The relationship between growth performance and metabolic rate flexibility varies with food availability in juvenile qingbo (Spinibarbus sinensis)

Combining mesocosms with models reveals effects of global warming and ocean acidification on a temperate marine ecosystem

Ocean warming and species exploitation have already caused large-scale reorganization of biological communities across the world. Accurate projections of future biodiversity change require a comprehensive understanding of how entire communities respond to global change. We combined a time-dynamic integrated food web modeling approach (Ecosim) with previous data from community-level mesocosm experiments to determine the independent and combined effects of ocean warming, ocean acidification and fisheries exploitation on a well-managed temperate coastal ecosystem. The mesocosm parameters enabled important physiological and behavioral responses to climate stressors to be projected for trophic levels ranging from primary producers to top predators, including sharks. Through model simulations, we show that under sustainable rates of fisheries exploitation, near-future warming or ocean acidification in isolation could benefit species biomass at higher trophic levels (e.g., mammals, birds, and demersal finfish) in their current climate ranges, with the exception of small pelagic fishes. However, under warming and acidification combined, biomass increases at higher trophic levels will be lower or absent, while in the longer term reduced productivity of prey species is unlikely to support the increased biomass at the top of the food web. We also show that increases in exploitation will suppress any positive effects of human-driven climate change, causing individual species biomass to decrease at higher trophic levels. Nevertheless, total future potential biomass of some fisheries species in temperate areas might remain high, particularly under acidification, because unharvested opportunistic species will likely benefit from decreased competition and show an increase in biomass. Ecological indicators of species composition such as the Shannon diversity index decline under all climate change scenarios, suggesting a trade-off between biomass gain and functional diversity. By coupling parameters from multilevel mesocosm food web experiments with dynamic food web models, we were able to simulate the generative mechanisms that drive complex responses of temperate marine ecosystems to global change. This approach, which blends theory with experimental data, provides new prospects for forecasting climate-driven biodiversity change and its effects on ecosystem processes.

Transcriptome analysis of the muscle of fast- and slow-growing phoenix barb (Spinibarbus denticulatus denticulatus)

Growth rate is a commercial trait in aquaculture that is influenced by multiple factors, among which genetic composition plays a fundamental role in the growth rate of species. The phoenix barb (Spinibarbus denticulatus denticulatus) is a widely distributed freshwater fish species in South China. Although S. d. denticulatus is reared in South China, the molecular mechanisms underlying the growth rate of the species remain unclear. Here, the authors performed transcriptome analysis of muscle tissues from fast-growing (FG) and slow-growing (SG) S. d. denticulatus at 90, 150, and 300 days after hatch (DAH) to elucidate its growth mechanism. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that differentially expressed genes (DEGs) between the two groups were enriched in pathways related to muscle growth, glycolysis, and energy and lipid metabolism. Nonetheless, a higher number of DEGs were identified in the FG vs. SG groups at 90 and 300 DAH compared with 150 DAH. DEGs identified at 90 DAH were mainly enriched in the GH/IGF axis, PI3K-Akt signalling pathway, AMPK signalling pathway and lipid metabolism highly expressed in FG individuals. DEGs identified at 300 DAH were mainly enriched in PI3K-Akt signalling pathway, glycolysis/gluconeogenesis, gene translation and lipid metabolism. In addition, some genes were expressed during the early growth stage in FG individuals but expressed during the late stage in SG individuals, indicating considerable variations in the expression profiles of growth-related genes at different developmental stages. Overall, these findings contribute to the understanding of the growth mechanism of S. d. denticulatus, which would be useful for the propagation of fast-growing breeds.

