. Future challenges for the study are also considered.
TL;DR: In this article, the authors attributed long-term climate moderation to chemical weathering; the higher the temperature and precipitation, the faster the weathering rate, and the more divalent cations were released to the environment.
TL;DR: In this paper, the degenerate complex Monge-Ampere equations of the form $(\omega+dd^c\f)^n = e^{t \f}\mu$ were studied.
Abstract: We study degenerate complex Monge-Ampere equations of the form $(\omega+dd^c\f)^n = e^{t \f}\mu$ where $\omega$ is a big semi-Kahler form on a compact Kahler manifold $X$ of dimension $n$, $t \in \R^+$, and $\mu=f\omega^n$ is a positive measure with density $f\in L^p(X,\omega^n)$, $p>1$. We prove the existence and unicity of continuous $\o$-plurisubharmonic solutions. In case $X$ is projective and $\omega=\psi^*\omega'$, where $\psi:X\to V$ is a proper birational morphism to a normal projective variety, $[\omega']\in NS_{\R} (V)$ is an ample class and $\mu$ has only algebraic singularities, we prove that the solution is smooth in the regular locus of the equation. We use these results to construct singular Kahler-Einstein metrics of non-positive curvature on projective klt pairs, in particular on canonical models of algebraic varieties of general type.
TL;DR: The neonicotinoids acetamiprid and thiamethoxam tested at the highest dose and fipronil at one‐five‐hundredth of LD50 have limited effects on the motor, sensory, and cognitive functions of the honeybee.
Abstract: Laboratory bioassays were conducted to evaluate on honeybee behavior the effects of sublethal doses of insecticides chronically administered orally or by contact. Emergent honeybees received a daily dose of insecticide ranging from one-fifth to one-five-hundredth of the median lethal dose (LD50) during 11 d. After exposure to fipronil (0.1 ng/bee and 0.01 ng/bee), acetamiprid (1 mug/bee and 0.1mug/bee) or thiamethoxam (1ng/bee and 0.1 ng/bee), behavioral functions of honeybees were tested on day 12. Fipronil, used at the dose of 0.1 ng/bee, induced mortality of all honeybees after one week of treatment. As a result of contact treatment at 0.01 ng/bee, honeybees spent significantly more time immobile in an open field apparatus and ingested significantly more water. In the olfactory conditioning paradigm, fipronil-treated honeybees failed to discriminate between a known and an unknown odorant. Thiamethoxam by contact induced either a significant decrease of olfactory memory 24 h after learning at 0.1 ng/bee or a significant impairment of learning performance with no effect on memory at 1 ng/bee. Responsiveness to antennal sucrose stimulation was significantly decreased for high sucrose concentrations in honeybees treated orally with thiamethoxam (1 ng/bee). The only significant effect of acetamiprid (administered orally, 0.1 mug/bee) was an increase in responsiveness to water. The neonicotinoids acetamiprid and thiamethoxam tested at the highest dose (one-tenth and one-fifth of their oral LD50 respectively) and fipronil at one-five-hundredth of LD50 have limited effects on the motor, sensory and cognitive functions of the honeybee. Our data on the intrinsic toxicity of the compounds after chronic exposure have to be taken into account for evaluation of risk to honeybees in field conditions.
TL;DR: It is shown that foraging ants can solve nutritional challenges for the colony by making intricate adjustments to their feeding behavior and nutrient processing, acting both as a collective mouth and gut.
TL;DR: The focus of this review is to describe the different aspects of what is known of the mechanism of membrane permeabilization and associated gene transfer and, by doing so, what are the actual limits of the DNA delivery into cells.
