Reproduction de : Thèse doctorat : Médecine. Sciences de la vie : Reims : 2006. / Titre provenant de l'écran-titre. Bibliogr. p.115-130.

Atmospheric carbon dioxide (CO2) has increased due to human activity from a pre-industrial value of about 280 ppm to the present level of 399 ppm. The ocean acts as an important natural carbon sink that effectively removes 1/3 of this anthropogenic CO2 from the atmosphere, buffering global warming effects. However, the dissolution of CO2 causes a dramatic change in seawater chemistry and ultimately results in the phenomenon commonly known as "ocean acidification" (OA). As a consequence, the pH value and the saturation states for calcium carbonate decline in the surface seawater, posing a threat to calcareous marine organisms that build their shells using exquisite biomineralization mechanisms. Biological minerals produced by marine organisms are compositionally and structurally more complex than geological minerals. Although changes in biomineral formation in response to OA has been intensively investigated, the features of calcified products in terms of their composition, architectures and mechanical properties have been overlooked in climate change research. The tubeworm is a favourite marine model organism in larval biology. Its life cycle is well understood hence provides a good opportunity to study OA impacts on the stochastic early life. In addition, the model enables comprehensive observation of the sophisticated biomineralization events. In this thesis, four studies on the biomineralization of Hydroides elegans, using a multidisciplinary collaborative approach combining larval biology and material science were conducted. (1) The tube mineral composition at different juvenile stages (4, 11, 18, 25 days) were characterized. (2) The impacts of different predicted OA scenarios (pH 8.1, 7.9, 7.6, and 7.4) on the resultant calcification products were compared. (3) A multiple-stressor investigation of OA (pH 8.1 and 7.8), reduced salinity (33 ‰ and 27 ‰) and increased temperature (25 °C and 29 °C) was conducted to further determine the more environmentally realistic OA impacts. (4) Calcification sites were examined by using a microscopy approach The main findings from each study were: (1) H. elegans produced both calcite and aragonite forms of CaCO3, which have distinctive physical and chemical properties. Thus, the tubeworm serves as an interesting model for studying OA impacts on biomineralization. The early juvenile stages are expected to be more sensitive to OA than the later life stages because the juvenile tubes are rich in aragonite and amorphous calcium carbonate. (2) Under experimental OA conditions, the composition and architecture of the tube structures were adversely affected, ultimately producing tubes with weaker mechanical properties. (3) Warming appeared to strengthen the tube structures and mitigated the adverse OA effects. (4) Calcification sites correlated to regions with higher pH values of 8.5 - 9.0. These regions may be sensitive to OA and should be further analyzed to study the mechanisms of OA impacts on calcification. This series of experiments study biomineralization and larval biology using a variety of modern multidisciplinary approaches provided new insights into the impacts of OA and climate change impacts on marine organisms and also helped us to project which species might adapt or succumb to future scenarios. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

The aim of this literature study is to compare and discuss different fields of paleolimnology, with a focus on three main research areas – eutrophication, acidification, and climate change. Pioneering work and the development of paleolimnological methods around these three areas were reviewed and synthesized. Paleolimnology started out as limnology and paleoecology, but has evolved tremendously over the past decades. Early paleolimnological studies focused on lake ontogeny and mechanics in the catchment such as weathering. The focus eventually shifted to nutrient loadings during the 1960s – 1970s as the debate on human induced eutrophication emerged. The important question to answer was which nutrient was the limiting factor in eutrophication. Acidification was the next topic of investigation during the 1980s – 1990s, and paleolimnology developed methods to infer past pH change based on chironomids and diatom fossils preserved in lake sediment. This research resulted in calibration sets and proxies which can be used to reconstruct past conditions. The paleolimnological community eventually shifted focus in the late 1990s to climate change and began to use lake sediment to reconstruct past climatic trends using multiproxy studies such as diatoms, chironomids and geochemistry. Varved lake sediment offered a much needed terrestrial high resolution option to the ice core records. History plays a fundamental role in all environmental issues and paleolimnology has the ability to provide historical records of past environmental conditions. Paleolimnology will most likely play a key role in management and restoration in the future. As technology and training sets develop, fast and cheap ways to interpret sediment proxies will emerge and maybe even fully automated identification of proxies.

