109 resultados para variance conditionnelle
em Université de Lausanne, Switzerland
Resumo:
We investigated the role of the number of loci coding for a neutral trait on the release of additive variance for this trait after population bottlenecks. Different bottleneck sizes and durations were tested for various matrices of genotypic values, with initial conditions covering the allele frequency space. We used three different types of matrices. First, we extended Cheverud and Routman's model by defining matrices of "pure" epistasis for three and four independent loci; second, we used genotypic values drawn randomly from uniform, normal, and exponential distributions; and third we used two models of simple metabolic pathways leading to physiological epistasis. For all these matrices of genotypic values except the dominant metabolic pathway, we find that, as the number of loci increases from two to three and four, an increase in the release of additive variance is occurring. The amount of additive variance released for a given set of genotypic values is a function of the inbreeding coefficient, independently of the size and duration of the bottleneck. The level of inbreeding necessary to achieve maximum release in additive variance increases with the number of loci. We find that additive-by-additive epistasis is the type of epistasis most easily converted into additive variance. For a wide range of models, our results show that epistasis, rather than dominance, plays a significant role in the increase of additive variance following bottlenecks.
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Cette thèse s'intéresse à étudier les propriétés extrémales de certains modèles de risque d'intérêt dans diverses applications de l'assurance, de la finance et des statistiques. Cette thèse se développe selon deux axes principaux, à savoir: Dans la première partie, nous nous concentrons sur deux modèles de risques univariés, c'est-à- dire, un modèle de risque de déflation et un modèle de risque de réassurance. Nous étudions le développement des queues de distribution sous certaines conditions des risques commun¬s. Les principaux résultats sont ainsi illustrés par des exemples typiques et des simulations numériques. Enfin, les résultats sont appliqués aux domaines des assurances, par exemple, les approximations de Value-at-Risk, d'espérance conditionnelle unilatérale etc. La deuxième partie de cette thèse est consacrée à trois modèles à deux variables: Le premier modèle concerne la censure à deux variables des événements extrême. Pour ce modèle, nous proposons tout d'abord une classe d'estimateurs pour les coefficients de dépendance et la probabilité des queues de distributions. Ces estimateurs sont flexibles en raison d'un paramètre de réglage. Leurs distributions asymptotiques sont obtenues sous certaines condi¬tions lentes bivariées de second ordre. Ensuite, nous donnons quelques exemples et présentons une petite étude de simulations de Monte Carlo, suivie par une application sur un ensemble de données réelles d'assurance. L'objectif de notre deuxième modèle de risque à deux variables est l'étude de coefficients de dépendance des queues de distributions obliques et asymétriques à deux variables. Ces distri¬butions obliques et asymétriques sont largement utiles dans les applications statistiques. Elles sont générées principalement par le mélange moyenne-variance de lois normales et le mélange de lois normales asymétriques d'échelles, qui distinguent la structure de dépendance de queue comme indiqué par nos principaux résultats. Le troisième modèle de risque à deux variables concerne le rapprochement des maxima de séries triangulaires elliptiques obliques. Les résultats théoriques sont fondés sur certaines hypothèses concernant le périmètre aléatoire sous-jacent des queues de distributions. -- This thesis aims to investigate the extremal properties of certain risk models of interest in vari¬ous applications from insurance, finance and statistics. This thesis develops along two principal lines, namely: In the first part, we focus on two univariate risk models, i.e., deflated risk and reinsurance risk models. Therein we investigate their tail expansions under certain tail conditions of the common risks. Our main results are illustrated by some typical examples and numerical simu¬lations as well. Finally, the findings are formulated into some applications in insurance fields, for instance, the approximations of Value-at-Risk, conditional tail expectations etc. The second part of this thesis is devoted to the following three bivariate models: The first model is concerned with bivariate censoring of extreme events. For this model, we first propose a class of estimators for both tail dependence coefficient and tail probability. These estimators are flexible due to a tuning parameter and their asymptotic distributions are obtained under some second order bivariate slowly varying conditions of the model. Then, we give some examples and present a small Monte Carlo simulation study followed by an application on a real-data set from insurance. The objective of our second bivariate risk model is the investigation of tail dependence coefficient of bivariate skew slash distributions. Such skew slash distributions are extensively useful in statistical applications and they are generated mainly by normal mean-variance mixture and scaled skew-normal mixture, which distinguish the tail dependence structure as shown by our principle results. The third bivariate risk model is concerned with the approximation of the component-wise maxima of skew elliptical triangular arrays. The theoretical results are based on certain tail assumptions on the underlying random radius.
