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A core of functional complementary bacteria infects oysters in Pacific Oyster Mortality Syndrome
No full textInternational audienceBackground The Pacific oyster Crassostrea gigas is one of the main cultivated invertebrate species worldwide. Since 2008, oyster juveniles have been confronted with a lethal syndrome known as the Pacific Oyster Mortality Syndrome (POMS). POMS is a polymicrobial disease initiated by a primary infection with the herpesvirus OsHV-1 µVar that creates an oyster immunocompromised state and evolves towards a secondary fatal bacteremia. Results In the present article, we describe the implementation of an unprecedented combination of metabarcoding and metatranscriptomic approaches to show that the sequence of events in POMS pathogenesis is conserved across infectious environments. We also identified a core bacterial consortium which, together with OsHV-1 µVar, forms the POMS pathobiota. This bacterial consortium is characterized by high transcriptional activities and complementary metabolic functions to exploit host's resources. A significant metabolic specificity was highlighted at the bacterial genus level, suggesting low competition for nutrients between members of the core bacteria. Conclusions Lack of metabolic competition between the core bacteria might favor complementary colonization of host tissues and contribute to the conservation of the POMS pathobiota across distinct infectious environments
Analysis of the Relative Entropy Asymmetry in the Regularization of Empirical Risk Minimization
No full textInternational audienceThe effect of the relative entropy asymmetry is analyzed in the empirical risk minimization with relative entropy regularization (ERM-RER) problem. A novel regularization is introduced, coined Type-II regularization, that allows for solutions to the ERM-RER problem with a support that extends outside the support of the reference measure. The solution to the new ERM-RER Type-II problem is analytically characterized in terms of the Radon-Nikodym derivative of the reference measure with respect to the solution. The analysis of the solution unveils the following properties of relative entropy when it acts as a regularizer in the ERM-RER problem: i) relative entropy forces the support of the Type-II solution to collapse into the support of the reference measure, which introduces a strong inductive bias that dominates the evidence provided by the training data; ii) Type-II regularization is equivalent to classical relative entropy regularization with an appropriate transformation of the empirical risk function. Closed-form expressions of the expected empirical risk as a function of the regularization parameters are provided
Differences in the behavior and diet between shoaling and solitary surgeonfish (Acanthurus triostegus)
No full textInternational audienceVariation in behavior within marine and terrestrial species can influence the functioning of the ecosystems they inhabit. However, the contribution of social behavior to ecosystem function remains underexplored. Many coral reef fish species provide potentially insightful models for exploring how social behavior shapes ecological function because they exhibit radical intraspecific variation in sociality within a shared habitat. Here, we provide an empirical exploration on how the ecological function of a shoaling surgeonfish (Acanthurus triostegus) may differ from that of solitary conspecifics on two Pacific coral reefs combining insight from behavioral observations, stable isotope analysis, and macronutrient analysis of gut and fecal matter. We detected important differences in how the social mode of A. triostegus affected its spatial and feeding ecology, as well as that of other reef fish species. Specifically, we found increased distance traveled and area covered by shoaling fish relative to solitary A. triostegus. Additionally, shoaling A. triostegus primarily grazed within territories of other herbivorous fish and had piscivorous and nonpiscivorous heterospecific fish associated with the shoal, while solitary A. triostegus grazed largely grazed outside of any territories and did not have any such interactions with heterospecific fish. Results from stable isotope analysis show a difference in δ15N isotopes between shoaling and solitary fish, which suggests that these different social modes are persistent. Further, we found a strong interaction between social behavior and site and carbohydrate and protein percentages in the macronutrient analysis, indicating that these differences in sociality are associated with measurable differences in both the feeding ecology and nutrient excretion patterns. Our study suggests that the social behavior of individuals may play an important and underappreciated role in mediating their ecological function