Ecologists studying acid-damaged zooplankton communities have often documented a time lag in recovery following pH increases. While previous work has provided a solid understanding of the local factors that may delay recovery (e.g. competition), less is known about the role of dispersal. The work in this thesis was conducted to test the hypothesis that dispersal limitation contributes to delays in the recovery of acid-damaged zooplankton communities. To assess the role of dispersal during recovery I pursued three objectives: 1) To measure dispersal in the field and determine the relative importance of various dispersal vectors for contributing acid-sensitive colonists to lakes; 2) to determine if spatial structure in recovering zooplankton communities exists across the landscape independent of environmental gradients; and 3) to determine if an interaction between dispersal and local environmental variables could influence recovery. Data collected for Objective 1 demonstrated that overland dispersal rates for acid-sensitive species in Killarney Park were relatively low, but some species were found emerging from the diapausing egg bank or dispersing through streams to recovering lakes. Spatial modeling and variation partitioning analyses for Objective 2 revealed spatial patterns indicative of dispersal limitation in recovering Killarney Park zooplankton communities. Enclosure experiments conducted for Objective 3 suggested that the colonization of the acid-sensitive copepod Epischura lacustris may be influenced by an interaction between dispersal levels and pH, such that higher dispersal levels may be required for establishment in lakes that are early in the process of pH recovery. Enclosure experiments also indicated that community resistance and low dispersal levels might hinder the reestablishment of the acid-sensitive copepod Skistodiaptomus oregonensis. Taken together, my results strongly suggest that dispersal limitation could contribute to delays in zooplankton community recovery. The recovery of acid-sensitive copepod species may be particularly difficult, as their reestablishment in recovering lakes appears to be influenced by Allee effects, community resistance, and an interaction between pH and dispersal levels. While dispersal rates could be artificially increased by human intervention, this would carry the risk of introducing invasive species. As a result, patience and continued monitoring of recovering lakes may be the best management approaches at this time. / Thesis (Ph.D, Biology) -- Queen's University, 2011-12-20 22:49:05.193

No description available.

The Vo sector of the vacuolar H+-ATPase is a multi-subunit complex that forms a proteolipid pore. The largest subunit in this complex is the a subunit which has four isoforms (a1-a4). The isoform(s) critical for secretory vesicle acidification has yet to be identified. Using a cell line derived from rat pheochromocytoma in which Voa1 and/or Voa2 had been down-regulated this study revealed that Voa1, and to a lesser extent, Voa2 are critical for acidifying dense-core vesicles (DCVs). The acidification defects resulting from down-regulation of Voa1 and Voa1/ Voa2 were suppressed by the expression of knockdown-resistant Voa1. Defects in DCV acidification resulted in reductions in their transmitter uptake and storage. Lastly, Ca2+-dependent peptide secretion appeared normal in Voa1 and Voa1/ Voa2 knockdown cells. . This study demonstrated that Voa1 and Voa2 cooperatively regulate dense-core vesicle acidification as well as transmitter uptake/storage, while they may not be critical for dense-core vesicle exocytosis.

The Vo sector of the vacuolar H+-ATPase is a multi-subunit complex that forms a proteolipid pore. The largest subunit in this complex is the a subunit which has four isoforms (a1-a4). The isoform(s) critical for secretory vesicle acidification has yet to be identified. Using a cell line derived from rat pheochromocytoma in which Voa1 and/or Voa2 had been down-regulated this study revealed that Voa1, and to a lesser extent, Voa2 are critical for acidifying dense-core vesicles (DCVs). The acidification defects resulting from down-regulation of Voa1 and Voa1/ Voa2 were suppressed by the expression of knockdown-resistant Voa1. Defects in DCV acidification resulted in reductions in their transmitter uptake and storage. Lastly, Ca2+-dependent peptide secretion appeared normal in Voa1 and Voa1/ Voa2 knockdown cells. . This study demonstrated that Voa1 and Voa2 cooperatively regulate dense-core vesicle acidification as well as transmitter uptake/storage, while they may not be critical for dense-core vesicle exocytosis.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv. / Härtill 5 uppsatser.

Thesis (M.S.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains viii, 169 p. : ill. (some col.), col. maps. Includes abstract. Includes bibliographical references (p. 62-67).

Thèse (M.A.) -- Université Laval, 1997. / Bibliogr.: f. [64]-74. Publié aussi en version électronique.