In situ cardiac performance of Atlantic cod (Gadus morhua) at cold temperatures: long-term acclimation, acute thermal challenge and the role of adrenaline

The resting and maximum in situ cardiac performance of Newfoundland Atlantic cod (Gadus morhua) acclimated to 10, 4 and 0°C were measured at their respective acclimation temperatures, and when acutely exposed to temperature changes: i.e. hearts from 10°C fish cooled to 4°C, and hearts from 4°C fish measured at 10 and 0°C. Intrinsic heart rate (f(H)) decreased from 41 beats min(-1) at 10°C to 33 beats min(-1) at 4°C and 25 beats min(-1) at 0°C. However, this degree of thermal dependency was not reflected in maximal cardiac output (Q(max) values were ~44, ~37 and ~34 ml min(-1) kg(-1) at 10, 4 and 0°C, respectively). Further, cardiac scope showed a slight positive compensation between 4 and 0°C (Q(10)=1.7), and full, if not a slight over compensation between 10 and 4°C (Q(10)=0.9). The maximal performance of hearts exposed to an acute decrease in temperature (i.e. from 10 to 4°C and 4 to 0°C) was comparable to that measured for hearts from 4°C- and 0°C-acclimated fish, respectively. In contrast, 4°C-acclimated hearts significantly out-performed 10°C-acclimated hearts when tested at a common temperature of 10°C (in terms of both Q(max) and power output). Only minimal differences in cardiac function were seen between hearts stimulated with basal (5 nmol l(-1)) versus maximal (200 nmol l(-1)) levels of adrenaline, the effects of which were not temperature dependent. These results: (1) show that maximum performance of the isolated cod heart is not compromised by exposure to cold temperatures; and (2) support data from other studies, which show that, in contrast to salmonids, cod cardiac performance/myocardial contractility is not dependent upon humoral adrenergic stimulation.

Thermal acclimation to 4 or 10 degrees C imparts minimal benefit on swimming performance in Atlantic cod (Gadus morhua L.).

Thermal acclimation is frequently cited as a means by which ectothermic animals improve their Darwinian fitness, i.e. the beneficial acclimation hypothesis. As the critical swimming speed (U (crit)) test is often used as a proxy measure of fitness, we acclimated Atlantic cod (Gadus morhua) to 4 and 10 degrees C and then assessed their U (crit) swimming performance at their respective acclimation temperatures and during acute temperature reversal. Because phenotypic differences exist between different populations of cod, we undertook these experiments in two different populations, North Sea cod and North East Arctic cod. Acclimation to 4 or 10 degrees C had a minimal effect on swimming performance or U (crit), however test temperature did, with all groups having a 10-17% higher U (crit) at 10 degrees C. The swimming efficiency was significantly lower in all groups at 4 degrees C arguably due to the compression of the muscle fibre recruitment order. This also led to a reduction in the duration of "kick and glide" swimming at 4 degrees C. No significant differences were seen between the two populations in any of the measured parameters, due possibly to the extended acclimation period. Our data indicate that acclimation imparts little benefit on U (crit) swimming test in Atlantic cod. Further efforts need to identify the functional consequences of the long-term thermal acclimation process.

Molecular characterisation and expression of Atlantic cod (Gadus morhua) myoglobin from two populations held at two different acclimation temperatures.

Much previous research has demonstrated the plasticity of myoglobin concentrations in both cardiac and skeletal myocytes in response to hypoxia and training. No study has yet looked at the effect of thermal acclimation on myoglobin in fish. Atlantic cod (Gadus morhua) from two different populations, i.e. the North Sea and the North East Arctic, were acclimated to 10 and 4 degrees C. Both the myoglobin mRNA and myoglobin protein in cod hearts increased significantly by up to 3.7 and 2.3 fold respectively as a result of acclimation to 4 degrees C. These increments were largest in the Arctic population, which in earlier studies have been shown to possess cold compensated metabolic demands at low temperatures. These metabolic demands associated with higher mitochondrial capacities may have driven the increase in cardiac myoglobin concentrations, in order to support diffusive oxygen supply. At the same time the increase in myoglobin levels may serve further functions during cold acclimation, for example, protection of the cell against reactive oxygen species, and scavenging nitric oxide, thereby contributing to the regulation of mitochondrial volume density.

