Abstract
There is increasing interest in documenting and explaining the existence of marked intraspecific variation in metabolic rate in animals, with fishes providing some of the best‐studied examples. After accounting for variation due to other factors, there can typically be a two to three‐fold variation among individual fishes for both standard and maximum metabolic rate (SMR and MMR). This variation is reasonably consistent over time (provided that conditions remain stable), and its underlying causes may be influenced by both genes and developmental conditions. In this paper, current knowledge of the extent and causes of individual variation in SMR, MMR and aerobic scope (AS), collectively its metabolic phenotype, is reviewed and potential links among metabolism, behaviour and performance are described. Intraspecific variation in metabolism has been found to be related to other traits: fishes with a relatively high SMR tend to be more dominant and grow faster in high food environments, but may lose their advantage and are more prone to risk‐taking when conditions deteriorate. In contrast to the wide body of research examining links between SMR and behavioural traits, very little work has been directed towards understanding the ecological consequences of individual variation in MMR and AS. Although AS can differ among populations of the same species in response to performance demands, virtually nothing is known about the effects of AS on individual behaviours such as those associated with foraging or predator avoidance. Further, while factors such as food availability, temperature, hypoxia and the fish's social environment are known to alter resting and MMRs in fishes, there is a paucity of studies examining how these effects vary among individuals, and how this variation relates to behaviour. Given the observed links between metabolism and measures of performance, understanding the metabolic responses of individuals to changing environments will be a key area for future research because the environment will have a strong influence on which animals survive predation, become dominant and ultimately have the highest reproductive success. Although current evidence suggests that variation in SMR may be maintained within populations via context‐dependent fitness benefits, it is suggested that a more integrative approach is now required to fully understand how the environment can modulate individual performance via effects on metabolic phenotypes encompassing SMR, MMR and AS.
Highlights
Fishes have provided some of the best examples of intraspecific variation in morphological features that reveal adaptations to local environments
As mentioned earlier, no relationship between variation in metabolism (SMR, maximum possible aerobic metabolic rate (MMR) and aerobic scope (AS)) and mass of metabolically active organs was found in S. trutta (Norin & Malte, 2012) but a positive relationship was found in A. anguilla, with 38% of the variation in Standard metabolic rate (SMR) being explained by the mass of internal organs, in particular the liver (Boldsen et al, 2013)
P. phoxinus that experienced a period of food deprivation and subsequent compensatory growth were observed to have an elevated SMR and reduced AS compared with fish that had been feeding ad libitum throughout the entire period, there was no change in MMR (Killen, 2014).These results suggest that an individual’s MMR may be relatively uninfluenced by the fish’s nutritional state and that AS is primarily driven by the degree of plasticity within an individual’s SMR
Summary
Fishes have provided some of the best examples of intraspecific variation in morphological features that reveal adaptations to local environments. Much of the variation in duration and peak SDA can be explained by differences in fish size and species, ambient temperature and composition of a given meal (Secor, 2009), there remains considerable variation that can probably be attributed to inherent differences between individuals In both S. meridionalis and S. salar, it has been shown that individuals with a relatively high SMR for their size had a higher peak and overall magnitude of SDA but had a shorter duration of the SDA response, indicating that the metabolism of these individuals was quicker to return to resting levels after each meal compared with low SMR individuals (Fu et al, 2005; Millidine et al, 2009). Redpath et al (2010) Redpath et al (2010) Redpath et al (2010) Finstad et al (2007a) McCarthy (2001) Yamamoto et al (1998) Cutts et al (1999) Killen et al (2014) Killen et al (2014) Sloat & Reeves (2014) Metcalfe et al (1995) Reid et al (2011) Reid et al (2012) Sloat & Reeves (2014)
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