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SUMMARY Heavy metal presence in the environment is a serious concern since some of them can be toxic to plants, animals and humans once accumulated along the food chain. Cadmium (Cd) is one of the most toxic heavy metal. It is naturally present in soils at various levels and its concentration can be increased by human activities. Several plants however have naturally developed strategies allowing them to grow on heavy metal enriched soils. One of them consists in the accumulation and sequestration of heavy metals in the above-ground biomass. Some plants present in addition an extreme strategy by which they accumulate a limited number of heavy metals in their shoots in amounts 100 times superior to those expected for a non-accumulating plant in the same conditions. Understanding the genetic basis of the hyperaccumulation trait - particularly for Cd - remains an important challenge which may lead to biotechnological applications in the soil phytoremediation. In this thesis, Thlaspi caerulescens J. & C. Presl (Brassicaceae) was used as a model plant to study the Cd hyperaccumulation trait, owing to its physiological and genetic characteristics. Twenty-four wild populations were sampled in different regions of Switzerland. They were characterized for environmental and soil parameters as well as intrinsic characteristics of plants (i.e. metal concentrations in shoots). They were as well genetically characterized by AFLPs, plastid DNA polymorphism and genes markers (CAPS and microsatellites) mainly developed in this thesis. Some of the investigated genes were putatively linked to the Cd hyperaccumulation trait. Since the study of the Cd hyperaccumulation in the field is important as it allows the identification of patterns of selection, the present work offered a methodology to define the Cd hyperaccumulation capacity of populations from different habitats permitting thus their comparison in the field. We showed that Cd, Zn, Fe and Cu accumulations were linked and that populations with higher Cd hyperaccumulation capacity had higher shoot and reproductive fitness. Using our genetic data, statistical methods (Beaumont & Nichols's procedure, partial Mantel tests) were applied to identify genomic signatures of natural selection related to the Cd hyperaccumulation capacity. A significant genetic difference between populations related to their Cd hyperaccumulation capacity was revealed based on somè specific markers (AFLP and candidate genes). Polymorphism at the gene encoding IRTl (Iron-transporter also participating to the transport of Zn) was suggested as explaining part of the variation in Cd hyperaccumulation capacity of populations supporting previous physiological investigations. RÉSUMÉ La présence de métaux lourds dans l'environnement est un phénomène préoccupant. En effet, certains métaux lourds - comme le cadmium (Cd) -sont toxiques pour les plantes, les animaux et enfin, accumulés le long de la chaîne alimentaire, pour les hommes. Le Cd est naturellement présent dans le sol et sa concentration peut être accrue par différentes activités humaines. Certaines plantes ont cependant développé des stratégies leur permettant de pousser sur des sols contaminés en métaux lourds. Parmi elles, certaines accumulent et séquestrent les métaux lourds dans leurs parties aériennes. D`autres présentent une stratégie encore plus extrême. Elles accumulent un nombre limité de métaux lourds en quantités 100 fois supérieures à celles attendues pour des espèces non-accumulatrices sous de mêmes conditions. La compréhension des bases génétiques de l'hyperaccumulation -particulièrement celle du Cd - représente un défi important avec des applications concrètes en biotechnologies, tout particulièrement dans le but appliqué de la phytoremediation des sols contaminés. Dans cette thèse, Thlaspi caerulescens J. & C. Presl (Brassicaceae) a été utilisé comme modèle pour l'étude de l'hyperaccumulation du Cd de par ses caractéristiques physiologiques et génétiques. Vingt-quatre populations naturelles ont été échantillonnées en Suisse et pour