An allele-specific, stochastic gene expression process controls the expression of multiple Ly49 family genes and generates a diverse, MHC-specific NK cell receptor repertoire.

Mouse NK cells express MHC class I-specific inhibitory Ly49 receptors. Since these receptors display distinct ligand specificities and are clonally distributed, their expression generates a diverse NK cell receptor repertoire specific for MHC class I molecules. We have previously found that the Dd (or Dk)-specific Ly49A receptor is usually expressed from a single allele. However, a small fraction of short-term NK cell clones expressed both Ly49A alleles, suggesting that the two Ly49A alleles are independently and randomly expressed. Here we show that the genes for two additional Ly49 receptors (Ly49C and Ly49G2) are also expressed in a (predominantly) mono-allelic fashion. Since single NK cells can co-express multiple Ly49 receptors, we also investigated whether mono-allelic expression from within the tightly linked Ly49 gene cluster is coordinate or independent. Our clonal analysis suggests that the expression of alleles of distinct Ly49 genes is not coordinate. Thus Ly49 alleles are apparently independently and randomly chosen for stable expression, a process that directly restricts the number of Ly49 receptors expressed per single NK cell. We propose that the Ly49 receptor repertoire specific for MHC class I is generated by an allele-specific, stochastic gene expression process that acts on the entire Ly49 gene cluster.

Iowa’s Bridge and Highway Climate Change and Extreme Weather Vulnerability Assessment Pilot, HEPN-707, 2015

The Iowa Department of Transportation (DOT) is responsible for approximately 4,100 bridges and structures that are a part of the state’s primary highway system, which includes the Interstate, US, and Iowa highway routes. A pilot study was conducted for six bridges in two Iowa river basins—the Cedar River Basin and the South Skunk River Basin—to develop a methodology to evaluate their vulnerability to climate change and extreme weather. The six bridges had been either closed or severely stressed by record streamflow within the past seven years. An innovative methodology was developed to generate streamflow scenarios given climate change projections. The methodology selected appropriate rainfall projection data to feed into a streamflow model that generated continuous peak annual streamflow series for 1960 through 2100, which were used as input to PeakFQ to estimate return intervals for floods. The methodology evaluated the plausibility of rainfall projections and credibility of streamflow simulation while remaining consistent with U.S. Geological Survey (USGS) protocol for estimating the return interval for floods. The results were conveyed in an innovative graph that combined historical and scenario-based design metrics for use in bridge vulnerability analysis and engineering design. The pilot results determined the annual peak streamflow response to climate change likely will be basin-size dependent, four of the six pilot study bridges would be exposed to increased frequency of extreme streamflow and would have higher frequency of overtopping, the proposed design for replacing the Interstate 35 bridges over the South Skunk River south of Ames, Iowa is resilient to climate change, and some Iowa DOT bridge design policies could be reviewed to consider incorporating climate change information.

Orchestration signals in the classroom: managing the jigsaw collaborative learning flow

The orchestration of collaborative learning processes in face-to-facephysical settings, such as classrooms, requires teachers to coordinate students indicating them who belong to each group, which collaboration areas areassigned to each group, and how they should distribute the resources or roles within the group. In this paper we present an Orchestration Signal system,composed of wearable Personal Signal devices and an Orchestration Signal manager. Teachers can configure color signals in the manager so that they are transmitted to the wearable devices to indicate different orchestration aspects.In particular, the paper describes how the system has been used to carry out a Jigsaw collaborative learning flow in a classroom where students received signals indicating which documents they should read, in which group they were and in which area of the classroom they were expected to collaborate. The evaluation results show that the proposed system facilitates a dynamic, visual and flexible orchestration.

Muscle moment-arms: a key element in muscle-force estimation.

A clear and rigorous definition of muscle moment-arms in the context of musculoskeletal systems modelling is presented, using classical mechanics and screw theory. The definition provides an alternative to the tendon excursion method, which can lead to incorrect moment-arms if used inappropriately due to its dependency on the choice of joint coordinates. The definition of moment-arms, and the presented construction method, apply to musculoskeletal models in which the bones are modelled as rigid bodies, the joints are modelled as ideal mechanical joints and the muscles are modelled as massless, frictionless cables wrapping over the bony protrusions, approximated using geometric surfaces. In this context, the definition is independent of any coordinate choice. It is then used to solve a muscle-force estimation problem for a simple 2D conceptual model and compared with an incorrect application of the tendon excursion method. The relative errors between the two solutions vary between 0% and 100%.

