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71.
Lea A. Randall Des H. V. Smith Breana L. Jones David R. C. Prescott Axel Moehrenschlager 《PloS one》2015,10(5)
A detailed understanding of the population dynamics of many amphibian species is lacking despite concerns about declining amphibian biodiversity and abundance. This paper explores temporal patterns of occupancy and underlying extinction and colonization dynamics in a regionally imperiled amphibian species, the Northern leopard frog (Lithobates pipiens) in Alberta. Our study contributes to elucidating regional occupancy dynamics at northern latitudes, where climate extremes likely have a profound effect on seasonal occupancy. The primary advantage of our study is its wide geographic scale (60,000 km2) and the use of repeat visual surveys each spring and summer from 2009–2013. We find that occupancy varied more dramatically between seasons than years, with low spring and higher summer occupancy. Between spring and summer, colonization was high and extinction low; inversely, colonization was low and extinction high over the winter. The dynamics of extinction and colonization are complex, making conservation management challenging. Our results reveal that Northern leopard frog occupancy was constant over the last five years and thus there is no evidence of decline or recovery within our study area. Changes to equilibrium occupancy are most sensitive to increasing colonization in the spring or declining extinction in the summer. Therefore, conservation and management efforts should target actions that are likely to increase spring colonization; this could be achieved through translocations or improving the quality or access to breeding habitat. Because summer occupancy is already high, it may be difficult to improve further. Nevertheless, summer extinction could be reduced by predator control, increasing water quality or hydroperiod of wetlands, or increasing the quality or quantity of summer habitat. 相似文献
72.
Benjamin Arthur Mark Hindell Marthan Bester Phil Trathan Ian Jonsen Iain Staniland W. Chris Oosthuizen Mia Wege Mary-Anne Lea 《PloS one》2015,10(3)
Strategies employed by wide-ranging foraging animals involve consideration of habitat quality and predictability and should maximise net energy gain. Fidelity to foraging sites is common in areas of high resource availability or where predictable changes in resource availability occur. However, if resource availability is heterogeneous or unpredictable, as it often is in marine environments, then habitat familiarity may also present ecological benefits to individuals. We examined the winter foraging distribution of female Antarctic fur seals, Arctocephalus gazelle, over four years to assess the degree of foraging site fidelity at two scales; within and between years. On average, between-year fidelity was strong, with most individuals utilising more than half of their annual foraging home range over multiple years. However, fidelity was a bimodal strategy among individuals, with five out of eight animals recording between-year overlap values of greater than 50%, while three animals recorded values of less than 5%. High long-term variance in sea surface temperature, a potential proxy for elevated long-term productivity and prey availability, typified areas of overlap. Within-year foraging site fidelity was weak, indicating that successive trips over the winter target different geographic areas. We suggest that over a season, changes in prey availability are predictable enough for individuals to shift foraging area in response, with limited associated energetic costs. Conversely, over multiple years, the availability of prey resources is less spatially and temporally predictable, increasing the potential costs of shifting foraging area and favouring long-term site fidelity. In a dynamic and patchy environment, multi-year foraging site fidelity may confer a long-term energetic advantage to the individual. Such behaviours that operate at the individual level have evolutionary and ecological implications and are potential drivers of niche specialization and modifiers of intra-specific competition. 相似文献
73.
Jan-Patrick Stellmann Klarissa Hanja Stürner Kim Lea Young Susanne Siemonsen Tim Friede Christoph Heesen 《PloS one》2015,10(2)
BackgroundGadolinium-enhancing (GD+) lesions and T2 lesions are MRI outcomes for phase-2 treatment trials in relapsing-remitting Multiple Sclerosis (RRMS). Little is known about predictors of lesion development and regression-to-the-mean, which is an important aspect in early baseline-to-treatment trials.ObjectivesTo quantify regression-to-the-mean and identify predictors of MRI lesion development in placebo cohorts.Methods21 Phase-2 and Phase-3 trials were identified by a systematic literature research. Random-effects meta-analyses were performed to estimate development of T2 and GD+ after 6 months (phase-2) or 2 years (phase-3). Predictors of lesion development were evaluated with mixed-effect meta-regression.ResultsThe mean number of GD+-lesions per scan was similar after 6 months (1.19, 95%CI: 0.87-1.51) and 2 years (1.19, 95%CI: 1.00-1.39). 39% of the patients were without new T2-lesion after 6 month and 19% after 2 years (95%CI: 12-25%). Mean number of baseline GD+-lesions was the best predictor for new lesions after 6 months.ConclusionBaseline GD-enhancing lesions predict evolution of Gd- and T2 lesions after 6 months and might be used to control for regression to the mean effects. Overall, proof-of-concept studies with a baseline to treatment design have to face a regression to 1.2 GD+lesions per scan within 6 months. 相似文献
74.
