Temperature and nutrient effects on the relative importance of brown and green pathways for stream ecosystem functioning: A mesocosm approach

In addition to global warming, aquatic ecosystems are currently facing multiple global changes among which include changes in nitrogen (N) loads. While several studies have investigated both temperature and N impacts on aquatic ecosystems independently, knowledge on their interactive effects remains scarce. In forested headwater streams, decomposition of leaf litter represents the main process ensuring the transfer of nutrients and energy to higher trophic levels, followed by autochthonous primary production, mainly ensured by phototrophic biofilms. The main aim of this study was to disentangle the independent and combined effects of temperature increase and nutrient availability on the relative importance of brown and green processes involved in stream functioning. We hypothesised that water temperature and nutrients would lead to a general increase in leaf‐litter decomposition and primary production, but that the intensity of these effects would be largely modulated by competitive interactions arising between microorganisms as well as by the top‐down control of microorganisms by macro‐invertebrates. Macro‐invertebrates would, in turn, be bottom‐up controlled by microbial resources quality. To test these hypotheses, we conducted a 56‐day experiment in artificial streams containing leaf litter, microbial decomposers and biofilm inoculum, and an assemblage of macro‐invertebrates. Two water inorganic N:phosphorus (P) ratios (33 and 100, molar ratios) and two temperatures (ambient, +2°C) were manipulated, each treatment being replicated three times. Fungal and biofilm growth as well as leaf‐litter decomposition and primary production were quantified. Top‐down impacts of invertebrate primary consumers on brown and green compartments were evaluated using exclosures while bottom‐up control was evaluated through the measurement of resource stoichiometry and fatty acid profiles, as well as quantification of macro‐invertebrate growth and survival. Contrary to expectations, microbial decomposition was not significantly stimulated by nutrient or temperature manipulations, while primary production was only improved under ambient temperature. In the + 2°C treatment with high N:P, greater biofilm biomass was associated with lower fungal development, which indicates competition for nutrients in these conditions. Temperature increased macro‐invertebrate growth and leaf‐litter consumption, but this effect was independent of any improvement of basal resource quality, suggesting that temperature mediated changes in consumer metabolism and activity was the main mechanism involved. Most of our hypotheses that were based on simplified laboratory observations have been rejected in our semi‐controlled mesocosms. Our study suggests that the complexity of biological communities might greatly affect the response of ecosystems to multiple stressors, and that interactions between organisms must be explicitly taken into account when investigating the impacts of global change on ecosystem functioning

Vaccine breakthrough hypoxemic COVID-19 pneumonia in patients with auto-Abs neutralizing type I IFNs

Life-threatening `breakthrough' cases of critical COVID-19 are attributed to poor or waning antibody response to the SARS- CoV-2 vaccine in individuals already at risk. Pre-existing autoantibodies (auto-Abs) neutralizing type I IFNs underlie at least 15% of critical COVID-19 pneumonia cases in unvaccinated individuals; however, their contribution to hypoxemic breakthrough cases in vaccinated people remains unknown. Here, we studied a cohort of 48 individuals ( age 20-86 years) who received 2 doses of an mRNA vaccine and developed a breakthrough infection with hypoxemic COVID-19 pneumonia 2 weeks to 4 months later. Antibody levels to the vaccine, neutralization of the virus, and auto- Abs to type I IFNs were measured in the plasma. Forty-two individuals had no known deficiency of B cell immunity and a normal antibody response to the vaccine. Among them, ten (24%) had auto-Abs neutralizing type I IFNs (aged 43-86 years). Eight of these ten patients had auto-Abs neutralizing both IFN-a2 and IFN-., while two neutralized IFN-omega only. No patient neutralized IFN-ss. Seven neutralized 10 ng/mL of type I IFNs, and three 100 pg/mL only. Seven patients neutralized SARS-CoV-2 D614G and the Delta variant (B.1.617.2) efficiently, while one patient neutralized Delta slightly less efficiently. Two of the three patients neutralizing only 100 pg/mL of type I IFNs neutralized both D61G and Delta less efficiently. Despite two mRNA vaccine inoculations and the presence of circulating antibodies capable of neutralizing SARS-CoV-2, auto-Abs neutralizing type I IFNs may underlie a significant proportion of hypoxemic COVID-19 pneumonia cases, highlighting the importance of this particularly vulnerable population

COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study

Background: The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms. Methods: International, prospective observational study of 60 109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms. Results: ‘Typical’ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (≤ 18 years: 69, 48, 23; 85%), older adults (≥ 70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each P < 0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country. Interpretation: This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men