Thermal plasticity of mitochondria: a latitudinal comparison between Southern Ocean molluscs

Mitochondrial volume density (Vv((mt,f))), cristae surface density (Sv((im,mt))), cristae surface area (Sv((im,f))) and citrate synthase (CS) activity were analysed as indicators of thermal acclimation in foot muscle of the limpet, Nacella concinna, and the clam, Laternula elliptica, collected from 4 locations within the Southern Ocean, South Georgia (54 degrees S, N. concinna only), Signy (60 degrees S), Jubany (L. elliptica only -62 degrees S) and Rothera (67 degrees S). Animals were acclimated to 0.0 degrees C whilst a sub-set of N. concinna (South Georgia, Signy and Rothera) and L. elliptica (Rothera) were acclimated to 3.0 degrees C. At 0.0 degrees C N. concinna had higher Vv((mt,f)), Sv((im,mt)), Sv((im,f)) and muscle fibre specific CS activity than L. elliptica which correlated with the more active life style of N. concinna. However, mitochondrial density was very low, 1-2% in both species, suggesting that low temperature compensation of mitochondrial density is not a universal evolutionary response of Antarctic marine ectotherms. Both Sv((im,mt)) and Sv((im,f)) were reduced by warm acclimation of N. concinna. South Georgia N. concinna maintained muscle fibre specific CS activity after acclimation, in contrast to N. concinna from Rothera and Signy and L. elliptica from Rothera, indicating that they have the physiological plasticity to respond to their warmer, more variable thermal environment.

Health of farmed fish: its relation to fish welfare and its utility as welfare indicator

This brief review focuses on health and biological function as cornerstones of fish welfare. From the function-based point of view, good welfare is reflected in the ability of the animal to cope with infectious and non-infectious stressors, thereby maintaining homeostasis and good health, whereas stressful husbandry conditions and protracted suffering will lead to the loss of the coping ability and, thus, to impaired health. In the first part of the review, the physiological processes through which stressful husbandry conditions modulate health of farmed fish are examined. If fish are subjected to unfavourable husbandry conditions, the resulting disruption of internal homeostasis necessitates energy-demanding physiological adjustments (allostasis/acclimation). The ensuing energy drain leads to trade-offs with other energy-demanding processes such as the functioning of the primary epithelial barriers (gut, skin, gills) and the immune system. Understanding of the relation between husbandry conditions, allostatic responses and fish health provides the basis for the second theme developed in this review, the potential use of biological function and health parameters as operational welfare indicators (OWIs). Advantages of function- and health-related parameters are that they are relatively straightforward to recognize and to measure and are routinely monitored in most aquaculture units, thereby providing feasible tools to assess fish welfare under practical farming conditions. As the efforts to improve fish welfare and environmental sustainability lead to increasingly diverse solutions, in particular integrated production, it is imperative that we have objective OWIs to compare with other production forms, such as high-density aquaculture. However, to receive the necessary acceptance for legislation, more robust scientific backing of the health- and function-related OWIs is urgently needed.

