Influence de la structure du paysage sur l'assemblage des prédateurs terricoles dans les zones agricoles non cultivées

L'assemblage des arthropodes en milieu agricole dépend de plusieurs facteurs agissant à des échelles plus ou moins larges, pouvant aller des caractéristiques locales de l'habitat jusqu'à la structure du paysage. Dans le but de lutter naturellement contre les ravageurs des cultures, il s'avère alors essentiel de déterminer quels paramètres sont liés à une grande abondance et diversité d'arthropodes prédateurs. L'objectif de ce projet de maîtrise est de déterminer quelle est l'influence du paysage sur l'assemblage des prédateurs terricoles (Coleoptera: Carabidae et Cicindelidae) au sein des zones agricoles non cultivées. Nos principales hypothèses sont que: 1) l'influence du paysage est plus grande que celle des pratiques agronomiques et de l'environnement local et 2) l'influence du paysage est maximale en milieu de saison lorsque le paysage est bien défini. Un échantillonnage à l'aide de pièges-fosses a été effectué, en 2006 et 2007, en bordure de 20 fossés adjacents à des champs de maïs, répartis au sein du bassin versant du ruisseau Vacher (Lanaudière, Québec, Canada). Des données relatives aux pratiques agronomiques effectuées dans le fossé et le champ de maïs adjacent ont été relevées de même que les caractéristiques du fossé échantillonné. Une cartographie du paysage a également été réalisée autour de chaque site (aux échelles 200 et 500 mètres) et suivie d'analyses spatiales (composition et configuration du paysage). Les résultats montrent que le paysage est la plus importante variable permettant d'expliquer les différences d'abondance et diversité de carabes au sein du bassin versant. De plus, l'influence du paysage sur l'assemblage des carabes s'avère varier en fonction de la saison, atteignant son maximum en Juillet-Août lorsque le paysage est bien défini. Les espèces étudiées individuellement ont également été plus influencées par le paysage en milieu de saison malgré quelques différences pouvant partiellement être allouées aux caractéristiques biologiques et écologiques de chaque espèce. En conclusion, cette étude a permis de montrer qu'il est essentiel de tenir compte de facteurs à grande échelle comme la structure du paysage, de la saison et des caractéristiques biologiques et écologiques des espèces lorsque l'on étudie l'assemblage des arthropodes en milieu agricole. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Carabes, Pratiques agronomiques, Environnement local, Structure du paysage, Variation saisonnière, Caractéristiques biologiques et écologiques, Partition de la variation

Jouer avec le paradoxe:l'exemple des Pokot du KenyaTome 1

In Kenya, The Pokot Community is made of approximately 190,000 persons (1989 Census). They are Kushitic Nilots and belong to the Kalenjin group. Native of the Sekerr Mountain and the Cherangani Hills, they are an agropastoral and sedentary people organized byeight age-class with current names but without handing over ceremonies. Duribng the first decades of the 19th century, a third of them left the mountains and migrated to the East plains. Some of them settled on the Masol Plains, while others went Eastwards and reached Nginyang where they settled near Turkana Community. They are the East plains pastoral Pokot. Then some of them left, raided the Maasai on the West side and chased the Karimojong out of their lands up to Amudat in Uganda, and settled there. They are the West plains Pokot. Their migrations lead them to adopt a new way of life. They became semi-nomads and pastoralists on the East and West plains. Adopting a way of life similar to the Turkana and the Karimojong, they borrowed their generation classes which determined the syncretic socio-political systems still in effect today. This thesis is focused on the question: What do such syncretic constructions observed in the three settlement zones impose upon the Pokot community as a whole and on each of its members. Such syncretic systems can exist if, and only if, the Pokot discover the most judicious solution to their paradoxes generated by the simultaneous exigence of contradictory age classes and generation classes systemes.Les Pokot du Kenya sont une communaute de 190,000 persons (recensement 1989). Nilote couchitiques, il appartiennent a l'aire culturelle Kalenjin. Originaires de montagnes, les Sekerr et les Cherangani, ils sont agropasteurs sedentaires, et ont developpe traditionnellement une organisation socio-politique fondee sur huit classes d'age aux noms recurrents, mais sans ceremonies de transmission de pouvoir pou le changement de status de chaque classe, hormis le rite d'entree par la circoncision. Au debut du XIXeme sicle, un tiers d'entre eux environ quitte les hautes terres vers l'est et s'installent dans les plaines de Masol. D'auttres poursuivent a l;est jusqu'a Nginyang, pres des Turkana, ou ils s'installent. La certains poursuivent encore, chassant les Maasai a l'ouest jusqu'a Kitale. Penetrant en territire Karimojong, ils repoussent le Karimojon jusqu'a la frontiere ougandaise actuelle. Leurs migrations, leur nouveau mode de vie: Ils sont pasteurs semi-nomaded dans les plaines, le contact avec le Turkana a l'est, les Karimojong a l'ouets et lieurs systemes de classes generationnelles determinent la formation de systemes syncretique tres diversifies chez les Pokot. L'objet de la these est centre sur la question des exigences de telles constructions syncretiques observees dans les trois zones de peuplement, et pour la communaute des Pokot dans son ensemble, et pour chacun de ses membres. De tels systemes syncretiques ne peuvent aboutir que si et seulement si les Pokot inventent les solutions les plus judicieuses aux paradoxes nes de la simultaneite des deux systemes contradictoires

Translation and fates of the gag protein of 1731, a Drosophila melanogaster retrotransposon

AbstractAn entire copy of 1731, a Drosophila melanogaster retrotransposon, was tagged by fusing in frame its putative gag gene with the reporter LacZ sequence. The high transfection efficiency of Drosophila virilis cells added to the absence of 1731 in their genome allowed, by combining histochemical staining and immunological detections, the demonstration of the translation of the 1731 gag gene. The gag protein is gathered in virus-like particles. Its occurrence in nuclei is consistent with a nuclear localization signal. The expression of the sense construction was inhibited by cotransfections with its antisense homologue

Copper nanoparticles of well-controlled size and shape: a new advance in synthesis and self-organization.