Les MOOC : analyse de dispositifs médiatisés et d'usages par des apprenants

International audienceLa troisième et dernière partie de notre atelier a porté sur la question de la description et de la catégorisation des MOOC. Les discussions menées avec F. Mangenot et I. Quentin ont nourri cette réflexion. Je me suis interrogée sur l'objet MOOC en m'intéressant tout d'abord à quelques typologies phares (Siemens, 2012 ; Daniel, 2012 ; Gilliot & al., 2013 ; Cisel, 2013 ; Rosselle & al., 2014) basées sur différents cadres théoriques. Ces typologies ont été crées afin d'analyser des MOOC existants et d'aider à la conception de MOOC à venir. J'ai montré les apports et limites de ces typologies. Parmi les limites principales, j'ai relevé : la multiplicité actuelle des typologies, peut-être par manque de recul en raison de la " nouveauté " des MOOC ; la focalisation de ces typologies sur l'analyse de la conception pédagogique des MOOC sans que d'autres dimensions ne soient réellement prises en compte. Afin de dépasser ces limites, je me suis référée à d'autres travaux (Grover & al., 2013 ; Conole, 2013 ; Caron & al., 2014) s'appuyant davantage sur des recherches précédentes en technologies éducatives et en EIAH. Ces travaux abordent les MOOC de façon plus complexe et m'ont permis de proposer une approche systémique visant à appréhender ces dispositifs en prenant en considération plusieurs angles d'analyse (discours sur la conception pédagogique, conception pédagogique elle-même, discours sur les utilisations, usages et pratiques et utilisations, usages et pratiques en eux-mêmes) en fonction des types d'acteurs (usagers, enseignants et animateurs, concepteurs, institutions) impliqués à différents niveaux dans le " phénomène " MOOC. Suite à cette présentation, les participants à l'atelier ont été amenés à réfléchir en groupe soit aux typologies présentées dans un premier temps, soit à l'approche introduite à la fin de mon court exposé. Voici les remarques principales formulées par les participants, qui se sont pour la plupart intéressés à l'utilisation et à l'analyse de l'approche proposée : D'un point de vue théorique, l'emploi du terme " système " a été questionné en raison des nombreuses références liées à celui-ci. Ont été proposés les termes " complexité " ou " transversalité ". Toutefois, après discussion, l'ancrage théorique fondé sur les travaux d'Engeström ayant été précisé, l'utilisation de ce terme a été acceptée. Concernant les catégories d'acteurs proposées, il a été souligné que celles-ci ne pouvaient englober l'ensemble des acteurs de façon pertinente. En effet, d'un point de vue macro au niveau des institutions, il conviendrait de distinguer les acteurs qui financent, régulent, réglementent, relèvent d'une dimension politique ou idéologique, etc. Au sujet des enseignants et animateurs, il serait également nécessaire de proposer des catégories plus précises. Pour ce qui est des " dimensions analysées " proposées dans notre approche, des références aux travaux de D. Paquelin sur l' " état prescrit ", " état perçu ", " état prévu ", " état vécu " ont été suggérées. Afin d'approfondir mon approche, des liens avec les travaux de B. Albero ont également été abordés pour appréhender les dispositifs MOOC dans une approche sociotechnique croisant différents niveaux d'analyse. D'un point de vue pratique, l'approche systémique proposée a été utilisée par l'un des groupes de l'atelier afin d'aider à la conception d'un MOOC à venir. Je n'avais pas envisagé cette approche sous cet angle dans la mesure où j'y voyais davantage une analyse de l'existant qu'un soutien direct à la conception. Toutefois, il est évident que l'analyse de l'existant est indispensable pour la conception à venir