Fanconi anemia and genome stability : the role of FANCM

RÉSUMÉ: Le génome de toute cellule est susceptible d'être attaqué par des agents endogènes et exogènes. Afin de préserver l'intégrité génomique, les cellules ont développé des multitudes de mécanismes. La réplication de l'ADN, une étape importante durant le cycle cellulaire, constitue un stress et présente un danger important pour l'intégrité du génome. L'anémie de Fanconi est une maladie héréditaire rare dont les protéines impliquées semblent jouer un rôle crucial dans la réponse au stress réplicatif. La maladie est associée à une instabilité chromosomique ainsi qu'à une forte probabilité de développer des cancers. Les cellules des patients souffrant de l'anémie de Fanconi sont sensibles à des agents interférant avec la réplication de l'ADN, et plus particulièrement àdes agents qui fient les deux brins d'ADN d'une manière covalente. L'anémie de Fanconi est une maladie génétiquement hétérogène. Treize protéines ont pu être identifiées. Elles semblent figurer dans une même voie de signalisation qui est aussi connue sous le nom de « FA/BRCA pathway », car un des gènes est identique au gène BRCA2 (breast cancer susceptibility gene 2). Huit protéines forment un complexe nucléaire dont l'intégrité est nécessaire à la monoubiquitination de deux autres protéines, FANCD2 et FANCI, en réponse à un stress réplicatif. A ce jour, la fonction moléculaire des protéines du « FA/BRCA pathway »reste encore mal décrite. Au début de mon travail de thèse, nous avons donc décidé de purifier les protéines du complexe nucléaire et d'étudier leurs propriétés biochimiques. Nous avons tout d'abord étudié les cinq protéines connues à l'époque qui sont FANCA, FANCC, FANCE, FANCF et FANCG. Par la suite, nous avons étendu notre étude à des protéines découvertes plus récemment, FANCL, FANCM et FAAP24, en concentrant finalement notre travail sur la caractérisation de FANCM. FANCM, contrairement aux autres protéines du complexe, est constituée de deux domaines conservés suggérant un rôle important dans le métabolisme de l'ADN. Il s'agit d'un domaine « DEAH box hélicase »situé dans la partie N-terminale et d'un domaine « ERCC4 nuclease »situé dans la partie C-terminale de la protéine. Dans cette étude, nous avons purifié avec succès la protéine FANCM entière à partir d'un système hétérologue. Nous montrons que FANCM s'attache de manière spécifique à des jonctions de Holliday et des fourches de réplication. De plus, nous démontrons que FANCM peut déplacer le point de jonction de ces structures via son domaine hélicase de manière dépendante de l'ATP. FANCM est aussi capable de dissocier de grands intermédiaires de la recombinaison, via la migration de jonctions de Holliday à travers une région d'homologie de 2.6 kb. Tous ces résultats suggèrent que FANCM peut s'attacher spécifiquement à des fourches de réplication et à des jonctions de Holliday in vitro et que son domaine hélicase est associé à une activité migratoire efficace. Nous pensons que FANCM peut avoir un rôle direct sur les intermédiaires de réplication. Ceci est en accord avec l'idée que les protéines de l'anémie de Fanconi coordonnent la réparation de l'ADN au niveau des fourches de réplication arrêtées. Nos résultats donnent une première indication quant au rôle de FANCM dans la cellule et peuvent contribuer à élucider la fonction de cette voie de signalisation peu comprise jusqu'à présent. SUMMARY: The genome of every cell is subject to a constant offence by endogenous and exogenous agents. Not surprisingly; cells have evolved a multitude of mechanisms which aim at preserving genomic integrity. A key step during the life cycle of a cell, DNA replication itself, constitutes a special danger to the integrity of the genome. The proteins defective in the rare hereditary disease Fanconi anemia (FA) are suspected to play a crucial role in the cellular response to DNA replication stress. The disease is associated with chromosomal instability and pronounced cancer susceptibility. Cells from Fanconi anemia patients are sensitive to a variety of agents which interfere with DNA replication, DNA interstrand cross-linking agents being particularly threatening to their survival. Fanconi anemia is a genetically heterogeneous disease with 13 different proteins identified, which seem to work together in a common pathway. Since one of the FA genes is identical to the breast cancer susceptibility gene BRCA2, it is also referred to as the FA/BRCA pathway. Eight proteins form a nuclear complex, whose integriry is required for the monoubiquitination of two other FA proteins, FANCD2 and FANCI, in response to DNA replication stress. Despite intensive research, the function of the FA/BRCA pathway at a molecular level has remained largely elusive so far. At the beginning of my thesis, we therefore decided to purify the proteins of the FA core complex and to investigate their biochemical properties. We started with the five proteins which were known at that time, FANCA, FANCC, FANCE, FANCF, and FACG. Later on, we extended our studies to the newly discovered proteins FANCL, FANCM, and FAAP24, and eventually focused our work on the characterisation of FANCM. In contrast to the other core complex proteins, FANCM contains two conserved domains, which point to a role in DNA metabolism: an N-terminal DEAH box helicase domain and a C-terminal ERCC4 nuclease domain. In this study, we have successfully purified full-length FANCM from a recombinant source. We show that purified FANCM binds to branched DNA molecules, such as Holliday junctions and replication forks, with high specificity and affinity. In addition, we demonstrate that FANCM can translocate the junction point of branched DNA molecules due to its helicase domain in an ATPase-dependent manner. FANCM can even dissociate large recombination intermediates, via branch migration of Holliday junctions through a 2.6 kb region of homology. Taken together, our data suggest that FANCM can specifically bind to replication forks and Holliday junctions in vitro, and that its DEAH box helicase domain is associated with a potent branch migration activity. We propose that FANCM might have a direct role in the processing of DNA replication intermediates. This is consistent with the current view that FA proteins coordinate DNA repair at stalled replication forks. Our findings provide a first hint as to the context in which FANCM might play a role in the cell. We are optimistic that they might be key to further elucidate the function of a pathway which is far from being understood.

