60 research outputs found
Predicting where a radiation will occur: Acoustic and molecular surveys reveal overlooked diversity in Indian Ocean Island crickets (Mogoplistinae: Ornebius)
Recent theory suggests that the geographic location of island radiations (local accumulation of species diversity due to cladogenesis) can be predicted based on island area and isolation. Crickets are a suitable group for testing these predictions, as they show both the ability to reach some of the most isolated islands in the world, and to speciate at small spatial scales. Despite substantial song variation between closely related species in many island cricket lineages worldwide, to date this characteristic has not received attention in the western Indian Ocean islands; existing species descriptions are based on morphology alone. Here we use a combination of acoustics and DNA sequencing to survey these islands for Ornebius crickets. We uncover a small but previously unknown radiation in the Mascarenes, constituting a three-fold increase in the Ornebius species diversity of this archipelago (from two to six species). A further new species is detected in the Comoros. Although double archipelago colonisation is the best explanation for species diversity in the Seychelles, in situ cladogenesis is the best explanation for the six species in the Mascarenes and two species of the Comoros. Whether the radiation of Mascarene Ornebius results from intra- or purely inter- island speciation cannot be determined on the basis of the phylogenetic data alone. However, the existence of genetic, song and ecological divergence at the intra-island scale is suggestive of an intra-island speciation scenario in which ecological and mating traits diverge hand-in-hand. Our results suggest that the geographic location of Ornebius radiations is partially but not fully explained by island area and isolation. A notable anomaly is Madagascar, where our surveys are consistent with existing accounts in finding no Ornebius species present. Possible explanations are discussed, invoking ecological differences between species and differences in environmental history between islands. (Résumé d'auteur
Genetic control of yield and yield components in winter oilseed rape (Brassica napus L.) grown under nitrogen limitation
A non-intrusive reduced basis approach for parametrized heat transfer problems
Computation Fluid Dynamics (CFD) simulation has become a routine design tool for i) predicting accurately the thermal performances of electronics set ups and devices such as cooling system and ii) optimizing configurations. Although CFD simulations using discretization methods such as finite volume or finite element can be performed at different scales, from component/board levels to larger system, these classical discretization techniques can prove to be too costly and time consuming, especially in the case of optimization purposes where similar systems, with different design parameters have to be solved sequentially. The design parameters can be of geometric nature or related to the boundary conditions. This motivates our interest on model reduction and particularly on reduced basis methods. As is well documented in the literature, the offline/online implementation of the standard RB method (a Galerkin approach within the reduced basis space) requires to modify the original CFD calculation code, which for a commercial one may be problematic even impossible. For this reason, we have proposed in a previous paper, with an application to a simple scalar convection diffusion problem, an alternative non-intrusive reduced basis approach (NIRB) based on a two-grid finite element discretization. Here also the process is two stages: offline, the construction of the reduced basis is performed on a fine mesh; online a new configuration is simulated using a coarse mesh. While such a coarse solution, can be computed quickly enough to be used in a rapid decision process, it is generally not accurate enough for practical use. In order to retrieve accuracy, we first project every such coarse solution into the reduced space, and then further improve them via a rectification technique. The purpose of this paper is to generalize the approach to a CFD configuration
Modeling N dynamics to assess environmental impacts of cropped soils
Models are useful tools to evaluate environmental impacts associated with nitrogen management in cropping systems and to predict them correctly. The purpose of this chapter was to analyze whether existing models satisfactorily simulate N losses in agroecosystems, require input data that are accessible, and can incorporate agricultural and climatic changes. The literature on 62 nitrogen models was reviewed. Each model was analyzed to identify the processes simulated, the equations used, the time and space scales, the input data and their degree of accessibility, and finally its performance. The review showed that a wide range of formalisms have been developed to model N processes. N losses such as nitrate leaching give better performance than N gas emissions, underlining the need to improve the understanding and modeling of denitrification and volatilization. It also revealed the narrow range of crop families parameterized and validated with field measurements. The main trend in modeling over the last 15 years has been the shift from mechanistic models to functional models, with a simplification of the equations involved and an aggregation of modules according to specific objectives. The more recent models have thus generally been based on specific contexts and cannot be directly extrapolated to other pedoclimatic and crop contexts, yet this is necessary for evaluating scenarios involving changes in land use and management or climatic uncertainties
Vinasse organic matter quality and mineralization potential, as influenced by raw material, fermentation and concentration processes