Social isolation does not alter the relationship between flexibility in metabolic rate and growth in grass carp (Ctenopharyngodon idella) under changing food availability

Growth and energy metabolism are highly flexible in fish species in response to food availability, and these two traits depend to some extent on the social rearing environment (e.g., isolated vs. group rearing). Currently, how social rearing environments influence flexibility in metabolic rate of fish and their ecological consequences (e.g., somatic growth) remain largely unknown. Here, we investigated how social isolation (i.e., group-reared vs. isolation-reared) and food availability (i.e., high vs. low) affect metabolic rates, growth and their correlations in a group-living fish, grass carp (Ctenopharyngodon idella), which were subjected to a 4-week growth experiment. The metabolic rates (e.g., standard metabolic rate, SMR; maximum metabolic rate, MMR; aerobic scope, AS = MMR-SMR) and morphology (e.g., body mass and length) of the fish in four treatments were measured at the beginning and end of the growth experiment, and then the growth parameters (e.g., food intake, FI; feeding efficiency, FE; and specific growth rate, SGR) were also obtained. We found that social isolation did impair growth of fish with individuals showing a lower SGR compared to those group-reared fish irrespective of food availability. However, the growth advantage of group-reared fish under two food availabilities did not result from their FIs or FEs. Metabolic rates (i.e., SMR) seemed to decrease in response to social isolation, but increased greater when fish were reared at high food ration. These shifts in metabolic rates were positively linked with individual differences in somatic growth; individuals who increased metabolic rates more grew faster, while those who increased their metabolic rates less or even reduced had a lower growth, but these links were independent on both social isolation and food ration. These results suggested that social isolation can inhibit the growth of individual fish, but not the AS. Flexibility in metabolic rates could confer a growth advantage under changing food availability, but the links between variation in energy metabolism and growth were not altered by social deprivation. Our study demonstrates the importance of metabolic plasticity accounting for inter-individual difference in growth performance under the challenges of changing food resource.

Meta-analysis reveals variance in tolerance to climate change across marine trophic levels

Marine ecosystems are currently facing a variety of anthropogenic perturbations, including climate change. Trophic differences in response to climate change may disrupt ecological interactions and thereby threaten marine ecosystem function. Yet, we still do not have a comprehensive understanding of how different trophic levels respond to climate change stressors in marine ecosystems. By including 1278 experiments, comprising 236 different marine species from 18 different phyla in a meta-analysis of studies measuring the direct effect of ocean acidification and ocean warming on marine organisms, we found that higher trophic level species display greater tolerance to ocean acidification but greater sensitivity to warming. In contrast, marine herbivores were the most vulnerable trophic level to both acidification and warming. Such imbalances in the community and a general reduction of biodiversity and biomass in lower trophic levels can significantly disrupt the system and could drive negative bottom-up effects. In conclusion, with ocean acidification and elevated temperatures, there is an alarming risk that trophic disparity may disrupt species interactions, and thereby drive community destabilization under ocean climate change.

The time course of metabolic plasticity and its consequences for growth performance under variable food supply in the northern pike

Many species up- or downregulate their resting metabolic rate (RMR) when they encounter favourable or unfavourable feeding conditions, respectively. This is thought to promote faster growth when food is abundant and conserve energy reserves when food is scarce. The time it takes to express metabolic plasticity remain little studied. Here, we develop a conceptual model showing how rapid or slow metabolic plasticity alter growth trajectories in response to changes in food supply. We test predictions from the model in a food manipulation experiment with young-of-the-year northern pike, Esox lucius, a species that experience drastic changes in food supply in nature. We find that metabolic plasticity is expressed gradually over several weeks in this species. Rapid changes in food supply thus caused apparent trait-environment mismatches that persisted for at least five weeks. Contrary to predictions, pike grew faster at high food levels when they had previously experienced low food levels and downregulated their RMR. This was not owing to increases in food intake but probably reflected that low RMRs increased the energetic scope for growth when feeding conditions improved. This highlights the important but complex effects of metabolic plasticity on growth dynamics under variable resource levels on ecologically relevant time scales.