Patients âgées vulnérables au cabinet: comment les identifier et quelles ressources mobiliser [Vulnerable older patients in primary care how to identify them? Which ressources to mobilize? ].

Trust is essential to foster and preserve a long-term relationship between primary care physicians and their patients suffering from chronic diseases. However, this relation remains insufficient to successfully manage more complex situations, such as those of older patients with multiple diseases and disability. For the primary care physician, a significant limitation is the time required to plan and coordinate interventions supplied by different health and social care providers. This article describes a structured approach to support primary care physicians in this difficult task and help them to identify vulnerable older patients requiring to mobilize and coordinate health and social care resources. Current and future resources available to family physicians to complete this challenging task are further described.

Climate change and plant distribution: local models predict high-elevation persistence

Mountain ecosystems will likely be affected by global warming during the 21st century, with substantial biodiversity loss predicted by species distribution models (SDMs). Depending on the geographic extent, elevation range and spatial resolution of data used in making these models, different rates of habitat loss have been predicted, with associated risk of species extinction. Few coordinated across-scale comparisons have been made using data of different resolution and geographic extent. Here, we assess whether climate-change induced habitat losses predicted at the European scale (10x10' grid cells) are also predicted from local scale data and modeling (25x25m grid cells) in two regions of the Swiss Alps. We show that local-scale models predict persistence of suitable habitats in up to 100% of species that were predicted by a European-scale model to lose all their suitable habitats in the area. Proportion of habitat loss depends on climate change scenario and study area. We find good agreement between the mismatch in predictions between scales and the fine-grain elevation range within 10x10' cells. The greatest prediction discrepancy for alpine species occurs in the area with the largest nival zone. Our results suggest elevation range as the main driver for the observed prediction discrepancies. Local scale projections may better reflect the possibility for species to track their climatic requirement toward higher elevations.

The behavioral relevance of multisensory neural response interactions.

Sensory information can interact to impact perception and behavior. Foods are appreciated according to their appearance, smell, taste and texture. Athletes and dancers combine visual, auditory, and somatosensory information to coordinate their movements. Under laboratory settings, detection and discrimination are likewise facilitated by multisensory signals. Research over the past several decades has shown that the requisite anatomy exists to support interactions between sensory systems in regions canonically designated as exclusively unisensory in their function and, more recently, that neural response interactions occur within these same regions, including even primary cortices and thalamic nuclei, at early post-stimulus latencies. Here, we review evidence concerning direct links between early, low-level neural response interactions and behavioral measures of multisensory integration.

