Horizon / Pleins textes

    Contribution of trees to the conservation of biodiversity and ecosystem services in agricultural landscapes

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    The production of sufficient food for an increasing global population while conserving natural capital is a major challenge to humanity. Tree-mediated ecosystem services are recognized as key features of more sustainable agroecosystems but the strategic management of tree attributes for ecosystem service provision is poorly understood. Six agroforestry and tree cover transition studies, spanning tropical/subtropical forest zones in three continents, were synthesized to assess the contribution of tree cover to the conservation of biodiversity and ecosystem services. Loss of native earthworm populations resulted in 76% lower soil macroporosity when shade trees were absent in coffee agriculture. Increased tree cover contributed to 53% increase in tea crop yield, maintained 93% of crop pollinators found in the natural forest and, in combination with nearby forest fragments, contributed to as much as 86% lower incidence for coffee berry borer. In certain contexts, shade trees contributed to negative effects resulting from increases in abundance of white stem borer and lacebugs and resulted in 60% reduction of endangered tree species compared to forest. Managing trees for ecosystem services requires understanding which tree species to include and how to manage them for different socio-ecological contexts. This knowledge needs to be shared and translated into viable options with farming communities

    Out of Southern East Asia of the brown rat revealed by large-scale genome sequencing

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    The geographic origin and migration of the brown rat (Rattus norvegicus) remain subjects of considerable debate. In this study, we sequenced whole genomes of 110 wild brown rats with a diverse world-wide representation. We reveal that brown rats migrated out of southern East Asia, rather than northern Asia as formerly suggested, into the Middle East and then to Europe and Africa, thousands of years ago. Comparison of genomes from different geographical populations reveals that many genes involved in the immune system experienced positive selection in the wild brown rat

    Flaviviruses produce a subgenomic flaviviral RNA that enhances mosquito transmission

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    Mosquito-borne flaviviruses (MBFVs) are a global public health burden. MBFVs have several unique 3UTR structures that inhibit the host RNA decay machinery to produce subgenomic flaviviral RNAs (sfRNAs). Number of sfRNA species and their relative quantities are dependent on the 3UTR tertiary structures and can vary between tissues. Two recent in vivo studies demonstrated that sfRNA enhances mosquito transmission, resulting in increased infection rate of saliva. Transmission efficiency is determined by the immune response. First evidence points to sfRNA interference with the Toll and RNAi immune pathways. However, a more complex picture that includes flexibility in sfRNA production and interaction with immune-related proteins remains to be explored

    Deciphering landscape evolution with karstic networks : a Pyrenean case study [+ Corrigendum in Quater. Geochronol. 2020, vol. 57, art. 101050, 2 p.]

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    The rates and chronologies of valley incision are closely modulated by the tectonic uplift of active mountain ranges and were controlled by repeated climate changes during the Quaternary. The continental collision between the Iberian and Eurasian plates induced a double-vergence orogen, the Pyrenees, which has been considered a mature mountain range despite significant seismicity and evidence of neotectonics. Nevertheless, recent studies indicated that the range may have never reached a steady state. One option for resolving this controversy is to quantify the incision rates since the Miocene by reconstructing the vertical movement of geometric markers such as fluvial terraces. However, the few available ages for the Pyrenean terrace systems do not exceed the Middle Pleistocene. Thus, we study alluvium-filled horizontal epiphreatic passages in limestone karstic networks to increase the span of this dataset. Such landforms are used as substitutes of fluvial terraces because they represent former valley floors. These features record the transient position of former local base levels during the process of valley deepening. The Tet river valley (southern Pyrenees) is studied near the Villefranche-de-Conflent limestone gorge, where 8 cave levels have been recognized over a vertical height of 600 m. In this setting, already published Al-26/Be-10 cosmogenic burial data were limited to the last similar to 5 Ma. This work extends this initial dataset through the acquisition of cosmogenic Be-10/Ne-21 data, which should enable us to reconstruct a more complete valley incision chronology. We also revise the Al-26/Be-10 record for the lowest portion of the valley. The obtained quantitative results are surprising relative to certain geological evidence, and the limitations of such an approach in the investigated geodynamic context are discussed. In particular, sampling within a detrital deposit (the Escaro Formation) and in the riverbeds suggests that the Al-26/Be-10 ratios that are associated with the lower cave levels could have been inherited by pre-burial episodes. Similarly, pre-burial catchment denudation rates that do not exceed hundreds of cm/ka are probably tainted by the same amalgamation processes

