HAL-IRD
Not a member yet
83947 research outputs found
Sort by
Rehabilitating the benefits of gene tree correction in the presence of incomplete lineage sorting
No full textInternational audienceGene trees play an important role in various areas of phylogenomics. However, their reconstruction often relies on limited-length sequences and may not account for complex evolutionary events, such as gene duplications, losses, or incomplete lineage sorting (ILS), which are not modeled by standard phylogenetic methods. To address these challenges, it is common to first infer gene trees using fast algorithms for conventional models, then refine them through species tree-aware correction methods. Recently, it has been argued that such corrections can lead to overfitting and force gene trees to resemble the species tree, thereby obscuring genuine gene-level variation caused by ILS. In this paper, we challenge and refute this hypothesis, and we demonstrate that, when applied carefully, correction methods can offer significant benefits, even in the presence of ILS
Reversible Strong Metal‐Support Interactions in Co/TiO 2 Catalysts Driven by CO 2
No full textInternational audienceStrong metal–support interactions can significantly influence catalytic performance. On titania supports, these interactions often involve the formation of a substoichiometric TiO X overlayer during high‐temperature reduction, which can be reversed by treatments under dioxygen. Under CO 2 hydrogenation conditions, where water is produced, complete removal of the TiO X overlayer has been reported, raising questions about its stability in the presence of a mild oxidant such as CO 2 . In this study, in situ and operando techniques were employed to examine the effect of varying conditions on both the titania overlayer and cobalt species in a Co/TiO 2 catalyst. After reduction at 350 °C, the overlayer consisted of stoichiometric anatase TiO 2 , while cobalt remained partially reduced. Exposure to CO 2 /H 2 at 220 °C enabled complete cobalt reduction without affecting the TiO 2 overlayer. In contrast, pure CO 2 at 220 °C caused overlayer removal and full cobalt oxidation. The impact of this CO 2 ‐mediated reversibility on CO 2 hydrogenation was also evaluated. Although steady‐state activity was largely unaffected, the transient regime showed substantial changes in selectivity and behavior. These results demonstrate that different treatments can strongly influence both the stability and reactivity of Co/TiO 2 catalysts, highlighting the importance of dynamic SMSI effects in CO 2 hydrogenation
Marine litter, microplastic pollution and organic additives assessments in polar areas through an opportunistic cruise ship-based approach
No full textInternational audienceThis study presents findings from the opportunistic cruise, which performed microplastic and chemicalcontaminant sampling in surface waters, sediments, and ice in a sector of the western Arctic and the southwesternpart of the Antarctic Peninsula. Microplastics were detected in 100 % of the samples. Floating microplasticdensities (100–5000 μm) reached up to 314,251 items/km2 in Antarctica and 63,593 items/km2 in theArctic. The smallest particles (100–300 μm) dominated in southwestern Antarctic Peninsula (97 %) where thefibers (80 %) and fragments (19 %) were the main components. In the eastern Arctic, the two size classes(100–300 μm and 300–1000 μm) were more evenly distributed (58 % and 40 % respectively) and polymer diversity.Sediment microplastic concentrations were higher in the Arctic (up to 470 items/kg) compared tosouthwestern Antarctic Peninsula (maximum 399 items/kg). OrganoPhosphate Esters and PhthAlate Esters werealso measured for the first time in southwestern Antarctic Peninsula seawater (35.18 ±18.31 ng/L and 72.68 ±39.71 ng/L, respectively) and ice (50.44 ±24.79 ng/L and 16.72 ±11.46 ng/L, respectively). This studydemonstrates the utility of cruise ship-based sampling for monitoring remote regions and it contributes criticalbaseline data for global microplastic assessments.Cette étude présente les résultats d’une campagne opportuniste menée à bord d’un navire, au cours de laquelle des échantillonnages de microplastiques et de contaminants chimiques ont été réalisés dans les eaux de surface, les sédiments et la glace, dans un secteur de l’Arctique occidental et dans la partie sud-ouest de la péninsule Antarctique. Des microplastiques ont été détectés dans 100 % des échantillons. Les densités de microplastiques flottants (100–5000 µm) ont atteint jusqu’à 314 251 particules/km² en Antarctique et 63 593 particules/km² dans l’Arctique. Les plus petites particules (100–300 µm) dominaient dans la région sud-ouest de la péninsule Antarctique (97 %), où les fibres (80 %) et les fragments (19 %) constituaient les principaux types de particules. Dans l’Arctique oriental, les deux classes de taille (100–300 µm et 300–1000 µm) étaient plus équitablement réparties (58 % et 40 % respectivement), avec une plus grande diversité de polymères. Les concentrations de microplastiques dans les sédiments étaient plus élevées dans l’Arctique (jusqu’à 470 particules/kg) que dans la région sud-ouest de la péninsule Antarctique (maximum de 399 particules/kg). Des esters organophosphorés et des esters de phtalates ont également été mesurés pour la première fois dans l’eau de mer de la région sud-ouest de la péninsule Antarctique (35,18 ± 18,31 ng/L et 72,68 ± 39,71 ng/L, respectivement) ainsi que dans la glace (50,44 ± 24,79 ng/L et 16,72 ± 11,46 ng/L, respectivement). Cette étude démontre l’intérêt des prélèvements réalisés à partir de navires de croisière pour le suivi des régions éloignées et apporte des données de référence essentielles pour les évaluations globales des microplastiques