Actes du Colloque CIPAM & Cos 10, 19-23 novembre 2018 - Tahiti, Polynésie française: Nature et Culture: de la recherche à l'innovation, la valorisation et/ou la préservation
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Droits exclusifs d'importation et vivacité de la concurrence inter-marques : Le cas de la commercialisation de champagne à la Martinique
No full textInternational audienceRéférence : Venayre F., 2023, « Droits exclusifs d'importation et vivacité de la concurrence inter-marques : Le cas de la commercialisation de champagne à la Martinique », Revue Lamy de la Concurrence, n° 123, janvier, pp. 19-22
Circulations et partages d’expertise (France, Grande-Bretagne, États-Unis) : la bombe et les essais nucléaires français en Polynésie entre indépendance stratégique et dépendance technologique (1957-1998)
No full textInternational audienceEntre 1966 et 1996, 193 essais nucléaires sont réalisés par la France en Polynésie française, territoire d’outre-mer du Pacifique Sud. Cette région, nucléarisée, est investie dès 1946 par les puissances nucléaires que sont les États-Unis et la Grande-Bretagne. Quelle est la part de coopération technique par-delà l’affirmation d’une acquisition solitaire de la bombe par la France gaullienne, pour des raisons d’indépendance stratégique et de prestige politique
Du continent invisible à l'Aukus. L'Indo-Pacifique vue de l'Indo-Pacifique... et d'ailleurs
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La bombe et les essais nucléaires français entre indépendance stratégique et dépendance technologique (1957-1975)
No full textInternational audienceEntre 1960 et 1996, 210 essais nucléaires sont réalisés par la France dans le cadre de son programme nucléaire militaire. Quelle est la part de coopération technique par-delà l’affirmation d’une acquisition solitaire de la bombe par la France gaullienne, pour des raisons d’indépendance stratégique et de prestige politique ? Cet article revient sur les circonstances du renoncement à une bombe franco-américaine, qui tiennent à des choix politiques mais aussi des circonstances conjoncturelles, et les hésitations qui conduisent finalement à la solitude européenne de la France entre 1957 et 1959. La rupture relative de 1958, puis le choix en 1959-1960 de viser une force de frappe française, incluant la bombe H, se comprennent à la lumière des contraintes du jeu diplomatique et des divergences au sein de l’exécutif et des armées. Ce choix n’émancipe pas les décideurs ni les exécutants de toute dépendance étrangère. L’article montre dans quelle mesure les ressources des États-Unis et de la Grande-Bretagne ont été mobilisées à différents niveaux de coopération pour construire le Centre d’expérimentation du Pacifique (CEP) et y réaliser 193 essais en milieu insulaire
Relative Contributions of Sea Surface Temperature and Atmospheric Nonlinearities to ENSO Asymmetrical Rainfall Response
No full textInternational audienceHere, we investigate the relative roles of atmospheric nonlinearities and asymmetrical sea surface temperature (SST) forcing in the El Nino-Southern Oscillation (ENSO) asymmetrical rainfall response. Applying a vertically integrated water vapor budget to the ERA5 reanalysis leads to a simple analytical equation for precipitation anomalies. This formulation reveals that ENSO rainfall anomalies are dominated by the linear component of the dynamical term (i.e., the anomalous moisture convergence due to the effect of circulation anomalies on climatological humidity). Nonlinearities in this term and the linear thermodynamical term (i.e., the effect of climatological circulation on humidity anomalies) both strengthen central Pacific rainfall anomalies for both ENSO phases. In contrast, the nonlinear term associated with the effect of anomalous divergence on anomalous moisture (i.e., the mixed term) weakens La Nina dry and strengthens El Nino wet anomalies, in particular during extreme El Nino events when it contributes to about 40% of the eastern Pacific wet anomalies. Overall, atmospheric nonlinearities directly account for similar to 70% of the positively skewed ENSO rainfall distribution east of the date line, and similar to 50% of the negatively skewed rainfall distribution in the western Pacific. The remaining ENSO rainfall asymmetries are attributable to the asymmetrical ENSO SST pattern. This asymmetrical SST pattern also has contributions from atmospheric nonlinearities through the Bjerknes feedback loop, in addition to those from oceanic nonlinearities. Our estimates are thus likely a lower bound of the contribution of atmospheric nonlinearities to the overall ENSO rainfall asymmetry
