Repeatability of standard metabolic rate, active metabolic rate and aerobic scope in young brown trout during a period of moderate food availability

Abstract

SUMMARYStandard 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.

Variation in Metabolic Rate among Individuals Is Related to Tissue-Specific Differences in Mitochondrial Leak Respiration

“…Additional support for such a link is found in mammalian species, where the liver also contributes to a disproportionately large fraction of basal metabolic rate (Rolfe and Brown 1997). Our observations illustrate that an understanding of interindividual variability in SMR and MMR can be gained only through consideration of the mitochondrial properties of tissue specifically linked to particular whole-organism metabolic traits (John-Alder 1983;Garland 1984;Garland and Else 1987;Norin and Malte 2012).…”

“…We then determined the MMR of each fish by measuring its oxygen consumption in a closed respirometry system immediately following exhaustive exercise. The exhaustion protocol consisted of continuously chasing the fish against a circular current (Norin and Malte 2012), with fish being defined as exhausted when they could no longer swim, were unresponsive, and did not resist being picked up by hand. Both metabolic measurements were found to be repeatable when the same group of fish as used in this experiment were maintained on a stable food regime (repeatability of SMR: r p 0.78, n p 38, P !…”

“…However, while a positive correlation between minimum and maximum metabolic rates at the intraspecific level has indeed been found in some contexts Biro and Stamps 2010;Careau et al 2014aCareau et al , 2014b, this is not the case in others (Chappell et al 2004(Chappell et al , 2007Gomes et al 2004;Careau et al 2014b). The mechanisms underlying this purported link are also equivocal, with some studies reporting a positive relationship between metabolic rates and underlying traits such as organ size (Konarzewski and Ksiazek 2013) or mitochondrial density (Norin and Malte 2012), whereas others find no relationship (Selman et al 2001;Chappell et al 2007;Larsen et al 2011;Norin and Malte 2012;Boldsen et al 2013). This makes it impossible to explain mechanisms behind variation in AS, since it could be a consequence of variation in minimum and maximum metabolic rates that is either concomitant and connected or independent and separated.…”

“…Previous studies examining the relationship between different mitochondrial properties and rates of whole-body metabolism have typically focused on a single tissue (Brookes et al 1998;Chung et al 2011;Larsen et al 2011;Coen et al 2012;Jacobs et al 2012;Schlagowski et al 2013; but see Norin and Malte 2012). However, the link between mitochondrial properties and metabolic traits may be tissue specific for two main reasons (Amara et al 2007;Trzcionka et al 2008;Brown et al 2012).…”

“…Alternatively, (iii) if metabolic traits are not correlated, we predict that tissues and/or mitochondrial properties differ in how they influence SMR and MMR. We chose brown trout as our study organism because they are known to exhibit consistent differences in SMR and MMR among individuals of the same age maintained under standardized conditions (Norin and Malte 2011;Auer et al 2015b). We analyzed mitochondrial properties in the liver and the white muscle, as these tissues account for a large proportion of an individual's overall metabolic rate by virtue of their mass-specific oxygen consumption and relative mass, respectively (Porter and Brand 1995;Coen et al 2012).…”