Portail "HAL-Francophonie Afrique et Océan Indien"
Not a member yet
43052 research outputs found
Sort by
Predicting current and future distributions of Malagasy bats: Implications for management of coronavirus spillover
No full textInternational audienceGlobal environmental change is known to be an important factor for the emergence of infectious diseases. Habitat modification of wild animal hosts favor pathogen spillover, particularly in degraded tropical ecosystems. We predicted the distribution of seven of eight bat families on Madagascar in response to climate change and urbanization, based on ecological niche modeling. We found major restructuring of bat-suitable habitats with a large-scale reduction in habitat suitability across all coastal regions of the northern half of the island for all bat families except Molossidae. Indeed, molossid bats follow the anticipated pattern of human population growth and underlines the need for a precise assessment of spillover potential of their associated alpha-coronaviruses
Bat things come in threes: within-host dynamics of herpesvirus triple infection in bats
No full textInternational audienceCo-infections are a common feature of wildlife systems, yet the factors influencing within-host viral dynamics remain largely unclear. In bats, understanding viral community ecology is essential for elucidating shedding patterns and potential drivers of zoonotic spillover risk. In this study, we explore the genetic diversity and within-host dynamics of herpesviruses (HSV) in Mormopterus francoismoutoui, a tropical insectivorous bat endemic to Reunion Island. Over 3 consecutive years, we collected saliva samples from seven roosts, including samples from recaptured individuals. Illumina sequencing of HSV PCR-positive samples revealed a high diversity of strains (n = 20), belonging to alpha, beta, and gamma-HSV subfamilies. Co-infection was frequent, with 44% of bats shedding strains from all three subfamilies. While most shedding patterns appeared random across subfamilies, our results suggest that gamma-HSV negatively affects the probability of alpha-HSV co-shedding. We also demonstrated a lower HSV diversity in juveniles as compared to adults, while pregnancy appeared to increase viral diversity-although this requires further confirmation. Longitudinal recaptures revealed an accumulation of multiple HSV latent infections over life, as the probability to be infected with a new subfamily increased with time interval between recaptures. Within-host strain dynamics were highly variable, with 79% of bats either gaining or losing strains, consistent with latency and reactivation mechanisms. This study provides rare empirical insight into the within-host viral ecology of a natural reservoir host and can help uncover complex pathways by which viruses interact.IMPORTANCEUnderstanding viral dynamics in bats is critical for anticipating and mitigating zoonotic emergence. This study provides rare, longitudinal insight into herpesvirus co-shedding patterns in Mormopterus francoismoutoui, an endemic bat species on Reunion Island. Here, we revealed high strain diversity and frequent multi-subfamily shedding, highlighting complex within-host viral ecology, shaped by host age, reproductive status, and infection history. Interactions between viral subfamilies suggest competitive dynamics that may influence shedding. These findings deepen our understanding of viral persistence and reactivation in bats and underscore the need to investigate how environmental and anthropogenic stressors may modulate co-shedding and increase the likelihood of spillover events
Calving-driven fjord dynamics resolved by seafloor fibre sensing
No full textInternational audienceAbstract Interactions between melting ice and a warming ocean drive the present-day retreat of tidewater glaciers of Greenland 1–3 , with consequences for both sea level rise 4 and the global climate system 5 . Controlling glacier frontal ablation, these ice–ocean interactions involve chains of small-scale processes that link glacier calving—the detachment of icebergs 6 —and submarine melt to the broader fjord dynamics 7,8 . However, understanding these processes remains limited, in large part due to the challenge of making targeted observations in hazardous environments near calving fronts with sufficient temporal and spatial resolution 9 . Here we show that iceberg calving can act as a submarine melt amplifier through excitation of transient internal waves. Our observations are based on front-proximal submarine fibre sensing of the iceberg calving process chain. In this chain, calving initiates with persistent ice fracturing that coalesces into iceberg detachment, which in turn excites local tsunamis, internal gravity waves and transient currents at the ice front before the icebergs eventually decay into fragments. Our observations show previously unknown pathways in which tidewater glaciers interact with a warming ocean and help close the ice front ablation budget, which current models struggle to do 10 . These insights provide new process-scale understanding pertinent to retreating tidewater glaciers around the globe