    U/Pb dating of geodic calcite : new insights on Western Europe major tectonic events and associated diagenetic fluids

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    This study presents the first application of the U/Pb dating method to highly Pb-depleted diagenetic geodic calcites of the Jurassic formations of the Paris Basin that leads to a reappraisal of the palaeohydrological history of this region. Composite U/Pb ages from multiple geodes, combined with delta O-18 analyses, reveal two main phases of diagenetic fluid circulations linked with major regional tectonic events. Dogger formations recorded a first diagenetic fluid episode at 147.8 +/- 3.8 Ma, i.e. at the very beginning of the emersion of the basin during the Tithonian period and 30 Ma earlier than previously assumed. delta O-18 results confirmed that most of the calcitic cement phases that closed the porosity of these formations precipitated at the beginning of the Cretaceous period. Oxfordian formations recorded another major meteoric fluid circulation at 33.5 +/- 2.8 Ma related to the initial stage of the European Cenozoic Rift System (ECRIS). Consequently, the porosity of the Mesozoic formations of the studied area may have been closed sooner than previously thought, before the main ECRIS rifting phase of Oligocene age. This study shows that U/Pb dating of secondary geodic calcite offers a new powerful way for reconstructing the coupled palaeohydrological and diagenetic history of sedimentary basins

    Public engagement and communication : who is in charge ?

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    Recent advances in environmental science from the Euro-Mediterranean and surrounding regions

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    The geochemistry and isotopic composition (18O, 2H) of groundwater from the alluvial phreatic aquifer in the Wady Guenniche basin (NE of Tunisia), were investigated in order to reveal the origin of the water salinity. The major geochemical processes in the aquifer are evaporite mineral dissolution and mineral exchange with clays. The salinization of groundwater would be a limiting factor in their use for irrigation. The stable isotopic composition of water indicates a groundwater recharge in current climate condition and the point closest to the sea indicates the possible beginning of a seawater intrusion as a result of the intensive exploitation of resources. The tritium data confirm a recent recharge younger than 1950

    Terrains et fugues de Georges Balandier

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    Cet article étudie la place de Georges Balandier dans la formation de l'approche situationnelle en anthropologie, à partir de la problématique politique introduite avec le concept de "situation coloniale" dans les années 1950 et du point de vue épistémologique, pour l'enquête sur les contextes de "contacts culturels" urbains et politiques en Afrique. Ces deux questions ont rapproché les études africaines françaises et britanniques dans les années 1950 et 1960

    Recruitment success and growth variability of mugilids in a West African estuary impacted by climate change

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    With the persistence of a drought since the late 1960s, some West African estuaries became permanently reversed in term of salinity gradient and hypersaline waters are present in their upstream part (salinity >60). To understand the mechanisms regulating fish recruitment intensity in these estuaries and evaluate the consequences of freshwater shortages on juvenile habitat quality, a growth study was conducted in the Saloum hypersaline estuary (Senegal). The Mugilidae fish family, highly representative of estuarine environments, was targeted and several species sampled (Chelon dumerili, Mugil bananensis and M. cf. curema sp. M). Juveniles were sampled monthly all the year round in three areas of the estuary exhibiting strongly contrasted habitat conditions. Otolith sections were used to estimate the ages, reconstruct growth trajectories, estimate the duration of the oceanic larval phase, and evaluate juvenile growth variability along the salinity gradient. Analyses revealed that the temporal recruitment variability of C. dumerili, with 2 annual cohorts, was not mainly induced by growth-selection mechanisms, but probably more by predation pressures. Juveniles exhibited significantly faster growth rates in the lower salinity suggesting that benthic food availability was a strong factor controlling habitat quality of early juveniles. Salinity had also a clear impact when reducing the growth in hypersaline conditions and/or selecting slower growing individuals. Moderate freshwater inputs positively affected the nursery function of the estuary for mugilids by enhancing the productivity of the first trophic levels. In a long term, the global change could have an impact of the mugilid fishery and its management
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