Sensitivity of Antarctic fish to ocean warming - an energy budget approach

Like the Arctic, the Antarctic region hosts some of the hot spots of climatic change. At the western Antarctic Peninsula, alterations of air and water temperature, pH, salinity and sea-ice regime were reported and associated shifts in species abundance and changes in food web structure have already become evident. In contrast, for most high-Antarctic regions, no climate related changes have yet been found. However, future temperature increases are also projected for these areas. Ocean warming affects marine ectotherms by directly impacting their body temperature and thus physiology. Antarctic marine ectotherms, such as fish, are highly adjusted to the very cold and stable conditions of the Southern Ocean and are suggested to be highly temperature sensitive. Fish constitute an important link in Antarctic food webs by being prey and predator alike. While various studies focused on the impact of elevated temperature on lower organisational levels in Antarctic fish, trade-offs of increased temperature for the whole organism remain unclear, but are highly relevant from an ecological perspective. Thus, this thesis aimed to assess the impact of increasing temperature on Antarctic fish at the whole-organism level from an energy budget perspective. The energy taken up by an organism can be allocated to different vital functions, such as routine metabolism, growth, reproduction and excretion. When routine metabolic costs are covered, energy can be allocated to growth and reproduction, the factors influencing a species abundance and population structure. In the first study of this thesis, energy allocation to routine metabolism as well as response patterns to an acute increase of temperature in the fish species Lepidonotothen squamifrons, Trematomus hansoni and Lepidonotothen nudifrons were analysed using oxygen consumption measurements. While metabolic responses to changing temperature were comparable in all species, metabolic costs of high-Antarctic fish were higher at habitat temperatures. Starting from higher metabolic rates at habitat temperature, it was hypothesised that high-Antarctic species might achieve critical thermal thresholds much earlier than low-latitude species when temperature increases. In the second study, temperature-dependent trade-offs at the whole-organism-level in Antarctic fish were analysed measuring different energy budget parameters. The results indicated a lower thermal tolerance of the high-Antarctic Trematomus bernacchii compared to the low-Antarctic Lepidonotothen nudifrons. After nine weeks of acclimation to elevated temperatures (4 degree Celsius), routine metabolic rates of T. bernacchii returned to baseline levels (0 degree Celsius). However, mass growth was reduced by 84% at 2 degree Celsius, likely due to less efficient food assimilation. In nature, such severe reductions in fish growth could delay sexual maturity and reduce production. In the third study, temperature-dependent growth rates of fish species from different latitudes were assessed. Polar and especially Antarctic species showed low growth and a narrow thermal tolerance window for growth performance compared to temperate species. A further climate induced reduction of already low growth rates could significantly affect population structures and abundances of polar fish. In conclusion, this thesis indicates differences in energy allocation, such as potentially higher routine metabolism, among low- and high-Antarctic fish. These could contribute to a high thermal sensitivity of high-Antarctic species. On the whole-organism level, this thermal sensitivity was displayed by significant reductions of already low growth rates at elevated temperatures. Finally, these results suggest that ocean warming may have far-reaching consequences for Antarctic fish production and population structures with potential extensive implications for entire Antarctic ecosystems and food webs

Depression and Anxiety in Current Middle Grade Fiction: Finding Quality, Authentic Portrayals for Use in Bibliotherapy

Young adults need a safe environment to learn about mental illness, and librarians must ensure that books being recommended authentically and realistically portray mental illness. The purpose of this study is to analyze the authenticity of fiction titles for middle school students that include content related to depression and anxiety to support recommendations to school counselors for bibliotherapy. The research questions this study sought to address included the following: Do the plots and characters of young adult novels written for middle school students realistically and authentically portray mental illness, and what criteria can be used to determine a novel\u27s quality as a bibliotherapy tool for school counselors to use with young adults dealing with or wanting to learn about mental illness? This study utilized qualitative content analysis to examine ten books that include content related to depression and anxiety published between 2008 and 2016. This researcher identified four criteria to determine a novel\u27s authenticity in portraying anxiety and depression which include stereotypes, symptomology, diagnosis, and treatment. Criteria identified to determine a novel\u27s quality as a bibliotherapy tool include the following eight areas: cognitive behavioral therapy qualities, themes to create personal change, education of readers, positive role model, positive coping skills, healthy relationships and environments, stigma addressed or dispelled, and developmental appropriateness. Nine of the ten novels analyzed were found to realistically portray depression and anxiety, and seven were found to be quality bibliotherapy tools. Therefore, seven of the ten novels studied are recommended to counselors for use in bibliotherapy

Cardiorespiratory responses in an Antarctic fish suggest limited capacity for thermal acclimation