chacune d'elles les paramètres environnementaux, pédologique et les caractéristiques intrinsèques aux plantes (concentrations en métaux lourds) ont été déterminés. Les populations ont été caractérisées génétiquement par des AFLP, des marqueurs chloroplastiques et des marqueurs de gènes spécifiques, particulièrement ceux potentiellement liés à l'hyperaccumulation du Cd (CAPS et microsatellites). La plupart ont été développés au cours de cette thèse. L'étude de l'hyperaccumulation du Cd en conditions naturelles est importante car elle permet d'identifier la marque, éventuelle de sélection naturelle. Ce travail offre ainsi une méthodologie pour définir et comparer la capacité des populations à hyperaccumuler le Cd dans différents habitats. Nous avons montré que les accumulations du Cd, Zn, Fe et Cu sont liées et que les populations ayant une grande capacité d'hyperaccumuler le Cd ont également une meilleure fitness végétative et reproductive. Des méthodes statistiques (l'approche de Beaumont & Nichols, tests de Martel partiels) ont été utilisées sur les données génétiques pour identifier la signature génomique de la sélection naturelle liée à la capacité d'hyperaccumuler le Cd. Une différenciation génétique des populations liée à leur capacité d'hyperaccumuler le Cd a été mise en évidence sur certains marqueurs spécifiques. En accord avec les études physiologiques connues, le polymorphisme au gène codant IRT1 (un transporteur de Fe impliqué dans le transport du Zn) pourrait expliquer une partie de la variance de la capacité des populations à hyperaccumuler le Cd.
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The population-genetic consequences of monogamy and male philopatry (a rare breeding system in mammals) were investigated using microsatellite markers in the semisocial and anthropophilic shrew Crocidura russula. A hierarchical sampling design over a 16-km geographical transect revealed a large genetic diversity (h = 0.813) with significant differentiation among subpopulations (F-ST = 5-6%), which suggests an exchange of 4.4 migrants per generation. Demic effective-size estimates were very high, due both to this limited gene inflow and to the inner structure of subpopulations. These were made of 13-20 smaller units (breeding groups), comprising an estimate of four breeding pairs each. Members of the same breeding groups displayed significant coancestries (F-LS = 9-10%), which was essentially due to strong male kinship: syntopic males were on average related at the half-sib level. Female dispersal among breeding groups was not complete (similar to 39%), and insufficient to prevent inbreeding. From our results, the breeding strategy of C. russula seems less efficient than classical mammalian systems (polygyny and male dispersal) in disentangling coancestry from inbreeding, but more so in retaining genetic variance.
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Analysis of variance is commonly used in morphometry in order to ascertain differences in parameters between several populations. Failure to detect significant differences between populations (type II error) may be due to suboptimal sampling and lead to erroneous conclusions; the concept of statistical power allows one to avoid such failures by means of an adequate sampling. Several examples are given in the morphometry of the nervous system, showing the use of the power of a hierarchical analysis of variance test for the choice of appropriate sample and subsample sizes. In the first case chosen, neuronal densities in the human visual cortex, we find the number of observations to be of little effect. For dendritic spine densities in the visual cortex of mice and humans, the effect is somewhat larger. A substantial effect is shown in our last example, dendritic segmental lengths in monkey lateral geniculate nucleus. It is in the nature of the hierarchical model that sample size is always more important than subsample size. The relative weight to be attributed to subsample size thus depends on the relative magnitude of the between observations variance compared to the between individuals variance.