Introduction of snow and geomorphic disturbance variables into predictive models of alpine plant distribution in the Western Swiss Alps

Indirect topographic variables have been used successfully as surrogates for disturbance processes in plant species distribution models (SDM) in mountain environments. However, no SDM studies have directly tested the performance of disturbance variables. In this study, we developed two disturbance variables: a geomorphic index (GEO) and an index of snow redistribution by wind (SNOW). These were developed in order to assess how they improved both the fit and predictive power of presenceabsence SDM based on commonly used topoclimatic (TC) variables for 91 plants in the Western Swiss Alps. The individual contribution of the disturbance variables was compared to TC variables. Maps of models were prepared to spatially test the effect of disturbance variables. On average, disturbance variables significantly improved the fit but not the predictive power of the TC models and their individual contribution was weak (5.6% for GEO and 3.3% for SNOW). However their maximum individual contribution was important (24.7% and 20.7%). Finally, maps including disturbance variables (i) were significantly divergent from TC models in terms of predicted suitable surfaces and connectivity between potential habitats, and (ii) were interpreted as more ecologically relevant. Disturbance variables did not improve the transferability of models at the local scale in a complex mountain system, and the performance and contribution of these variables were highly species-specific. However, improved spatial projections and change in connectivity are important issues when preparing projections under climate change because the future range size of the species will determine the sensitivity to changing conditions.

Statistical mechanics of multi-edge networks

Statistical properties of binary complex networks are well understood and recently many attempts have been made to extend this knowledge to weighted ones. There are, however, subtle yet important considerations to be made regarding the nature of the weights used in this generalization. Weights can be either continuous or discrete magnitudes, and in the latter case, they can additionally have undistinguishable or distinguishable nature. This fact has not been addressed in the literature insofar and has deep implications on the network statistics. In this work we face this problem introducing multiedge networks as graphs where multiple (distinguishable) connections between nodes are considered. We develop a statistical mechanics framework where it is possible to get information about the most relevant observables given a large spectrum of linear and nonlinear constraints including those depending both on the number of multiedges per link and their binary projection. The latter case is particularly interesting as we show that binary projections can be understood from multiedge processes. The implications of these results are important as many real-agent-based problems mapped onto graphs require this treatment for a proper characterization of their collective behavior.

Radiation risks : a way to inform patient : 3.10

Purpose: Diagnostic radiology involving ionizing radiation often leads to crucial information but also involves risk. Estimated cancer risks associated with CT range between 1 in 1000 to 1 in 10 000, depending on age and exposure settings. The aim of this contribution is to provide radiologists a way to inform a patient about these risks on a collective and individual base. Materials and methods: After a brief review of the effects of ionizing radiations, conversion from dose indicators into effective dose will be presented for radiography, fluoroscopy and CT. The Diagnostic Reference Level (DRL) concept will be then introduced to enable the reader to compare the level of exposure of various examinations. Finally, the limit of effective dose will be explained and risk projections after various radiological procedures for adults and children will be presented. Results: From an individual standpoint the benefit of a well justified and optimized CT examination clearly outweigh its risk of inducing a fatal cancer. The uncertainties associated with the effective dose concept should be kept in mind in order to avoid cancer risk projections after an examination on an individual basis. Conclusion: Risk factors or effective dose are not the simplest tools to communicate when dealing with radiological risks. Thus, a set of categories should be preferred as proposed in the ICRP (International Commission on Radiation Protection) report 99.

Plannification hospitalière: Quel scénario démographique pour prédire les besoins en soins hospitaliers?