Metabolic phenotype mediates the outcome of competitive interactions in a response-surface field experiment

Competition and metabolism should be linked. Intraspecific variation in metabolic rates and, hence, resource demands covary with competitive ability. The effects of metabolism on conspecific interactions, however, have mostly been studied under laboratory conditions. We used a trait-specific response-surface design to test for the effects of metabolism on pairwise interactions of the marine colonial invertebrate, Bugula neritina in the field. Specifically, we compared the performance (survival, growth, and reproduction) of focal individuals, both in the presence and absence of a neighbor colony, both of which had their metabolic phenotype characterized. Survival of focal colonies depended on the metabolic phenotype of the neighboring individual, and on the combination of both the focal and neighbor colony metabolic phenotypes that were present. Surprisingly, we found pervasive effects of neighbor metabolic phenotypes on focal colony growth and reproduction, although the sign and strength of these effects showed strong microenvironmental variability. Overall, we find that the metabolic phenotype changes the strength of competitive interactions, but these effects are highly contingent on local conditions. We suggest future studies explore how variation in metabolic rate affects organisms beyond the focal organism alone, particularly under field conditions.

Meta-analysis reveals that resting metabolic rate is not consistently related to fitness and performance in animals

Explaining variation in the fitness of organisms is a fundamental goal in evolutionary ecology. Maintenance energy metabolism is the minimum energy required to sustain biological processes at rest (resting metabolic rate: RMR) and is proposed to drive or constrain fitness of animals; however, this remains debated. Hypotheses have been proposed as to why fitness might increase with RMR (the 'increased intake' or 'performance' hypothesis), decrease with RMR (the 'compensation' or 'allocation' hypothesis), or vary among species and environmental contexts (the 'context dependent' hypothesis). Here, we conduct a systematic review and meta-analysis of the literature, finding 114 studies with 355 relationships between RMR and traits that may be related to fitness. We show that individuals with relatively high RMR generally have high fitness overall, which might be supported by an increased energy intake. However, fitness proxies are not interchangeable: the nature of the RMR-fitness relationship varied substantially depending on the specific trait in question, and we found no consistent relationship between RMR and those traits most closely linked with actual fitness (i.e., lifetime reproductive success). We hypothesise that maintaining high RMR is not costly when resources are unlimited, and we propose ideas for future studies to identify mechanisms underlying RMR-fitness relationships.

Energetic mechanisms for coping with changes in resource availability

Given current anthropogenic alterations to many ecosystems and communities, it is becoming increasingly important to consider whether and how organisms can cope with changing resources. Metabolic rate, because it represents the rate of energy expenditure, may play a key role in mediating the link between resource conditions and performance and thereby how well organisms can persist in the face of environmental change. Here, we focus on the role that energy metabolism plays in determining organismal responses to changes in food availability over both short-term ecological and longer-term evolutionary timescales. Using a meta-analytical approach encompassing multiple species, we find that individuals with a higher metabolic rate grow faster under high food levels but slower once food levels decline, suggesting that the association between metabolism and life-history traits shifts along resource gradients. We also find that organisms can cope with changing resource availability through both phenotypic plasticity and genetically based evolutionary adaptation in their rates of energy metabolism. However, the metabolic rates of individuals within a population and of species within a lineage do not all respond in the same manner to changes in food availability. This diversity of responses suggests that there are benefits but also costs to changes in metabolic rate. It also underscores the need to examine not just the energy budgets of organisms within the context of metabolic rate but also how energy metabolism changes alongside other physiological and behavioural traits in variable environments.

Ecological and evolutionary consequences of metabolic rate plasticity in response to environmental change

Basal or standard metabolic rate reflects the minimum amount of energy required to maintain body processes, while the maximum metabolic rate sets the ceiling for aerobic work. There is typically up to three-fold intraspecific variation in both minimal and maximal rates of metabolism, even after controlling for size, sex and age; these differences are consistent over time within a given context, but both minimal and maximal metabolic rates are plastic and can vary in response to changing environments. Here we explore the causes of intraspecific and phenotypic variation at the organ, tissue and mitochondrial levels. We highlight the growing evidence that individuals differ predictably in the flexibility of their metabolic rates and in the extent to which they can suppress minimal metabolism when food is limiting but increase the capacity for aerobic metabolism when a high work rate is beneficial. It is unclear why this intraspecific variation in metabolic flexibility persists-possibly because of trade-offs with the flexibility of other traits-but it has consequences for the ability of populations to respond to a changing world. It is clear that metabolic rates are targets of selection, but more research is needed on the fitness consequences of rates of metabolism and their plasticity at different life stages, especially in natural conditions. This article is part of the theme issue 'The role of plasticity in phenotypic adaptation to rapid environmental change'.

