HAL Portal UPF (Université de la Polynésie française)
Not a member yet
3802 research outputs found
Sort by
Sur les routes de la migration : circulations, risque et gestion de l’incertitude
No full textDepuis la fin des années 1990 le cadrage croissant des migrations dans les termes d’un « risque » sécuritaire, dans les pays de destination, a fait l’objet d’une abondante littérature, en particulier dans le champ de la science politique et de la géographie critique. Étonnement en revanche, les sciences sociales se sont très peu penchées sur l’appréhension des risques migratoires par les migrant·es, contrairement à l’économie des migrations qui s’est tôt saisie de cette question, faisant du risque et de sa gestion par les populations migrantes une composante cruciale des rationalités migratoires. Le dossier thématique « Sur les routes de la migration : circulations, risque et gestion de l’incertitude » vise à pallier cette absence dans le champ des sciences sociales. Les contributions prennent acte de la place prépondérante des risques dans l’expérience migratoire et entendent inaugurer une réflexion structurée sur cet aspect — hyper-central mais négligé — des épreuves mobilitaires. Face à ce constat, elles posent une première série de jalons empiriques et théoriques pour baliser ce champ de recherche, en appui sur des études de cas ancrées dans des espaces géographiques variés — Guyane, littoral nord français, Île-de-France, Asie du Sud-Est — et portant sur des populations diverses — demandeurs et demandeuses d’asile, populations roms, travailleurs et travailleuses migrant·es
Variations on the Expectation Due to Changes in the Probability Measure
No full textFeature paperInternational audienceIn this paper, closed-form expressions for the variation of the expectation of a given function due to changes in the probability measure (probability distribution drifts) are presented. These expressions unveil interesting connections with Gibbs probability measures, information projections, Pythagorean identities for relative entropy, mutual information, and lautum information
L’instrumentalisation par les concurrents de la procédure polynésienne de contrôle préalable des aménagements commerciaux
No full textInternational audienceLe titre II du livre III du code de la concurrence polynésien prévoit, pour le commerce de détail, un contrôle ex ante des opérations d’aménagement commercial, bien qu’il s’agisse d’opérations de croissance interne des entreprises. Ce dispositif (également existant en Nouvelle-Calédonie), conduit les autorités locales de concurrence à appliquer un système de notification proche de celui du contrôle des concentrations, ce qui est pour le moins discutable et en porte-à-faux avec les principes fondamentaux de l’antitrust (Destours S., 2023, « L’impossible contrôle juridictionnel des autorisations d’aménagement commercial par les autorités de concurrence du Pacifique au regard des principes du droit de la concurrence », Revue Lamy de la Concurrence, n° 129, juillet-août, pp. 46-54). Si les effets négatifs du contrôle de la croissance interne sur la productivité ont déjà pu être soulignés (Montet C. et Venayre F., 2024, « Coût de la vie en outre-mer et politique de la concurrence en Polynésie française », Mélanges offerts à Louis Vogel : La vie du droit, LGDJ, octobre), la récente actualité de la Cour administrative d’appel (CAA) de Paris vient illustrer comment l’instrumentalisation du droit par les concurrents permet de ralentir de manière considérable les investissements des rivaux, mais aussi vient obscurcir la compréhension des justiciables
Cryptic Diversity and Genetic Differentiation of Mesophotic Hydroids in the Southwestern Indian Ocean
No full textInternational audienceThe western Indian Ocean (WIO) is recognized as a marine biodiversity hotspot with complex oceanographic circulation resulting in limited connectivity between remote islands. This ocean region comprises several subregions of varying biodiversity, with the northern Mozambique Channel standing out as the core of this hotspot. Although the hydroids in this region are known to include cryptic species and show contrasting connectivity patterns, the mesophotic depths remain largely unexplored. The Deep Reef Refuge Hypothesis suggests that mesophotic coral ecosystems may act as refuges. However, this hypothesis is based on several prerequisites that could be affected by the presence of cryptic species. We investigated the genetic diversity and connectivity of seven hydroid species by collecting samples at euphotic and mesophotic depths around the islands of Mayotte and Reunion. Population genetic patterns were investigated using multivariate analyses and Bayesian clustering, with 8-18 microsatellite markers per species. The results revealed greater genetic diversity in Mayotte than in Reunion, even though fewer samples were collected there. This is in line with the location of the heart of the hotspot in the northern part of the WIO. In addition, all species exhibited strong genetic differentiation between samples from the two islands, supporting the "one island, one species" hypothesis previously proposed for hydroids in the region. However, contrasting values were obtained among depths depending on the species and the island, demonstrating the importance of a multi-species approach. The inclusion of mesophotic samples from the Taxella eximia/gracilicaulis and Macrorhynchia phoenicea species complexes provides new insights into the true biodiversity of these genera, revealing additional cryptic species and putative hybridization. Furthermore, the genetic connectivity estimation performed here among depths highlights several species that could be evaluated in terms of the vertical connectivity prerequisite of the Deep Reef Refuge Hypothesis in Mayotte and Reunion