Les MOOC : analyse de dispositifs médiatisés et d'usages par des apprenants

International audienceLa troisième et dernière partie de notre atelier a porté sur la question de la description et de la catégorisation des MOOC. Les discussions menées avec F. Mangenot et I. Quentin ont nourri cette réflexion. Je me suis interrogée sur l'objet MOOC en m'intéressant tout d'abord à quelques typologies phares (Siemens, 2012 ; Daniel, 2012 ; Gilliot & al., 2013 ; Cisel, 2013 ; Rosselle & al., 2014) basées sur différents cadres théoriques. Ces typologies ont été crées afin d'analyser des MOOC existants et d'aider à la conception de MOOC à venir. J'ai montré les apports et limites de ces typologies. Parmi les limites principales, j'ai relevé : la multiplicité actuelle des typologies, peut-être par manque de recul en raison de la " nouveauté " des MOOC ; la focalisation de ces typologies sur l'analyse de la conception pédagogique des MOOC sans que d'autres dimensions ne soient réellement prises en compte. Afin de dépasser ces limites, je me suis référée à d'autres travaux (Grover & al., 2013 ; Conole, 2013 ; Caron & al., 2014) s'appuyant davantage sur des recherches précédentes en technologies éducatives et en EIAH. Ces travaux abordent les MOOC de façon plus complexe et m'ont permis de proposer une approche systémique visant à appréhender ces dispositifs en prenant en considération plusieurs angles d'analyse (discours sur la conception pédagogique, conception pédagogique elle-même, discours sur les utilisations, usages et pratiques et utilisations, usages et pratiques en eux-mêmes) en fonction des types d'acteurs (usagers, enseignants et animateurs, concepteurs, institutions) impliqués à différents niveaux dans le " phénomène " MOOC. Suite à cette présentation, les participants à l'atelier ont été amenés à réfléchir en groupe soit aux typologies présentées dans un premier temps, soit à l'approche introduite à la fin de mon court exposé. Voici les remarques principales formulées par les participants, qui se sont pour la plupart intéressés à l'utilisation et à l'analyse de l'approche proposée : D'un point de vue théorique, l'emploi du terme " système " a été questionné en raison des nombreuses références liées à celui-ci. Ont été proposés les termes " complexité " ou " transversalité ". Toutefois, après discussion, l'ancrage théorique fondé sur les travaux d'Engeström ayant été précisé, l'utilisation de ce terme a été acceptée. Concernant les catégories d'acteurs proposées, il a été souligné que celles-ci ne pouvaient englober l'ensemble des acteurs de façon pertinente. En effet, d'un point de vue macro au niveau des institutions, il conviendrait de distinguer les acteurs qui financent, régulent, réglementent, relèvent d'une dimension politique ou idéologique, etc. Au sujet des enseignants et animateurs, il serait également nécessaire de proposer des catégories plus précises. Pour ce qui est des " dimensions analysées " proposées dans notre approche, des références aux travaux de D. Paquelin sur l' " état prescrit ", " état perçu ", " état prévu ", " état vécu " ont été suggérées. Afin d'approfondir mon approche, des liens avec les travaux de B. Albero ont également été abordés pour appréhender les dispositifs MOOC dans une approche sociotechnique croisant différents niveaux d'analyse. D'un point de vue pratique, l'approche systémique proposée a été utilisée par l'un des groupes de l'atelier afin d'aider à la conception d'un MOOC à venir. Je n'avais pas envisagé cette approche sous cet angle dans la mesure où j'y voyais davantage une analyse de l'existant qu'un soutien direct à la conception. Toutefois, il est évident que l'analyse de l'existant est indispensable pour la conception à venir

Chronic effects of REE-enriched sediments on the reproductive cycle of Gammarus fossarum (Crustacea Amphipoda)

International audienc

Do leaf‐litter decomposers control biofilm primary production and benthic algal community structure in forest streams? Insights from an outdoor mesocosm experiment

International audience1. Forested headwater streams are generally considered to be light‐limited ecosystems where primary production is reduced, and the main source of energy and nutrients is composed of allochthonous detritus. We hypothesised that in these ecosystems, the development of primary producers might also be limited by (1) competition for nutrients with leaf‐litter decomposers (e.g. bacteria and fungi), and (2) leaf‐litter leachates or allelopathic compounds produced by aquatic fungi. 2. To test these hypotheses, a 48‐day mesocosm experiment was performed in 12 artificial streams containing stream water inoculated with epilithic biofilm suspensions collected from a forested headwater stream. Three different treatments were applied: control without leaf litter (C), microbially conditioned leaf litter added at the beginning of the experiment and left to decompose throughout the experiment (L), or leaf litter renewed three times during the experiment (RL). 3. We predicted that (1) the presence of litter, through microbial nutrient immobilisation and allelopathy, would reduce primary production and that (2) this effect would be amplified by litter renewal. We also predicted that nutrient competition would mean that (3) leaf‐litter decomposers will alter primary producer community composition and physiology. These predictions were tested by analysing biofilm development, physiology, stoichiometry, and benthic algal community structure. To distinguish between the effects of nutrient immobilisation and allelopathy, the biofilm responses to leaf‐litter leachates collected after different microbial conditioning durations were also measured in a parallel laboratory experiment. 4. Contrary to our expectations, by day 28, primary producer growth was higher in the mesocosms containing leaf litter (L and RL) despite the rapid decrease in dissolved nutrients when leaf litter was present. After 48 days, the lowest phototrophic biofilm development was observed when leaf litter was renewed (RL), whereas phototrophic biofilm development was similar in the C and L treatments. Biofilm stoichiometry indicated that this effect was most probably related to greater nitrogen limitation in the RL treatment. The presence of leaf litter also affected primary producers' photophysiology, which could be attributed to changes in taxonomic composition and to physiological adjustments of primary producers. 5. Laboratory measurements showed that despite a strong inhibition of primary producer growth by unconditioned leaf‐litter leachates, microbially conditioned leaf litter had either low or no effects on the development of primary producers. 6. These results reveal that leaf‐litter decomposers can have both positive and negative effects on primary producers underlining the need to consider microbial interactions when investigating the functioning of forested headwater streams

