La sélection naturelle est un des facteurs dominants lors de l'évolution répétée et parallèle observée notamment chez les poissons des régions tempérées du Nord. Ainsi, au sein des populations de Coregonus clupeaformis, l'écotype nain s'est différencié plusieurs fois à partir d'un écotype normal, notamment dans six lacs du bassin versant de la rivière St-Jean (Maine, USA et Québec, CA). Cette étude porte sur les caractéristiques de l'habitat ainsi que sur la disponibilité des ressources et leurs variations temporelles influençant le niveau de différenciation atteint entre les écotypes de ces populations. Les résultats appuient les hypothèses théoriques faisant intervenir le rôle des fluctuations environnementales (biomasse et structure des ressources) dans la variation des pressions sélectives et le rôle de la compétition pour les ressources (disponibilités réduites) dans l'établissement et le maintien d'un degré de différenciation. Le rôle de d'autres interactions trophiques comme les relations prédateurs-proies semble aussi impliqué dans ce mécanisme de divergence. / Natural selection is one of the dominant factors in repeated parallel evolution observed notably in north temperate fish populations. In Coregonus clupeaformis populations located in six lakes of the St-John’s river watershed (Maine, USA and Québec, CA), a dwarf ecotype has differentiated from a normal ecotype many times. Here we study habitat and resource features, it temporal variations in relation to the observed level of differentiation between ecotypes of these populations. The results support the hypotheses that environmental fluctuation (zooplankton community structure and biomass) cause variation in selective pressure and that the resource competition (availability of habitat and resources) influence the establishment and persistence of a degree of differentiation. Trophic interactions such as predator-prey relationships seem also to be involved in giving rise to this divergence.

Nous avons documenté la génétique du paysage du grand brochet (Esox lucius) en nous basant sur l’analyse de 22 microsatellites, incluant 10 nouveaux marqueurs développés ici, dans le système lac Ontario – fleuve Saint-Laurent. La structure génétique des populations était globalement très faible mais spatialement variable ; le niveau moyen de différenciation génétique dans la section amont (Ontario) de l’aire d’étude était trois fois plus important que celui observé dans le secteur aval (Québec). Vingt variables environnementales furent considérées et les différentes masses d’eau, la présence de barrages et la stabilité interannuelle du niveau d’eau s’avérèrent positivement associées à l’intensité de la différenciation génétique. Une importante variation du niveau d’eau influe sur la qualité et la localisation annuelle des habitats de reproduction du grand brochet, l’instabilité locale de l’habitat prenant la forme d’une variation interannuelle du niveau d’eau semble localement inhiber la structure génétique de populations, probablement en empêchant la philopatrie. Mots clés : Esox lucius, grand brochet, génétique du paysage, structure génétique de populations, variation environnementale, stabilité de l’habitat, marqueurs microsatellites, gestion, conservation. / In this study, we documented the landscape genetics of northern pike (Esox lucius) based on the analysis of 22 microsatellites, comprising 10 markers developed for the purpose of this study, in the Lake Ontario – St. Lawrence River system. Population genetic structure over the whole study area was globally very weak but spatially variable with mean level of differentiation in the upstream (Ontario) section of the studied area being three-fold higher than observed in the downstream (Québec) sector. Twenty environmental variables were considered and different water masses, dams’ presence and inter-annual water level stability were positively associated to the extent of genetic differentiation. Since high water level variation impacts on yearly quality and localization of northern pike spawning habitats, local habitat instability which is under the form of inter-annual water level variation seems to locally impede population genetic structure, perhaps by inhibiting philopatry behavior. Keywords: Esox lucius, northern pike, landscape genetics, population genetic structure, environmental variation, habitat stability, microsatellite markers, management, conservation.