Climate change and infectious diseases of wildlife: Altered interactions between pathogens, vectors and hosts

Infectious diseases result from the interactions of host, pathogens, and, in the case of vector-borne diseases, also vectors. The interactions involve physiological and ecological mechanisms and they have evolved under a given set of environmental conditions. Environmental change, therefore, will alter host-pathogen-vector interactions and, consequently, the distribution, intensity, and dynamics of infectious diseases. Here, we review how climate change may impact infectious diseases of aquatic and terrestrial wildlife. Climate change can have direct impacts on distribution, life cycle, and physiological status of hosts, pathogens and vectors. While a change in either host, pathogen or vector does not necessarily translate into an alteration of the disease, it is the impact of climate change on the interactions between the disease components which is particularly critical for altered disease risks. Finally, climate factors can modulate disease through modifying the ecological networks host-pathogen-vector systems are belonging to, and climate change can combine with other environmental stressors to induce cumulative effects on infectious diseases. Overall, the influence of climate change on infectious diseases involves different mechanisms, it can be modulated by phenotypic acclimation and/or genotypic adaptation, it depends on the ecological context of the host-pathogen-vector interactions, and it can be modulated by impacts of other stressors. As a consequence of this complexity, non-linear responses of disease systems under climate change are to be expected. To improve predictions on climate change impacts on infectious disease, we suggest that more emphasis should be given to the integration of biomedical and ecological research for studying both the physiological and ecological mechanisms which mediate climate change impacts on disease, and to the development of harmonized methods and approaches to obtain more comparable results, as this would support the discrimination of case-specific versus general mechanisms

Seasonal changes in the behaviour and respiration physiology of the freshwater duck mussel, Anodonta anatina.

For low-energy organisms such as bivalves, the costs of thermal compensation of biological rates (synonymous with acclimation or acclimatization) may be higher than the benefits. We therefore conducted two experiments to examine the effect of seasonal temperature changes on behaviour and oxygen consumption. In the first experiment, we examined the effects of seasonal temperature changes on the freshwater bivalve Anodonta anatina, taking measurements each month for a year at the corresponding temperature for that time of year. There was no evidence for compensation of burrowing valve closure duration or frequency, or locomotory speed. In the second experiment, we compared A. anatina at summer and winter temperatures (24 and 4°C, respectively) and found no evidence for compensation of the burrowing rate, valve closure duration or frequency, or oxygen consumption rates during burrowing, immediately after valve closure or at rest. Within the experimental limits of this study, the evidence suggests that thermal compensation of biological rates is not a strategy employed by A. anatina. We argue that this is due to either a lack of evolutionary pressure to acclimatize, or evolutionary pressure to not acclimatize. Firstly, there is little incentive to increase metabolic rate to enhance predatory ability given that these are filter feeders. Secondly, maintained low energetic demand, enhanced at winter temperatures, is essential for predator avoidance, i.e. valve closure. Thus, we suggest that the costs of acclimatization outweigh the benefits in A. anatina.

Dehydrin expression as a potential diagnostic tool for cold stress in white clover

Cold acclimation is important for crop survival in environments undergoing seasonal low temperatures. It involves the induction of defensive mechanisms including the accumulation of different cryoprotective molecules among which are dehydrins (DHN). Recently several sequences coding for dehydrins were identified in white clover (Trifolium repens). This work aimed to select the most responsive to cold stress DHN analogues in search for cold stress diagnostic markers. The assessment of dehydrin transcript accumulation via RT-PCR and immunodetection performed with three antibodies against the conserved K-, Y-, and S-segment allowed to outline different dehydrin types presented in the tested samples. Both analyses confirmed that YnKn dehydrins were underrepresented in the controls but exposure to low temperature specifically induced their accumulation. Strong immunosignals corresponding to 37–40 kDa with antibodies against Y- and K-segment were revealed in cold-stressed leaves. Another ‘cold-specific’ band at position 52–55 kDa was documented on membranes probed with antibodies against K-segment. Real time RT-qPCR confirmed that low temperatures induced the accumulation of SKn and YnSKn transcripts in leaves and reduced their expression in roots. Results suggest that a YnKn dehydrin transcript with GenBank ID: KC247805 and the immunosignal at 37–40 kDa, obtained with antibodies against Y- and K-segment are reliable markers for cold stress in white clover. The assessment of SKn (GenBank ID: EU846208) and YnSKn (GenBank ID: KC247804) transcript levels in leaves could serve as additional diagnostic tools.

