158 research outputs found
A Common Eider Ă King Eider Hybrid Captured on the Kent Peninsula, Nunavut
On 25 June 2002, we captured and recorded measurements of a male common eider (Somateria mollissima) Ă king eider (S. spectabilis) hybrid at Nauyak Lake, on the Kent Peninsula, Nunavut. This is the first documented capture of a hybrid eider, rarely observed in North America. Structural body measurements and mass of the hybrid were intermediate compared to those of Pacific common eiders (S. m. v-nigrum) at the same study site and king eiders at a nearby study site during the same time of year. The plumage of the captured hybrid had characteristics of both parent species. Mate pairing on overlapping spring staging or wintering areas of common and king eiders may occasionally result in hybrid offspring.Le 25 juin 2002, nous avons capturĂ© un hybride composĂ© dâun eider Ă duvet (Somateria mollissima) Ă un eider Ă tĂȘte grise (S. spectabilis) au lac Nauyak, dans la pĂ©ninsule de Kent, au Nunavut, puis nous avons pris note de ses mesures. Il sâagit de la premiĂšre capture rĂ©pertoriĂ©e dâun eider hybride, ce qui est rarement observĂ© en AmĂ©rique du Nord. Les mesures et la masse de la structure corporelle de lâhybride Ă©taient intermĂ©diaires comparativement Ă celles des eiders Ă duvet du Pacifique (S. m. v-nigrum) du mĂȘme lieu dâĂ©tude et Ă celles des eiders Ă tĂȘte grise dâun lieu dâĂ©tude avoisinant pendant la mĂȘme pĂ©riode de lâannĂ©e. Le plumage de lâhybride que nous avons capturĂ© prĂ©sentait des caractĂ©ristiques des deux espĂšces. Il arrive parfois que les accouplements aux haltes migratoires du printemps ou aux aires dâhivernage partagĂ©es par les eiders Ă duvet et les eiders Ă tĂȘte grise donnent lieu Ă une progĂ©niture hybride
Resilience: Easy to use but hard to define
First conceptualized in the 1970s, resilience has become a popular term in the ecological literature, used in the title, abstract, or keywords of approximately 1% of papers identified by ISI Web of Science in the field of environmental sciences and ecology in 2011. However, many papers make only passing reference to the term and do not explain what resilience means in the context of their study system, despite there being a number of possible definitions. In an attempt to determine how resilience is being used in ecological studies, we surveyed 234 papers published between 2004 and 2011 that were identified under the topic âresilienceâ by ISI Web of Science. Of these, 38% used the word resilience fewer than three times (often in the abstract or keyword list), 66% did not define the term, and 71% did not provide a citation to the resilience literature. Studies that defined resilience most often discussed it as pertaining to an entire ecosystem under continuous rather than discrete disturbance. Given the complex nature of this concept, we believe that care should be taken to properly describe what is meant by the term resilience in ecological studies
Breeding Bird Surveys at Alexandra Fiord, Ellesmere Island, Nunavut (1980â2008)
Long-term monitoring of bird populations in the Arctic is of considerable interest as this area is experiencing rapid climate warming; however, multi-decadal studies in the Canadian High Arctic are rare. Over five summers between 1980 and 2008, we conducted breeding bird surveys by walking transects and mapping territories in a periglacial lowland on east-central Ellesmere Island, Nunavut. In all survey years, snow bunting (Plectrophenax nivalis), Lapland longspur (Calcarius lapponicus), and Baird's sandpiper (Calidris bairdii) were the most abundant species. Over the study period, the assemblage of breeding bird species appears to have changed little, except for an increase in Lapland longspur. In the summer of 2008, we also compared two techniques for censusing territories. We found that spot-mapping, a simple and cost-effective method, produced similar results to the more labour-intensive active-flushing. Spot-mapping is therefore suitable for conducting bird surveys in northern locations where the vegetation is short, the terrain is flat, and the visibility is extensive. In the coming years, it will be important to continue monitoring Arctic birds to determine how climate change is affecting their breeding populations.La surveillance Ă long terme des populations d'oiseaux de l'Arctique revĂȘt un intĂ©rĂȘt considĂ©rable Ă la lumiĂšre du changement climatique rapide que connaĂźt cette rĂ©gion. Cela dit, il faut remarquer