International audienceHere, we report a new synthetic route for spherical small copper nanoparticles (CuNPs) with size ranging from 3.5 nm to 11 nm and with an unprecedented associated monodispersity (<10%). This synthesis is based on the reduction of an organometallic precursor (CuCl(PPh3)3) by tert-butylamine borane in the presence of dodecylamine (DDA) at a moderate temperature (50 to 100 °C). Because of their narrow size distribution, the CuNPs form long-range 2D organizations (several μm(2)). The wide range of CuNPs sizes is obtained by controlling the reaction temperature and DDA-to-copper phosphine salt ratio during the synthesis process. The addition of oleic acid (OA) after the synthesis stabilizes the CuNPs (no coalescence) for several weeks under a nitrogen atmosphere. The nature and the reactivity of the ligands were studied by IR and UV-visible spectroscopy. We thus show that just after synthesis the nanoparticles are coated by phosphine and DDA. After adding OA, a clear exchange between phosphine and OA is evidenced. This exchange is possible thanks to an acid-base reaction between the free alkylamine in excess in the solution and OA. OA is then adsorbed on the NPs surface in the form of carboxylate. Furthermore, the use of oleylamine (OYA) instead of DDA as the capping agent allows one to obtain other NP shapes (nanorods, triangles and nanodisks). We get evidence that OYA allows the selective adsorption of chloride ions derived from the copper precursor on the different crystallographic faces during the growth of CuNPs that induces the formation of anisotropic shapes such nanorods or triangles

Transient electrochemistry: beyond simply temporal resolution:

Some physicochem. intrigues for which transient electrochem. was necessary to solve the problem are summarized in this feature article. First, we highlight the main constraints to be aware of to access to low time scales, and particularly focus on the effects of stray capacitances. Then, the electron transfer rate const. measured for redox mols. in a self-assembled monolayer configuration is compared to the conductance measured through the same systems, but at the single mol. level. This evidences strong conformational changes when mols. are trapped in the nanogap created between both electrodes. We also report about dendrimers, for which a short electrochem. perturbation induces creation of a diffusion layer within the mol., allowing the electron hopping rate to be measured and analyzed in terms of mol. motions of the redox centers. Finally, we show that transient electrochem. provides also useful information when coupled to other methodologies. For example, when an ultrasonic field drives very fast movements of a bubble situated above the electrode surface, the motion can be dectected indirectly through a modification of the diffusion flux. Another field concerns pulse radiolysis, and we describe how the reactivity (at the electrode or within the soln.) of radicals created by a radiolytic pulse can be quantified, widening the possibilities of electrochem. to operate in biol. media

Epigenomic Consequences of Immortalized Plant Cell Suspension Culture

Plant cells grown in culture exhibit genetic and epigenetic instability. Using a combination of chromatin immunoprecipitation and DNA methylation profiling on tiling microarrays, we have mapped the location and abundance of histone and DNA modifications in a continuously proliferating, dedifferentiated cell suspension culture of Arabidopsis. We have found that euchromatin becomes hypermethylated in culture and that a small percentage of the hypermethylated genes become associated with heterochromatic marks. In contrast, the heterochromatin undergoes dramatic and very precise DNA hypomethylation with transcriptional activation of specific transposable elements (TEs) in culture. High throughput sequencing of small interfering RNA (siRNA) revealed that TEs activated in culture have increased levels of 21-nucleotide (nt) siRNA, sometimes at the expense of the 24-nt siRNA class. In contrast, TEs that remain silent, which match the predominant 24-nt siRNA class, do not change significantly in their siRNA profiles. These results implicate RNA interference and chromatin modification in epigenetic restructuring of the genome following the activation of TEs in immortalized cell culture

The fabrication and characterization of adjustable nanogaps between gold electrodes on chip for electrical measurement of single molecules

This work reports on a new method to fabricate mechanically controllable break junctions (MCBJ) with finely adjustable nanogaps between two gold electrodes on solid state chips for characterizing electron transport properties of single molecules. The simple, low cost, robust and reproducible fabrication method combines conventional photolithography, chemical etching and electrodeposition to produce suspended electrodes separated with nanogaps. The MCBJ devices fabricated by the method can undergo many cycles in which the nanogap width can be precisely and repeatedly varied from zero to several nanometers. The method improves the success rate of the MCBJ experiments. Using these devices the electron transport properties of a typical molecular system, commercially available benzene-1,4-dithiol (BDT), have been studied. The I-V and G-V characteristic curves of BDT and the conductance value for a single BDT molecule established the excellent device suitability for molecular electronics research.NSF [20620130427]; MOST in China [2007DFC40440, 2009CB930703]; State Key Laboratory of Supramolecular Structure and Materials [SKLSSM200701]; Jilin Univ., China ; CNRS (UMR 8640 'PASTEUR'), Ecole Normale Superieure (ENS), University Pierre and Marie Curie (UPMC) ; French Ministry of Research in France through ANR REEL ; US-NSF [DMR-03-05242