Glacially Enhanced Silicate Weathering Revealed by Holocene Lake Records
No full textInternational audienceHow glaciation affects drawdown by chemical weathering influences the weathering‐climate feedback strength, which controls the exogenic carbon cycle and planetary habitability. However, the role of glaciers remains elusive as glaciation alters multiple factors controlling weathering, the net effect of which is ambiguous even in directionality. To isolate and quantify the effect of glaciers, we developed a novel multi‐proxy system for constraining catchment‐scale weathering fluxes in the past. This approach utilizes the correlation between Ge/Si and Si isotope ratios in modern rivers and the preservation of these signals in lacustrine sediments. Reconstructed weathering fluxes in two Icelandic catchments with different glacial histories during the past 10,000 years show that chemical weathering fluxes are roughly 10 times higher when a catchment is glaciated versus ice‐free. The synchronous variations in weathering fluxes with the expansion and contraction of glaciers indicate that glaciation may rapidly amplify climatic variations via a positive feedback
Automatic Detection of Large‐Scale Traveling Ionospheric Disturbances Using GNSS Data and Image Processing Techniques
No full textInternational audienceLarge‐scale traveling ionospheric disturbances (LSTIDs) are wave‐like structures propagating through the ionosphere from auroral to lower latitudes, affecting radar‐based technologies and satellite navigation. Due to their disruptive effects, timely detection is crucial. This work presents an autonomous detection technique based on travel‐time diagrams of detrended Total Electron Content (TEC). Our method employs a network of GNSS receivers across Europe, selected using a K‐Means clustering algorithm to ensure comprehensive spatial coverage. Applying image processing techniques, we identify propagating features of positive and negative amplitude in detrended TEC keograms. These features are fitted using the RANdom SAmple Consensus method to estimate propagation speed along the North‐South direction. Following feature identification, we refine our results by merging positive and negative perturbations and filtering out false positives based on physical constraints. This methodology allowed us to compile a catalog of LSTID with periods ranging from 30 to 90 min, spanning 2021–2024. To validate our approach, we conducted case studies and statistical analyses, confirming accuracy and reliability. Additionally, testing in North America and Japan demonstrated the algorithm broader applicability. Our findings, obtained with user‐defined parameters tailored to examine LSTIDs with periodicities in the 30–90 min range, show an average speed of 629 ± 215 m/s and period of 62 ± 14 min. A direct relation with auroral electrojet indices confirms that stronger auroral currents produce faster, higher amplitude and shorter period LSTIDs. Furthermore, our analysis reveals a link between LSTID occurrences and geomagnetic activity, reinforcing previous findings
L’évaluation swahilie
No full textL'évaluation swahilie, qui fait partie de l'évaluation « faite en Afrique » (Made in Africa), est un cadre culturellement ancré, participatif et démocratique destiné à guider les évaluations dans le domaine du développement. S'inspirant de la sagesse des proverbes swahilis, cette approche met l'accent sur l'inclusivité, les connaissances empiriques, la responsabilité éthique et l'apprentissage collectif. Elle offre des orientations philosophiques et méthodologiques applicables non seulement dans le contexte africain, mais aussi dans divers environnements culturels et politiques où la voix des communautés, l'éthique relationnelle et la pertinence contextuelle sont essentielles. En intégrant la sagesse indigène dans une démarche de recherche systématique, l’évaluation swahilie offre une alternative aux paradigmes traditionnels qui négligent souvent les modes de connaissance locaux, ce qui peut conduire à des évaluations moins démocratiques ou moins transformatrices
The Effect of adsorption phenomena on the transport in complex electrolytes
