Relation between growth rate and metabolic organization of white muscle, liver and digestive tract in cod, Gadus morhua

109

SUMMARY Adjustments in mitochondrial properties and capacities are crucial in acclimatization to seasonal cold as well as in evolutionary cold adaptation of marine ectotherms. To examine whether gene expression mechanisms contribute to different settings of aerobic capacities in populations of cod (Gadus morhua) along a latitudinal cline, maximum activities of key enzymes of mitochondrial metabolism and their respective mRNA levels were compared in white muscle and liver of cold (4°C) and warm (10°C) acclimated individuals from cod populations of the North Sea and the Barents Sea,respectively. In white muscle, cold acclimation caused a parallel increase in citrate synthase (CS) and in cytochrome c oxidase (COX) activities,but with a much larger effect in the cold eurythermal Arctic population. In liver, cold acclimation was accompanied by increments in CS activities, but differences between populations were minor. Overall COX activities in liver were not affected by cold acclimation, but were higher in the cold adapted population. In both populations increments in muscle CS capacities were tightly correlated with elevated mRNA levels, suggesting transcriptional control of citrate synthase levels in muscle. In liver, CS mRNA levels differed between populations but were not affected by cold acclimation, so that post-transcriptional control may contribute to elevated functional levels in this tissue. Mitochondrial-encoded COX2 mRNA levels were not limiting for functional activities in both tissues, in favour of post-transcriptional control or limitations by other transcripts of the COX complex. Altogether,the differentiation in gene expression between both populations was more strongly expressed at 4°C. The comparison of functional levels and transcript levels may reflect genetic differentiation at functional sites, in line with genetic differences between the two populations previously established by non-coding genetic markers.

Section: Discussionsupporting

confidence: 89%

“…Liver size and composition vary with growth rate, temperature and season in cod (Holdway and Beamish, 1984;Pelletier et al, 1994) and liver is used for lipid storage, especially in gadoids. In the present study, hepatosomatic indices increased with cold acclimation in .…”

Section: Discussionmentioning

confidence: 99%

Mitochondrial mechanisms of cold adaptation in cod (Gadus morhuaL.) populations from different climatic zones

Lucassen

Koschnick

Eckerle

et al. 2006

109

“…A decrease in mitochondrial coupling (i.e. lower RCR) within the intestine could have contributed to the low food intake, because this would have resulted in limited production of ATP for nutrient absorption, nutrient transport and protein synthesis (Pelletier et al, 1994). Since the digestive track is involved in the central regulation of food intake (Jordi et al, 2015;Lin et al, 2000), the low food intake may also reflect a more general drop in intestinal function (Eya et al, 2012), but this requires further study.…”

Section: Discussionmentioning

confidence: 99%

Inadequate food intake at high temperatures is related to depressed mitochondrial respiratory capacity

Salin

Auer

Anderson

et al. 2016

Animals, especially ectotherms, are highly sensitive to the temperature of their surrounding environment. Extremely high temperature, for example, induces a decline of average performance of conspecifics within a population, but individual heterogeneity in the ability to cope with elevating temperatures has rarely been studied. Here, we examined inter-individual variation in feeding ability and consequent growth rate of juvenile brown trout Salmo trutta acclimated to a high temperature (19°C), and investigated the relationship between these metrics of whole-animal performances and among-individual variation in mitochondrial respiration capacity. Food was provided ad libitum, yet intake varied ten-fold amongst individuals, resulting in some fish losing weight whilst others continued to grow. Almost half of the variation in food intake was related to variability in mitochondrial capacity: low intake (and hence growth failure) was associated with high leak respiration rates within liver and muscle mitochondria, and a lower coupling of muscle mitochondria. These observations, combined with the inability of fish with low food consumption to increase their intake despite ad libitum food levels, suggest a possible insufficient capacity of the mitochondria for maintaining ATP homeostasis. Individual variation in thermal performance is likely to confer variation in the upper limit of an organism's thermal niche and might affect the structure of wild populations in warming environments.

“…Most data available on cardiac tissue of teleost fish are presented as U g −1 tissue in the literature and for Table S2, our data on enzymatic activities were therefore normalized to wet tissue mass (similar patterns were found for both normalization types). Protocols for measuring enzyme activities were modified and adapted from Thibeault et al (1997) (for LDH, PDH, CS, HOAD and CIV), Bergmeyer (1983) (for CI+CIII and MDH), Pelletier et al (1994) (for AAT and PK), and from Janssen et al (2007) (for CI). In all cases, the enzymatic reactions were initiated with the addition of substrates and the blank was measured without substrates, except for PK, MDH, AAT and CI+CIII, where the reaction medium without sample was used.…”

Section: Determination Of Enzymatic Activitymentioning

confidence: 99%

Thermal sensitivity and phenotypic plasticity of cardiac mitochondrial metabolism in European perch, Perca fluviatilis

Ekström

Sandblom

Blier

et al. 2016

Cellular and mitochondrial metabolic capacity of the heart has been suggested to limit performance of fish at warm temperatures. We investigated this hypothesis by studying the effects of acute temperature increases (16, 23, 30, 32.5 and 36°C) on the thermal sensitivity of 10 key enzymes governing cardiac oxidative and glycolytic metabolism in two populations of European perch (Perca fluviatilis) field-acclimated to 15.5 and 22.5°C, as well as the effects of acclimation on cardiac lipid composition. In both populations of perch, the activity of glycolytic ( pyruvate kinase and lactate dehydrogenase) and tricarboxylic acid cycle ( pyruvate dehydrogenase and citrate synthase) enzymes increased with acute warming. However, at temperatures exceeding 30°C, a drastic thermally induced decline in citrate synthase activity was observed in the cold-and warmacclimated populations, respectively, indicating a bottleneck for producing the reducing equivalents required for oxidative phosphorylation. Yet, the increase in aspartate aminotransferase and malate dehydrogenase activities occurring in both populations at temperatures exceeding 30°C suggests that the malate-aspartate shuttle may help to maintain cardiac oxidative capacities at high temperatures. Warm acclimation resulted in a reorganization of the lipid profile, a general depression of enzymatic activity and an increased fatty acid metabolism and oxidative capacity. Although these compensatory mechanisms may help to maintain cardiac energy production at high temperatures, the activity of the electron transport system enzymes, such as complexes I and IV, declined at 36°C in both populations, indicating a thermal limit of oxidative phosphorylation capacity in the heart of European perch.