Growth at moderately elevated temperature alters the physiological response of the photosynthetic apparatus to heat stress in pea (Pisum sativum L.) leaves

The impact of heat stress on the functioning of the photosynthetic apparatus was examined in pea (Pisum sativum L.) plants grown at control (25 °C; 25 °C-plants) or moderately elevated temperature (35 °C; 35 °C-plants). In both types of plants net photosynthesis (Pn) decreased with increasing leaf temperature (LT) and was more than 80% reduced at 45 °C as compared to 25 °C. In the 25 °C-plants, LTs higher than 40 °C could result in a complete suppression of Pn. Short-term acclimation to heat stress did not alter the temperature response of Pn. Chlorophyll a fluorescence measurements revealed that photosynthetic electron transport (PET) started to decrease when LT increased above 35 °C and that growth at 35 °C improved the thermal stability of the thylakoid membranes. In the 25 °C-plants, but not in the 35 °C-plants, the maximum quantum yield of the photosystem II primary photochemistry, as judged by measuring the Fv/Fm ratio, decreased significantly at LTs higher than 38 °C. A post-illumination heat-induced reduction of the plastoquinone pool was observed in the 25 °C-plants, but not in the 35 °C-plants. Inhibition of Pn by heat stress correlated with a reduction of the activation state of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Western-blot analysis of Rubisco activase showed that heat stress resulted in a redistribution of activase polypeptides from the soluble to the insoluble fraction of extracts. Heat-dependent inhibition of Pn and PET could be reduced by increasing the intercellular CO2 concentration, but much more effectively so in the 35 °C-plants than in the 25 °C-plants. The 35 °C-plants recovered more efficiently from heat-dependent inhibition of Pn than the 25 °C-plants. The results show that growth at moderately high temperature hardly diminished inhibition of Pn by heat stress that originated from a reversible heat-dependent reduction of the Rubisco activation state. However, by improving the thermal stability of the thylakoid membranes it allowed the photosynthetic apparatus to preserve its functional potential at high LTs, thus minimizing the after-effects of heat stress.

Life-long growth of Quercus ilex L. at natural CO2 springs acclimates sulphur, nitrogen and carbohydrate metabolism of the progeny to elevated pCO2

The aim of the present study was to analyse whether offspring of mature Quercus ilex trees grown under life-long elevated pCO2 show alterations in the physiological response to elevated pCO2 in comparison with those originating from mature trees grown at current ambient pCO2. To investigate changes in C- (for changes in photosynthesis, biomass and lignin see Polle, McKee & Blaschke Plant, Cell and Environment 24, 1075–1083, 2001), N-, and S-metabolism soluble sugar, soluble non-proteinogenic nitrogen compounds (TSNN), nitrate reductase (NR), thiols, adenosine 5′-phosphosulphate (APS) reductase, and anions were analysed. For this purpose Q. ilex seedlings were grown from acorns of mother tree stands at a natural spring site (elevated pCO2) and a control site (ambient pCO2) of the Laiatico spring, Central Italy. Short-term elevated pCO2 exposure of the offspring of control oaks lead to higher sugar contents in stem tissues, to a reduced TSNN content in leaves, and basipetal stem tissues, to diminished thiol contents in all tissues analysed, and to reduced APS reductase activity in both, leaves and roots. Most of the components of C-, N- and S-metabolism including APS reductase activity which were reduced due to short-term elevated pCO2 exposure were recovered by life-long growth under elevated pCO2 in the offspring of spring oaks. Still TSNN contents in phloem exudates increased, nitrate contents in lateral roots and glutathione in leaves and phloem exudates remained reduced in these plants. The present results demonstrated that metabolic adaptations of Q. ilex mother trees to elevated pCO2 can be passed to the next generation. Short- and long-term effects on source-to-sink relation and physiological and genetic acclimation to elevated pCO2 are discussed.