Repeatability of standard metabolic rate, active metabolic rate and aerobic scope in young brown trout during a period of moderate food availability.
ABSTRACT Standard metabolic rate (SMR) and active metabolic rate (AMR) are two fundamental physiological parameters providing the floor and ceiling in aerobic energy metabolism. The total amount of energy available within these two parameters confines constitutes the absolute aerobic scope (AAS). Previous studies on fish have found SMR to closely correlate with dominance and position in the social hierarchy, and to be highly repeatable over time when fish were provided an ad libitum diet. In this study we tested the temporal repeatability of individual SMR, AMR and AAS, as well as repeatability of body mass, in young brown trout (Salmo trutta L.) fed a moderately restricted diet (0.5-0.7% fish mass day⁻¹). Metabolism was estimated from measurements of oxygen consumption rate (M(.)(O₂)) and repeatability was evaluated four times across a 15-week period. Individual body mass was highly repeatable across the entire 15 week experimental period whereas residual body-mass-corrected SMR, AMR and AAS showed a gradual loss of repeatability over time. Individual residual SMR, AMR and AAS were significantly repeatable in the short term (5 weeks), gradually declined across the medium term (10 weeks) and completely disappeared in the long term (15 weeks). We suggest that this gradual decline in repeatability was due to the slightly restricted feeding regime. This is discussed in the context of phenotypic plasticity, natural selection and ecology.
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ABSTRACT: Abstract Repeatability is an important concept in evolutionary analyses because it provides information regarding the benefit of repeated measurements and, in most cases, a putative upper limit to heritability estimates. Repeatability (R) of different aspects of energy metabolism and behavior has been demonstrated in a variety of organisms over short and long time intervals. Recent research suggests that consistent individual differences in behavior and energy metabolism might covary. Here we present new data on the repeatability of body mass, standard metabolic rate (SMR), voluntary exploratory behavior, and feeding rate in a semiaquatic salamander and ask whether individual variation in behavioral traits is correlated with individual variation in metabolism on a whole-animal basis and after conditioning on body mass. All measured traits were repeatable, but the repeatability estimates ranged from very high for body mass (R = 0.98), to intermediate for SMR (R = 0.39) and food intake (R = 0.58), to low for exploratory behavior (R = 0.25). Moreover, repeatability estimates for all traits except body mass declined over time (i.e., from 3 to 9 wk), although this pattern could be a consequence of the relatively low sample size used in this study. Despite significant repeatability in all traits, we find little evidence that behaviors are correlated with SMR at the phenotypic and among-individual levels when conditioned on body mass. Specifically, the phenotypic correlations between SMR and exploratory behavior were negative in all trials but significantly so in one trial only. Salamanders in this study showed individual variation in how their exploratory behavior changed across trials (but not body mass, SMR, and feed intake), which might have contributed to observed changing correlations across trials.Physiological and Biochemical Zoology 04/2014; 87(3):384-96. · 2.46 Impact Factor
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ABSTRACT: Most animals experience temperature variations as they move through the environment. For ectotherms in particular, temperature has a strong influence on habitat choice. While well-studied at the species level, less is known about factors affecting the preferred temperature of individuals. Especially lacking is information on how physiological traits are linked to thermal preference and whether such relationships are affected by factors such feeding history and growth trajectory.This study examined these issues in the common minnow Phoxinus phoxinus, to determine the extent to which feeding history, standard metabolic rate (SMR) and aerobic scope (AS), interact to affect temperature preference.Individuals were either: 1) food-deprived for 21 days, then fed ad libitum for the next 74 days; or 2) fed ad libitum throughout the entire period. All animals were then allowed to select preferred temperatures using a shuttle-box, and then measured for SMR and AS at 10°C, estimated by rates of oxygen uptake. Activity within the shuttle-box under a constant temperature regime was also measured.In both food-deprived and control fish, SMR was negatively correlated with preferred temperature. The SMR of the food-deprived fish was elevated compared to the controls, probably due to the effects of compensatory growth, and so these growth-compensated fish preferred temperatures that were on average 2.85°C cooler than controls fed a maintenance ration throughout the study. Fish experiencing compensatory growth also displayed a large reduction in activity. In growth-compensated fish and controls, activity measured at 10°C was positively correlated with preferred temperature.Individual fish prefer temperatures that vary predictably with SMR and activity level, which are both plastic in response to feeding history and growth trajectories. Cooler temperatures probably allow individuals to reduce maintenance costs and divert more energy towards growth. A reduction in SMR at cooler temperatures, coupled with a decrease in spontaneous activity, would also allow individuals to increase surplus aerobic scope for coping with environmental stressors. In warming climates, however, aquatic ectotherms could experience frequent fluctuations in food supply with long-lasting effects on metabolic rate due to compensatory growth, while simultaneously having limited access to preferred cooler habitats.This article is protected by copyright. All rights reserved.Journal of Animal Ecology 05/2014; 83:1513-1522. · 4.84 Impact Factor
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ABSTRACT: Selenium (Se) is known to cause chronic toxicity in aquatic species. In particular, dietary exposure of fish to selenomethionine (SeMet), the primary form of Se in the diet, is of concern. Recent studies suggest that chronic exposure to elevated dietary SeMet alters energy and endocrine homeostasis in adult fish. However, little is known about the direct effects of dietary SeMet exposure in juvenile fish. The objective of the present study was to investigate sublethal physiological effects of dietary SeMet exposure in juvenile fathead minnow (Pimephales promelas). Twenty days-post-hatch fathead minnow were exposed for 60 days to different measured concentrations (2.8, 5.4, 9.9, 26.5μgSe/g dry mass [dm]) of Se in food in the form of SeMet. After exposure, samples were collected for Se analysis and fish were subjected to a swimming performance challenge to assess critical swim speed (Ucrit), tail beat frequency and tail beat amplitude, oxygen consumption (MO2), cost of transport (COT), standard metabolic rate (SMR), active metabolic rate (AMR), and factorial aerobic scope (F-AS). Ucrit was decreased in the 26.5μgSe/gdm exposure group compared to the control group. Tail beat frequency and tail beat amplitude were significantly reduced in fish fed 9.9 and 26.5μgSe/g. An increase in MO2 and COT was observed in the 9.9 and 26.5μgSe/g exposure groups compared to the control group. While the AMR of the high dose group was increased relative to control, there were no significant differences in SMR and F-AS. Energy storage capacity was measured via whole body triglyceride and glycogen concentrations. Triglyceride concentrations in non-swam fish were elevated in the 5.4μgSe/g group relative to controls. Fatigued (swam) fish had significantly lower whole body triglycerides than non-swam fish. All non-swam SeMet exposure groups had significantly decreased whole body glycogen concentrations compared to controls, while the 5.4 and 26.5μgSe/g exposure groups had significantly greater whole body glycogen concentrations in swam versus non-swam fish. A decrease in whole body cortisol was observed in swam fish in the 5.4μgSe/g exposure group compared to control fish. Whole body cortisol was greater in control, 9.9 and 26.5μgSe/g swam fish compared to non-swam fish. These results suggest that exposure to environmentally relevant concentrations of dietary SeMet impairs swimming performance, aerobic capacity, and energy homeostasis, potentially impacting survivability of juvenile fish in Se impacted aquatic ecosystems.Aquatic toxicology (Amsterdam, Netherlands) 06/2014; 155C:91-100. · 3.12 Impact Factor