Flexibility in metabolic rate confers a growth advantage under changing food availability

Abstract

Phenotypic flexibility in physiological, morphological and behavioural traits can allow organisms to cope with environmental challenges. Given recent climate change and the degree of habitat modification currently experienced by many organisms, it is therefore critical to quantify the degree of phenotypic variation present within populations, individual capacities to change and what their consequences are for fitness. Flexibility in standard metabolic rate (SMR) may be particularly important since SMR reflects the minimal energetic cost of living and is one of the primary traits underlying organismal performance. SMR can increase or decrease in response to food availability, but the consequences of these changes for growth rates and other fitness components are not well known. We examined individual variation in metabolic flexibility in response to changing food levels and its consequences for somatic growth in juvenile brown trout (Salmo trutta). SMR increased when individuals were switched to a high food ration and decreased when they were switched to a low food regime. These shifts in SMR, in turn, were linked with individual differences in somatic growth; those individuals that increased their SMR more in response to elevated food levels grew fastest, while growth at the low food level was fastest in those individuals that depressed their SMR most. Flexibility in energy metabolism is therefore a key mechanism to maximize growth rates under the challenges imposed by variability in food availability and is likely to be an important determinant of species’ resilience in the face of global change.

Differential effects of food availability on minimum and maximum rates of metabolism

“…A decrease in AS with increasing food levels may therefore represent an increasing constraint on the organism [21]. However, it is important to note that the effect of food availability on AS that we observed is driven entirely by a change in SMR which itself can also have positive effects on growth rate [10] as well as digestion efficiency [25]. As such, the overall impact of metabolic flexibility on organismal performance will likely depend on the costs and benefits associated with changes in both these metabolic traits.…”

“…from this mean [1,10]. MMR was then determined using an exhaustive chase protocol followed immediately by measurement of peak excess post-exercise oxygen consumption using closed-system respirometry [1,10]. Briefly, each fish was chased to exhaustion (less than 2 min) against a circular current (600 l h −1 ) in a bucket.…”

“…AS is the absolute difference between maximum and SMR and is a measure of the degree to which metabolism can be increased above baseline requirements to finance important functions such as digestion, locomotion, growth and reproduction. SMR is thought to reflect the cost of maintaining the metabolic machinery needed to finance MMR [7,8] and is known to be a flexible trait, typically changing as an increasing function of food availability [9,10]. As such, food-induced shifts in SMR may also affect MMR in parallel.…”

Influence of food, body size, and fragmentation on metabolic rate in a sessile marine invertebrate

“…Importantly, this ability to alter metabolic rate can have implications for the life history of an individual (Stearns, ). In brown trout, for example, individuals that were best able to adjust metabolic rate had the highest growth rate under changing food availability (Auer, Salin, Rudolf, Anderson, & Metcalfe, ). Similarly, growth rate is positively correlated with the magnitude of the factorial scope during SDA in the common starfish, Asterias rubens (Vahl, ).…”

Energetic Consequences of Stranding of Juvenile Atlantic Salmon (Salmo salar L.)

“…However, we could not find such a negative impact, neither during summer and winter, nor during trapping and beaching. Hatchery reared fish may have lower ability to regulate their metabolism down in periods with low food availability than wild fish [41], but we cannot see that this should have affected our interpretation of results from the experiments. As mentioned in methods, the channels have been used for growth experiments based on available food in the channels (e.g.…”