Polar fishes are at high risk from increasing seawater temperatures. Characterising the 30 physiological responses to such changes may both clarify mechanisms that permit life 31 under extreme conditions, and identify limitations in the response to continued global 32 warming. We hypothesised that Notothenia coriiceps would show physiological 33 compensation after an acute exposure to 5oC, and following 6wk warm acclimation, 34 compared to ambient temperature (0oC). However, initial tachycardia (22.4±2.8 vs. 35 12.8±1.1min-1; P<0.01) was not reversed by acclimation (21.0±1.9min-1). 36 Hyperventilation (45.5±3.1 vs. 21.4±2.4min-1; P<0.001) showed a modest reduction 37 (38.0±2.9min-1; P<0.05), while resting oxygen consumption (0.52±0.08mmol.kg–1.h– 38 1) was acutely increased at 5oC (1.07±0.10mmol.kg–1.h–1; P<0.001) but unchanged 39 with acclimation. Autonomic blockade showed initial responses were mainly of vagal 40 origin, with little subsequent withdrawal or recovery in long-term heart rate variability 41 after 6wk. Given the limited cardiorespiratory capacity to withstand sustained 42 warming, effective physiological compensation likely requires a more prolonged 43 acclimation period

Screening Breakdown on the Route toward the Metal-Insulator Transition in Modulation Doped Si/SiGe Quantum Wells

Exploiting the spin resonance of two-dimensional (2D) electrons in SiGe/Si quantum wells we determine the carrier-density-dependence of the magnetic susceptibility. Assuming weak interaction we evaluate the density of states at the Fermi level D(E_F), and the screening wave vector, q_TF. Both are constant at higher carrier densities n, as for an ideal 2D carrier gas. For n < 3e11 cm-2, they decrease and extrapolate to zero at n = 7e10 cm-2. Calculating the mobility from q_TF yields good agreement with experimental values justifying the approach. The decrease in D(E_F) is explained by potential fluctuations which lead to tail states that make screening less efficient and - in a positive feedback - cause an increase of the potential fluctuations. Even in our high mobility samples the fluctuations exceed the electron-electron interaction leading to the formation of puddles of mobile carriers with at least 1 micrometer diameter.Comment: 4 pages, 3 figure

The role of dietary methionine concentrations on growth, metabolism and N-retention in cobia (Rachycentron canadum) at elevated water temperatures

This study determined impacts of dietary methionine concentrations at two temperatures on growth, feeding efficiency and N-metabolites in juvenile cobia. Methionine concentrations of the experimental diets were deficient (M9; 9 g/kg), sufficient (M12; 12 g/kg) and surplus (M16, 16 g/kg). Water temperature was normal (30°C) or elevated (34°C). Twenty cobia in triplicate tanks were fed the experimental diets for 6 weeks. Both methionine and temperature affected cobia's growth and feeding efficiency. Cobia fed M9 performed lower than the fish fed M12 and M16 diets. Additionally, cobia reared at 34°C performed poorer than at 30°C, probably due to lower voluntary feed intake in the fish reared at 34°C. Protein efficiency ratio and protein productive value in cobia fed M9 diet were less than M12 or M16 diets. This was confirmed with the improved retentions of indispensable amino acids (AAs). No interactions between methionine and temperature were observed in growth and protein accretion. At 30°C, CF improved, while HSI and VSI declined upon methionine supplementation levels. Of which an interaction between temperature and methionine was present. Plasma, muscle and liver free AA and N-metabolites were affected by methionine and temperature. Furthermore, temperature affected cobia's lipid class composition, resulting in increased phospholipids and cholesterol at 34°C.Agência financiadora / Código de projetos European Union's H2020 Programme 691150 MINECO Spain project EFISHDIGEST AGL2014-52888 European Social Fund FCT IF/00482/2014/CP1217/CT0005 National Funds through FCT CCMAR/Multi/04326/2013 Norwegian Agency for Development Cooperation NORHED QZA-0485 SRV-13/0010info:eu-repo/semantics/publishedVersio

Spin dynamics in semiconductors

This article reviews the current status of spin dynamics in semiconductors which has achieved a lot of progress in the past years due to the fast growing field of semiconductor spintronics. The primary focus is the theoretical and experimental developments of spin relaxation and dephasing in both spin precession in time domain and spin diffusion and transport in spacial domain. A fully microscopic many-body investigation on spin dynamics based on the kinetic spin Bloch equation approach is reviewed comprehensively.Comment: a review article with 193 pages and 1103 references. To be published in Physics Reports

The effects of thermal acclimation on cardio-respiratory performance in an Antarctic fish (Notothenia coriiceps).

