Hétérogénéité horizontale des peuplements microphytoplanctoniques et zooplanctoniques en relation avec les paramètres abiotiques dans la retenue El Kansera (Maroc)

La répartition horizontale du phytoplancton et du zooplancton a été étudiée dans le lac-réservoir El Kansera en période de stabilité thermique, en relation avec certains paramètres abiotiques (transparence, matières en suspension, conductivité, température, oxygène dissous, pH, nutriments azotés et phosphorés).La répartition longitudinale du phytoplancton montre un gradient décroissant, avec des maxima de biomasse (poids frais) situés au 2/3 de la longueur du réservoir, et des pics de chlorophylle a enregistrés vers l'amont de la retenue. L'abondance du zooplancton suit une évolution quasi-analogue à celle du phytoplancton avec en plus, une répartition hétérogène des Rotifères et des différents stades de développement des Crustacés. Les Rotifères et les petits stades de développement des Cladocères ou des Copépodes sont concentrés dans la zone médiane du lac, tandis que les stades adultes de ces Crustacés dominent vers l'aval. La prédation vertébrée des " Carpes Chinoises ", associée à la mauvaise qualité de la nourriture algale en période d'étiage (blooms à Microcystis), seraient à l'origine de cette répartition. Les résultats de cette étude permettent de distinguer 3 zones de la retenue : la zone d'embouchure de l'oued** Beht (station S1) agitée, turbide et peu oxygènée est la moins productive, la zone médiane (stations S2 et S3), constituant la transition entre le milieu lotique et lacustre, est la plus enrichie en peuplements algaux et la plus peuplée par le zooplancton. Enfin, la zone lacustre proprement dite (stations S4 et S5) est assez productive et constitue un site idéal pour les adultes des Crustacés.The goal of this study is to assess the degree of horizontal heterogeneity of phytoplankton and zooplankton communities in the lake-reservoir El Kansera (Morocco), in order to define the principal factors responsible for the plankton distribution in the lake.Five stations have been studied; station S1 is the most influenced by allochthonous inputs from oued Beht (a tributary), stations S2 and S3 represent a transition between the lotic and lacustrine environments, and stations S4 and S5 represent true lacustrine conditions.The phytoplankton and zooplankton samplings were carried out during two seasons in 1996 (spring and summer), with a plankton net which consisted of a silk cone (height: 120 cm, mesh size: 40 µm). An average sample was prepared by several vertical tows. The samplings of chlorophyll and abiotic parameters were performed at different depths with a polyvinylchloride bottle with a capacity of 5 L and an automatic closing device. The phytoplankton counting was done according to the method of Legendre and Watt (1972). The algal biomass (µg.L-1) was estimated by chlorophyll-a (method of Lorenzen 1967) and wet weight (method of Lohmann (1908). Zooplankton counting was done in a Dolfuss cell (method of Pont 1983). The biomass of Rotifers, Cladocerans or Copepods (µg.L-1) was calculated according to the method of Dumont et al. (1975) and Bottrell et al. (1976). The physico-chemical analyses were performed at LPEE (Public Laboratory of Essay and Studies). Temperature, pH and conductivity were measured in situ, with a sounding Horiba U7. Dissolved oxygen was measured by the method of Winkler (Rodier 1984). Water transparency was measured by Secchi disc (Reynolds). Suspended matter was determined according to the method of AFNOR (1994). Nitrates and total phosphorus were analysed by colorimetry, respectively after reduction on a cadmium column and mineralization in acid medium (AFNOR 1994).The lake-reservoir El Kansera presents a longitudinal gradient (oued Beht-dyke) of biotic and abiotic parameters in relation both to morphometric and hydrologic characteristics and to the importance of allochthonous inputs and the nutrient cycles (nitrates and phosphorus). The maximum phytoplankton abundance (wet weight) is observed at 2/3 of the lake's length, and the chlorophyll-a peaks are recorded in the upper zone. In the spring, two alga species are dominant in the lake, Scenedesmus ecornis and Cyclotella ocellata, whereas in summer, one species is abundant (Microcystis aeruginosa).Zooplankton abundance shows a similar evolution to that of the phytoplankton, with a longitudinal heterogeneity of Rotifers (Brachionus calyciflorus, Polyarthra vulgaris and Keratella tropica) and different development stages of Cladocerans (Bosminalongirostris and Diaphanosoma brachyurum) and Copepods (Acanthocyclops robustus). Rotifers and the small stages of Crustaceans are concentrated in the median zone, whereas the Crustacean adults are dominant in the deeper point of the reservoir. Vertebrate predation by the " Chinese carp " and the degraded quality of the algae (blooms of Microcystis) also seem to contribute to this distribution.The results of the study, confirmed by the statistical Student test, indicate three zones in the lake-reservoir: the upper zone (station S1), which is located at the mouth of the oued Beht, is the least productive due to its shallow depth, low oxygenation, high turbidity and frequent mixing. The intermediate zone, between lotic and lacustrine conditions (stations S2 and S3), is strongly enriched with nutrients (nitrates and phosphorus) and characterised by a higher productivity; this zone presents dense phytoplanktonic populations. The lacustrine zone (stations S4 and S5) is of intermediate productivity, and offers good conditions for large size classes of Crustacea