Contexte: L'évolution démographique est un facteur essentiel pour la planification hospitalière. Le scenario démographique moyen de l'OFS ne répond que partiellement aux exigences de la planification pour le canton du Valais ; il ne permet pas de faire des projections par région hospitalière. De plus, la croissance en 2010 et 2011 selon le scenario OFS est inferieure a celle observée. Nous avons développe un scenario ajuste en tenant compte de l'évolution récente de la population valaisanne, et ce par région hospitalière. Méthode: La population de départ et les taux d'accroissement du au solde naturel et migratoire 2012 ont été déterminés à partir des données réelles 2011. Entre 2002 et 2011, le taux d'accroissement migratoire a fortement varie. Les taux 2011 ont donc été ajustés en fonction des taux moyens d'accroissement migratoire 2002-2011 calcules pour chaque région hospitalière. Pour les années 2013-2025, les écarts de taux d'accroissement naturel et migratoire du scenario OFS ont été repris tel quel. Résultats: Entre 2000 et 2010, la population valaisanne est passée de 276'170 a 312'684 habitants (+13.2%). Entre 2012 et 2025, les deux scenarios prévoient une poursuite de la croissance de la population, mais de manière moins soutenue, particulièrement selon le scenario OFS. Ainsi, en 2020, la population devrait atteindre 348'783 habitants (+11.5%) selon le scenario ajuste et 330'616 (+5.7%) selon le scenario OFS. La part de la population âgée de 65 ans et plus passera de 17.1% en 2010 a 20.5% en 2020 selon le scenario ajuste et a 21.4% selon le scenario OFS. Conclusion: Au vu des limites du scenario moyen de l'OFS, il est pertinent de développer des alternatives tenant compte au mieux des spécificités démographiques cantonales. Le scenario ajuste prédit une croissance plus forte de la population, ce qui a un impact important sur les besoins en soins hospitaliers et la planification hospitalière.

Spatial visualization of DNA in solution.

An image analysis method is presented which allows for the reconstruction of the three-dimensional path of filamentous objects from two of their projections. Starting with stereo pairs, this method is used to trace the trajectory of DNA molecules embedded in vitreous ice and leads to a faithful representation of their three-dimensional shape in solution. This computer-aided reconstruction is superior to the subjective three-dimensional impression generated by observation of stereo pairs of micrographs because it enables one to look at the reconstructed molecules from any chosen direction and distance and allows quantitative analysis such as determination of distances, curvature, persistence length, and writhe of DNA molecules in solution.

EADock : design of a new molecular docking algorithm and some of its applications

