The aerobic scope of an antarctic fish,Pagothenia borchgrevinki and its significance for metabolic cold adaptation

Summary Resting weight-specific oxygen consumption of the cryopelagic Antarctic nototheniid Pagothenia borchgrevinki at 0°C was 39.6 ml kg^-1 · h^-1 for a 50 g fish, with oxygen consumption being described by the regression equation: log₁₀ VO₂(ml/h)=–1.104+0.825 log₁₀ M_b (g). These values are considerably below those raported by Wohlschlag (1964a,b). VO₂ max. in forced swimming was described by the regression equation: log₁₀ VO₂ max = –0.507+0.823 log₁₀ M_b. Despite low basal metabolism, factorial aerobic scope is similar to that reported for most other teleost fish, as is the cost of net transport. Myotomal muscles were used only at the highest swimming speeds and once they were recruited the fish fatigued rapidly. After swimming, oxygen debt was repaid rapidly, with a half-time of 20 min.     

Changes in body temperature influence the scaling of VO2max and aerobic scope in mammals

Debate on the mechanism(s) responsible for the scaling of metabolic rate with body size in mammals has focused on why the maximum metabolic rate (VO2max ) appears to scale more steeply with body size than the basal metabolic rate (BMR). Consequently, metabolic scope, defined as VO2max/BMR, systematically increases with body size. These observations have led some to suggest that VO2max, and BMR are controlled by fundamentally different processes, and to discount the generality of models that predict a single power-law scaling exponent for the size dependence of the metabolic rate. We present a model that predicts a steeper size dependence for VO2max than BMR based on the observation that changes in muscle temperature from rest to maximal activity are greater in larger mammals. Empirical data support the model's prediction. This model thus provides a potential theoretical and mechanistic link between BMR and VO2 max.     

Size as a complex trait and the scaling relationships of its components across teleosts

Evolutionary Ecology - Body size influences nearly every aspect of an organism’s biology and ecology. When studying body size, researchers often focus on a single dimension, such as length,...     

Intraspecific temperature dependence of the scaling of metabolic rate with body mass in fishes and its ecological implications

Metabolism constitutes a fundamental property of all organisms. Metabolic rate is commonly described to scale as a power function of body size and exponentially with temperature, thereby treating the effects of body size and temperature independently. Mounting evidence shows that the scaling of metabolic rate with body mass itself depends on temperature. Across‐species analyses in fishes suggest that the mass‐scaling exponent decreases with increasing temperature. However, whether this relationship holds at the within‐species level has rarely been tested. Here, we re‐analyse data on the metabolic rates of four freshwater fish species, two coregonids and two cyprinids, that cover wide ranges of body masses and their naturally experienced temperatures. We show that the standard metabolic rate of the coregonids is best fit when accounting for a linear temperature dependence of the scaling of metabolic rate with body mass, whereas a constant mass‐scaling exponent is supported in case of the cyprinids. Our study shows that phenotypic responses to temperature can result in temperature‐dependent scaling relationships at the species level and that these responses differ between taxa. Together with previous findings, these results indicate that evolutionarily adaptive and phenotypically plastic responses to temperature affect the scaling of metabolic rate with body mass in fishes.     

Contribution of aerobic and anaerobic scope to the total metabolic scope of the desert skink,Chalcides ocellatus (Forskal)

• 1.1. Measurements of aerobic scope (resting and active oxygen consumption rates) and anaerobic scope (resting and active production of lactate rates in the whole body homogenates) were carried out on the desert skink, Chalcides ocellatus at temperatures between 10 and 40°C.
• 2.2. The aerobic scope was maximal around the preferred body temperature with a low thermal temperature dependence above the preferred levels.
• 3.3. During initial stages of forced activity, C. ocellatus employed anaerobic metabolism as its major energy source.

     

Global and regional brain metabolic scaling and its functional consequences

Background  

Information processing in the brain requires large amounts of metabolic energy, the spatial distribution of which is highly heterogeneous, reflecting the complex activity patterns in the mammalian brain.     

Allometric scaling of lung volume and its consequences for marine turtle diving performance

Marine turtle lungs have multiple functions including respiration, oxygen storage and buoyancy regulation, so lung size is an important indicator of dive performance. We determined maximum lung volumes (V(L)) for 30 individuals from three species (Caretta caretta n=13; Eretmochelys imbricata n=12; Natator depressus n=5) across a range of body masses (M(b)): 0.9 to 46 kg. V(L) was 114 ml kg(-1) and increased with M(b) with a scaling factor of 0.92. Based on these values for V(L) we demonstrated that diving capacities (assessed via aerobic dive limits) of marine turtles were potentially over-estimated when the V(L)-body mass effect was not considered (by 10 to 20% for 5 to 25 kg turtles and by >20% for turtles > or =25 kg). While aerobic dive limits scale with an exponent of 0.6, an analysis of average dive durations in free-ranging chelonian marine turtles revealed that dive duration increases with a mass exponent of 0.51, although there was considerable scatter around the regression line. While this highlights the need to determine more parameters that affect the duration-body mass relationship, our results provide a reference point for calculating oxygen storage capacities and air volumes available for buoyancy control.     

