Chemical and mineralogical effects of saline water movement through a soil during evaporation

Cet article illustre les résultats d'une expérience menée dans le but d'étudier les effets de l'évaporation dans un sol homogène reconstitué. Les conditions expérimentales sont celles qui caractérisent les zones de polders du lac Tchad. Les données obtenues montrent que les phénomènes de capillarité déterminent un transfert des ions en solution vers la surface du sol. Puisque l'évaporation se réalise dans cette zone, les concentrations ioniques des solutions deviennent très élevées. Les simulations et les calculs théoriques montrent que dans ce milieu et sous ces conditions des argiles magnésiennes précipitent : ceci est confirmé par leurs observations au microscope électronique à transmissio

Interactions between BRCA2 and RAD51 for promoting homologous recombination in Leishmania infantum.

In most organisms, the primary function of homologous recombination (HR) is to allow genome protection by the faithful repair of DNA double-strand breaks. The vital step of HR is the search for sequence homology, mediated by the RAD51 recombinase, which is stimulated further by proteins mediators such as the tumor suppressor BRCA2. The biochemical interplay between RAD51 and BRCA2 is unknown in Leishmania or Trypanosoma. Here we show that the Leishmania infantum BRCA2 protein possesses several critical features important for the regulation of DNA recombination at the genetic and biochemical level. A BRCA2 null mutant, generated by gene disruption, displayed genomic instability and gene-targeting defects. Furthermore, cytological studies show that LiRAD51 can no longer localize to the nucleus in this mutant. The Leishmania RAD51 and BRCA2 interact together and the purified proteins bind single-strand DNA. Remarkably, LiBRCA2 is a recombination mediator that stimulates the invasion of a resected DNA double-strand break in an undamaged template by LiRAD51 to form a D-loop structure. Collectively, our data show that LiBRCA2 and LiRAD51 promote HR at the genetic and biochemical level in L. infantum, the causative agent of visceral leishmaniasis

Cenozoic tectonics of the Western Approaches Channel basins and its control of local drainage systems

International audienceLe domaine des Approches occidentales de la Manche constitue une zone clé pour caractériser l'évolution post-rift des marges continentales NW européennes associées à la collision Afrique/Europe. Malgré les divers témoins des inversions cénozoïques jalonnant le pourtour de la Manche, la structuration et l'amplitude des mouvements demeurent néanmoins incertaines au sein de la partie méridionale française des Approches occidentales. Il en est de même sur le rôle de l'inversion de la mer du Nord dans la mise en place du Fleuve Manche qui drainait un bassin versant bien supérieur à la Manche actuelle durant les grandes régressions plio-quaternaires et alimentait les éventails sous-marins Celtique et Armoricain en bas de pente. La réalisation des campagnes de sismique-réflexion haute résolution GEOMOC et GEOBREST03 dont les résultats font l'objet de cet article permettent de répondre à ces questions en complétant la connaissance géologique de la Manche. Les nouvelles observations soulignent le diachronisme et le contraste de l'amplitude des mouvements du système de failles associées à l'inversion du bassin d'Iroise. Celle-ci se fait en deux épisodes: un épisode paroxysmal paléogène décomposé en deux phases, éocène (Yprésien probable) et oligocène, et un épisode néogène plus modéré réactivant partiellement les structures impliquées antérieurement. Les déformations se concentrent le long de l'accident nord Iroise (NIF) situé dans le prolongement de la faille Médio-Manche et entraîne localement des plissements de la couverture sédimentaire à l'aplomb des accidents profonds. L'inversion induit ainsi un soulèvement de près de 700 m du plateau médian situé au sud de l'accident nord Iroise. La cartographie isochrone des séquences sismiques identifiées démontre également le contrôle majeur des structures tectoniques sur la mise en place des dépôts néogènes. Le soulèvement de la partie orientale du bassin favorise ainsi la mise en place de vastes prismes progradants d'âge miocène supérieur, et contrôle le développement postérieur du réseau des paléo-vallées constituant l'extrémité occidentale du fleuve Manche. Ce réseau présente une géométrie en baïonnette marquée par de brutaux changements de directions variant de N040 à N070, cette dernière direction caractérisant la plus grande partie des failles néogènes associées au bassin d'Iroise. Les paléo-vallées se seraient développées lors d'une chute du niveau marin au-delà du rebord de plate-forme et la stratigraphie établie à travers cette étude amène à placer le début des incisions au Pliocène (Reurévien ou pré-Tiglien). La chute amplifiée par l'inversion du bassin d'Iroise serait suivie d'un basculement tardif de la plate-forme externe à l'instar des observations réalisées sur de nombreuses marges du pourtour nord atlantique