Plasticity in expression clarifies the ecological drivers and evolutionary history of cannibalism in invasive cane toads ( Rhinella marina )
No full textInternational audienceAbstract When rapid evolutionary change occurs in a trait’s expression, what role is played by proximate factors that induce variation in expression? We assessed drivers of variation in a recently evolved behaviour—targeted cannibalism by invasive cane toad tadpoles (Rhinella marina) in Australia—to better understand its evolution. Because targeted cannibalism probably evolved due to intense intraspecific competition, we first assessed effects of two proximate factors that influence resource availability—cannibal density and developmental stage—on rates of cannibalism. We then used published data to quantify evolutionary shifts in the impact of another potential driver of variation—tadpole mass. In laboratory trials, rates of cannibalism increased with cannibal development and rearing density, and cannibals reared at higher densities began consuming eggs earlier in embryonic development. Analyses of published data revealed that ancestral-range tadpoles were less cannibalistic than invasive conspecifics, and ancestral rates of cannibalism increased more slowly with larval mass. Thus, larval cannibalism is plastic in both ancestral and derived populations. Our work clarifies the ecological drivers and evolutionary history of targeted cannibalism and cannibal-induced defences in invasive Australian cane toad tadpoles and illustrates the importance of considering proximate drivers of trait variation when investigating rapid evolution
Coral Skeletal Cores as Windows Into Past Symbiodiniaceae Community Dynamics
No full textInternational audienceThe symbiosis between the dinoflagellate Symbiodiniaceae family and reef-building corals underpins the productivity of coral reefs. This relationship facilitates the deposition of calcium-carbonate skeletons that build the reef structure thanks to the energy derived from photosynthesis. The loss of Symbiodiniaceae from coral tissues-resulting in coral bleaching-impedes coral growth and can lead to mass mortality if the symbiosis fails to recover. Given that Symbiodiniaceae communities are dynamic and can shift in response to environmental stressors in the decades to centuries-long lifespan of coral colonies, understanding these changes is crucial. Although the reconstruction of Symbiodiniaceae communities from coral skeleton records has recently been demonstrated as feasible, no studies have yet assessed reconstructions across different species and locations. Here, we present an approach to use coral skeletons for reconstructing the Symbiodiniaceae community on decadal and centennial scales and for resolving dynamics related to coral species and the environmental history of sampling locations. For this, we used dated coral skeleton cores from Porites lobata and Diploastrea heliopora, species commonly used as climate archives, sampled in Palau and Papua New Guinea. We also examined the effect of various DNA extraction protocols on community reconstruction. Here we show that the reconstructed Symbiodiniaceae communities significantly varied across all cores and DNA extraction methods, with decalcification-based protocols enhancing the retrieval of skeletal-bound DNA. Moreover, we observed distinct community dynamics related to the specific coral host and sampling location. Notably, associations of Symbiodiniaceae dynamics with past heat stress events were apparent in cores of both species from Palau. Our findings enable a deeper understanding of the temporal and spatial variability in Symbiodiniaceae communities, offering insights that may refine the use of paleobiological proxies in climate studies and reveal broader ecological trends and microbially aided adaptation pathways in corals.</div
Microbiota of host sea anemones and their associated anemonefish show contrasting responses to a bleaching event
No full textInternational audienceSea anemones form complex holobiont communities that include not only microorganisms (microbiota) but also metazoans, such as anemonefish. Previous studies have revealed the significant impacts of bleaching events on anemone microbiota and on anemonefish physiology. However, the impacts of bleaching on anemonefish microbiota remain understudied, despite the potential for microbial dysbiosis to favor the emergence of pathogens and opportunistic microbes which could be detrimental for anemonefish.As a consequence, we sampled microbiota in situ from healthy and bleached anemones (Radianthus magnifica) and their associated anemonefish (Amphiprion maohiensis) during the 2019 bleaching event in the lagoon of Mo’orea, French Polynesia. Metabarcoding was used to examine the diversity of Symbiodiniaceae and bacterial communities.Our results revealed significant differences in the assemblages of Symbiodiniaceae and bacteria between healthy and bleached anemones. Specifically, the alpha diversity of these microbial communities was higher in bleached anemones, suggesting microbial dysbiosis and an increase in opportunistic taxa. In contrast, no differences were observed in the bacterial assemblages of anemonefish associated with healthy and bleached anemones. Despite this lack of correlation between anemonefish microbiota and anemone bleaching status, we found that anemonefish living within the same anemone had nevertheless similar bacterial assemblages. As a consequence, we hypothesized that anemone bleaching does not significantly impact the microbiota of anemonefish, and that direct skin-to-skin contact among anemonefish is the primary factor influencing their microbiota composition