Christian Thaler Tobias Faizy Jan Sedlacik Brigitte Holst Jan-Patrick Stellmann Kim Lea Young Christoph Heesen Jens Fiehler Susanne Siemonsen 《PloS one》2015,10(12)
Background
Magnetic Resonance Imaging (MRI) is an established tool in diagnosing and evaluating disease activity in Multiple Sclerosis (MS). While clinical-radiological correlations are limited in general, hypointense T1 lesions (also known as Black Holes (BH)) have shown some promising results. The definition of BHs is very heterogeneous and depends on subjective visual evaluation.Objective
We aimed to improve clinical-radiological correlations by defining BHs using T1 relaxation time (T1-RT) thresholds to achieve best possible correlation between BH lesion volume and clinical disability.Method
40 patients with mainly relapsing-remitting MS underwent MRI including 3-dimensional fluid attenuated inversion recovery (FLAIR), magnetization-prepared rapid gradient echo (MPRAGE) before and after Gadolinium (GD) injection and double inversion-contrast magnetization-prepared rapid gradient echo (MP2RAGE) sequences. BHs (BHvis) were marked by two raters on native T1-weighted (T1w)-MPRAGE, contrast-enhancing lesions (CE lesions) on T1w-MPRAGE after GD and FLAIR lesions (total-FLAIR lesions) were detected separately. BHvis and total-FLAIR lesion maps were registered to MP2RAGE images, and the mean T1-RT were calculated for all lesion ROIs. Mean T1 values of the cortex (CTX) were calculated for each patient. Subsequently, Spearman rank correlations between clinical scores (Expanded Disability Status Scale and Multiple Sclerosis Functional Composite) and lesion volume were determined for different T1-RT thresholds.Results
Significant differences in T1-RT were obtained between all different lesion types with highest T1 values in visually marked BHs (BHvis: 1453.3±213.4 ms, total-FLAIR lesions: 1394.33±187.38 ms, CTX: 1305.6±35.8 ms; p<0.05). Significant correlations between BHvis/total-FLAIR lesion volume and clinical disability were obtained for a wide range of T1-RT thresholds. The highest correlation for BHvis and total-FLAIR lesion masks were found at T1-RT>1500 ms (Expanded Disability Status Scale vs. lesion volume: rBHvis = 0.442 and rtotal-FLAIR = 0.497, p<0.05; Multiple Sclerosis Functional Composite vs. lesion volume: rBHvis = -0.53 and rtotal-FLAIR = -0.627, p<0.05).Conclusion
Clinical-radiological correlations in MS patients are increased by application of T1-RT thresholds. With the short acquisition time of the MP2RAGE sequences, quantitative T1 maps could be easily established in clinical studies. 相似文献75.
Valeria Sabaj Mario Galindo Daniela Silva Lea Sandoval Juan C. Rodríguez 《Molecular biology reports》2010,37(6):2927-2933
Toxoplasma gondii is one of the most successful protozoan parasites given its ability to manipulate the immune system and establish a chronic infection. It is a parasite with a significant impact on human health, mainly in immunocompromised patients. In Europe and North America, only a few clonal genotypes (I, II and III) seem to be responsible for the vast majority of Toxoplasma infections. Surface antigen 2 gene (SAG2) has been extensively used for genotyping T. gondii isolates. The analysis of this locus reveals that in Northern hemisphere, human disease causing isolates are mainly type II, whereas T. gondii isolated from different animals are both type II and III. Since the immune response depends on parasite genotype, it seems relevant to characterize parasites producing human toxoplasmosis in different geographical areas. The growing information about the prevalent T. gondii genotypes in South America mostly refers to domestic animals. This is the first report of genetic characterization of T. gondii isolates from clinical samples in Chile, South America. All the samples analyzed corresponded to SAG2 type I isolates, and they differ from classic SAG2 type I by genetic polymorphisms. This study contributes to the scarce available information on T. gondii at South America, and reinforces an emerging concept suggesting that SAG2 type I, rather than II, parasites are a frequent cause of clinical toxoplasmosis in this continent. 相似文献
76.
