Éducation bancaire : l’émergence d’un espace financiarisé et privatisé d’encadrement des pauvres

International audienc

High shell deposition of the invasive clam Corbicula fluminea (Müller, 1774) on alluvial bars: exploratory investigations and biogeomorphological research perspectives

The exotic, invasive freshwater bivalve Corbicula fluminea (Bivalvia: Corbiculidae) has spread globally in rivers around the World within the last eighty years. Due to low inter-specific competition outside its native range, this mollusc often produces large quantities of shell within invaded rivers. These shells are deposited on alluvial bars during floods, potentially inducing changes in riverine geomorphological and ecological functioning. Based on observations undertaken on the middle Garonne River, we suggest that within invaded river systems, and at specific locations on alluvial bars, C. fluminea may represent a new factor contributing to the process of habitat construction and to the modification of the local physicochemical properties of the substrate. We suggest that deposited shells can be used as biochemical markers for several elements, such as heavy metals, and as geomorphic biomarkers for studying recent floodplain evolution and associated in-channel sedimentation rates.Le mollusque aquatique d’eau douce C. fluminea s’est répandu à travers le Monde depuis environ quatre-vingt ans. En raison d’une faible compétition interspécifique en dehors de son aire d’extension originelle, ce mollusque produit souvent de grandes quantités de coquilles dans les cours d’eau envahis. Ces coquilles se déposent sur les bancs alluviaux lors des crues, induisant potentiellement des modifications du fonctionnement géomorphologique et écologique de la zone riveraine. A partir d’observations entreprises sur la moyenne Garonne, nous suggérons que dans les hydrosystèmes fluviaux envahis, et à certains emplacements sur les bancs alluviaux, C. fluminea représente potentiellement un nouveau facteur de construction de l’habitat riverain et de modification des propriétés physicochimiques locales du substrat. Nous suggérons que les coquilles déposées peuvent être utilisées comme des marqueurs biogéochimiques de plusieurs éléments, par exemple les métaux lourds, et comme des bio-marqueurs géomorphologiques pour l’étude de l’évolution récente des plaines d’inondation et des taux de sédimentation au sein du lit mineur

Do diet variations influence body condition of the French Mediterranean planktivorous teleosts?

International audienc

Do diet variations influence body condition of the French Mediterranean planktivorous teleosts?

International audienc

Do diet variations influence body condition of the French Mediterranean planktivorous teleosts?

International audienc

Effect of source/sink ratios on yield components, growth dynamics and structural characteristics of oil palm (Elaeis guineensis) bunches

UMR AGAP - équipe AFEF - Architecture et fonctionnement des espèces fruitièresSource/sink ratios are known to be one of the main determinants of oil palm growth and development. A long-term experiment (9 years) was conducted in Indonesia on mature oil palms subjected to continuous bunch ablation and partial defoliation treatments to artificially modify source/sink ratios. During the experiment, all harvested bunches were dissected and phenological measurements were carried out to analyse the effect of source/sink ratios on yield components explaining variations in bunch number, the number of fruits per bunch and oil dry weight per fruit. An integrative variable (supply/demand ratio) describing the ratio between the assimilate supply from sources and the growing organ demand for carbohydrate was computed for each plant on a daily basis from observations of the number of developing organs and their sink strength, and of climate variables. Defoliation and bunch ablation affected the bunch number and the fruit number per bunch. Variations in bunch number per month were mainly due to variations in the fraction of aborted inflorescence and in the ratio between female and male inflorescences. Under fluctuating trophic conditions, variations in fruit number per bunch resulted both from changes in fruit-set and in the number of branches (rachillae) per inflorescence. For defoliated plants, the decrease in the number of developing reproductive sinks appeared to be sufficient to maintain fruit weight and oil concentration at the control level, without any major decrease in the concentration of non-structural carbohydrate reserves. Computation of the supply/demand ratio revealed that each yield component had a specific phase of sensitivity to supply/demand ratios during inflorescence development. Establishing quantitative relationships between supply/demand ratios, competition and yield components is the first step towards a functional model for oil palm