que peu d'Ă©tudes Ă©chelonnĂ©es sur plusieurs dĂ©cennies ont Ă©tĂ© rĂ©alisĂ©es dans l'ExtrĂȘme-Arctique canadien. Au cours de cinq Ă©tĂ©s rĂ©partis entre 1980 et 2008, nous avons effectuĂ© le dĂ©nombrement d'oiseaux nicheurs en traversant des transects et en cartographiant des territoires situĂ©s sur les basses terres pĂ©riglaciaires de l'Ăźle d'Ellesmere, au Nunavut. Au cours de toutes les annĂ©es visĂ©es par le dĂ©nombrement, le bruant des neiges (Plectrophenax nivalis), le bruant lapon (Calcarius lapponicus) et le bĂ©casseau de Baird (Calidris bairdii) se sont avĂ©rĂ©s les espĂšces les plus abondantes. Au cours de la pĂ©riode visĂ©e par l'Ă©tude, l'assemblage d'espĂšces d'oiseaux nicheurs semble avoir peu changĂ©, sauf pour ce qui est d'une augmentation de bruants lapons. Ă l'Ă©tĂ© 2008, nous avons Ă©galement comparĂ© deux techniques de recensement des territoires. Nous avons effectivement constatĂ© que la mĂ©thode des plans quadrillĂ©s, une mĂ©thode simple et abordable, donnait des rĂ©sultats semblables Ă la mĂ©thode de dispersion active qui demande beaucoup plus de travail. Par consĂ©quent, la mĂ©thode des plans quadrillĂ©s convient bien Ă la rĂ©alisation de recensements d'oiseaux dans les emplacements nordiques oĂč la vĂ©gĂ©tation est courte, oĂč le terrain est plat et oĂč la visibilitĂ© est vaste. Au cours des annĂ©es Ă venir, il sera important de continuer Ă surveiller les oiseaux de l'Arctique afin de dĂ©terminer quelles sont les incidences du changement climatique sur les populations d'oiseaux nicheurs
Spring-neap tide-induced beach water table fluctuations in a sloping coastal aquifer
Predictions of water table fluctuations in coastal aquifers are needed for numerous coastal and water resources engineering problems. Most previous investigations have been based on the Boussinesq equation for the case of a vertical beach. In this note an analytical solution based on shallow water expansion for the spring- neap tide- induced water table fluctuations in a coastal aquifer is presented. Unlike most previous investigations, multitidal signals are considered with a sloping coastal aquifer. The new solution is verified by comparing with field observations from Ardeer, Scotland. On the basis of the analytical approximation the influences of higher- order components on water table elevation are examined first. Then, a parametric study has been performed to investigate the effects of the amplitude ratio (lambda), frequency ratio (omega), and phases (delta(1) and delta(2)) on the tide- induced water table fluctuations in a sloping sandy beach
Demonstrating approaches to chemically modify the surface of Ag nanoparticles in order to influence their cytotoxicity and biodistribution after single dose acute intravenous administration
With the advance in material science and the need to diversify market applications, silver nanoparticles (AgNPs) are modified by different surface coatings. However, how these surface modifications influence the effects of AgNPs on human health is still largely unknown. We have evaluated the uptake, toxicity and pharmacokinetics of AgNPs coated with citrate, polyethylene glycol, polyvinyl pyrolidone and branched polyethyleneimine (Citrate AgNPs, PEG AgNPs, PVP AgNPs and BPEI AgNPs, respectively). Our results demonstrated that the toxicity of AgNPs depends on the intracellular localization that was highly dependent on the surface charge. BPEI AgNPs ( potential=+46.5mV) induced the highest cytotoxicity and DNA fragmentation in Hepa1c1c7. In addition, it showed the highest damage to the nucleus of liver cells in the exposed mice, which is associated with a high accumulation in liver tissues. The PEG AgNPs ( potential=-16.2mV) showed the cytotoxicity, a long blood circulation, as well as bioaccumulation in spleen (34.33 mu g/g), which suggest better biocompatibility compared to the other chemically modified AgNPs. Moreover, the adsorption ability with bovine serum albumin revealed that the PEG surface of AgNPs has an optimal biological inertia and can effectively resist opsonization or non-specific binding to protein in mice. The overall results indicated that the biodistribution of AgNPs was significantly dependent on surface chemistry: BPEI AgNPs>Citrate AgNPs=PVP AgNPs>PEG AgNPs. This toxicological data could be useful in supporting the development of safe AgNPs for consumer products and drug delivery applications
Modulation of SOCS protein expression influences the interferon responsiveness of human melanoma cells
