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Science, culture and (eco-)ethics
Louis Legendre
Ethics in Science and Environmental Politics , 2004,
Abstract: EE Book 16 focuses on achievements and shortcomings of modern marine ecology. It also analysis the crux of all science: human capabilities and limitations of conducting research - of critically perceiving the world in and around us. Louis Legendre further examines the relationships between science and culture and underlines the significance of ethics, especially eco-ethics.
Interactive Effects of Viral and Bacterial Production on Marine Bacterial Diversity
Chiaki Motegi, Toshi Nagata, Takeshi Miki, Markus G. Weinbauer, Louis Legendre, Fereidoun Rassoulzadegan
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0076800
Abstract: A general model of species diversity predicts that the latter is maximized when productivity and disturbance are balanced. Based on this model, we hypothesized that the response of bacterial diversity to the ratio of viral to bacterial production (VP/BP) would be dome-shaped. In order to test this hypothesis, we obtained data on changes in bacterial communities (determined by terminal restriction fragment length polymorphism of 16S rRNA gene) along a wide VP/BP gradient (more than two orders of magnitude), using seawater incubations from NW Mediterranean surface waters, i.e., control and treatments with additions of phosphate, viruses, or both. In December, one dominant Operational Taxonomic Unit accounted for the major fraction of total amplified DNA in the phosphate addition treatment (75±20%, ± S.D.), but its contribution was low in the phosphate and virus addition treatment (23±19%), indicating that viruses prevented the prevalence of taxa that were competitively superior in phosphate-replete conditions. In contrast, in February, the single taxon predominance in the community was held in the phosphate addition treatment even with addition of viruses. We observed statistically robust dome-shaped response patterns of bacterial diversity to VP/BP, with significantly high bacterial diversity at intermediate VP/BP. This was consistent with our model-based hypothesis, indicating that bacterial production and viral-induced mortality interactively affect bacterial diversity in seawater.
Controlling Effects of Irradiance and Heterotrophy on Carbon Translocation in the Temperate Coral Cladocora caespitosa
Pascale Tremblay, Christine Ferrier-Pagès, Jean Fran？ois Maguer, Cécile Rottier, Louis Legendre, Renaud Grover
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0044672
Abstract: Temperate symbiotic corals, such as the Mediterranean species Cladocora caespitosa, live in seasonally changing environments, where irradiance can be ten times higher in summer than winter. These corals shift from autotrophy in summer to heterotrophy in winter in response to light limitation of the symbiont’s photosynthesis. In this study, we determined the autotrophic carbon budget under different conditions of irradiance (20 and 120 μmol photons m？2 s？1) and feeding (fed three times a week with Artemia salina nauplii, and unfed). Corals were incubated in H13CO3？-enriched seawater, and the fate of 13C was followed in the symbionts and the host tissue. The total amount of carbon fixed by photosynthesis and translocated was significantly higher at high than low irradiance (ca. 13 versus 2.5–4.5 μg cm？2 h？1), because the rates of photosynthesis and carbon fixation were also higher. However, the percent of carbon translocation was similar under the two irradiances, and reached more than 70% of the total fixed carbon. Host feeding induced a decrease in the percentage of carbon translocated under low irradiance (from 70 to 53%), and also a decrease in the rates of carbon translocation per symbiont cell under both irradiances. The fate of autotrophic and heterotrophic carbon differed according to irradiance. At low irradiance, autotrophic carbon was mostly respired by the host and the symbionts, and heterotrophic feeding led to an increase in host biomass. Under high irradiance, autotrophic carbon was both respired and released as particulate and dissolved organic carbon, and heterotrophic feeding led to an increase in host biomass and symbiont concentration. Overall, the maintenance of high symbiont concentration and high percentage of carbon translocation under low irradiance allow this coral species to optimize its autotrophic carbon acquisition, when irradiance conditions are not favourable to photosynthesis.
Discovery and functional characterization of two diterpene synthases for sclareol biosynthesis in Salvia sclarea (L.) and their relevance for perfume manufacture
Anne Caniard, Philipp Zerbe, Sylvain Legrand, Allison Cohade, Nadine Valot, Jean-Louis Magnard, J？rg Bohlmann, Laurent Legendre
BMC Plant Biology , 2012, DOI: 10.1186/1471-2229-12-119
Abstract: Based on previous general knowledge of diterpene biosynthesis in angiosperms, and based on mining of our recently published transcriptome database obtained by deep 454-sequencing of cDNA from clary sage calices, we cloned and functionally characterized two new diterpene synthase (diTPS) enzymes for the complete biosynthesis of sclareol in clary sage. A class II diTPS (SsLPPS) produced labda-13-en-8-ol diphosphate as major product from geranylgeranyl diphosphate (GGPP) with some minor quantities of its non-hydroxylated analogue, (9 S, 10 S)-copalyl diphosphate. A class I diTPS (SsSS) then transformed these intermediates into sclareol and manool, respectively. The production of sclareol was reconstructed in vitro by combining the two recombinant diTPS enzymes with the GGPP starting substrate and in vivo by co-expression of the two proteins in yeast (Saccharomyces cerevisiae). Tobacco-based transient expression assays of green fluorescent protein-fusion constructs revealed that both enzymes possess an N-terminal signal sequence that actively targets SsLPPS and SsSS to the chloroplast, a major site of GGPP and diterpene production in plants.SsLPPS and SsSS are two monofunctional diTPSs which, together, produce the diterpenoid specialized metabolite sclareol in a two-step process. They represent two of the first characterized hydroxylating diTPSs in angiosperms and generate the dihydroxylated labdane sclareol without requirement for additional enzymatic oxidation by activities such as cytochrome P450 monoxygenases. Yeast-based production of sclareol by co-expresssion of SsLPPS and SsSS was efficient enough to warrant the development and use of such technology for the biotechnological production of scareol and other oxygenated diterpenes.Diterpenoids constitute a large class of chemically diverse metabolites that is widely distributed throughout the plant kingdom with more than 12,000 known compounds, the majority of which derives from bicyclic ‘labdane-related’ diterpene
Extrema of low eigenvalues of the Dirichlet-Neumann Laplacian on a disk
Eveline Legendre
Mathematics , 2007, DOI: 10.4153/CJM-2010-042-8
Abstract: We study extrema of the first and the second mixed eigenvalues of the Laplacian on the disk among some families of Dirichlet-Neumann boundary conditions. We show that the minimizer of the second eigenvalue among all mixed boundary conditions lies in a compact 1-parameter family for which an explicit description is given. Moreover, we prove that among all partitions of the boundary with bounded number of parts on which Dirichlet and Neumann conditions are imposed alternately, the first eigenvalue is maximized by the uniformly distributed partition.
