6 results on '"B Voegeli"'
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2. Electron transport in multilayered Co/Cu nanowires
- Author
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Bernard Doudin, J.-Ph. Ansermet, A. Blondel, and B. Voegeli
- Subjects
Materials science ,Condensed matter physics ,Magnetoresistance ,Nanoporous ,Nanowire ,Giant Magnetoresistance ,Giant magnetoresistance ,Magnetic Multilayers ,Condensed Matter Physics ,Electron transport chain ,Electronic, Optical and Magnetic Materials ,Volume (thermodynamics) ,Spin diffusion ,Spin-flip - Abstract
The magnetoresistance (MR) of magnetic multilayers formed by electrodeposition of Co and Cu in the parallel pores of nanoporous polycarbonate membranes was measured in the current-perpendicular-to-plane (CPP-MR) geometry, with Co and Cu thicknesses in the range 2–50 nm. Ratios reaching 20% at ambient temperature and 30% at 20 K were obtained. A systematic study of the magnetoresistance as a function of the Co and Cu thicknesses was interpreted in terms of a two-current model. The volume and interface resistance asymmetry parameters could be deduced and the ability to determine the spin diffusion length by this method was discussed. An estimate of the Cu spin flip length has been found. Comparison of the data at 20 and 300 K showed that the product of the resistance change and the maximum resistance is temperature invariant.
3. Physiological responses to increased brood size and ectoparasite infestation: Adult great tits favour self-maintenance.
- Author
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Wegmann M, Voegeli B, and Richner H
- Subjects
- Animals, Basal Metabolism physiology, Female, Heat-Shock Proteins metabolism, Male, Oxidative Stress physiology, Passeriformes, Reactive Oxygen Species metabolism, Behavior, Animal physiology, Clutch Size physiology, Feeding Behavior physiology, Flea Infestations physiopathology, Stress, Physiological physiology
- Abstract
Different types of stressors trigger responses of different physiological systems, and these responses may contribute differentially to the maintenance of homeostasis, to trade-offs and the evolution of life-history traits. To manipulate two common stressors during reproduction, we infested half of the nests in a naturally breeding great tit population with ectoparasites and simultaneously manipulated brood size, using a 2×2 experimental design. Parents in this model species commonly compensate for ectoparasites by an increase in food provisioning. We assessed parental responses to these concurrent stressors by measuring several physiological stress parameters such as changes in metabolic rate, oxidative stress and expression of heat-shock proteins (Hsp), and explored how these stressors affect the trade-off between self-maintenance and reproduction. Neither flea infestation nor brood size manipulation affected adult metabolic rate, oxidative damage or Hsp levels. Furthermore, we found no interactive effect of the two treatments on adults. However, nestlings in infested nests had lower body mass and lower survival. Nestlings in enlarged broods were lighter and had lower survival, although parents of enlarged broods increased food provisioning rate. The findings suggest that adults favour maintenance of cellular homeostasis, and physiological equilibrium over current reproduction, and that the costs induced by both stressors, flea infestation and increased brood size, are carried by the offspring. It emphasizes the importance of self-maintenance over reproduction in life-history decisions, and more generally the need of including physiological traits for understanding the evolution of life-histories., (Copyright © 2015 Elsevier Inc. All rights reserved.)