No full textInternational audienceOver the last decade, numerous impedance studies of the conductivity of suspensions containing colloidal (dielectric, semiconducting or metallic) particles have often led to the conclusion that the well-known Maxwell theory is insufficient to quantitatively explain the properties of these systems. We review some of the most characteristic results and show how the applicability of the Maxwell’s theory can be restored taking into account the adsorption phenomena occurring during AC impedance measurements in nanoparticle suspensions. The latter can drastically change the capacitance of the metal-electrolyte cell boundaries from the standard value, making it strongly dependent on the nanoparticle concentration. This factor significantly affects conductivity measurements through RC circuit characteristics. We present an analysis of available impedance measurement data of the dependence of conductivity on the nanoparticle concentration in this new paradigm. In order to emphasize the novelty and the acute sensitivity of ac-diagnosis to the presence of adsorption phenomena at the metal-electrolyte interface, direct adsorption determinations at such interfaces by using two modern experimental techniques are also presented. The main result of this work is the restoration of Maxwell’s theory, attributing the observed discrepancies to variations in cell conductance
The Djourdé-Sinassi magmatic-migmatitic complex, Northern Cameroon: a record of vertical extrusion of the Pan-African partially molten orogenic root
No full textInternational audienceThe Djourdé-Sinassi magmatic-migmatitic complex is part of the juvenile Neoproterozoic Garoua Domain located in Northern Cameroon. It is surrounded by the Zalbi, Poli and Rey-Bouba greenstone belts, limited to the east by the sinistral Tcholliré-Banyo Shear zone and to the south by the Poli Thrust System. The Djourdé-Sinassi magmatic-migmatitic complex is subdivided into a western magmatic domain made of diorite, tonalite, granodiorite, with numerous enclaves of mafic and ultramafic rocks, and an eastern domain dominated by metatexite migmatites enclosing ubiquitous mafic to ultramafic rafts. The plutonic rocks of the western domain display a gently dipping to vertical magmatic fabric with variable trends. Locally, trains of hornblendite enclaves with lobate boundaries and dismembered into a network of felsic veins points to injection of mafic magma that mingled with a host magmatic mush and/or partially molten rocks. The migmatites display a foliation delineated by the alternation of leucosome and mesosome layers, that are mainly subvertical and wrapped around the metric to kilometric size rafts of mafic and ultramafic rocks. A texturally continuous network of leucosome veins concordant to discordant relative to the syn-migmatitic foliation and the mineral assemblage attests for syntectonic melt segregation under granulite facies conditions (Hbl + Pl ± Bt ± Grt±Opx±Cpx ; peak: ≥800 °C/8–10 kbar). The magmatic fabric of plutonic rocks and the syn-migmatitic foliation are locally transposed into subvertical shear zones with a steeply plunging mineral and stretching lineation. Kinematic criteria are identified in the subhorizontal plane perpendicular to the lineation, which indicates that deformation was not plane strain and occurred in 3D. N-S to NE-SW striking shear zones are sinistral whereas E-W to WNW-ESE trending ones are dextral. These shear zones first developed in the presence of melt but then under solid-state during progressive retrogression from amphibolite to greenschist facies (Ab+Qtz + Ep ± Op ± Chl+Ser+Ep). These data suggest that the Djourdé-Sinassi magmatic-migmatitic complex corresponds to the former root of the Central African Orogenic Belt originating from partial melting of a juvenile mafic crust. This root has been vertically extruded under a pure-shear dominated constrictional regime with vertical stretching in the presence of melt coeval with the injection of mantle-derived mafic magmas and was then progressively exhumed towards the surface. This deformation pattern is consistent with the position of the Sinassi complex surrounded by greenstone belts and on a larger scale, confined in between the West African − Congo cratons and Saharan metacraton.Le complexe magmatique-migmatitique de Djourdé-Sinassi fait partie du domaine Néoproterozoïque juvénile de Garoua, situé dans le Nord du Cameroun, entouré par les ceintures de roches vertes de Zalbi, Poli et Rey-Bouba, limité à l’est par la zone de cisaillement senestre de Tcholliré-Banyo et au sud par le système de faille de Poli. Le complexe magmatique-migmatitique de Djourdé-Sinassi est subdivisé en un domaine magmatique à l’ouest composée de diorite, tonalite, granodiorite et granite avec de nombreuses enclaves de roches mafiques et ultramafiques, et une partie à l’est dominée par des migmatites métatexitiques contenant des enclaves mafiques à ultramafiques omniprésentes. Les roches plutoniques à l’est présentent une fabrique magmatique légèrement pentée à verticale à orientation variable. Localement, des trains d’enclaves de hornblendite aux contours lobés et disloqués par un réseau