Feasibility of cultivation of Spinibarbus sinensis with coconut oil and its effect on disease resistance (nonspecific immunity, antioxidation and mTOR and NF-kB signaling pathways)

Application of traditional bait in aquaculture caused environment pollution and disease frequent occurrence. Residual coconut could be re-utilized to culture Spinibarbus sinensis as dietary supplement. Therefore, a novel integrated system of the improvement of yield, antioxidant and nonspecific immunity of Spinibarbus sinensis by dietary residual coconut was proposed and investigated. Spinibarbus sinensis could grow well in all supplement residual coconut groups. Survival rate, yield, whole fish body composition under 15-45% groups were increased compared with control group (CK). Bioactive substances (polyphenols and vitamin) in residual coconut enhanced AKP, ACP, phagocytic, SOD, CAT activities through up-regulating AKP, ACP, SOD, CAT genes expression levels. Theoretical analysis showed bioactive substances regulated these genes expressions and enzyme activities as stimulus signal, component, active center. Moreover, residual coconut improved mTOR and NF-kB signaling pathway. Furthermore, residual coconut inhibited Aeromonas hydrophila that increased resistance to diseases. This technology completed the solid waste recovery and the Spinibarbus sinensis culture simultaneously.

Behavioral adjustments to prior predation experience and food deprivation of a common cyprinid fish species vary between singletons and a group

Fish often undergo predation stress and food shortages in nature, and living in groups may provide the ecological benefits of decreased predator risk but the costs of increased food competition. The main aim of the present study was to test whether the behavioral response of qingbo (Spinibarbus sinensis) to predators and/or starvation differed between a singleton and a group. We measured the locomotor activity and distance to a predator and/or food item of prior predator-experienced, starved, double-treated and control qingbo; the qingbo were tested both as singletons and in a group (five individuals). Fish from all groups showed increased activity when tested collectively compared to individually. The predator-experienced fish showed decreased locomotor activity to predators as an antipredator strategy when tested as singletons; however, increased locomotor activity occurred when tested in a group, which might be partially due to the decreased predator risk when living in a group and thus higher levels of boldness. As expected, starvation elicited increased activity indicating increased foraging willingness when tested in a group; however, the difference between starved and normal-fed fish was no longer significant when they were tested as singletons, possibly due to the increased predation risk and decreased food competition when living individually and higher behavioral variation among individual fish than among those in a shoal. Compared with the control fish, the double-treated fish showed no difference in activity when tested both individually and collectively (except a slower speed when tested in a group). The reason for the results from the singletons might be an offset of the effect of predator exposure and starvation. The reason for this difference in the group might be due to the impaired body condition indicated by a slower swimming speed as a consequence of severe stress. The present study demonstrated that behavioral adjustment was closely related to the size of the group, which might be due to differences in the predation risk and food competition.

Predator stress decreases standard metabolic rate and growth in juvenile crucian carp under changing food availability

