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48 results for “torpor”

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Data from: Individual differences in torpor expression in adult mice are related to relative birth weight

Daily torpor is a physiological adaptation in small mammals and birds, characterised by drastic reductions in metabolism and body temperature. Energy-constraining conditions, such as cold and starvation, are known to cause the expression of daily torpor. However, the reason for high degrees of inter- and intra- individual variation in torpor expression (TE) in similar situations is not clear. As littermates of altricial animals are exposed to an uneven allocation of maternal resources from conception to weaning, we tested whether early nutritional experiences have long-term effects on TE in adults. We used full-sibling littermates of laboratory mice that as adults were starved overnight to induce torpor. We measured body weight from birth until adulthood as an indicator of nutritional status, and calculated the relative body weight (RBW) as an indicator of the difference in nutritional status within a litter. After maturation, we subjected mice to five repeated torpor induction trials involving 24 hours of fasting and 5 days of recovery. Half of the female mice displayed great individual variation in TE, whereas male mice rarely exhibited daily torpor. In females, RBW at birth influenced TE, irrespective of body weight in adulthood; thus, female mice born with low RBWs displayed high TE in adulthood. In conclusion, we provide evidence that TE in mice differs among littermates, and that this variation is linked closely to heterogeneous nutritional experiences during the foetal period.

opencc-zeroDec 2017View details →

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Data from: Torpor reduces predation risk by compensating for the energetic cost of antipredator foraging behaviours

Foraging activity is needed for energy intake but increases the risk of predation, and antipredator behavioural responses, such as reduced activity, generally reduce energy intake. Hence, mortality and indirect effects of predation risk are dependent on the energy requirements of prey. Torpor, a controlled reduction in resting metabolism and body temperature, is a common energy-saving mechanism of small mammals that enhances their resistance to starvation. Here we test the hypothesis that torpor could also reduce predation risk by compensating for the energetic cost of antipredator behaviours. We measured the foraging behaviour and body temperature of house mice in response to manipulation of perceived predation risk by adjusting levels of ground cover and starvation risk by 24-h food withdrawal every third day. We found that a voluntary reduction in daily food intake in response to lower cover (high predation risk) was matched by the extent of a daily reduction in body temperature. Our study provides the first experimental evidence of a close link between energy-saving torpor responses to starvation risk and behavioural responses to perceived predation risk. By reducing the risk of starvation, torpor can facilitate stronger antipredator behaviours. These results highlight the interplay between capacity for reducing metabolic energy expenditure, optimal decisions about foraging behaviour, and the life-history ecology of prey.

opencc-zeroDec 2017View details →

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Data from: Nocturnal torpor by superb fairy-wrens: a key mechanism for reducing winter daily energy expenditure

Many passerine birds are small and require a high mass-specific rate of resting energy expenditure, especially in the cold. The energetics of thermoregulation is therefore an important aspect of their ecology, yet few studies have quantified thermoregulatory patterns in wild passerines. We used miniature telemetry to record the skin temperature (Tskin) of free-living superb fairy-wrens (Malurus cyaneus, 8.6 g; n = 6 birds over N = 7 to 22 days) and determine the importance of controlled reductions in body temperature during resting to their winter energy budgets. Fairy-wrens routinely exhibited large daily fluctuations in Tskin between maxima of 41.9 ± 0.6°C and minima of 30.4 ± 0.7°C, with overall individual minima of 27.4 ± 1.1°C (maximum daily range: 14.7 ± 0.9 °C). These results provide strong evidence of nocturnal torpor in this small passerine, which we calculated to provide a 42% reduction in resting metabolic rate at a Ta of 5 °C compared to active-phase Tskin. A capacity for energy-saving torpor has important consequences for understanding the behaviour and life-history ecology of superb fairy-wrens. Moreover, our novel field data suggest that torpor could be more widespread and important than previously thought within passerines, the most diverse order of birds.

opencc-zeroDec 2018View details →

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Data from: The importance of mammalian torpor for survival in a post-fire landscape

Wildfires have increased in frequency and intensity worldwide with climate change as a main driving factor. While a number of studies have focused on population changes in regard to fires, there are essentially no quantitative data on behavioural and physiological adjustments that are vital for the persistence of individuals during and after fires. Here we show that brown antechinus, a small insectivorous marsupial mammal, (i) endured a prescribed fire in situ, (ii) remained in their scorched home range despite unburned areas nearby, and (iii) substantially increased post-fire torpor use and thus reduced foraging requirements and exposure to predators. Hence, torpor is a physiological adaptation that, although not quantified in this context previously, appears to play a key role in post-fire survival for this and other heterothermic species.

opencc-zeroDec 2014View details →

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Data from: Solar radiation during rewarming from torpor in elephant shrews: supplementation or substitution of endogenous heat production?

Many small mammals bask in the sun during rewarming from heterothermy, but the implications of this behaviour for their energy balance remain little understood. Specifically, it remains unclear whether solar radiation supplements endogenous metabolic thermogenesis (i.e., rewarming occurs through the additive effects of internally-produced and external heat), or whether solar radiation reduces the energy required to rewarm by substituting (i.e, replacing) metabolic heat production. To address this question, we examined patterns of torpor and rewarming rates in eastern rock elephant shrews (Elephantulus myurus) housed in outdoor cages with access to either natural levels of solar radiation or levels that were experimentally reduced by means of shade cloth. We also tested whether acclimation to solar radiation availability was manifested via phenotypic flexibility in basal metabolic rate (BMR), non-shivering thermogenesis (NST) capacity and/or summit metabolism (Msum). Rewarming rates varied significantly among treatments, with elephant shrews experiencing natural solar radiation levels rewarming faster than conspecifics experiencing solar radiation levels equivalent to approximately 20% or 40% of natural levels. BMR differed significantly between individuals experiencing natural levels of solar radiation and conspecifics experiencing approximately 20% of natural levels, but no between-treatment difference was evident for NST capacity or Msum. The positive relationship between solar radiation availability and rewarming rate, together with the absence of acclimation in maximum non-shivering and total heat production capacities, suggests that under the conditions of this study solar radiation supplemented rather than substituted metabolic thermogenesis as a source of heat during rewarming from heterothermy.

opencc-zeroDec 2014View details →

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Dataset: Cool birds: First evidence of energy-saving nocturnal torpor in free-living common swifts Apus apus resting in their nests

<a name="_Hlk94722524"></a>Daily torpor is a means of saving energy by controlled lowering of the metabolic rate (MR) during resting, usually coupled with a decrease in body temperature. We studied nocturnal daily torpor under natural conditions in free-living common swifts Apus apus resting in their nests as a family using two non-invasive approaches. First, we monitored nest temperature (Tnest) in up to 50 occupied nests per breeding season in 2010-2015. Drops in Tnest were the first indication of torpor. Among <a name="_Hlk97457770"></a>16,673 observations, we detected 423 events of substantial drops in Tnest of on average 8.6°C. Second, we measured MR of the families inside nest boxes prepared for calorimetric measurements during cold periods in the breeding seasons of 2017 and 2018. We measured oxygen consumption and carbon dioxide production using a mobile indirect respirometer and calculated the percentage reduction in MR. During six torpor events observed, MR was gradually reduced by on average 56% from the reference value followed by a decrease in Tnest of on average 7.6 °C. In contrast, MR only decreased by about 33% on nights without torpor. Our field data gave an indication of daily torpor, which is used as a strategy for energy saving in free-living common swifts.

opencc-zeroFeb 2022View details →

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