- Published
- 2015
- Full Text
- View/download PDF
4. Parasites suppress immune-enhancing effect of methionine in nestling great tits.
- Author
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Wegmann M, Voegeli B, and Richner H
- Subjects
- Acute-Phase Proteins metabolism, Animal Diseases immunology, Animal Diseases parasitology, Animals, Body Weight drug effects, Dietary Supplements, Flea Infestations immunology, Immunity drug effects, Inflammation immunology, Passeriformes growth & development, Passeriformes immunology, Adjuvants, Immunologic pharmacology, Flea Infestations parasitology, Immunity physiology, Methionine pharmacology, Parasites, Passeriformes parasitology, Siphonaptera
- Abstract
After birth, an organism needs to invest both in somatic growth and in the development of efficient immune functions to counter the effects of pathogens, and hence an investment trade-off is predicted. To explore this trade-off, we simultaneously exposed nestling great tits (Parus major) to a common ectoparasite, while stimulating immune function. Using a 2 × 2 experimental design, we first infested half of the nests with hen fleas (Ceratophyllus gallinae) on day 3 post-hatch and later, on day 9-13 post-hatch, and then supplemented half of the nestlings within each nest with an immuno-enhancing amino acid (methionine). We then assessed the non-specific immune response by measuring both the inflammatory response to a lipopolysaccharide (LPS) and assessing the levels of acute phase proteins (APP). In parasite-infested nestlings, methionine had a negative effect on body mass close to fledging. Methionine had an immune-enhancing effect in the absence of ectoparasites only. The inflammatory response to LPS was significantly lower in nestlings infested with fleas and was also lower in nestlings supplemented with methionine. These patterns of immune responses suggest an immunosuppressive effect of ectoparasites that could neutralise the immune-enhancing effect of methionine. Our study thus suggests that the trade-off between investment in life history traits and immune function is only partly dependent on available resources, but shows that parasites may influence this trade-off in a more complex way, by also inhibiting important physiological functions.
- Published
- 2015
- Full Text
- View/download PDF
5. Heterozygosity is linked to the costs of immunity in nestling great tits (Parus major).
- Author
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Voegeli B, Saladin V, Wegmann M, and Richner H
- Abstract
There is growing evidence that heterozygosity-fitness correlations (HFCs) are more pronounced under harsh conditions. Empirical evidence suggests a mediating effect of parasite infestation on the occurrence of HFCs. Parasites have the potential to mediate HFCs not only by generally causing high stress levels but also by inducing resource allocation tradeoffs between the necessary investments in immunity and other costly functions. To investigate the relative importance of these two mechanisms, we manipulated growth conditions of great tit nestlings by brood size manipulation, which modifies nestling competition, and simultaneously infested broods with ectoparasites. We investigated under which treatment conditions HFCs arise and, second, whether heterozygosity is linked to tradeoff decisions between immunity and growth. We classified microsatellites as neutral or presumed functional and analyzed these effects separately. Neutral heterozygosity was positively related to the immune response to a novel antigen in parasite-free nests, but not in infested nests. For nestlings with lower heterozygosity levels, the investments in immunity under parasite pressure came at the expenses of reduced feather growth, survival, and female body condition. Functional heterozygosity was negatively related to nestling immune response regardless of the growth conditions. These contrasting effects of functional and neutral markers might indicate different underlying mechanisms causing the HFCs. Our results confirm the importance of considering marker functionality in HFC studies and indicate that parasites mediate HFCs by influencing the costs of immune defense rather than by a general increase in environmental harshness levels.
- Published
- 2013
- Full Text
- View/download PDF
6. Parasites as mediators of heterozygosity-fitness correlations in the Great Tit (Parus major).
- Author
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Voegeli B, Saladin V, Wegmann M, and Richner H
- Subjects
- Animals, Female, Genetic Variation, Genotype, Likelihood Functions, Linear Models, Male, Microsatellite Repeats genetics, Parasite Load, Passeriformes genetics, Passeriformes growth & development, Polymerase Chain Reaction, Switzerland, Body Size physiology, Genetic Fitness genetics, Heterozygote, Passeriformes parasitology, Siphonaptera physiology
- Abstract
Positive correlations between heterozygosity and fitness traits are frequently observed, and it has been hypothesized, but rarely tested experimentally, that parasites play a key role in mediating the heterozygosity-fitness association. We evaluated this hypothesis in a wild great tit (Parus major) population by testing the prediction that the heterozygosity-fitness association would appear in broods experimentally infested with a common ectoparasite, but not in parasite-free broods. We simultaneously assessed the effects of parental and offspring heterozygosity on nestling growth and found that body mass of nestlings close to independence, which is a strong predictor of post-fledging survival, increased significantly with nestling levels of heterozygosity in experimentally infested nests, but not in parasite-free nests. Heterozygosity level of the fathers also showed a significant positive correlation with offspring body mass under an experimental parasite load, whereas there was no correlation with the mothers' level of heterozygosity. Thus, our results indicate a key role for parasites as mediators of the heterozygosity-fitness correlations., (© 2012 The Authors. Journal of Evolutionary Biology © 2012 European Society For Evolutionary Biology.)
- Published
- 2012
- Full Text
- View/download PDF
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