Abstract: Cell membranes can be transiently permeabilized under application of electric pulses. This treatment allows hydrophilic therapeutic molecules, such as anticancer drugs and DNA, to enter into cells and tissues. This process, called electropermeabilization or electroporation, has been rapidly developed over the last decade to deliver genes to tissues and organs, but there is a general agreement that very little is known about what is really occurring during membrane electropermeabilization. It is well accepted that the entry of small molecules, such as anticancer drugs, occurs mostly through simple diffusion after the pulse while the entry of macromolecules, such as DNA, occurs through a multistep mechanism involving the electrophoretically driven interaction of the DNA molecule with the destabilized membrane during the pulse and then its passage across the membrane. Therefore, successful DNA electrotransfer into cells depends not only on cell permeabilization but also on the way plasmid DNA interacts with the plasma membrane and, once into the cytoplasm, migrates towards the nucleus. The focus of this review is to describe the different aspects of what is known of the mechanism of membrane permeabilization and associated gene transfer and, by doing so, what are the actual limits of the DNA delivery into cells.
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TL;DR: In this paper, it was shown that if the boundary of a minimiser is sufficiently flat in the unit ball, then it is a smooth piece of hypersurface, similar to the de Giorgi-gi theory for minimal surfaces.
Abstract: The de Giorgi theory for minimal surfaces consists in studying sets whose indicator function is a (local) minimum of the BV norm. In this paper we replace the BV norm by the $H^\sigma$ norm, with $\sigma<1/2$, and try to understand what the minimisers look like. Parallel to the de Giorgi theory we prove that, if the boundary of a minimiser is sufficiently flat in the unit ball, then it is a smooth piece of hypersurface.
University of Bergen1, University of Copenhagen2, National Institutes of Health3, National University of Ireland, Galway4, University of Turin5, Ghent University6, University of Siena7, Istanbul University8, University of Southern Denmark9, University of Hamburg10, University of Edinburgh11, Karolinska Institutet12, Paul Sabatier University13
TL;DR: Overweight prevalence in youth remained high across the countries examined and the primary factors linked to overweight were breakfast consumption and physical activity.
Abstract: Objectives:
To examine overweight prevalence and its association with demographic and lifestyle factors in 11–15 year olds in the HBSC 2005–2006 survey.
TL;DR: This work presents a method for the triple functionalisation of oxidised SWCNTs with the anti-cancer drug doxorubicin, a monoclonal antibody, and a fluorescent marker at non-competing binding sites, and shows that the complex is efficiently taken up by cancer cells with subsequent intracellular release of doxorbicin.
TL;DR: It is proposed that Top1cc produce transcription arrests with R‐loop formation and generate DSBs that activate ATM in post‐mitotic cells.
Abstract: Ataxia telangiectasia mutated (ATM), the deficiency of which causes a severe neurodegenerative disease, is a crucial mediator for the DNA damage response (DDR). As neurons have high rates of transcription that require topoisomerase I (TOP1), we investigated whether TOP1 cleavage complexes (TOP1cc)—which are potent transcription-blocking lesions—also produce transcription-dependent DNA double-strand breaks (DSBs) with ATM activation. We show the induction of DSBs and DDR activation in post-mitotic primary neurons and lymphocytes treated with camptothecin, with the induction of nuclear DDR foci containing activated ATM, γ-H2AX (phosphorylated histone H2AX), activated CHK2 (checkpoint kinase 2), MDC1 (mediator of DNA damage checkpoint 1) and 53BP1 (p53 binding protein 1). The DSB–ATM–DDR pathway was suppressed by inhibiting transcription and γ-H2AX signals were reduced by RNase H1 transfection, which removes transcription-mediated R-loops. Thus, we propose that Top1cc produce transcription arrests with R-loop formation and generate DSBs that activate ATM in post-mitotic cells.
TL;DR: It is concluded that while DNA barcoding is an invaluable tool for detecting errors in identifications and for identifying plants at juvenile stages, its limited ability to identify collections will constrain the practical implementation of DNA-based tropical plant biodiversity programs.