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Knowledge of the quantitative genetics of resistance to parasitism is key to appraise host evolutionary responses to parasite selection. Here, we studied effects of common origin (i.e. genetic and pre-hatching parental effects) and common rearing environment (i.e. post-hatching parental effects and other environment effects) on variance in ectoparasite load in nestling Alpine swifts (Apus melba). This colonial bird is intensely parasitized by blood sucking louse-flies that impair nestling development and survival. By cross-fostering half of the hatchlings between pairs of nests, we show strong significant effect of common rearing environment on variance (90.7% in 2002 and 90.9% in 2003) in the number of louse-flies per nestling and no significant effect of common origin on variance in the number of louse-flies per nestling. In contrast, significant effects of common origin were found for all the nestling morphological traits (i.e. body mass, wing length, tail length, fork length and sternum length) under investigation. Hence, our study suggests that genetic and pre-hatching parental effects play little role in the distribution of parasites among nestling Alpine swifts, and thus that nestlings have only limited scope for evolutionary responses against parasites. Our results highlight the need to take into consideration environmental factors, including the evolution of post-hatching parental effects such as nest sanitation, in our understanding of host-parasite relationships.
Resumo:
Natural selection favors alleles that increase the number of offspring produced by their carriers. But in a world that is inherently uncertain within generations, selection also favors alleles that reduce the variance in the number of offspring produced. If previous studies have established this principle, they have largely ignored fundamental aspects of sexual reproduction and therefore how selection on sex-specific reproductive variance operates. To study the evolution and consequences of sex-specific reproductive variance, we present a population-genetic model of phenotypic evolution in a dioecious population that incorporates previously neglected components of reproductive variance. First, we derive the probability of fixation for mutations that affect male and/or female reproductive phenotypes under sex-specific selection. We find that even in the simplest scenarios, the direction of selection is altered when reproductive variance is taken into account. In particular, previously unaccounted for covariances between the reproductive outputs of different individuals are expected to play a significant role in determining the direction of selection. Then, the probability of fixation is used to develop a stochastic model of joint male and female phenotypic evolution. We find that sex-specific reproductive variance can be responsible for changes in the course of long-term evolution. Finally, the model is applied to an example of parental-care evolution. Overall, our model allows for the evolutionary analysis of social traits in finite and dioecious populations, where interactions can occur within and between sexes under a realistic scenario of reproduction.
Resumo:
In a series of seminal articles in 1974, 1975, and 1977, J. H. Gillespie challenged the notion that the "fittest" individuals are those that produce on average the highest number of offspring. He showed that in small populations, the variance in fecundity can determine fitness as much as mean fecundity. One likely reason why Gillespie's concept of within-generation bet hedging has been largely ignored is the general consensus that natural populations are of large size. As a consequence, essentially no work has investigated the role of the fecundity variance on the evolutionary stable state of life-history strategies. While typically large, natural populations also tend to be subdivided in local demes connected by migration. Here, we integrate Gillespie's measure of selection for within-generation bet hedging into the inclusive fitness and game theoretic measure of selection for structured populations. The resulting framework demonstrates that selection against high variance in offspring number is a potent force in large, but structured populations. More generally, the results highlight that variance in offspring number will directly affect various life-history strategies, especially those involving kin interaction. The selective pressures on three key traits are directly investigated here, namely within-generation bet hedging, helping behaviors, and the evolutionary stable dispersal rate. The evolutionary dynamics of all three traits are markedly affected by variance in offspring number, although to a different extent and under different demographic conditions.
