The benefit of being nevertheless: energy savings while in the winter season dormancy within the fish come from inactivity and you can frigid weather, not regarding metabolic rate anxiety

Metabolic rate depression, an active downregulation of resting cellular energy turnover and thus standard (resting) metabolic rate (SMR), is a unifying strategy underlying the persistence of organisms in such energy-limited environments, including hibernating endotherms. However, controversy exists about its involvement in winter-dormant aquatic ectotherms. To address this debate, we conducted simultaneous, multi-day measurements of whole-animal oxygen consumption rate (a proxy of metabolic rate) and spontaneous movement in a model winter-dormant marine fish, the cunner (Tautogolabrus adspersus). Winter dormancy in cunner involved a dampened diel rhythm of metabolic rate, such that a low and stable metabolic rate persisted throughout the 24 h day. Based on the thermal sensitivity (Q_ten) of SMR as well as correlations of metabolic rate and movement, the reductions in metabolic rate were not attributable to metabolic rate depression, but rather to reduced activity under the cold and darkness typical of the winter refuge among substrate. Previous reports of metabolic rate depression in cunner, and possibly other fish species, during winter dormancy were probably confounded by variation in activity. Unlike hibernating endotherms, and excepting the few fish species that overwinter in anoxic waters, winter dormancy in fishes, as exemplified by cunner, need not involve metabolic rate depression. Rather, energy savings come from inactivity combined with passive physico-chemical effects of the cold on SMR, demonstrating that thermal effects on activity can greatly influence temperature–metabolism relationships, and illustrating the benefit of simply being still in energy-limited environments.

1. Records

Frigid weather, food-bad winter season away from temperate in order to highest latitudes brings a serious bottleneck into the poleward dedication from animals, and has triggered new regular occurrence out-of winter months dormancy, a beneficial reversible seasonal phenotype described as laziness, a minimal body’s temperature, accelerated and you will a minimal metabolic process [1–3]. An inactive overwintering means get facilitate this new perseverance away from kinds during the new cool maximum of its assortment, also marine ectotherms , and will be viewed given that a tactic to expand geographical range to your cooler tall of one’s thermal market. But not, the fresh new systems fundamental winter months dormancy are badly know, particularly in ectotherms .

Kcalorie burning despair, a beneficial reversible and you will productive downregulation from sleeping cellular times turnover so you’re able to well underneath the simple or basal (we.e. resting) metabolism (SMR or BMR; the latest baseline cost-of-living in the ectotherms or endotherms, respectively), is a type of strategy used by organisms to undergo opportunity-restricted environment [6,7]. In hibernating animals, a deep kcalorie burning anxiety is typical and you may results from productive anxiety of time metabolic rate in addition to couch potato Arrhenius physico-chemicals aftereffects of air conditioning on account of good resetting of one’s system temperature lay-area . not, aside from whenever specific variety come across anoxic seas into the winter months (e.g. specific freshwater turtles) , there is conflict regarding the entry to metabolic process despair by winter-inactive ectotherms, and therefore normally overwinter below normoxic standards [step 1,8]. Simply, this controversy is obtainable as the dormancy and you may metabolic process despair in the ectotherms would be hard to separate of lethargy and you may lowest metabolic rates as a consequence of couch potato physico-chemical results of frigid heat .

Biologists have used the thermal sensitivity (Q₁₀) of metabolic rate over the transition from an active to dormant state as a tool to identify involvement of metabolic rate depression in winter-dormant ectotherms. A Q₁₀ > 3.5 is thought to indicate an active depression of metabolic rate beyond the passive physico-chemical effects of temperature on metabolism where the typical Q₁₀ is approximately 2–3 [7,9,10]. Such analyses have suggested considerable interspecific variation in the capacity for metabolic rate depression among winter-dormant ectotherms [1,11,12]. For example, among a diverse range of winter-dormant fish species, metabolic rate depression has been either implicated [10,13–18] or excluded [9,19,20]. Among the latter species, winter dormancy has been suggested simply to be a period of inactivity [8,9]. Inactivity alone could lead to substantial decreases in measured metabolic rates because voluntary activity, which underlies fundamental behaviours such as foraging and patrolling territories, has been estimated to represent up to 67% of routine metabolic rate in fishes . Indeed, activity is a significant component of daily energy expenditure in animals [22,23]. Thus, while never assessed in earlier studies on winter-dormant fishes, it is possible that high Q₁₀ values for measured metabolic rates, traditionally interpreted as a metabolic rate depression (i.e. active downregulation of SMR), could be caused entirely by inactivity in the cold, which would greatly lower metabolic rate to resting levels (i.e. SMR) compared with warm, active individuals exhibiting routine levels of metabolic rate . However, the roles of reduced activity versus metabolic rate depression in determining variation in metabolic rate in winter-dormant ectotherms have never been elucidated, in part because the relationships between metabolic rate and activity are challenging to measure, especially at frigid temperatures.