Existence and non uniqueness of constant scalar curvature toric Sasaki metrics
Eveline Legendre
Mathematics , 2010, DOI: 10.1112/S0010437X1100529X
Abstract: We study compatible toric Sasaki metrics with constant scalar curvature on co-oriented compact toric contact manifolds of Reeb type of dimension at least 5. These metrics come in rays of transversal homothety due to the possible rescaling of the Reeb vector fields. We prove that there exist Reeb vector fields for which the transversal Futaki invariant (restricted to the Lie algebra of the torus) vanishes. Using existence result of [25], we show that a co-oriented compact toric contact 5-manifold whose moment cone has 4 facets admits a finite number of rays of transversal homothetic compatible toric Sasaki metrics with constant scalar curvature. We point out a family of well-known toric contact structures on $S^2\times S^3$ admitting two non isometric and non transversally homothetic compatible toric Sasaki metrics with constant scalar curvature.
Toric geometry of convex quadrilaterals
Eveline Legendre
Mathematics , 2009,
Abstract: We provide an explicit resolution of the Abreu equation on convex labeled quadrilaterals. This confirms a conjecture of Donaldson in this particular case and implies a complete classification of the explicit toric K\"ahler-Einstein and toric Sasaki-Einstein metrics constructed in [6,22,14]. As a byproduct, we obtain a wealth of extremal toric (complex) orbi-surfaces, including K\"ahler-Einstein ones, and show that for a toric orbi-surface with 4 fixed points of the torus action, the vanishing of the Futaki invariant is a necessary and sufficient condition for the existence of K\"ahler metric with constant scalar curvature. Our results also provide explicit examples of relative K-unstable toric orbi-surfaces that do not admit extremal metrics.
Toric K？hler-Einstein metrics and convex compact polytopes
Eveline Legendre
Mathematics , 2011,
Abstract: We show that any compact convex simple lattice polytope is the moment polytope of a K\"ahler-Einstein orbifold, unique up to orbifold covering and homothety. We extend the Wang-Zhu Theorem \cite{WZ} giving the existence of a K\"ahler-Ricci soliton on any toric monotone manifold on any compact convex simple labelled polytope satisfying the combinatoric condition corresponding to monotonicity. We obtain that any compact convex simple polytope $P\subset \bR^n$ admits a set of inward normals, unique up to dilatation, such that there exists a symplectic potential satisfying the Guillemin boundary condition (with respect to these normals) and the K\"ahler-Einstein equation on $P\times \bR^n$. We interpret our result in terms of existence of singular K\"ahler-Einstein metrics on toric manifolds.
β-多样性的研究：应用多元回归和典范分析研究生态方差的分解
Pierre,Legendre
植物生态学报 植物生态学报 , 2007, DOI: 10.17521/cjpe.2007.0124
Abstract: ？β-多样性刻画了地理区域中不同地点物种组成的变化，是理解生态系统功能、生物多样性保护和生态系统管理的一个重要概念。该文介绍了如何从群落组成，相关环境和空间数据角度去分析β-多样性。β-多样性可以通过计算每个地点的多样性指数，进而对可能解释点之间差异的因子所作的假设进行检验来研究。也可以将涵盖所有点的群落组成数据表看作是一系列环境和空间变量的函数，进行直接分析。这种分析应用统计方法将多样性指数或群落组成数据表的方差进行关于环境和空间变量的分解。该文对方差分解进行阐述。方差分解是利用环境和空间变量来解释β-多样性的一种方法。β-多样性是生态学家用来比较不同地点或同一地点不同生态群落的一种手段。方差分解就是将群落组成数据表的总方差无偏分解成由各个解释变量所决定的子方差。调整的决定系数提供了针对多元回归和典范冗余分析的无偏估计。方差分解后，可以对感兴趣的方差解释部分进行显著性检验，同时绘出基于这部分方差解释的预测图。
L'image de ce qui ne peut être vu (entretien)
Legendre, Pierre
- , 1992, DOI: https://doi.org/10.7202/015201ar
Abstract:
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