Abstract: Background Large-scale plant diversity inventories are critical to develop informed conservation strategies. However, the workload required for classic taxonomic surveys remains high and is particularly problematic for megadiverse tropical forests. Methodology/Principal Findings Based on a comprehensive census of all trees in two hectares of a tropical forest in French Guiana, we examined whether plant DNA barcoding could contribute to increasing the quality and the pace of tropical plant biodiversity surveys. Of the eight plant DNA markers we tested (rbcLa, rpoC1, rpoB, matK, ycf5, trnL, psbA-trnH, ITS), matK and ITS had a low rate of sequencing success. More critically, none of the plastid markers achieved a rate of correct plant identification greater than 70%, either alone or combined. The performance of all barcoding markers was noticeably low in few species-rich clades, such as the Laureae, and the Sapotaceae. A field test of the approach enabled us to detect 130 molecular operational taxonomic units in a sample of 252 juvenile trees. Including molecular markers increased the identification rate of juveniles from 72% (morphology alone) to 96% (morphology and molecular) of the individuals assigned to a known tree taxon. Conclusion/Significance We conclude that while DNA barcoding is an invaluable tool for detecting errors in identifications and for identifying plants at juvenile stages, its limited ability to identify collections will constrain the practical implementation of DNA-based tropical plant biodiversity programs.
TL;DR: A convergent phenotype composition has been achieved through different mutations with different evolutionary histories, with some variants showing a long history of balancing selection among Eurasian and African populations, and one recent variant showing a fast spread in East Asia, likely due to positive selection.
Abstract: Because pathogens are powerful selective agents, host-cell surface molecules used by pathogens as identification signals can reveal the signature of selection. Most of them are oligosaccharides, synthesized by glycosyltransferases. One known example is balancing selection shaping ABO evolution as a consequence of both, A and B antigens being recognized as receptors by some pathogens, and anti-A and/or anti-B natural antibodies produced by hosts conferring protection against the numerous infectious agents expressing A and B motifs. These antigens can also be found in tissues other than blood if there is activity of another enzyme, FUT2, a fucosyltransferase responsible for ABO biosynthesis in body fluids. Homozygotes for null variants at this locus present the nonsecretor phenotype (se), because they cannot express ABO antigens in secretions. Multiple independent mutations have been shown to be responsible for the nonsecretor phenotype, which is coexisting with the secretor phenotype in most populations. In this study, we have resequenced the coding region of FUT2 in 732 individuals from 39 worldwide human populations. We report a complex pattern of natural selection acting on the gene. Although frequencies of secretor and nonsecretor phenotypes are similar in different populations, the point mutations at the base of the phenotypes are different, with some variants showing a long history of balancing selection among Eurasian and African populations, and one recent variant showing a fast spread in East Asia, likely due to positive selection. Thus, a convergent phenotype composition has been achieved through different mutations with different evolutionary histories.
TL;DR: The application of network theory to the analysis of interaction data reveals an unexpectedly complex picture of drug-target interactions, and confirms that the topology ofdrug-target networks depends implicitly on data completeness, drug properties, and target families.
Abstract: The availability of interaction data between small molecule drugs and protein targets has increased substantially in recent years. Using seven different databases, we were able to assemble a total of 4767 unique interactions between 802 drugs and 480 targets, which means that on average every drug is currently acknowledged to interact with 6 targets. The application of network theory to the analysis of these data reveals an unexpectedly complex picture of drug–target interactions. The results confirm that the topology of drug–target networks depends implicitly on data completeness, drug properties, and target families. The implications for drug discovery are discussed.
TL;DR: This work shows that new neurons in the DG are recruited into neuronal networks that support retrieval of remote spatial memory and that their activation is situation-specific, and reveals that once selected, new hippocampal neurons are durably incorporated into memory circuits, and also that their recruitment into hippocampal networks contributes predominantly to the updating and strengthening of a previously encoded memory.
Abstract: The dentate gyrus (DG), a hippocampal subregion, continuously produces new neurons in the adult mammalian brain that become functionally integrated into existing neural circuits. To what extent this form of plasticity contributes to memory functions remains to be elucidated. Using mapping of activity-dependent gene expression, we visualized in mice injected with the birthdating marker 5-bromo-2'-deoxyuridine the recruitment of new neurons in a set of controlled water maze procedures that engage specific spatial memory processes and require hippocampal-cortical networks. Here, we provide new evidence that adult-generated hippocampal neurons make a specific but differential contribution to the processing of remote spatial memories. First, we show that new neurons in the DG are recruited into neuronal networks that support retrieval of remote spatial memory and that their activation is situation-specific. We further reveal that once selected, new hippocampal neurons are durably incorporated into memory circuits, and also that their recruitment into hippocampal networks contributes predominantly to the updating and strengthening of a previously encoded memory. We find that initial spatial training during a critical period, when new neurons are more receptive to surrounding neuronal activity, favors their subsequent recruitment upon remote memory retrieval. We therefore hypothesize that new neurons activated during this critical period become tagged so that once mature, they are preferentially recruited into hippocampal networks underlying remote spatial memory representation when encountering a similar experience.