Do leaf litter decomposers control benthic algae production and community structure? Insights from an outdoor mesocosm experiment

International audienc

Organic-matter decomposition as a bioassessment tool of stream functioning: A comparison of eight decomposition-based indicators exposed to different environmental changes

International audienceOrganic-matter decomposition has long been proposed as a tool to assess stream functional integrity, but this indicator largely depends on organic-matter selection. We assessed eight decomposition-based indicators along two well-known environmental gradients, a nutrient-enrichment gradient (0.2-1.4 mg DIN/L) in central Portugal and an acidification gradient (pH: 4.69-7.33) in north-eastern France to identify the most effective organicmatter indicator for assessing stream functional integrity. Functional indicators included natural leaf litter (alder and oak) in 10-mm and 0.5-mm mesh bags, commercial tea (Lipton green and rooibos teas in 0.25-mm mesh bags), wood sticks (wood tongue depressors) and cotton strips. Biotic indices based on benthic macroinvertebrates (IPtIN for Portugal and IBGN for France) were calculated to compare the effectiveness of structural and functional indicators in detecting stream impairment and to assess the relationship between both types of indicators. The effectiveness of organic-matter decomposition rates as a functional indicator depended on the stressor considered and the substrate used. Decomposition rates generally identified nutrient enrichment and acidification in the most acidic streams. Decomposition rates of alder and oak leaves in coarse-mesh bags, green and rooibos teas and wood sticks were positively related with pH. Only decomposition rates of rooibos tea and wood sticks were related with DIN concentration; decomposition rates along the nutrient-enrichment gradient were confounded by differences in shredder abundance and temperature among streams. Stream structural integrity was good to excellent across streams; the IPtI N index was unrelated to DIN concentration, while the IBGN index was positively related with pH. The relationships between decomposition rates and biotic indices were loose in most cases, and only decomposition rates of alder leaves in coarse-mesh bags and green tea were positively related with the IBGN. Commercial substrates may be a good alternative to leaf litter to assess stream functional integrity, especially in the case of nutrient enrichment

Effects of a salmon fish farm on benthic habitats in a high-energy hydrodynamic system: The case of the Rade de Cherbourg (English Channel)

(IF 3.02 [2018]; Q1)International audienceThe Rade de Cherbourg (RdC), in the North Cotentin (Normandy, English Channel) is the only French coastal zone where an offshore salmon farm has been in operation over the past three decades. Our study leads to the identification of the Ecological Quality status of benthic habitats based on a one-year survey (2013–2014) underneath and near the cages as well as in non-impacted areas lying outside the influence of salmon farming. The semi-diurnal high tide regime of the Rade de Cherbourg (5 to 8 m tidal range from neap to spring tide) should prevent any significant accumulation of Organic Matter (OM) under the cages. Nevertheless, higher Total Organic Carbon (TOC) and the presence of opportunistic species at sampling stations under and near the cages indicate an impact of salmon farming on the benthic habitats. Three benthic assemblages are identified, corresponding to three sediment types with different levels of OM enrichment. The presence of several indicator species, such as the polychaete worm Capitella minima belonging to the Capitellidae, reflects the local impact of fish farming without long-term accumulation of OM in the shallow waters of the RdC. Moreover, one of the main characteristics of the macrofauna of the RdC and neighbouring zones is the current very high abundance and dominance of the tanaid Apseudopsis latreillii in diverse sediment types. Benthic indices (AMBI, M-AMBI, and BO2A) were also able to distinguish three main zones in relation to the distance to salmon cages