La mise en place de barrières à la reproduction et, par conséquent, la spéciation elle-même, engendrent et maintiennent la biodiversité. Les principaux objectifs de mes travaux étaient premièrement d'identifier l'ampleur des différences d'expression de gènes entre des jeunes espèces de grand corégones nains, normaux, ainsi que leurs hybrides. Par la suite, grâce à une technique révolutionnaire de séquençage, nous avons obtenu de l'information de séquence et de polymorphisme pour plusieurs milliers de gènes. Finalement, le génotypage de marqueurs SNPs en populations naturelles et simultanément dans une famille de poissons hybrides a permis d'évaluer l'effet de la sélection naturelle sur la divergence génétique des corégones. Ainsi, cette thèse apporte une meilleure compréhension de la divergence adaptive et de l'isolement reproducteur chez le corégone, tout en identifiant spécifiquement des gènes candidats impliqués dans le processus de spéciation.

The density, diversity, and nest-site selection of riparian breeding birds were studied from 1982 to 1985 in mesquite (Prosopis glandulosa) and tamarisk (Tamarix chinensis) communites along the Colorado River in northern Arizona. Avian density in tamarisk communities was significantly greater (P=0.052 and 0.024 in 1984 and 1985, respectively) than avian density in native mesquite communities with similar vegetative cover and height attributes. Avian diversity was similar in both communities. Breeding bird densities in tamarisk were higher than those reported from other geographic areas. Vegetation structure and shrub species composition were measured at nest sites of eleven species of riparian birds in a tamarisk community to examine avian habitat relationships. Riparian birds exhibited differences in their choice of nesting habitat. Discriminant analysis indicated that Bell's Vireo (Vireo bellii), Yellow Warbler (Dendroica petechia) and Yellow-breasted Chat (Icteria virens) were relative generalists in nest site selection, while Common Yellowthroat (Geothlypis trichas) and Northern Oriole (Icterus galbula) were relative habitat specialists. Bell's Vireo and American Coot (Fulica americana) nested in habitats that were the most different. Willow Flycatcher (Empidonax traillii) and Yellow Warbler nested in habitats that were the most similar. Willow Flycatcher and Yellow Warbler consistently used habitat most similar to that used by all other species. Nest placement preferences of six riparian passerines were examined in the tamarisk community to test the null hypothesis that nest placement in any given species of shrub was random. Ninety-five of 105 nests sampled were located in tamarisk. Five of the six species of passerines exhibited a significant preference for tamarisk for nest placement. A highly significant preference for tamarisk was shown by the four species with the smallest median frequency of tamarisk in their nesting habitat. The usefulness of tamarisk for nest placement was higher than that reported from other areas.

The major goal is to reveal the need to understand the dynamics and impacts of landscape change from a current temporal perspective. This is performed here through the study of various settings in the landscape along Highways 180 and 64/180 in Arizona, being proposed for State Scenic Road designation. Selected landscape segments is the subject and the highways are a flexible platform from which to observe and assess these landscapes. Once sources, kinds of, and magnitude of possible or potential landscape changes and impacts are identified, this study proceeds to prescribe landscape planning strategies for their scenic and open space protection and enhancement. Potential landscape change and its impact should be predicted in order to plan and manage for the protection and enhancement of desired landscape values into the future. It can input people's perceptions to appreciate landscape values from varied perspectives such as: aesthetic, ecological, cultural, and socioeconomic.

Theses (M.A.)--Marshall University, 2006. / Title from document title page. Includes abstract. Document formatted into pages: contains iii, 72 p. Bibliography: p. 71-72.