Mycorrhizal respiration: implications for global scaling relationships

Most plant species form mycorrhizas, yet these are neglected by plant physiologists. One consequence of this neglect is reduced ability to predict plant respiration, because respiration rate (R) in mycorrhizal roots might be higher than in non-mycorrhizal roots owing to increased substrate availability associated with enhanced nutrient uptake, coupled with increased respiratory product demand. Other predictions include that mycorrhizal colonization will affect scaling of R with tissue nitrogen concentrations; that mycorrhizal and non-mycorrhizal root R differ in their response to nutrient supply; and that the impact of colonization on R is related to fungal biomass. Failure to examine properly the role of colonization in determining root R means that current interpretations of root and soil respiration data might be flawed.     

Expanding the organismal scope of proteomics: cross-species protein identification by mass spectrometry and its implications

Due to the limited applicability of conventional protein identification methods to the proteomes of organisms with unsequenced genomes, researchers have developed approaches to identify proteins using mass spectrometry and sequence similarity database searches. Both the integration of mass spectrometry with bioinformatics and genomic sequencing drive the expanding organismal scope of proteomics.     

Cortisol in teleosts: dynamics,mechanisms of action,and metabolic regulation

Cortisol is the principal corticosteriod in teleost fishes and its plasma concentrations rise dramatically during stress. The relationship between this cortisol increase and its metabolic consequences are subject to extensive debate. Much of this debate arises from the different responses of the many species used, the diversity of approaches to manipulate cortisol levels, and the sampling techniques and duration. Given the extreme differences in experimental approach, it is not surprising that inconsistencies exist within the literature. This review attempts to delineate common themes on the physiological and metabolic roles of cortisol in teleost fishes and to suggest new approaches that might overcome some of the inconsistencies on the role of this multifaceted hormone. We detail the dynamics of cortisol, especially the exogenous and endogenous factors modulating production, clearance and tissue availability of the hormone. We focus on the mechanisms of action, the biochemical and physiological impact, and the interaction with other hormones so as to provide a conceptual framework for cortisol under resting and/or stressed states. Interpretation of interactions between cortisol and other glucoregulatory hormones is hampered by the absence of adequate hormone quantification, resulting in correlative rather than causal relationships.The use of mammalian paradigms to explain the teleost situation is generally inappropriate. The absence of a unique mineralocorticoid and likely minor importance of glucose in fishes means that cortisol serves both glucocorticoid and mineralocorticoid roles; the unusual structure of the fish glucocorticoid receptor may be a direct consequence of this duality. Cortisol affects the metabolism of carbohydrates, protein and lipid. Generally cortisol is hyperglycaemic, primarily as a result of increases in hepatic gluconeogenesis initiated as a result of peripheral proteolysis. The increased plasma fatty acid levels during hypercortisolaemia may assist to fuel the enhanced metabolic rates noted for a number of fish species. Cortisol is an essential component of the stress response in fish, but also plays a significant role in osmoregulation, growth and reproduction. Interactions between cortisol and toxicants may be the key to the physiology of this hormone, although cortisol's many important housekeeping functions must not be ignored. Combining molecular approaches with isolated cell systems and the whole fish will lead to an improved understanding of the many faces of this complex hormone in an evolutionary and environmental framework.     

Lens optical properties in the eyes of large marine predatory teleosts

The optical properties of the crystalline lenses were studied in a variety of large predatory teleosts (bony fishes) that forage in the open ocean, some of them at considerable depths. We found the first fish lenses that are free of measurable longitudinal spherical aberration, i.e., are perfectly monofocal, in contrast to the multifocal lenses that are typical for smaller fishes living close to the surface. In fact, none of the lenses investigated in this study were clearly multifocal. Most, but not all, of the lenses had long normalized focal lengths (focal length/lens radius) of up to 3.3 lens radii. A monofocal lens of long focal length, combined with spectrally suitably placed cone pigments, may be the optimal solution for vision of high spatial and spectral resolutions in a habitat where the available spectrum of light is limited.     

Vacuolated prolactin cells in the pituitary gland of several marine teleosts

A morphometric study of prolactin cell ultrastructure in the pituitary gland of the Corkwing wrasse, Crenilabrus melops L., showed that cytoplasmic vacuoles, which accounted for 25% of the cell volume, were associated with signs of decreased secretory activity. The Golgi apparatus, mitochondria and rough endoplasmic reticulum, all contributed relatively little to the total cell volume, and there was no sign of secretory-granule release by exocytosis. All vacuoles were intracellular and membrane-bound, and probably derived from rough endoplasmic reticulum, Golgi apparatus and the nuclear envelope. It is thought that smaller vacuoles coalesce to form larger ones. The secretory granules were small and sparse, and this could account for the chromophobia of prolactin cells in light-microscopy preparations. Similar vacuoles were reported in the prolactin cells of the gobiid fish, Chaparrudo flavescens, Pomatoschistus pictus, Pomatoschistus minutus and Pomatoschistus microps . The vacuoles in Chuparrudo were of similar ultrastructure to those in Crenilabrus .     

