Torpor in mammals and birds

Wang, Lawrence C.H.; Wolowyk, Michael W.

doi:10.1139/z88-017

Cited by 92 publications

(47 citation statements)

References 25 publications

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“…The reduction in MR and T b during entrance and torpor undoubtedly conserves energy, but arousal and IBE are quite expensive. In Richardson's ground squirrels (Urocitellus richardsonii), up to 88% of the energy expended over the hibernation season may be used during arousal and IBE (Wang and Wolowyk, 1988), so these phases are assumed to be important. Many things change during arousal and IBE, including gene expression, protein synthesis and gluconeogenesis (Carey et al, 2003), and some hibernators appear to spend much of the IBE in non-REM sleep (Daan et al, 1991).…”

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confidence: 99%

Metabolic suppression in mammalian hibernation: the role of mitochondria

Staples

2014

Journal of Experimental Biology

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Hibernation evolved in some small mammals that live in cold environments, presumably to conserve energy when food supplies are low. Throughout the winter, hibernators cycle spontaneously between torpor, with low metabolism and near-freezing body temperatures, and euthermia, with high metabolism and body temperatures near 37°C. Understanding the mechanisms underlying this natural model of extreme metabolic plasticity is important for fundamental and applied science. During entrance into torpor, reductions in metabolic rate begin before body temperatures fall, even when thermogenesis is not active, suggesting active mechanisms of metabolic suppression, rather than passive thermal effects. Mitochondrial respiration is suppressed during torpor, especially when measured in liver mitochondria fuelled with succinate at 37°C in vitro. This suppression of mitochondrial metabolism appears to be invoked quickly during entrance into torpor when body temperature is high, but is reversed slowly during arousal when body temperature is low. This pattern may reflect body temperaturesensitive, enzyme-mediated post-translational modifications of oxidative phosphorylation complexes, for instance by phosphorylation or acetylation.KEY WORDS: Heat, Body temperature, Thermoregulation, Thermogenesis, Oxidative phosphorylation, Post-translational modification, Acetylation, Phosphorylation IntroductionMost mammals are strict endotherms, i.e. they maintain fairly constant body temperatures (T b ) near 37°C using heat derived primarily from endogenous metabolism. In cold environments, mammals retain some of this heat by regulating insulation (using underfur and/or subcutaneous fat), peripheral blood circulation (using vasoconstriction and/or countercurrent heat exchangers) and ventilatory evaporation. At very cold temperatures, the high gradient between T b and ambient temperature (T a ) causes large heat loss by radiation and conduction, which is also affected by convection of water or air. For small mammals, the high body surface area, relative to volume, results in greater mass-specific rates of heat loss. While large land mammals can increase insulation by changing the quality (microstructure) and quantity (length, density) of underfur, this option is limited for small mammals. Imagine a 70 mm long lemming growing fur 100 mm long; it might stay warm, but when it tripped over that fur it would be easy prey.Despite the challenges, many small mammals thrive in cold environments. To compensate for high heat loss, these mammals upregulate their capacities to produce metabolic heat. Though COMMENTARY Department of Biology, University of Western Ontario, London, ON, Canada, N6A 5B8.*Author for correspondence (jfstaple@uwo.ca) effective, this strategy requires large quantities of fuel during winter when food availability is typically low. Many small mammals use stored food to power thermogenic metabolism. For example, American red squirrels (Tamiascurius hudsonicus) cache spruce cones and feed on the seeds throughout winter, allowing th...

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confidence: 99%

Metabolic suppression in mammalian hibernation: the role of mitochondria

Staples

2014

Journal of Experimental Biology

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“…(Wang 1988). Among a wide range of mammals and birds, torpor is often classif ied as either shallow (daily) torpor or hibernation (seasonal) torpor (Geiser & Ruf 1995).…”

Section: Methodsmentioning

confidence: 99%

“…This bat was found in shallow torpor, which lasted for around 8-10 days in the peak winter season during the December to January month. Among the mammals, members of the order Chiroptera have been widely reported to exhibit torpor (Wang 1988;Barclay 2001;Geiser & Ruf, 1995;Willis & Brigham, 2003), though there is no such report from India till date. During the present study, all the individuals of were completely inactive in the months of December and January.…”

Section: Methodsmentioning

confidence: 99%

Ecological and Acoustic-call Characteristics of Blyth's Horseshoe bat, Rhinolophus Lepidus in Delhi,India

Mishra¹,

Dookia²,

Singh³

et al. 2018

ambi

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“…Using Wunder's (1975) model for estimating metabolic rate (MR), it was determined that hypothermia in the aardwolf during winter translates to a c. 18% energy saving (Anderson, 1994). The estimated reduction in metabolism is at the lower end of the 18-31% saving observed in most small mammalian species that exhibit daily hypothermia (Vogt & Lynch, 1982;Wang & Wolowyk, 1988). This suggests that the aardwolf does not fully exploit the energetic advantages of hypothermia.…”

Section: Body Temperaturementioning

confidence: 99%

Aardwolf adaptations: a review

Anderson¹

2004

Transactions of the Royal Society of South Africa

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The aardwolf Proteles cristatus has developed a number of anatomical and morphological adaptations for feeding on its termite prey. These adaptations preclude the aardwolf from feeding on other, larger (vertebrate) prey, especially during the winter months, when the T a drops below 9 º C and when Trinervitermes termites are largely unavailable. Winter is therefore a stressful period for aardwolves, as evidenced by increased juvenile mortality, a 20% decline in body mass and depletion of subcutaneous fat reserves. The aardwolf uses both physiological and behavioural means to overcome this period of food stress. An increased period is spent underground in the thermally-stable environment of the den. Den sharing is more common in the winter months and social thermoregulation may result in energy savings. While inactive the aardwolf lowers its T b (to an average of 34.1+1.6 º C during the middle of the inactive period during winter) and in some individuals this results in energy savings of up to 18%. Seasonal changes in pelage density and thermal conductance allow for more passive heat transfer during summer and improved heat retention during winter. Laboratory and field measurements of metabolic rate showed that the aardwolf has a low BMR and a low FMR (between 40 and 78% of that predicted by allometric equations). The aardwolf's metabolic rate is 11% lower during the winter months, resulting in reduced energy requirements during the period of limited food availability. Evaporative water loss rates are low, further reduced during the winter months, adaptations to survive in a desert environment and on a seasonally-unavailable food source. The aardwolf is therefore well adapted to feed on a diet of Trinervitermes termites, a food niche that has been largely unexploited by other animals, and it uses various ecological, behavioural and physiological adaptations to cope with this seasonally unavailable food source.

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Torpor in mammals and birds

Cited by 92 publications

References 25 publications

Metabolic suppression in mammalian hibernation: the role of mitochondria

Metabolic suppression in mammalian hibernation: the role of mitochondria

Ecological and Acoustic-call Characteristics of Blyth's Horseshoe bat, Rhinolophus Lepidus in Delhi,India

Aardwolf adaptations: a review

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