de veines felsiques indiquent l’injection de magma mafique qui s’est mélangé avec une masse magmatique hôte et/ou des roches partiellement fondues. Les migmatites affichent une foliation définie par l’alternance de niveaux de leucosome et de mésosome, principalement subverticale suivant une direction parallèle à l’alignement des enclaves de roches mafiques et ultramafiques de taille métrique à kilométrique. Un réseau continu de veines de leucosome, concordant et discordant par rapport à la foliation syn-migmatitique, atteste d’une ségrégation syntectonique du magma sous des conditions de faciès granulite (pic : ≥800 °C/8–10 kbar). La texture magmatique des roches plutoniques et la foliation syn-migmatitique sont localement transposées en zones de cisaillement subverticales avec une linéation minérale et d’étirement à plongement fort. Des critères cinématiques sont identifiés dans le plan subhorizontal perpendiculaire à la linéation, ce qui indique que la déformation n’était pas plane et s’est produite en 3D. Les zones de cisaillement orientées N-S à NE-SW affichent des critères cinématiques senestres, tandis que celles orientées E-W à WNW-ESE sont dextres. Ces zones de cisaillement se sont d’abord développées en présence de magma, puis à l’état solide lors de la rétrogression progressive du faciès amphibolite au faciès schiste vert (Ab+Qtz + Ep ± Op ± Chl+Ser+Ep). Ces données suggèrent que le complexe magmatique-migmatitique de Djourdé-Sinassi représente un témoin de la racine de la Ceinture Orogénique d’Afrique Centrale, issue de la fusion partielle d’une croûte mafique juvénile. Cette racine a ensuite été extrudée verticalement sous un régime dominé par le cisaillement pur avec un étirement vertical en présence de magma, coïncidant avec l’injection de magmas mafiques dérivés du manteau, et a été progressivement exhumée vers la surface. Ce schéma de déformation est cohérent avec la position du complexe de Sinassi, entouré de ceintures de roches vertes et, à une échelle plus large, confiné entre les cratons Ouest-Africain − Congo et le métacraton du Sahara
Wiggle and glide: fine-scale telemetry reveals unique diving strategies in benthic-foraging sea snakes
No full textInternational audienceAbstract Background The efficient acquisition of two critical but spatially separated resources –food and oxygen– governs the daily movements and diving patterns of air-breathing aquatic animals. Unlike pinnipeds, turtles and seabirds, fully marine (‘true’) sea snakes spend their entire lifecycle at sea and have evolved specialised movement behaviours. However, fine-scale data on the diving behaviour of free-ranging sea snakes remain scarce, limiting our understanding of their ecology and vulnerability to anthropogenic threats. Methods We used acoustic telemetry to track five individuals of two benthic-foraging sea snake species ( Hydrophis stokesii , H. major ) in Exmouth Gulf, Western Australia, and Baie des Citrons, New Caledonia. Each snake was continuously tracked using a directional hydrophone for up to 18 h, generating high-resolution, three-dimensional dive paths. After filtering, we analysed 106 dives from 46 h of tracking. Results Sea snakes primarily conducted U- and S-shaped dives and spent on average 97.2% of their time submerged. Most U-shaped dives were characterised by limited vertical and horizontal movement. S-shaped dives were more complex, with variable time on the seafloor and occasionally interrupted gradual ascents. Dive duration was positively correlated with post-dive surface interval, while depth and duration of the gradual ascent phase were influenced by environmental depth. We also identified distinctive, repetitive undulations (‘wiggles’) in the depth profiles of several dives completed by all three tracked H. stokesii . Conclusions These high-resolution data provide the first insights into the fine-scale diving patterns of benthic-foraging sea snakes. Like surface-foraging species, they appear to regulate air intake based on environmental depth and may be neutrally buoyant in the gradual ascent phase of S-shaped dives. We hypothesise that this phase facilitates efficient horizontal travel, despite potential increases in predation risk. The ‘wiggles’ observed in H. stokesii may have a functional role in buoyancy control, energy conservation, or foraging. Our study contributes to a deeper understanding of sea snake diving strategies, with implications for their ecology, physiology, and conservation
OneWater Data: towards a national FAIR water data platform and community
No full textInternational audienceAs part of the FAIR Water Data platform, we explain the importance of contributing to the co-construction of an ecosystem of FAIR services related to water.To achieve this goal, we present the general FAIR Factory method and illustrate it with various examples