Resumo:
Résumé Dans le rein, la vasopressine possède un rôle essentiel dans la régulation fine du transport d'eau et participe au contrôle de la réabsorption du sodium. Cette action est conduite par l'activation du récepteur à la vasopressine V2R situé dans l'anse de Henle, dans le tubule connecteur et dans le canal collecteur du néphron des rongeurs et conduit à la formation d'AMPc entraînant un mécanisme d'action caractérisé par deux phases distinctes. Le premier effet de la vasopressine est non génomique et a lieu rapidement après l'activation du récepteur, la deuxième phase est plus tardive et possède la caractéristique de moduler la transcription d'un réseau de gènes. Parmi ces gènes, plusieurs sont directement impliqués dans le transport d'eau et de sodium, comme l'Aqp2 et 3, ENaC et la Na,K-ATPase. L'identification des effets de la voie de signalisation de la vasopressine représente un point crucial pour la compréhension des mécanismes moléculaires de la réabsorption de l'eau et du sodium dans le néphron. L'analyse en série de l'expression de gènes (SAGE) réalisée en 2001 dans notre laboratoire a permis de caractériser le transcriptome dépendant de la vasopressine dans la lignée cellulaire mpkCCDc14,a dérivée du canal collecteur cortical (CCD) de souris. Deux des transcrits induits par la vasopressine (VIT) ont fait l'objet des études de ce travail de thèse. Le premier est VIT32 (Vasopressin induced transcript 32) qui code pour une protéine ne possédant aucune homologie avec des domaines protéiques dont la fonction est connue. Dans le système d'expression de l'ovocyte de Xenopus laevis, VIT32 induit la maturation des ovocytes et diminue le courant sensible à l'amiloride de manière dépendante de la voie des MAPK. Dans les mpkCCDc14, l'inhibition de la voie des MAPK diminue le courant sodique en diminuant l'activité de la Na,K-ATPase, mais sans modifier le courant d'ENaC. Ainsi la voie de signalisation des MAPK peut avoir des cibles différentes suivant le système dans lequel elle est étudiée. C'est pourquoi nous avons décidé de poursuivre l'étude de VIT32 dans un contexte physiologique en créant une souris dépourvue du gène codant pour VIT32 de manière conditionnelle (conditional knockout). La première partie de cette thèse a donc consisté à générer cette souris. Le deuxième transcrit induit par la vasopressine qui a été étudié dans cette thèse est RGS2 (Regulator of G protein Signaling 2). In vitro, il a été montré que RGS2 inhibe des voies de signalisation dépendantes de récepteurs couplés à des protéines Gq et Gs. Dans notre étude, nous avons montré que dans le néphron de rein de souris, RGS2 est colocalisé avec V2R. In vivo, la vasopressine sécrétée lors d'une restriction en eau imposée à des souris augmente l'expression de RGS2. De plus, l'accumulation d'AMPc engendrée par l'action de la vasopressine sur les canaux collecteurs est significativement plus grande chez les souris dépourvues de RGS2 (rgs2 -/-). Cette induction de la signalisation de la vasopressine est corrélée à une augmentation de la réabsorption d'eau chez les souris rgs2 -/-. Ainsi RGS2 serait impliqué dans le rétrocontrôle négatif de la voie de signalisation de la vasopressine. Abstract In the kidney, vasopressin plays a key role in the control of water balance and participates in salt reabsorption. These actions are induced by the activation of V2 vasopressin receptor (V2R) located in the loop of Henle, in the connecting tubule and in the collecting duct leading to an increase in intracellular cAMP levels. The V2R-mediated vasopressin action elicits a rapid, non-genomic effect, during which water and salt reabsorption is rapidly increased and a late or genomic effect characterised by the long-term regulation of water and salt reabsorption through the transcriptional activation of a gene network that includes Aqp2, Aqp3, ENaC and Na,K-ATPase. Serial analysis of gene expression (SAGE) performed in 2001 in our laboratory characterised the vasopressin induced transcripts (VIT) in the mpkCCDc14 cell line. Two of them are studied in