Food deprivation enhances disease resistance: Underlying mechanisms in oysters confronted with pacific oyster mortality syndrome
No full textInternational audienceVariation in food availability can shape host susceptibility and pathogen virulence, thereby impacting disease outcomes. An ad libitum diet may enhance host physiology and immunity but it can also favor pathogen proliferation. Here, we investigated how food availability (ad libitum vs. starvation) affects interactions between the oyster Magallana gigas and the herpesvirus OsHV-1 μVar initiating the panzootic Pacific oyster mortality syndrome (POMS). We found that starvation reduced oyster susceptibility to POMS. Through a comparative integrative-omics approach, we showed that (1) starvation induces metabolic rate depression, which may limit viral replication by reducing the availability of cellular energy that viruses can hijack, and (2) enhances autophagy and antiviral responses, thereby improving viral control. These results underscore the importance of nutritional status in shaping viral disease outcomes and may inform management strategies in aquaculture systems
Un système de protection sociale à l’épreuve des transitions : le cas de la Polynésie française
No full textCollectivité d’outre-mer dotée d’un statut d’autonomie, la Polynésie française possède un système de protection sociale original, resté peu documenté. En partie inspiré des assurances sociales métropolitaines, il s’est adapté au contexte local pour se structurer autour d’un organisme gestionnaire spécifique, la Caisse de prévoyance sociale (CPS), et d’une couverture généralisée contre les principaux risques sociaux, la Protection sociale généralisée (PSG). L’article retrace les caractéristiques de ce développement institutionnel et de son organisation. Il propose ensuite une analyse des défis contemporains auxquels ce système est confronté et qui se répercutent sur sa pérennité financière : inégalités socio-économiques, faiblesse de l’emploi formel et poids de l’économie informelle, vieillissement démographique rapide et dégradation de l’état de santé de la population. Ces défis font émerger des réflexions nouvelles quant à l’organisation des solidarités (familiales et professionnelles, nationales et territoriales) et leur articulation dans la prise en charge des risques sociaux
Modelling the Fundamental Niche to Predict the Effects of Climate Warming on Interactions Between Native and Invasive Mussels in South Africa
No full textInternational audienceAim Climate change is reshuffling the distribution of species globally and threatening to modify the structure and functioning of natural and managed ecosystems. Most studies predicting species distributions rely on statistical approaches that do not capture the species' fundamental niche. In contrast, energy budget models include lethal and sublethal levels of stress to explore traits, such as growth and reproduction, that drive ecological responses. We used models parameterised for two competing intertidal mussels, the native Perna perna and the invasive Mytilus galloprovincialis , to investigate their current and projected distributions. Location South African rocky shores. Taxa Mussels, Mytilus galloprovincialis and Perna perna . Methods We used previously parameterised dynamic energy budget (DEB) models. Model predictions were validated using a 2‐year dataset describing current conditions (body temperature and chlorophyll‐ a concentration) and fitness‐related traits (growth and reproductive effort) at nine sites: three western sites inhabited by Mytilus alone, three eastern sites occupied by Perna and three southern sites where the species coexist. We then tested the effects of three climate change scenarios on the model predictions of maximum size, growth rate and gonadosomatic index around South Africa. Results Current spatial patterns are likely to be maintained until the century's end, and the physiological mechanisms presently excluding Mytilus from the east coast (impaired growth due to food limitation) and Perna from the west coast (impaired reproduction due to cold temperatures), will continue to operate until the end of the century. Our model also revealed a possible change in the competitive hierarchy between these species as warming will favour the reproductive potential of Perna more than that of Mytilus . Conclusion Our approach of exploring the fundamental niche rather than using a statistical approach suggests that the effects of projected temperature conditions on the distributions of these species will be less severe than expected