Both dilute and concentrated vinasse can be spread on agricultural fields or used as organic fertilizer. The effects of different characteristics of the original raw material on the biochemical composition of vinasse and their C and N mineralization in soil were investigated. Vinasse samples were obtained from similar industrial fermentation processes based on the growth of microorganisms on molasses from different raw material (sugar beet or sugar cane) and vinasse concentration (dilute or concentrated). The nature of the raw material used for fermentation had the greatest effect on the nature and size of the resistant organic pool. This fraction included aromatic compounds originating from the raw material or from complex molecules and seemed to be quantitatively related to acid-insoluble N. Samples derived from sugar beet were richer in N compounds and induced greater net N mineralization. The effect of evaporation varied with the nature of the raw material. Concentration led to a slight increase in the abundance of phenolic compounds, acid-insoluble fraction, and a slight decrease in the labile fraction of vinasses partly or totally derived from sugar beet. The effect of the dilute vinasse from sugar cane was greater. The concentrated vinasse had a smaller labile fraction, induced N immobilization at the beginning of incubation, and exhibited greater N concentration in the acid-insoluble fraction than the dilute vinasse
Analyser et estimer les émissions de N2O dans les systÚmes de grandes cultures français
Les Ă©missions de N2O constituent la principale source dâĂ©missions de gaz Ă effet de serre dans les systĂšmes de grandes cultures français. NĂ©anmoins, ces estimations sont basĂ©es sur une mĂ©thode de rĂ©fĂ©rence (dite de niveau 1 et Ă©laborĂ©e par le GIEC) dont la prĂ©cision est relativement faible. Elle ne prend notamment pas en compte lâimpact du pĂ©doclimat ni des pratiques culturales (en dehors de la fertilisation azotĂ©e). Afin de contribuer Ă mettre au point une nouvelle mĂ©thode dâestimation, basĂ©e sur des donnĂ©es spĂ©cifiquement françaises (mĂ©thode dite de niveau 2) voire sur des modĂšles mĂ©canistes (niveau 3), les objectifs du projet NO GAS Ă©taient les suivants : (i) acquĂ©rir des donnĂ©es de rĂ©fĂ©rence sur une gamme relativement large de pĂ©doclimats et de systĂšmes de culture, (ii) d'Ă©valuer lâimpact de certaines pratiques culturales sur les Ă©missions de N2O et (iii) d'amĂ©liorer la calibration des modĂšles dâĂ©missions directes de N2O. Sur les campagnes 2010-11 et 2011-12, un rĂ©seau de dix sites expĂ©rimentaux a Ă©tĂ© mis en place. Les donnĂ©es recueillies ont Ă©tĂ© organisĂ©es dans une base de donnĂ©es partagĂ©e par lâensemble des partenaires du projet et dâautres contributeurs. Les donnĂ©es collectĂ©es ont permis de prĂ©ciser lâimpact du travail du sol, du drainage et de la fertilisation azotĂ©e sur les Ă©missions de N2O. Elles ont aussi mis en avant lâeffet prĂ©pondĂ©rant du climat et des caractĂ©ristiques du sol (notamment le pH) pour expliquer la variabilitĂ© des flux annuels de N2O Ă lâĂ©chelle du rĂ©seau. Ces donnĂ©es ont aussi servi Ă tester la capacitĂ© prĂ©dictive et amĂ©liorer la calibration des modules dâĂ©missions directes de N2O de trois modĂšles : STICS, CERS-EGC et celui de lâoutil SystâN. Elles sont aussi actuellement utilisĂ©es pour mettre au point une mĂ©thode dâestimation de niveau 2, en collaboration avec le CITEPA
Adding a diversity of legumes to a crop decision-support system: Maintaining satisfactory accuracy while keeping the model simple
International audienceIn a context of economic and environmental concerns in agriculture, legumes appear to be suitable alternative crops to diversify current cropping systems and reduce their dependence on synthetic nitrogen (N) fertiliser and protein from imported soya bean. However, legume-based cropping systems may increase N losses through nitrate leaching if the N available from legumes does not coincide with subsequent crop requirements. To help agricultural advisers manage N in these systems, we adapted the decision-support system SystâNÂź, designed to assess N losses in cropping systems, to simulate three annual and one perennial legume crops: pea, faba bean, soya bean and lucerne. To this end, we adapted and simplified existing submodels of legume functioning to include them in SystâN, to keep the latter simple. We adapted the submodels âBNFâ (i.e. biological N fixation) from the STICS model and âdormancyâ from the CropSyst model. We also added the ability to enter the flowering date to improve predictions (improvement in N fixationâs rRMSE from 57% to 41% and EF from 0.57 to 0.77). The equations and associated parameter set developed for the four legume crops yielded satisfying predictions of crop biomass (rMBE = 9%, EF = 0.82, rRMSE = 39%) and N content (rMBE = 5%, EF = 0.76, rRMSE = 37%). These performances support the philosophy of SystâNÂź that requires minimising the number of additional parameters for users when representing new crops or processes
Plasticity of Hypothalamic Dopamine Neurons during Lactation Results in Dissociation of Electrical Activity and Release
International audienceTuberoinfundibular dopamine (TIDA) neurons are the central regulators of prolactin (PRL) secretion. Their extensive functional plasticity allows a change from low PRL secretion in the non-pregnant state to the condition of hyperprolactinemia that characterizes lactation. To allow this rise in PRL, TIDA neurons are thought to become unresponsive to PRL at lactation and functionally silenced. Here we show that, contrary to expectations, the electrical properties of the system were not modified during lactation and that the neurons remained electrically responsive to a PRL stimulus, with PRL inducing an acute increase in their firing rate during lactation that was identical to that seen in non-pregnant mice. Furthermore, we show a long-term organization of TIDA neuron electrical activity with an harmonization of their firing rates, which remains intact during lactation. However, PRL-induced secretion of dopamine (DA) at the median eminence was strongly blunted during lactation, at least in part attributable to lack of phosphorylation of tyrosine hydroxylase, the key enzyme involved in DA synthesis. We therefore conclude that lactation, rather than involving electrical silencing of TIDA neurons, represents a condition of decoupling between electrical activity at the cell body and DA secretion at the median eminence
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