Trait-dependent declines of threatened endemic trees following plant invasion on a tropical oceanic island
No full textInternational audienceBiological invasions are a leading cause of the ongoing biodiversity crisis, and particularly so on islands. However, the role of invasive alien plants (IAPs) as a driver of native plant declines and extinctions remains unclear. The inherently slow and gradual nature of plant extinctions, especially that of long-lived woody species, could be a reason. Here, we examined temporal trends in subpopulations of 28 threatened endemic tree (TET) taxa. We questioned the frequency with which they decline in association with IAPs on Reunion Island (South-West Indian Ocean), and asked whether the most susceptible TET taxa exhibit characteristics that could reveal the underlying ecological mechanisms. We resurveyed 182 historically described subpopulations and tested whether observed trends of juvenile and adult TETs correlate with the abundance in IAPs using path analyses, while distinguishing TET taxa with respect to their leaf–height–seed characteristics and extinction risk. The trend of adult TETs was not affected by IAPs but that of juvenile TETs was negatively correlated with the abundance of IAPs in the understory layer. This was particularly the case for TET taxa with conservative resource-use strategies (low specific leaf area or low maximum height), whose juveniles might be particularly susceptible to competition with IAPs, but not for TET taxa with large seeds, whose metabolic reserves make seedlings more likely to attain a critical size. These findings suggest that IAPs can significantly contribute to the extinction dynamics of trees, primarily by limiting regeneration through competitive exclusion, and that their impacts vary depending on the traits of the affected taxa
The regeneration index, an agronomic tool to scale up agroecology
No full textInternational audienceAgroecology lays on well-established agronomic principles that are universal: endogenous soil fertility, plant nutrition in water and mineral nutrients, and crop protection against plant bio-aggressors, all ensured as much as possible by the biological activity in the cultivated ecosystem. However, their implementation must be adapted to the pedo-climatic and socio-economic contexts of each farm. A variety of tools exist to evaluate a farm's agroecological level and monitor its progression, often with a main objective of pedagogy. In parallel, downstream corporations engaged in the agroecological transition impose on their suppliers' specifications or certification labels often based on means, ill-adapted to the context of farms, and sometimes at odds with the agronomic principles underlying agroecology.To bridge this major gap between agronomic evaluation and economical valorization, and thus allow for a massive scale-up of agroecology in the field, there is a need for a tool that i) relies on a solid agronomic basis and integrates the key principles of agroecology; ii) does not impose means but sets goals that can be achieved in different technical ways; and iii) allows for direct economical valorization in the supply chain.We present here a new agronomic tool that has been developed to meet these three objectives: the Regeneration Index. After presenting the Regeneration Index's co-construction process, the details of its indicators and their scientific foundation, we enlighten with a case study the relevance of the Regeneration Index to reconcile actors of supply chains around a robust agronomic core in complementarity with environmental certifications
Unemployment impact of network sectors and employment protection legislation reforms: Evidence from selected african countries
No full textInternational audienceThis paper examines the dynamic effects of Employment Protection Legislation (EPL) reforms and Network Sector reforms on unemployment in selected African countries from 1990 to 2014. Reforms refer to changes in the EPL or Network Sector institutions index. Using local projections combined with augmented inverse probability weighting (LP–AIPW) and Entropy Balancing techniques to address endogeneity concerns, our findings show that EPL reforms reduce unemployment from the first year after their implementation, while Network Sector reforms also lower unemployment, with significant effects emerging from the second year onward. Robustness checks confirm that these results are consistent across alternative specifications, different definitions of reform episodes, and alternative labor-market outcomes such as employment and labor force participation. The heterogeneity analysis shows that both types of reforms reduce unemployment among men and young workers aged 15–24, while significant effects for women are concentrated among young female workers. Finally, we identify key transmission channels through which the reforms operate, including reductions in informality, increases in domestic investment and foreign direct investment, and short-run improvements in total factor productivity
Background Issues in X-Ray Diffraction and Raman Spectroscopy of Carbon Materials
