972 resultados para Gray, Ellen.
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Signatur des Originals: S 36/F11491
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Signatur des Originals: S 36/F12054
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Signatur des Originals: S 36/F12055
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Signatur des Originals: S 36/G00845
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Signatur des Originals: S 36/G00846
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Signatur des Originals: S 36/G00847
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Signatur des Originals: S 36/G01038
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Signatur des Originals: S 36/G01039
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Fil: Quiroga, Silvia. Universidad Nacional de Cuyo. Facultad de Filosofía y Letras
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The purpose of this study was to evaluate summer and fall residency and habitat selection by gray whales, Eschrichtius robustus, together with the biomass of benthic amphipod prey on the coastal feeding grounds along the Chukotka Peninsula. Thirteen gray whales were instrumented with satellite transmitters in September 2006 near the Chukotka Peninsula, Russia. Nine transmitters provided positions from whales for up to 81 days. The whales travelled within 5 km of the Chukotka coast for most of the period they were tracked with only occasional movements offshore. The average daily travel speeds were 23 km/day (range 9-53 km/day). Four of the whales had daily average travel speeds <1 km/day suggesting strong fidelity to the study area. The area containing 95% of the locations for individual whales during biweekly periods was on average 13,027 km**2 (range 7,097-15,896 km**2). More than 65% of all locations were in water <30 m, and between 45 and 70% of biweekly kernel home ranges were located in depths between 31 and 50 m. Benthic density of amphipods within the Bering Strait at depths <50 m was on average ~54 g wet wt/m**2 in 2006. It is likely that the abundant benthic biomass is more than sufficient forage to support the current gray whale population. The use of satellite telemetry in this study quantifies space use and movement patterns of gray whales along the Chukotka coast and identifies key feeding areas.
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The high levels of polychlorinated biphenyls (PCBs) and DDT in gray seal (Halichoerus grypus) and ringed seal (Phoca hispida botnica) in the Baltic Sea have been associated with pathological disruptions, including bone lesions and reproductive failures. The underlying environmental and toxicological mechanisms leading to these pathological changes are not yet fully understood. The present study investigated the relationship between the individual contaminant load and bone- and thyroid-related effects in adult gray seals (n = 30) and ringed seals (n = 46) in the highly contaminated Baltic Sea and in reference areas (Sable Island, Canada, and Svalbard, Norway). In the gray seals, multivariate and correlation analyses revealed a clear relationship between circulating 1,25-dihydroxyvitamin D3 (1,25(OH)2D), calcium, phosphate, and thyroid hormone (TH) levels and hepatic PCB and DDT load, which suggests contaminant-mediated disruption of the bone and thyroid homeostasis. Contaminants may depress 1,25(OH)2D levels or lead to hyperthyroidism, which may cause bone resorption. In the ringed seals, associations between circulating 1,25(OH)2D, THs, and hepatic contaminants were less prominent. These results suggest that bone lesions observed in the Baltic gray seals may be associated with contaminant-mediated vitamin D and thyroid disruption.
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The Paleocene-Eocene Thermal Maximum (PETM), ca. 55 Ma, was a period of extreme global warming caused by rapid emission of greenhouse gases. It is unknown what ended this episode of greenhouse warming, but high oceanic export productivity over thousands of years (as indicated by high accumulation rates of barium, Ba) may have been a factor in ending this warm period by carbon sequestration. However, Ba has a short oceanic residence time (~10 k.y.), so a prolonged global increase in Ba accumulation rates requires an increase in input of Ba to the ocean, increasing barite saturation. We use a novel proxy for barite saturation (Sr/Ba in marine barite) to demonstrate that the seawater saturation state with respect to barite did not change across the PETM. The observations of increased barite burial, no change in saturation, and the short residence time can be reconciled if Ba burial decreased at continental margin and shelf sites due to widespread occurrence of suboxic conditions, leading to Ba release into the water column, combined with increased biological export production at some pelagic sites, resulting in Ba sink reorganization.
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Background: Octopods have successfully colonised the world's oceans from the tropics to the poles. Yet, successful persistence in these habitats has required adaptations of their advanced physiological apparatus to compensate impaired oxygen supply. Their oxygen transporter haemocyanin plays a major role in cold tolerance and accordingly has undergone functional modifications to sustain oxygen release at sub-zero temperatures. However, it remains unknown how molecular properties evolved to explain the observed functional adaptations. We thus aimed to assess whether natural selection affected molecular and structural properties of haemocyanin that explains temperature adaptation in octopods. Results: Analysis of 239 partial sequences of the haemocyanin functional units (FU) f and g of 28 octopod species of polar, temperate, subtropical and tropical origin revealed natural selection was acting primarily on charge properties of surface residues. Polar octopods contained haemocyanins with higher net surface charge due to decreased glutamic acid content and higher numbers of basic amino acids. Within the analysed partial sequences, positive selection was present at site 2545, positioned between the active copper binding centre and the FU g surface. At this site, methionine was the dominant amino acid in polar octopods and leucine was dominant in tropical octopods. Sites directly involved in oxygen binding or quaternary interactions were highly conserved within the analysed sequence. Conclusions: This study has provided the first insight into molecular and structural mechanisms that have enabled octopods to sustain oxygen supply from polar to tropical conditions. Our findings imply modulation of oxygen binding via charge-charge interaction at the protein surface, which stabilize quaternary interactions among functional units to reduce detrimental effects of high pH on venous oxygen release. Of the observed partial haemocyanin sequence, residue 2545 formed a close link between the FU g surface and the active centre, suggesting a role as allosteric binding site. The prevalence of methionine at this site in polar octopods, implies regulation of oxygen affinity via increased sensitivity to allosteric metal binding. High sequence conservation of sites directly involved in oxygen binding indicates that functional modifications of octopod haemocyanin rather occur via more subtle mechanisms, as observed in this study.