<p>Abstract</p> <p>Background</p> <p>Endogenously produced interferons can regulate the growth of melanoma cells and are administered exogenously as therapeutic agents to patients with advanced cancer. We investigated the role of negative regulators of interferon signaling known as suppressors of cytokine signaling (SOCS) in mediating interferon-resistance in human melanoma cells.</p> <p>Methods</p> <p>Basal and interferon-alpha (IFN-α) or interferon-gamma (IFN-γ)-induced expression of SOCS1 and SOCS3 proteins was evaluated by immunoblot analysis in a panel of n = 10 metastatic human melanoma cell lines, in human embryonic melanocytes (HEM), and radial or vertical growth phase melanoma cells. Over-expression of SOCS1 and SOCS3 proteins in melanoma cells was achieved using the PINCO retroviral vector, while siRNA were used to inhibit SOCS1 and SOCS3 expression. Tyr<sup>701</sup>-phosphorylated STAT1 (P-STAT1) was measured by intracellular flow cytometry and IFN-stimulated gene expression was measured by Real Time PCR.</p> <p>Results</p> <p>SOCS1 and SOCS3 proteins were expressed at basal levels in melanocytes and in all melanoma cell lines examined. Expression of the SOCS1 and SOCS3 proteins was also enhanced following stimulation of a subset of cell lines with IFN-α or IFN-γ. Over-expression of SOCS proteins in melanoma cell lines led to significant inhibition of Tyr<sup>701</sup>-phosphorylated STAT1 (P-STAT1) and gene expression following stimulation with IFN-α (IFIT2, OAS-1, ISG-15) or IFN-γ (IRF1). Conversely, siRNA inhibition of SOCS1 and SOCS3 expression in melanoma cells enhanced their responsiveness to interferon stimulation.</p> <p>Conclusions</p> <p>These data demonstrate that SOCS proteins are expressed in human melanoma cell lines and their modulation can influence the responsiveness of melanoma cells to IFN-α and IFN-γ.</p
Low-oxygen waters limited habitable space for early animals
The oceans at the start of the Neoproterozoic Era (1,000â541 million years ago, Ma) were dominantly anoxic, but may have become progressively oxygenated, coincident with the rise of animal life. However, the control that oxygen exerted on the development of early animal ecosystems remains unclear, as previous research has focussed on the identification of fully anoxic or oxic conditions, rather than intermediate redox levels. Here we report anomalous cerium enrichments preserved in carbonate rocks across bathymetric basin transects from nine localities of the Nama Group, Namibia (~550â541âMa). In combination with Fe-based redox proxies, these data suggest that low-oxygen conditions occurred in a narrow zone between well-oxygenated surface waters and fully anoxic deep waters. Although abundant in well-oxygenated environments, early skeletal animals did not occupy oxygen impoverished regions of the shelf, demonstrating that oxygen availability (probably >10âÎŒM) was a key requirement for the development of early animal-based ecosystems
Numerical assessment of 3D macrodispersion in heterogeneous porous media
Hydrodynamic dispersion is a key controlling factor of solute transport in heterogeneous porous media that critically depends on dimensionality. It has been shown that the transverse macrodispersion (asymptotic dispersion transverse to the mean velocity direction) vanishes only in 2D and not in 3D. Using classical Gaussian correlated permeability fields with a lognormal distribution of variance ÏÂČy, we determine numerically the longitudinal and transverse dispersivities as functions of heterogeneity and dimensionality. We show that the transverse macrodispersion steeply increases with ÏÂČy underlying the essential role of flow lines braiding, a mechanism specific to 3D systems. The transverse macrodispersion remains however at least two orders of magnitude smaller than the longitudinal macrodispersion, which increases even more steeply with ÏÂČy. At moderate to high levels of heterogeneity, the transverse dispersion also converges much faster to its asymptotic regime than do the longitudinal dispersion. Braiding cannot be thus taken as the sole mechanism responsible for the high longitudinal macrodispersions. It could be either supplemented or superseded by stronger velocity correlations in 3D than in 2D. This assumption is supported by the much larger longitudinal macrodispersions obtained in 3D than in 2D, up to a factor of 7 for ÏÂČy = 7.56
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