No full textInternational audienceRemoving background signals is a common preprocessing step, but it is not without drawbacks. In X-ray diffraction data, background correction can artificially symmetrize diffraction peaks, which becomes a critical issue for lamellar materials such as graphenic carbon when the Laue indices lie in the plane (e.g., the 10 and 11 peaks). We discuss several approaches to background correction and their implications for the resulting data. In Raman spectroscopy, defects activate the phonon density of states, leading to higher intensity below the D band than above the G band, with respect to the Raman shift. After discussing the linear and circular polarization on the Raman selection rules, we show how flattening the background-a widely used measure of disorder-alters the ID/IG ratio. Finally, principal component analysis (PCA) provides a useful preliminary exploration of data structure; however, because its components may include negative contributions, it cannot be directly applied to spectral decomposition. In contrast, non-negative component decomposition offers an optimal way to preserve the Raman background, even in the presence of luminescence. We confirm our analysis with ANOVA p-values
First evidence of human borreliosis local transmission in Cambodia
No full textInternational audienceWe report the first cases of confirmed human local transmission of borreliosis in Cambodia. Four patients, including cases with no travel history, presented typical clinical signs and tested positive for Borrelia burgdorferi antibodies. These findings confirm the presence, circulation, and local transmission of Borrelia in Cambodia. These results are important to convince for the need and the development of surveillance of tick-borne diseases in Southeast Asia
Assessing the persistence of semi-natural species-rich grasslands under changes in grazing practices: Insights for grassland restoration
No full textInternational audienceGrazing practices are well-known to shape plant populations and communities in semi-natural grasslands and the conservation and restoration of these ecosystems relies heavily on maintaining traditional extensive grazing systems, which have persisted for centuries or even millennia. However the changes of grazing practices in relation to climate change and socio-economic factors can result in biodiversity loss, shifts in vegetation composition, soil degradation, and declines in ecosystem services and habitat quality. This study aimed to understand the medium-term (3-16 years) effects of changes in grazing practices by comparing two sheep grazing methods in semi-natural rangelands of Southern France: millennia-old traditional herding with shepherds and herding dogs, and the recent practice of fenced free grazing, which emerged at the beginning of the 21st century. Surveys were conducted at six paired study sites over three years, assessing vegetation, mesological data, and plant traits. While the five vegetation zones created by traditional herding remain identifiable, the transition to fenced grazing has induced, for the first time in these grasslands, a mid-term homogenization of plant communities, marked by the spread of xero-mesophilous species and the disappearance of the historical grazingintensity gradient. These findings highlight the ecological implications of altered grazing regimes, such as fenced grazing, for biodiversity conservation of rangelands with millennia-long grazing history, ecosystem functionality, and long-term persistence of high heritage value grasslands. They provide critical insights into designing adaptive and sustainable restoration strategies for degraded grasslands under changing environmental and socio-economic conditions
Ultramafic float rocks at Jezero crater (Mars): excavation of lower crustal rocks or mantle peridotites by impact cratering?
No full textInternational audienceBased on observation and data from meteorites and in situ scientific missions, experiments as well as models, the Martian mantle is assumed to share some compositional and mineralogical affinity with the terrestrial mantle. However, there might be subtle differences like the Martian mantle being more ferroan. Yet, we do not have any direct analysis of a Martian mantle rock to confirm this assumption. NASA’s Perseverance rover found olivine-rich boulder-sized float rocks on the upper Jezero fan (Mars). These boulders have an ultramafic composition and their mineralogy is dominantly composed of Fo73±3 olivine with high-Mg orthopyroxene, Cr-rich Ti-Fe oxides and minor plagioclase and high-Ca pyroxene. Microtextural and petrological analysis reveals that these minerals crystallized at equilibrium. In addition, these boulders are different from all the bedrocks analyzed by Perseverance along its traverse which are crustal igneous rocks and sediments. Comparing our data to Martian meteorites and available Mars bulk silicate models (BSM), we discuss that these boulders could represent primitive melts and/or lower crustal material, and we specifically hypothesize that they could be mantle peridotites. We propose that these putative mantle rocks could have been excavated by the succession of impacts from the shallow mantle or lower crust in the Isidis region where Jezero crater is located. These olivine-rich boulders could thereby constitute the first direct analysis of a Martian mantle rock