Sang Hoon Jeong Jae Hwan Kim Sang Min Yi Jin Ho Kim Kui Lea Park Sang Wook Son 《Biochemical and biophysical research communications》2010,394(3):612-615
Quantum dots (QDs) are rapidly emerging as an important class of nanoparticles (NPs) with potential applications in medicine. However, little is known about penetration of QDs through human skin. This study investigated skin penetration of QDs in both in vivo and in vitro human skin. Using the tape stripping method, this study demonstrates for the first time that QDs can actually penetrate through the stratum corneum (SC) of human skin. Transmission electron microscope (TEM) and energy diverse X-ray (EDX) analysis showed accumulation of QDs in the SC of a human skin equivalent model (HSEM) after dermal exposure to QDs. These findings suggest possible transdermal absorption of QDs after dermal exposure over a relatively long period of time. 相似文献
77.
Guilliams M Oldenhove G Noel W Hérin M Brys L Loi P Flamand V Moser M De Baetselier P Beschin A 《Journal of immunology (Baltimore, Md. : 1950)》2007,179(5):2748-2757
Tolerance to African trypanosomes requires the production of IFN-gamma in the early stage of infection that triggers the development of classically activated macrophages controlling parasite growth. However, once the first peak of parasitemia has been controlled, down-regulation of the type 1 immune response has been described. In this study, we have evaluated whether regulatory T cells (Tregs) contribute to the limitation of the immune response occurring during Trypanosoma congolense infection and hereby influence the outcome of the disease in trypanotolerant C57BL/6 host. Our data show that Foxp3+ Tregs originating from the naturally occurring Treg pool expanded in the spleen and the liver of infected mice. These cells produced IL-10 and limited the production of IFN-gamma by CD4+ and CD8+ effector T cells. Tregs also down-regulated classical activation of macrophages resulting in reduced TNF-alpha production. The Treg-mediated suppression of the type 1 inflammatory immune response did not hamper parasite clearance, but was beneficial for the host survival by limiting the tissue damages, including liver injury. Collectively, these data suggest a cardinal role for naturally occurring Tregs in the development of a trypanotolerant phenotype during African trypanosomiasis. 相似文献
78.
79.
Glutamate in plants: metabolism, regulation, and signalling 总被引:10,自引:0,他引:10
Glutamate occupies a central position in amino acid metabolism in plants. The acidic amino acid is formed by the action of glutamate synthase, utilizing glutamine and 2-oxoglutarate. However, glutamate is also the substrate for the synthesis of glutamine from ammonia, catalysed by glutamine synthetase. The alpha-amino group of glutamate may be transferred to other amino acids by the action of a wide range of multispecific aminotransferases. In addition, both the carbon skeleton and alpha-amino group of glutamate form the basis for the synthesis of gamma-aminobutyric acid, arginine, and proline. Finally, glutamate may be deaminated by glutamate dehydrogenase to form ammonia and 2-oxoglutarate. The possibility that the cellular concentrations of glutamate within the plant are homeostatically regulated by the combined action of these pathways is examined. Evidence that the well-known signalling properties of glutamate in animals may also extend to the plant kingdom is reviewed. The existence in plants of glutamate-activated ion channels and their possible relationship to the GLR gene family that is homologous to ionotropic glutamate receptors (iGluRs) in animals are discussed. Glutamate signalling is examined from an evolutionary perspective, and the roles it might play in plants, both in endogenous signalling pathways and in determining the capacity of the root to respond to sources of organic N in the soil, are considered. 相似文献
80.
Franciskovich JB Masters JJ Weber WW Klimkowski VJ Chouinard M Sipes PR Johnson LM Snyder DW Chastain MK Craft TJ Towner RD Gifford-Moore DS Froelich LL Smallwood JK Foster RS Smith GF Liebeschuetz JW Murray CW Young SC 《Bioorganic & medicinal chemistry letters》2007,17(24):6910-6913
Several P4 domain derivatives of the general d-phenylglycinamide-based scaffold (2) were synthesized and evaluated for their ability to bind to the serine protease factor Xa. Some of the more potent compounds were evaluated for their anticoagulant effects in vitro. A select subset containing various P1 indole constructs was further evaluated for their pharmacokinetic properties after oral administration to rats. 相似文献