3 Summary 3. 1 English The pharmaceutical industry has been facing several challenges during the last years, and the optimization of their drug discovery pipeline is believed to be the only viable solution. High-throughput techniques do participate actively to this optimization, especially when complemented by computational approaches aiming at rationalizing the enormous amount of information that they can produce. In siiico techniques, such as virtual screening or rational drug design, are now routinely used to guide drug discovery. Both heavily rely on the prediction of the molecular interaction (docking) occurring between drug-like molecules and a therapeutically relevant target. Several softwares are available to this end, but despite the very promising picture drawn in most benchmarks, they still hold several hidden weaknesses. As pointed out in several recent reviews, the docking problem is far from being solved, and there is now a need for methods able to identify binding modes with a high accuracy, which is essential to reliably compute the binding free energy of the ligand. This quantity is directly linked to its affinity and can be related to its biological activity. Accurate docking algorithms are thus critical for both the discovery and the rational optimization of new drugs. In this thesis, a new docking software aiming at this goal is presented, EADock. It uses a hybrid evolutionary algorithm with two fitness functions, in combination with a sophisticated management of the diversity. EADock is interfaced with .the CHARMM package for energy calculations and coordinate handling. A validation was carried out on 37 crystallized protein-ligand complexes featuring 11 different proteins. The search space was defined as a sphere of 15 R around the center of mass of the ligand position in the crystal structure, and conversely to other benchmarks, our algorithms was fed with optimized ligand positions up to 10 A root mean square deviation 2MSD) from the crystal structure. This validation illustrates the efficiency of our sampling heuristic, as correct binding modes, defined by a RMSD to the crystal structure lower than 2 A, were identified and ranked first for 68% of the complexes. The success rate increases to 78% when considering the five best-ranked clusters, and 92% when all clusters present in the last generation are taken into account. Most failures in this benchmark could be explained by the presence of crystal contacts in the experimental structure. EADock has been used to understand molecular interactions involved in the regulation of the Na,K ATPase, and in the activation of the nuclear hormone peroxisome proliferatoractivated receptors a (PPARa). It also helped to understand the action of common pollutants (phthalates) on PPARy, and the impact of biotransformations of the anticancer drug Imatinib (Gleevec®) on its binding mode to the Bcr-Abl tyrosine kinase. Finally, a fragment-based rational drug design approach using EADock was developed, and led to the successful design of new peptidic ligands for the a5ß1 integrin, and for the human PPARa. In both cases, the designed peptides presented activities comparable to that of well-established ligands such as the anticancer drug Cilengitide and Wy14,643, respectively. 3.2 French Les récentes difficultés de l'industrie pharmaceutique ne semblent pouvoir se résoudre que par l'optimisation de leur processus de développement de médicaments. Cette dernière implique de plus en plus. de techniques dites "haut-débit", particulièrement efficaces lorsqu'elles sont couplées aux outils informatiques permettant de gérer la masse de données produite. Désormais, les approches in silico telles que le criblage virtuel ou la conception rationnelle de nouvelles molécules sont utilisées couramment. Toutes deux reposent sur la capacité à prédire les détails de l'interaction moléculaire entre une molécule ressemblant à un principe actif (PA) et une protéine cible ayant un intérêt thérapeutique. Les comparatifs de logiciels s'attaquant à cette prédiction sont flatteurs, mais plusieurs problèmes subsistent. La littérature récente tend à remettre en cause leur fiabilité, affirmant l'émergence .d'un besoin pour des approches plus précises du mode d'interaction. Cette précision est essentielle au calcul de l'énergie libre de liaison, qui est directement liée à l'affinité du PA potentiel pour la protéine cible, et indirectement liée à son activité biologique. Une prédiction précise est d'une importance toute particulière pour la découverte et l'optimisation de nouvelles molécules actives. Cette thèse présente un nouveau logiciel, EADock, mettant en avant une telle précision. Cet algorithme évolutionnaire hybride utilise deux pressions de sélections, combinées à une gestion de la diversité sophistiquée. EADock repose sur CHARMM pour les calculs d'énergie et la gestion des coordonnées atomiques. Sa validation a été effectuée sur 37 complexes protéine-ligand cristallisés, incluant 11 protéines différentes. L'espace de recherche a été étendu à une sphère de 151 de rayon autour du centre de masse du ligand cristallisé, et contrairement aux comparatifs habituels, l'algorithme est parti de solutions optimisées présentant un RMSD jusqu'à 10 R par rapport à la structure cristalline. Cette validation a permis de mettre en évidence l'efficacité de notre heuristique de recherche car des modes d'interactions présentant un RMSD inférieur à 2 R par rapport à la structure cristalline ont été classés premier pour 68% des complexes. Lorsque les cinq meilleures solutions sont prises en compte, le taux de succès grimpe à 78%, et 92% lorsque la totalité de la dernière génération est prise en compte. La plupart des erreurs de prédiction sont imputables à la présence de contacts cristallins. Depuis, EADock a été utilisé pour comprendre les mécanismes moléculaires impliqués dans la régulation de la Na,K ATPase et dans l'activation du peroxisome proliferatoractivated receptor a (PPARa). Il a également permis de décrire l'interaction de polluants couramment rencontrés sur PPARy, ainsi que l'influence de la métabolisation de l'Imatinib (PA anticancéreux) sur la fixation à la kinase Bcr-Abl. Une approche basée sur la prédiction des interactions de fragments moléculaires avec protéine cible est également proposée. Elle a permis la découverte de nouveaux ligands peptidiques de PPARa et de l'intégrine a5ß1. Dans les deux cas, l'activité de ces nouveaux peptides est comparable à celles de ligands bien établis, comme le Wy14,643 pour le premier, et le Cilengitide (PA anticancéreux) pour la seconde.

Ant species distribution along a topographic gradient in a "terra-firme" forest reserve in Central Amazonia

In Amazonia, topographical variations in soil and forest structure within "terra-firme" ecosystems are important factors correlated with terrestrial invertebrates' distribution. The objective of this work was to assess the effects of soil clay content and slope on ant species distribution over a 25 km² grid covering the natural topographic continuum. Using three complementary sampling methods (sardine baits, pitfall traps and litter samples extracted in Winkler sacks), 300 subsamples of each method were taken in 30 plots distributed over a wet tropical forest in the Ducke Reserve (Manaus, AM, Brazil). An amount of 26,814 individuals from 11 subfamilies, 54 genera, 85 species and 152 morphospecies was recorded (Pheidole represented 37% of all morphospecies). The genus Eurhopalothrix was registered for the first time for the reserve. Species number was not correlated with slope or clay content, except for the species sampled from litter. However, the Principal Coordinate Analysis indicated that the main pattern of species composition from pitfall and litter samples was related to clay content. Almost half of the species were found only in valleys or only on plateaus, which suggests that most of them are habitat specialists. In Central Amazonia, soil texture is usually correlated with vegetation structure and moisture content, creating different microhabitats, which probably account for the observed differences in ant community structure.