Selective Feeding of Bdelloid Rotifers in River Biofilms

<div><p><i>In situ</i> pigment contents of biofilm-dwelling bdelloid rotifers of the Garonne River (France) were measured by high performance liquid chromatography (HPLC) and compared with pigment composition of surrounding biofilm microphytobenthic communities. Among pigments that were detected in rotifers, the presence of carotenoids fucoxanthin and myxoxanthophyll showed that the rotifers fed on diatoms and cyanobacteria. Unexpectedly, while diatoms strongly dominated microphytobenthic communities in terms of biomass, HPLC results hinted that rotifers selectively ingested benthic filamentous cyanobacteria. In doing so, rotifers could daily remove a substantial fraction (up to 28%) of this cyanobacterial biomass. The possibility that the rotifers hosted symbiotic myxoxanthophyll-containing cyanobacteria was examined by localisation of chlorophyll fluorescence within rotifers using confocal laser scanning microscopy (CLSM). CLSM results showed an even distribution of quasi–circular fluorescent objects (FO) throughout rotifer bodies, whereas myxoxanthophyll is a biomarker pigment of filamentous cyanobacteria, so the hypothesis was rejected. Our results also suggest that rotifers converted β-carotene (provided by ingested algae) into echinenone, a photoprotective pigment. This study, which is the first one to detail <i>in situ</i> pigment contents of rotifers, clearly shows that the role of cyanobacteria as a food source for meiobenthic invertebrates has been underestimated so far, and deserves urgent consideration.</p> </div

Examples of HPLC absorbance chromatograms obtained at 440 nm from field samples.

<p>(A) biofilm, (B): rotifer (946 individuals). 1: chlorophylls <i>c</i>; 2: fucoxanthin-like; 3: pheophorbide <i>a</i>; 4: fucoxanthin; 5: diadinoxanthin; 6: myxoxanthophyll; 7: cis-fucoxanthin; 8: zeaxanthin-like; 9: zeaxanthin; 10: lutein; 11: chlorophyll b; 12: echinenone; 13: chlorophyll a-like; 14: chlorophyll <i>a</i>; 15: pheophytin <i>a</i>; 16: α-carotene; 17: β-carotene 18: echinenone-like1; 19: echinenone-like 2.</p

Comparison of pigment proportions between rotifer gut contents (rotifers) and their habitat (biofilm).

<p>(A) Fucoxanthin: Chl<i>a</i>-eq; (B): Myxoxanthophyll:Chl<i>a</i>-eq; Error bars are SD (n = 3). Fucoxanthin (Fuco) and myxoxanthophyll (myxo) are biomarkers for diatoms and filamentous cyanobacteria respectively.</p

Simulation of inflorescence dynamics in oil palm and estimation of environment-sensitive phenological phases: a model based analysis

UMR AGAP - équipe AFEF - Architecture et fonctionnement des espèces fruitièresFor oil palm, yield variation is in large part due to variation in the number of harvested bunches. Each successively-produced phytomer carries a female (productive), male or aborted inflorescence. Since phytomer development takes 3–4 years and nearly two phytomers are produced per month, many inflorescences develop in parallel but have different phenological stages. Environment-dependent developmental rate, sex and abortion probability determine bunch productivity, which, in turn, affects other phytomers via source–sink relationships. Water deficit, solar radiation, temperature and day length are considered key external factors driving variation. Their impact is difficult to predict because of system complexity. To address this question we built a simple model (ECOPALM) to simulate the variation in number of harvested bunches. In this model, trophic competition among organs, expressed through a plant-scale index (Ic), drives sex determination and inflorescence abortion during specific sensitive phases at phytomer level. As a supplemental hypothesis, we propose that flowering is affected by photoperiod at phytomer level during a sensitive phase, thus, contributing to seasonal production peaks. The model was used to determine by parameter optimisation the influence of Ic and day length on inflorescence development and the stages at which inflorescences are sensitive to these signals. Parameters were estimated against observation of number of harvested bunches in Ivory Coast using a genetic algorithm. The model was then validated with field observations in Benin and Indonesia. The sensitive phases determined by parameter optimisation agreed with independent experimental evidence, and variation of Ic explained both sex and abortion patterns. Sex determination seemed to coincide with floret meristem individualisation and occurred 29–32 months before bunch harvest. The main abortion stage occurred 10 months before harvest – at the beginning of rapid growth of the inflorescence. Simulation results suggest involvement of photoperiod in the determination of bunch growth dynamics. This study demonstrates that simple modelling approaches can help extracting ecophysiological information from simple field observations on complex systems