During the first half of the `long' eighteenth century the English were, as a nation, vehemently anti-Catholic, yet the art that was most admired, collected and talked about, was Catholic in origin and subject matter (pictures showing the intercession of saints or the figure of God, for example). Such art might have been rejected by English collectors, certainly idolatry was chief among the heresies ascribed to the Papists, but the belief in the supremacy of Italian art was long-standing and tenacious in pan-European culture. The thesis demonstrates that rather than rejecting it, elaborate strategies were developed which allowed the cultural and social value of ownership and knowledge of this canonical art to accrue, whilst managing its potentially troubling content. For example, the royal ownership of the Raphael Cartoons (c. 1514) was a matter of increasing national pride during this period, which is surprising at first sight, given their provenance and their celebration of the apostolic succession of the Papacy from SS Peter and Paul. These meanings were not expunged from the Cartoons by English commentators, instead means were found to transpose them into a Protestant register and to maintain Raphael's reputation as the great universal artist. Each chapter of the thesis offers a different mode of address to the central theme, exploring, for example, the encounters grand tourists had with canonical art in Catholic churches in Rome and the ways in which the Catholic meanings of pictures were managed in a collection. In another chapter I explore how art was used and discussed within the Church of England. It has become clear that the Catholic associations of art did present a historically-significant political challenge to English connoisseurs and that, for example, new histories and theories of art, modified from their continental models, were developed to facilitate its acceptance. In addition, by paying careful attention to the ways in which issues of class, nationhood and culture were managed in relation to this problem, insights into the complex nature of anti-Catholicism in England have been gained.

Le travail présenté ici a pour but d’évaluer les mécanismes microstructuraux liés à l’amorçage de l’endommagement par fatigue d’un acier à usage pétrolier. Les microdéformations et les contraintes résiduelles (macrocontraintes) ont été déterminées par diffraction des rayons X en temps réel pendant des essais de fatigue en flexion alternée sur des éprouvettes plates prélevées dans la paroi d’un tube neuf. Les microdeformations sont estimées à partir de mesures de la largeur de corde à mi-hauteur (LCMH) d’un pic de diffraction et les contraintes résiduelles à partir du déplacement du pic. Les essais de fatigue sont réalisés pour cinq niveaux de contraintes différents. On observe trois stades de variation pendant l’évolution des microdeformations. On montre que leur amplitude et leur durée sont proportionnelles au niveau de contrainte alternée. Des variations similaires sont observées pour les contraintes résiduelles, avec des durées identiques à celles des microdéformations. Des évolutions dans la densité et la répartition des dislocations ont été observées par microscopie électronique en transmission à l’aide de la technique du faisceau d’ions focalisés. Pour comprendre le rôle de la structure initiale, des essais de fatigue sur éprouvettes recuites ont été réalisés dans les mêmes conditions d’essai. Là encore trois stades d’évolution sont observées mais avec un premier stade inversé du fait de l’état initial du réseau de dislocations. Les résultats obtenus sont très encourageants pour la prise en compte des évolutions microstructurales dans l’établissement d’un futur indicateur de dommage de la phase d’amorçage en fatigue à grand nombre de cycles des matériaux. / The present work aims to evaluate the microstructural mechanisms associated with the initiation of fatigue damage of steels used in the oil and gas industry. Microdeformations and residual stresses (macrostresses) were evaluated by X-ray diffraction in real time during alternating bending fatigue tests performed on flat test pieces taken from a pipe sample. Microdeformations were estimated from measurements of the full width at half maximum (FWHM) of the diffraction peak and residual stresses from the peak displacement. The fatigue tests were performed at five different stress levels. Three stages of changes during the evolution of microdeformation were detected. We show that their amplitude and duration are proportional to the level of alternating stress. Similar variations were observed for the residual stresses, with duration identical to those of the microdeformation. Changes in the density and distribution of dislocations were observed by transmission electron microscopy using the technique of focused ion beam. To understand the role of the initial structure, fatigue tests on annealed samples were performed under the same test conditions. Again, three stages of changes are observed but with an increase of the microdeformations instead of a decrease during the first stage due to the initial state of the dislocation network. The results are very encouraging for the consideration of the microstructural evolutions in the construction of a future counter of fatigue damage initiation in materials.

Zugl.: Turku, Univ., veränd. Diss., 2006

Graduation date: 1998