this thesis. The first one is VIT32 (Vasopressin induced transcript 32) that encodes a protein that has no homology with any protein domain of known function. In the Xenopus laevis oocyte, VIT32 induces oocyte maturation and downregulates the ENaC amiloride sensitive current via the activation of the MAPK pathway. In mpkCCDc14 cell line, the MAPK pathway inhibition leads to a decrease of Na,K-ATPase activity without affecting ENaC current. Therefore, the MAPK pathway can act on different targets depending on the cellular context. Thus, we decided to investigate the function of VIT32 in its physiological environment by performing a conditional knockout mouse of VIT32. The first part of this thesis consisted in generating this mouse. The second studied vasopressin induced transcript is RGS2 (Regulator of G protein Signaling 2). In vitro, RGS2 has been shown to inhibit Gq and Gs protein-coupled receptor pathway. In our study we show that RGS2 is co-localized with V2R in the mouse nephron. In vivo, vasopressin secreted during water restriction up-regulates RGS2 expression. Moreover, vasopressin-dependant accumulation of CAMP is significantly increased in the cortical collecting duct of RGS2 knockout mice. This increase is correlated with an increase in water reabsorption. RGS2 could be involved in the negative feedback regulation of V2R signalling. Résumé tout public Le corps humain est composé d'environ 60% d'eau répartie à l'intérieur et à l'extérieur des cellules de notre organisme. Les cellules, unités fondamentales du vivant, puisent l'oxygène et les nutriments indispensables à leur fonctionnement dans le liquide extracellulaire. La composition du milieu doit être constante, car les variations peuvent perturber considérablement et parfois fatalement la fonction des cellules. Ainsi les organismes pluricellulaires ont développé des mécanismes permettant de contrôler la constance du milieu extracellulaire afin de maintenir l'état d'équilibre nommé homéostasie. Le rein joue un rôle majeur dans cette homéostasie grâce à sa capacité de réabsorber l'eau et les solutés en fonction des besoins de l'organisme. Cette fonction du rein est régulée par différentes hormones comme la vasopressine, qui permet de contrôler la réabsorption fine de l'eau et des solutés. Dans leurs membranes, les cellules possèdent des récepteurs leur permettant de répondre aux signaux extracellulaires comme le sont entre autres les hormones. Ainsi les cellules sensibles à la vasopressine possèdent un récepteur nommé V2R qui permet d'intégrer les signaux de la vasopressine en déclenchant tout une cascade d'événements conduisant à une modification de l'expression de certaines protéines impliquées directement ou non dans la réabsorption de l'eau et des solutés. Une étude précédente élaborée au sein de notre laboratoire a permis de répertorier les protéines dont l'expression est augmentée par de la vasopressine. Deux de ces protéines ont fait l'objet des études de cette thèse. La première protéine induite par la vasopressine est VIT32 (Vasopressin induced transcript 32). Cette protéine est entre autres impliquée dans la réabsorption du sodium, mais la fonction précise de VIT32 dans ce transport n'a pas pu être déterminée. Une des approches possibles pour l'étude de la fonction d'une protéine est de supprimer son expression chez la souris et d'étudier les conséquences de son absence. Ces souris sont appelées des souris knockout, puisque la protéine en question ne peut plus agir. La première partie de cette thèse a donc consisté à générer une souris dépourvue du gène de VIT32. La deuxième protéine étudiée est RGS2 (Regulator of G protein Signaling 2). Cette protéine inhibe certaines voies de signalisation activées par différentes hormones. Dans cette partie du travail de thèse, nous avons pu mettre en évidence que RGS2 agit comme un inhibiteur de la voie de signalisation de la vasopressine. En modifiant cette signalisation, RGS2 serait donc un médiateur du contrôle de la réabsorption d'eau dans les cellules du rein sensibles à la vasopressine.