Animals adapt to the challenges of fluctuations in predator risk and food availability in their natural habitats. Phenotypic plasticity allows animals to handle environmental changes. However, the patterns of flexibility in metabolic rates and its ecological consequences under different predator stress and food availability conditions are poorly understood. Here, we used crucial carp (Carassius auratus) as a prey species and northern snakehead (Channa argus) as a predator to test whether predator stress influences metabolism and growth, and alters the link between flexibility in metabolic rate and its ecological consequences (e.g., growth) in crucial carp. The experiment was carried out under the conditions of predator stress (with or without a predator) and three food availabilities (satiation feeding 1 time per day, low food availability; 2 times per day, intermediate food availability; and 3 times per day, high food availability) for 3 weeks. After 21 days of feeding, the final body mass and body length in the two treatments increased compared to the initial values in all three food availabilities. The feeding intake (FI) and specific growth rate (SGR) of the two treatments increased with increasing food availability. The control treatment had a higher FI and SGR than the predator stress treatment in all three food availabilities. The feeding efficiency (FE) of the two treatments was higher at the high and intermediate food availabilities than at the low food availability. However, no effect of predator stress on FE was detected. The final values of original or standardized SMR were higher in the control treatment than the predator stress treatment at the intermediate and high food availabilities. The changes in SMR (ΔSMR) were higher in the control treatment than in the predator stress treatment. The positive correlation between the ΔSMR and SGR was found in the intermediate food availability in the predator stress treatment, suggesting that individuals with a higher flexibility in SMR had a larger growth rate and vice versa, but this relationship was dependent on food availability. Our results suggest that predator stress decreased maintenance metabolism, feeding and growth of juvenile crucial carp irrespective of food availability. Predator stress does not alter the growth advantages conferred by the metabolic plasticity of the fish under changing food availability.

The effects of temperature and food availability on growth, flexibility in metabolic rates and their relationships in juvenile common carp

Flexibility in phenotypic traits can allow organisms to handle environmental changes. However, the ecological consequences of flexibility in metabolic rates are poorly understood. Here, we investigated whether the links between growth and flexibility in metabolic rates vary between two temperatures. Common carp Cyprinus carpio were raised in three temperature treatments [the 18°C, 28°C and 28°C-food control (28°C-FC)] and fed to satiation of receiving food either once or twice daily for 4weeks. The morphology and metabolic rates (standard metabolic rate, SMR; maximum metabolic rate, MMR) were measured at the beginning and end of the experiment. The mean total food ingested by fish in the 28°C-FC treatment was the same as that by fish in the 18°C treatment at each food availability. The final SMR (not MMR and aerobic scope, AS=MMR-SMR) increased more in the 28°C and 28°C-FC treatments with twice-daily feedings than once-daily feedings. Fish in the 28°C treatment had a higher specific growth rate (SGR) than fish in the 28°C-FC and 18°C treatments at both food availabilities. However, no differences in feeding efficiency (FE) were found among the three treatments in fish fed twice daily. The flexibility in SMR was related to individual differences in SGR, not with food intake and FE; individuals who increased their SMR more had a smaller growth performance with twice-daily feedings at 28°C, but it did not exist at 18°C. Flexibility in SMR provides a growth advantage in juvenile common carp experiencing changes in food availability and this link is temperature-dependent.

Does aerobic capacity predict the spatial position of individuals within schools in juvenile qingbo (Spinibarbus sinensis)?

Schooling behavior is an adaptive trait of important biological and ecological significance in fish species. However, the question of how aerobic capacity and environmental factors (i.e., food and water velocity) affect the spatial positioning within fish schools has received little attention. Our study measured the aerobic capacity-as indicated by standard metabolic rate (SMR), maximum metabolic rate (MMR) and aerobic scope (AS)-and swimming performance of juvenile qingbo (Spinibarbus sinensis) and filmed their schooling behavior in a swim tunnel under both a control treatment and food stimulus treatment at three water velocities (20, 30 and 40cms^-1). Neither aerobic capacity nor swimming performance was related to spatial position within schools. Food stimulation did not trigger any change in the characteristics of spatial position at three water velocities. However, an intra-school positional preference was found between water velocities under the control treatment and food stimulus treatment. Individuals who preferred the rear of the school had smaller coefficients of variation in position under the two treatments, but this behavior was not correlated with any parameters for metabolic rates. Inter-school social interaction level, as indicated by total chase times, was not affected by either water velocity or food appearance. Although aerobic capacity and food stimulus did not influence the spatial position of individuals within schools, individual qingbo had spatial positional preferences within schools between different water speeds.