The Southern Ocean has experienced stable, cold temperatures for over 10 million years, yet particular regions are currently undergoing rapid warming. To investigate the impacts of warming on cardiovascular oxygen transport, we compared the cardio-respiratory performance in an Antarctic notothenioid (Notothenia coriiceps) that was maintained at 0 or 5°C for 6.0-9.5 weeks. When compared at the fish's respective acclimation temperature, the oxygen consumption rate and cardiac output were significantly higher in 5°C-acclimated than 0°C-acclimated fish. The 2.7-fold elevation in cardiac output in 5°C-acclimated fish (17.4 vs. 6.5 ml min-1 kg-1) was predominantly due to a doubling of stroke volume, likely in response to increased cardiac preload, as measured by higher central venous pressure (0.15 vs. 0.08 kPa); tachycardia was minor (29.5 vs. 25.2 beats min-1). When fish were acutely warmed, oxygen consumption rate increased by similar amounts in 0°C- and 5°C-acclimated fish at equivalent test temperatures. In both acclimation groups, the increases in oxygen consumption rate during acute heating were supported by increased cardiac output achieved by elevating heart rate, while stroke volume changed relatively little. Cardiac output was similar between both acclimation groups until 12°C when cardiac output became significantly higher in 5°C-acclimated fish, driven largely by their higher stroke volume. Although cardiac arrhythmias developed at a similar temperature (~14.5°C) in both acclimation groups, the hearts of 5°C-acclimated fish continued to pump until significantly higher temperatures (CTmax for cardiac function 17.7 vs. 15.0°C for 0°C-acclimated fish). These results demonstrate that N. coriiceps is capable of increasing routine cardiac output during both acute and chronic warming, although the mechanisms are different (heart rate-dependent versus primarily stroke volume-dependent regulation, respectively). Cardiac performance was enhanced at higher temperatures following 5°C acclimation, suggesting cardiovascular function may not constrain the capacity of N. coriiceps to withstand a warming climate

Exploring nature's natural knockouts: In vivo cardiorespiratory performance of Antarctic fishes during acute warming.

We tested the hypothesis that Blackfin icefish (Chaenocephalus aceratus), one of the six species in the family Channichthyidae (the icefishes) that do not express haemoglobin and myoglobin, lack regulatory cardiovascular flexibility during acute warming and activity. The experimental protocols were designed to optimize the surgical protocol and minimize stress. First, minimally invasive heart rate (fH) measurements were made during a thermal ramp until cardiac failure in C. aceratus and compared with the closely related red-blooded Black rockcod (Notothenia coriiceps). Then, integrative cardiovascular adjustments were more extensively studied using flow probes and intravascular catheters in C. aceratus during acute warming (from 0 to 8°C) at rest and after imposed activity. C. aceratus had a lower routine fH than N. coriiceps (9 min-1vs 14 min-1) and a lower peak fH during acute warming (38 min-1vs 55 min-1) with a similar cardiac breakpoint temperature (13 and 14°C, respectively). Routine cardiac output (Q̇) for C. aceratus at ∼0°C was much lower (26.6 ml min-1 kg-1) than previously reported, likely because fish in the present study had a low fH (12 min-1) indicative of a high routine vagal tone and low stress. C. aceratus increased oxygen consumption during acute warming and with activity. Correspondingly, Q̇ increased considerably (maximally 86.3 ml min-1 kg-1), as did vascular conductance (five-fold). Thus, unlike earlier suggestions, these data provide convincing evidence that icefish can mount a well-developed cardiovascular regulation of heart rate, cardiac output and vascular conductance, and this regulatory capacity provides flexibility during acute warming

Cardiac mitochondrial metabolism may contribute to differences in thermal tolerance of red- and white-blooded Antarctic notothenioid fishes

Studies in temperate fishes provide evidence that cardiac mitochondrial function and the capacity to fuel cardiac work contribute to thermal tolerance. Here, we tested the hypothesis that decreased cardiac aerobic metabolic capacity contributes to the lower thermal tolerance of the haemoglobinless Antarctic icefish, Chaenocephalus aceratus, compared with that of the red-blooded Antarctic species, Notothenia coriiceps. Maximal activities of citrate synthase (CS) and lactate dehydrogenase (LDH), respiration rates of isolated mitochondria, adenylate levels and changes in mitochondrial protein expression were quantified from hearts of animals held at ambient temperature or exposed to their critical thermal maximum (CTmax). Compared with C. aceratus, activity of CS, ATP concentration and energy charge were higher in hearts of N. coriiceps at ambient temperature and CTmax. While state 3 mitochondrial respiration rates were not impaired by exposure to CTmax in either species, state 4 rates, indicative of proton leakage, increased following exposure to CTmax in C. aceratus but not N. coriiceps. The interactive effect of temperature and species resulted in an increase in antioxidants and aerobic metabolic enzymes in N. coriiceps but not in C. aceratus. Together, our results support the hypothesis that the lower aerobic metabolic capacity of C. aceratus hearts contributes to its low thermal tolerance