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Background/Purpose: The trabecular bone score (TBS), a novel graylevel texture index determined from lumbar spine DXA scans, correlates with 3D parameters of trabecular bone microarchitecture known to predict fracture. TBS may enhance the identification of patients at increased risk for vertebral fracture independently of bone mineral density (BMD) (Boutroy JBMR 2010; Hans JBMR 2011). Denosumab treatment for 36 months decreased bone turnover, increased BMD, and reduced new vertebral fractures in postmenopausal women with osteoporosis (Cummings NEJM 2009). We explored the effect of denosumab on TBS over 36 months and evaluated the association between TBS and lumbar spine BMD in women who had DXA scans obtained from eligible scanners for TBS evaluation in FREEDOM. Methods: FREEDOM was a 3-year, randomized, double-blind trial that enrolled postmenopausal women with a lumbar spine or total hip DXA T-score __2.5, but not __4.0 at both sites. Women received placebo or 60 mg denosumab every 6 months. A subset of women in FREEDOM participated in a DXA substudy where lumbar spine DXA scans were obtained at baseline and months 1, 6, 12, 24, and 36. We retrospectively applied, in a blinded-to-treatment manner, a novel software program (TBS iNsightR v1.9, Med-Imaps, Pessac, France) to the standard lumbar spine DXA scans obtained in these women to determine their TBS indices at baseline and months 12, 24, and 36. From previous studies, a TBS _1.35 is considered as normal microarchitecture, a TBS between 1.35 and _1.20 as partially deteriorated, and 1.20 reflects degraded microarchitecture. Results: There were 285 women (128 placebo, 157 denosumab) with a TBS value at baseline and _1 post-baseline visit. Their mean age was 73, their mean lumbar spine BMD T-score was _2.79, and their mean lumbar spine TBS was 1.20. In addition to the robust gains in DXA lumbar spine BMD observed with denosumab (9.8% at month 36), there were consistent, progressive, and significant increases in TBS compared with placebo and baseline (Table & Figure). BMD explained a very small fraction of the variance in TBS at baseline (r2_0.07). In addition, the variance in the TBS change was largely unrelated to BMD change, whether expressed in absolute or percentage changes, regardless of treatment, throughout the study (all r2_0.06); indicating that TBS provides distinct information, independently of BMD. Conclusion: In postmenopausal women with osteoporosis, denosumab significantly improved TBS, an index of lumbar spine trabecular microarchitecture, independently of BMD.
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Unraveling the effect of selection vs. drift on the evolution of quantitative traits is commonly achieved by one of two methods. Either one contrasts population differentiation estimates for genetic markers and quantitative traits (the Q(st)-F(st) contrast) or multivariate methods are used to study the covariance between sets of traits. In particular, many studies have focused on the genetic variance-covariance matrix (the G matrix). However, both drift and selection can cause changes in G. To understand their joint effects, we recently combined the two methods into a single test (accompanying article by Martin et al.), which we apply here to a network of 16 natural populations of the freshwater snail Galba truncatula. Using this new neutrality test, extended to hierarchical population structures, we studied the multivariate equivalent of the Q(st)-F(st) contrast for several life-history traits of G. truncatula. We found strong evidence of selection acting on multivariate phenotypes. Selection was homogeneous among populations within each habitat and heterogeneous between habitats. We found that the G matrices were relatively stable within each habitat, with proportionality between the among-populations (D) and the within-populations (G) covariance matrices. The effect of habitat heterogeneity is to break this proportionality because of selection for habitat-dependent optima. Individual-based simulations mimicking our empirical system confirmed that these patterns are expected under the selective regime inferred. We show that homogenizing selection can mimic some effect of drift on the G matrix (G and D almost proportional), but that incorporating information from molecular markers (multivariate Q(st)-F(st)) allows disentangling the two effects.
