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 (Qten) 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.
The cold, food-bad winter season away from temperate in order to highest latitudes creates a significant bottleneck toward poleward dedication of pets, and has triggered the repeated density regarding winter season dormancy, good reversible seasonal phenotype characterized by laziness, a minimal body’s temperature, accelerated and a minimal metabolism [1–3]. A dormant overwintering strategy get assists the brand new dedication out of types from the the fresh new cool limit of its range, in addition to marine ectotherms , and may be looked at because a technique to enhance geographic ranges on cooler high of your thermal market. But not, the fresh new systems underlying cold weather dormancy are still badly knew, particularly in ectotherms .
Kcalorie burning anxiety, good reversible and productive downregulation out-of sleeping cellular energy return to help you really below the practical otherwise basal (i.age. resting) metabolic process (SMR or BMR; the fresh standard cost of living in the ectotherms otherwise endotherms, respectively), is a very common method employed by organisms to undergo time-limited surroundings [6,7]. Within the hibernating mammals, a serious k-calorie burning despair is common and you can comes from active depression of your time k-calorie burning plus passive Arrhenius physico-toxins outcomes of air conditioning on account of an effective resetting of one’s human anatomy temperature put-point . not, with the exception of when specific species run into anoxic seas when you look at the winter months (elizabeth.g. some freshwater turtles) , there is certainly debate about the use of kcalorie burning despair by winter-dormant ectotherms, hence generally overwinter significantly less than normoxic requirements [step one,8]. Partly, which controversy can be obtained just like the dormancy and you will kcalorie burning anxiety in ectotherms is hard to identify from listlessness and you may reduced metabolic costs through couch potato physico-chemical ramifications of frigid temperature .
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 http://www.datingranking.net/local-hookup/oshawa/ 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.
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