Shear instabilities of freely standing thermotropic smectic-A films

In this Letter we discuss theoretically the instabilities of thermotropic freely standing smectic-A films under shear flow\cite{re:wu}. We show that, in Couette geometry, the centrifugal force pushes the liquid crystal toward the outer boundary and induces smectic layer dilation close to the outer boundary. Under strong shear, this effect induces a layer buckling instability. The critical shear rate is proportional to $1/\sqrt{d}$, where $d$ is the thickness of the film.Comment: 12 pages, 2 figure

Integrative genetic map of repetitive DNA in the sole Solea senegalensis genome shows a Rex transposon located in a proto-sex chromosome

Repetitive sequences play an essential role in the structural and functional evolution of the genome, particularly in the sexual chromosomes. The Senegalese sole (Solea senegalensis) is a valuable flatfish in aquaculture albeit few studies have addressed the mapping and characterization of repetitive DNA families. Here we analyzed the Simple Sequence Repeats (SSRs) and Transposable elements (TEs) content from fifty-seven BAC clones (spanning 7.9 Mb) of this species, located in chromosomes by multiple fluorescence in situ hybridization (m-BAC-FISH) technique. The SSR analysis revealed an average density of 675.1 loci per Mb and a high abundance (59.69%) of dinucleotide coverage was observed, being 'AC' the most abundant. An SSR-FISH analysis using eleven probes was also carried out and seven of the 11 probes yielded positive signals. 'AC' probes were present as large clusters in almost all chromosomes, supporting the bioinformatic analysis. Regarding TEs, DNA transposons (Class II) were the most abundant. In Class I, LINE elements were the most abundant and the hAT family was the most represented in Class II. Rex/Babar subfamily, observed in two BAC clones mapping to chromosome pair 1, showed the longest match. This chromosome pair has been recently reported as a putative sexual proto-chromosome in this species, highlighting the possible role of the Rex element in the evolution of this chromosome. In the Rex1 phylogenetic tree, the Senegalese sole Rex1 retrotransposon could be associated with one of the four major ancient lineages in fish genomes, in which it is included O. latipes

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Dynamique du phytoplancton en relation avec certains paramètres physico-chimiques dans la retenue El Kansera (Maroc)

L'étude de la dynamique saisonnière du phytoplancton dans la retenue El Kansera a été réalisée dans le but de comprendre au mieux le phénomène d'eutrophisation de cet écosystème lacustre. La biomasse (exprimée en poids frais) a été suivie pendant un cycle et demi, d'avril 1995 à août 1996. Cette période étant marquée par la transition d'une année de sécheresse avec une année pluvieuse, la composition et la dynamique saisonnière des peuplements algaux est analysée en fonction des variables environnementales. En 1995, année de sécheresse, le peuplement algal est dominé par les cyanobactéries, en particulier Microcystis aeruginosa qui représente plus de 99 % de la biomasse algale totale. En 1996, année pluvieuse, le peuplement algal est plus diversifié et constitué d'une diatomée centrique (Cyclotella ocellata) et de Chlorococcales (Crucigenia apiculata, Scenedesmus ecornis, Oocystis lacustris...). La saison d'été est marquée en revanche par la recolonisation du milieu par M.aeruginosa. Les variables environnementales (climat, physico-chimie de l'eau et apports exogènes) semblent régir de près la succession phytoplanctonique dans la retenue El Kansera

Évolution saisonnière des peuplements phytoplanctoniques dans le lac-réservoir El Kansera (Maroc), en relation avec certains paramètres abiotiques et biotiques

L'étude de l'évolution saisonnière des peuplements phytoplanctoniques dans le lac-réservoir El Kansera vise à comprendre le phénomène d'eutrophisation de cet écosystème lacustre marocain. La biomasse (poids frais en mg/l et chlorophylle a en μg/l) et la densité algale ont été suivies durant deux années consécutives (1995 et 1996), marquées par de fortes variations climatiques. Durant la première année d'étude (année de sécheresse), le pic algal se situe au printemps-été (73 mg/l en juin) ; il est do- miné en biomasse par la Cyanobactérie Microcystis aeruginosa. La chlorophylle a atteint un maximum de 40μ/l. L'année suivante (année pluvieuse), le peuplement algal est plus diversifié, suite à l'enrichissement du milieu en sels nutritifs : Diatomées (Cyclo- tella ocellata) et Chlorococcales du genre Crucigenia et Scenedesmus se succèdent au printemps. Mais en été, la Cyanobactérie Microcystis aeruginosa recolonise le milieu avec une biomasse de 72,7 mg/l. Les variables environnementales (climat, physico-chimie de l'eau et apports exogènes de l'oued Beht notamment) semblent régir de près la succession phytoplanctonique dans la retenue El Kansera. Le zooplancton régule peu la production algale (de Microcystis notamment), en raison de la grande taille de cette espèce et de son caractère toxique. Selon le modèle de I'O.C.D.E (1982), la retenue passe d'un stade hypereutrophe en 1995 à un stade méso-eutrophe en 1996, avec un retour à l'eutrophie en saison d'été