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Oxygen uptake was studied during the establishment of cephalocaudal polarity in the very early chick embryo, i.e., 10 hr before (stage VI) and at laying (stage X). Oxygen fluxes in minute regions of the intact blastoderms were measured in vitro by scanning microspectrophotometry in the presence or absence of glucose. The oxygen consumption of the whole blastoderm remained constant (6 nmol O2 X hr-1) throughout the period studied, although the number of cells increased more than twofold. The regional oxygen fluxes varied from 0.41 to 1.13 nmol O2 X hr-1 X mm-2 at stage VI and from 0.42 to 0.70 nmol O2 X hr-1 X mm-2 at stage X. At stage VI, the oxygen flux in the center of the blastoderm was significantly higher than that in its periphery. This pattern remained evident when the values were corrected for cell number or for cytoplasmic volume. At stage X, there was a tendency for the oxygen fluxes to decrease from the posterior to the anterior regions of the area pellucida. Thus the pattern of oxidative metabolism in the late uterine embryos seems to change from radial to bilateral. This change of symmetry probably reflects the process of formation of the embryonic axis. In addition, the fact that the oxygen uptake was similar in the presence or absence of glucose suggests that early chick embryos metabolize essentially intracellular stores.
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L'objectif de cette étude est de vérifier la validité interne de la version française du questionnaire d'impulsivité d'Eysenck (I7), traduite par Dupont et al., sur un échantillon d'étudiants suisses (n = 220). Dans leur questionnaire, Eysenck et Eysenck proposent trois échelles : les deux premières évaluant deux composantes distinctes de l'impulsivité (l'Impulsivité caractérisant les individus qui agissent sans penser, sans être conscients des risques associés à leurs actions, et la Recherche d'aventure caractérisant les individus qui agissent en étant conscients, et en tenant compte des risques associés à leurs actions), et la troisième servant de « distracteur » (l'Empathie caractérisant les individus qui ont la faculté de s'identifier à l'autre). La structure à trois facteurs de l'instrument a été confirmée par notre analyse factorielle en composantes principales. La solution factorielle retenue n'explique toutefois qu'une faible proportion de la variance (21.9 %). L'homogénéité interne des échelles, mesurée à l'aide d'alphas de Cronbach, est acceptable pour l'échelle d'Impulsivité (.78) et de Recherche d'aventure (.71), mais elle est, en revanche, faible pour l'échelle d'Empathie (.62). Les échelles de l'I7 d'Eysenck entretiennent des corrélations cohérentes avec les cinq grandes dimensions de la personnalité mesurées par le NEO PI-R. L'Impulsivité est associée négativement à la dimension Conscience (r = - .32), alors que la Recherche d'aventures est associée positivement à la dimension Extraversion (r = .33). Le sexe a un impact sur les échelles Recherche d'aventure et Empathie. Les qualités métrologiques de la version française du questionnaire d'impulsivité d'Eysenck (I7) sont satisfaisantes, mais l'estimation d'autres indices de validité, comme la fidélité test-retest et la validité convergente, devrait être réalisée.
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OBJECTIVE: So far, associations between appraisals, maternal adjustment and coping following diagnosis of fetal anomaly have not been investigated in women who continue with their pregnancy. METHOD: This study measured maternal coping and adjustment after and appraisal of a diagnosis of fetal anomaly in 40 mothers who had continued with their pregnancy using a cross-sectional questionnaire design. RESULTS: Based on retrospective reporting, 35% of participants met full diagnostic criteria for post-traumatic stress disorder after having received the diagnosis. Women were significantly more depressed (p < 0.001) and anxious (p < 0.001) and reported significantly less positive affect (p < 0.05) after having received the diagnosis in comparison to the time after childbirth. There were no significant differences between emotion-focused and problem-focused coping. Stressful life events, women's age, number of people providing support and problem-focused coping explained 57.6% of variance in anxiety and depression after childbirth. Satisfaction with social support, emotion-focused coping and problem-focused coping significantly explained 40.6% of variance in positive affect after childbirth. CONCLUSION: Following a prenatal diagnosis and for the remainder of their pregnancy, particular attention should be paid to older mothers, those experiencing additional stressful life events and those who are socially isolated, as these women may experience greater distress after childbirth.