Initial results from a hydroacoustic network to monitor submarine lava flows near Mayotte Island

In 2019, a new underwater volcano was discovered at 3500 m below sea level (b.s.l.), 50 km east of Mayotte Island in the northern part of the Mozambique Channel. In January 2021, the submarine eruption was still going on and the volcanic activity, along with the intense seismicity that accompanies this crisis, was monitored by the recently created REVOSIMA (MAyotte VOlcano and Seismic Monitoring) network. In this framework, four hydrophones were moored in the SOFAR channel in October 2020. Surrounding the volcano, they monitor sounds generated by the volcanic activity and the lava flows. The first year of hydroacoustic data evidenced many earthquakes, underwater landslides, large marine mammal calls, along with anthropogenic noise. Of particular interest are impulsive signals that we relate to steam bursts during lava flow emplacement. A preliminary analysis of these impulsive signals (ten days in a year, and only one day in full detail) reveals that lava emplacement was active when our monitoring started, but faded out during the first year of the experiment. A systematic and robust detection of these specific signals would hence contribute to monitor active submarine eruptions in the absence of seafloor deep-tow imaging or swath-bathymetry surveys of the active area

Tracking Progress Toward EU Biodiversity Strategy Targets : EU Policy Effects in Preserving its Common Farmland Birds

Maximizing the area under biodiversity-related conservation measures is a main target of the European Union (EU) Biodiversity Strategy to 2020. We analyzed whether agrienvironmental schemes (AES) within EU common agricultural policy, special protected areas for birds (SPAs), and Annex I designation within EU Birds Directive had an effect on bird population changes using monitoring data from 39 farmland bird species from 1981 to 2012 at EU scale. Populations of resident and short-distance migrants were larger with increasing SPAs and AES coverage, while Annex I species had higher population growth rates with increasing SPAs, indicating that SPAs may contribute to the protection of mainly target species and species spending most of their life cycle in the EU. Because farmland birds are in decline and the negative relationship of agricultural intensification with their population growth rates was evident during the implementation of AES and SPAs, EU policies seem to generally attenuate the declines of farmland bird populations, but not to reverse them.Peer reviewe

Wintering bird communities are tracking climate change faster than breeding communities

Global climate change is driving species' distributions towards the poles and mountain tops during both non-breeding and breeding seasons, leading to changes in the composition of natural communities. However, the degree of season differences in climate-driven community shifts has not been thoroughly investigated at large spatial scales. We compared the rates of change in the community composition during both winter (non-breeding season) and summer (breeding) and their relation to temperature changes. Based on continental-scale data from Europe and North America, we examined changes in bird community composition using the community temperature index (CTI) approach and compared the changes with observed regional temperature changes during 1980-2016. CTI increased faster in winter than in summer. This seasonal discrepancy is probably because individuals are less site-faithful in winter, and can more readily shift their wintering sites in response to weather in comparison to the breeding season. Regional long-term changes in community composition were positively associated with regional temperature changes during both seasons, but the pattern was only significant during summer due to high annual variability in winter communities. Annual changes in community composition were positively associated with the annual temperature changes during both seasons. Our results were broadly consistent across continents, suggesting some climate-driven restructuring in both European and North American avian communities. Because community composition has changed much faster during the winter than during the breeding season, it is important to increase our knowledge about climate-driven impacts during the less-studied non-breeding season.Peer reviewe

Protected area characteristics that help waterbirds respond to climate warming

Protected area networks help species respond to climate warming. However, the contribution of a site's environmental and conservation-relevant characteristics to these responses is not well understood. We investigated how composition of nonbreeding waterbird communities (97 species) in the European Union Natura 2000 (N2K) network (3018 sites) changed in response to increases in temperature over 25 years in 26 European countries. We measured community reshuffling based on abundance time series collected under the International Waterbird Census relative to N2K sites' conservation targets, funding, designation period, and management plan status. Waterbird community composition in sites explicitly designated to protect them and with management plans changed more quickly in response to climate warming than in other N2K sites. Temporal community changes were not affected by the designation period despite greater exposure to temperature increase inside late-designated N2K sites. Sites funded under the LIFE program had lower climate-driven community changes than sites that did not received LIFE funding. Our findings imply that efficient conservation policy that helps waterbird communities respond to climate warming is associated with sites specifically managed for waterbirds.Peer reviewe