Advances in concepts and methods for the marine environment: implications for policy

Science-based indicators aimed at measuring the sustainability of human activities on the environment have become of prime importance in the policy arena. At the international level, the Commission on Sustainable Development and the Convention on Biological Diversity and other Multilateral Environmental Agreements have recognised the need to develop a set of scientific indicators related to changes in biodiversity and other environmental issues able to direct policy decisions. In the marine realm, the study of the effects of both ‘top-down’ extractive activities such as fishing is more and more dealt with, in conjunction with ‘bottom-up’ activities such as nutrient loading and the effects on biogeochemical cycles, marine geochemistry and ecosystem structure and functioning of other pollutants and contaminants. ‘Conventional’ approaches such as the identification of taxa, model organisms and related methodologies will continue playing a key role for the monitoring of human-induced changes in the marine environment. On the other hand, newly developed disciplines such as genomics, proteomics and biodiversity informatics are increasingly looked at as a source of information and applications that can respond to questions and concerns by the policy community such as the need to adapt to global and climate change in the marine environment so as to mitigate its societal implications.

Drought-induced forest decline: causes, scope and implications

A large number of episodes of forest mortality associated with drought and heat stress have been detected worldwide in recent decades, suggesting that some of the world's forested ecosystems may be already responding to climate change. Here, we summarize a special session titled 'Drought-induced forest decline: causes, scope and implications' within the 12th European Ecological Federation Congress, held in ávila (Spain) from 25 to 29 September 2011. The session focused on the interacting causes and impacts of die-off episodes at the community and ecosystem levels, and highlighted recent events of drought- and heat-related tree decline, advances in understanding mechanisms and in predicting mortality events, and diverse consequences of forest decline. Talks and subsequent discussion noted a potentially important role of carbon that may be interrelated with plant hydraulics in the multi-faceted process leading to drought-induced mortality; a substantial and yet understudied capacity of many forests to cope with extreme climatic events; and the difficulty of separating climate effects from other anthropogenic changes currently shaping forest dynamics in many regions of the Earth. The need for standard protocols and multi-level monitoring programmes to track the spatio-temporal scope of forest decline globally was emphasized as critical for addressing this emerging environmental issue.     

Modeling metabolic homeostasis and nutrient sensing in Drosophila: implications for aging and metabolic diseases

Over the past decade, numerous reports have underscored the similarities between the metabolism of Drosophila and vertebrates, with the identification of evolutionarily conserved enzymes and analogous organs that regulate carbohydrate and lipid metabolism. It is now well established that the major metabolic, energy-sensing and endocrine signaling networks of vertebrate systems are also conserved in flies. Accordingly, studies in Drosophila are beginning to unravel how perturbed energy balance impinges on lifespan and on the ensuing diseases when energy homeostasis goes awry. Here, we highlight several emerging concepts that are at the nexus between obesity, nutrient sensing, metabolic homeostasis and aging. Specifically, we summarize the endocrine mechanisms that regulate carbohydrate and lipid metabolism, and provide an overview of the neuropeptides that regulate feeding behavior. We further describe the various efforts at modeling the effects of high-fat or -sugar diets in Drosophila and the signaling mechanisms involved in integrating organ function. Finally, we draw attention to some of the cardinal discoveries made with these disease models and how these could spur new research questions in vertebrate systems.KEY WORDS: Metabolic homeostasis, Nutrient sensing, Drosophila     

Secretion of organic acids and bases by the kidneys of marine teleosts

In the experiments performed on kidneys of 5 species of marine Teleostei, morphological peculiarities in secretion of 8 fluorescent organic acids (uranin, primulin, tripaphlavin, erythrosin etc.) and in 5 organic bases (rhodamin C, auramin etc.) have been studied. At a very low concentration in the incubation medium--about 0.005 mg/ml--the substances mentioned penetrate into the epithelial cell of the canaliculus; its weak fluorescence appears, and soon they begin to be excreted in great amount through the apical part of the plasmolemma and accumulated in the canalicular lumen. All the substances studied accumulate in the cell and only some of them (uranin, primulin, titanic yellow, etc.) are secreted into the canalicular lumen. Penicillinum and probenecide inhibit penetration of the organic acids into the cell through the basal membrane. Uranin secretion into the canalicular lumen is inhibited in the presence of furocemid; amilorid, magnium and sulfate ions do not influence secretion of the organic acids. Secretion of the organic bases does not change when paraaminohippuric acid and furocemid are added to the medium, but it decreases when concentration of magnium ions increases.