TL;DR: It is shown that the projections between different sensory and motor cortical areas and the thalamus enabled us to highlight the existence of thalamic nuclei that, by their connections, may represent an alternative pathway for information transfer between different Sensory and Motor cortical areas.
TL;DR: The Large Area Telescope (LAT) instrument on the Fermi Gamma-Ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET, and the LAT spectrum for this region of the sky is well reproduced by a diffuse galactic gamma-rays emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.
Abstract: The diffuse Galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements by the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma-Ray Observatory indicated excess gamma-ray emission > 1 GeV relative to diffuse Galactic gamma-ray emission models consistent with directly measured CR spectra (the so-called ``EGRET GeV excess''). The excess emission was observed in all directions on the sky, and a variety of explanations have been proposed, including beyond-the-Standard-Model scenarios like annihilating or decaying dark matter. The Large Area Telescope (LAT) instrument on the Fermi Gamma-ray Space Telescope has measured the diffuse gamma-ray emission with improved sensitivity and resolution compared to EGRET. We report on LAT measurements of the diffuse gamma-ray emission for energies 100 MeV to 10 GeV and Galactic latitudes 10 deg. <= |b| <= 20 deg. The LAT spectrum for this region of the sky is well reproduced by a diffuse Galactic gamma-ray emission model that is consistent with local CR spectra and inconsistent with the EGRET GeV excess.
TL;DR: This investigation was supported in part through research grants from the Environment Agency and the UK Department of Environment, Food and Rural Affairs, the Spanish Ministry of Education and Science and the EC Marie Curie programme.
Abstract: This investigation was supported in part through research grants from the Environment Agency (Sussex Area) and the UK Department of Environment, Food and Rural Affairs, the Spanish Ministry of Education and Science (REN2003-00477), the
Government of Catalonia (Distinction Award for University Research 2004 to EGB) and the EC Marie Curie programme
TL;DR: In this article, the authors used a new data set including daily discharge in 18 sub-basins to analyze the variability of regional extremes in the Amazon basin, after recalling the diversity of the hydrological annual cycles within the Amazon Basin.
TL;DR: The findings do not support the hypothesis that large seeds germinate faster than small seeds, but rather that small seeds germine faster, and propose four alternative mechanisms that could account for the observed pattern.
Abstract: Summary 1. Theoretical models predict that large-seeded species should germinate more rapidly than smallseeded species, since large seeds are more likely to have higher post-dispersal seed predation than small seeds. A prompt germination strategy would therefore enable large seeds to reduce risks of mortality. 2. To assess this predicted relationship between seed mass and mean time to germination (MTG), we used a meta-analysis of published data sources. Our data base contained information for these two traits for 1037 tree species from five tropical areas worldwide (Brazil, India, Ivory Coast, Malaysia and Panama). Both cross-species analyses and phylogenetically independent contrasts (PIC) were conducted on the log-transformed values of seed mass and MTG. 3. Log-seed mass was a significantly phylogenetically conserved trait in all five data sets. Log-MTG was significantly phylogenetically conserved in all sites except for Malaysia and India. 4. Log-MTG and log-seed mass were significantly positively correlated in all sites except for Malaysia. PIC analyses showed a significantly positive relationship in Brazil, India and Ivory Coast but not in Malaysia and Panama. When all sites were combined, PIC analyses indicated a significant positive relationship between these two traits. 5. Our findings do not support the hypothesis that large seeds germinate faster than small seeds, but rather that small seeds germinate faster. We interpret our results in light of phylogenetic and biophysical constraints. We propose four alternative mechanisms that could account for the observed pattern, including developmental constraints, water absorption and investment to physical defences.