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1.
Willis CK Turbill C Geiser F 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2005,175(7):479-486
Data on thermal energetics for vespertilionid bats are under-represented in the literature relative to their abundance, as
are data for bats of very small body mass. Therefore, we studied torpor use and thermal energetics in one of the smallest
(4 g) Australian vespertilionids, Vespadelus vulturnus. We used open-flow respirometry to quantify temporal patterns of torpor use, upper and lower critical temperatures (T
uc and T
lc) of the thermoneutral zone (TNZ), basal metabolic rate (BMR), resting metabolic rate (RMR), torpid metabolic rate (TMR),
and wet thermal conductance (C
wet) over a range of ambient temperatures (T
a). We also measured body temperature (T
b) during torpor and normothermia. Bats showed a high proclivity for torpor and typically aroused only for brief periods. The
TNZ ranged from 27.6°C to 33.3°C. Within the TNZ T
b was 33.3±0.4°C and BMR was 1.02±0.29 mlO2 g−1 h−1 (5.60±1.65 mW g−1) at a mean body mass of 4.0±0.69 g, which is 55 % of that predicted for a 4 g bat. Minimum TMR of torpid bats was 0.014±0.006 mlO2 g−1 h−1 (0.079±0.032 mW g−1) at T
a=4.6±0.4°C and T
b=7.5±1.9. T
lc and C
wet of normothermic bats were both lower than that predicted for a 4 g bat, which indicates that V. vulturnus is adapted to minimising heat loss at low T
a. Our findings support the hypothesis that vespertilionid bats have evolved energy-conserving physiological traits, such as
low BMR and proclivity for torpor. 相似文献
2.
Thermoregulation in free‐ranging ground woodpeckers Geocolaptes olivaceus: no evidence of torpor 下载免费PDF全文
Heterothermic responses characterised by pronounced hypometabolism and reductions in body temperature (Tb) are one of the most effective ways in which small endotherms can offset the energetic cost of endothermic homeothermy. It remains unclear, therefore, why daily torpor and hibernation are restricted to only a subset of avian lineages. To further our understanding of the phylogenetic distribution of avian torpor, we investigated winter thermoregulation in the southern African ground woodpecker Geocolaptes olivaceus. We considered this species a good candidate for heterothermy, because it is resident year‐round in mountainous regions with cold winters and reliant on small ectothermic prey. We recorded Tb patterns in free‐ranging individuals and measured Tb and metabolic rates in captive individuals. Neither free‐ranging nor captive woodpeckers showed any indication of daily torpor or even shallow rest‐phase hypothermia. All birds maintained bimodally distributed Tb characteristic of classic endothemic homeothermy, with a mean rest‐phase Tb of 37.9 ± 0.2°C and no data below 37.0°C. The mean circadian amplitude of Tb was 4.2°C, equivalent to approximately twice the expected value. There was some evidence of seasonal acclimatisation in Tb, with a small decrease in rest‐phase Tb with the onset of the austral winter. Captive birds showed patterns of resting metabolic rate and Tb consistent with the classic model of endothermic homeothermy. The apparent absence of torpor in G. olivaceus supports the notion that, unlike the case in mammals, many avian taxa that may a priori be expected to benefit from deep heterothermy do not use it. 相似文献
3.
Turbill C Geiser F 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2006,176(2):165-172
During roosting in summer, reproductive female bats appear to use torpor less frequently and at higher body temperatures (T
b) than male bats, ostensibly to maximise offspring growth. To test whether field observations result from differences in thermal
physiology or behavioural thermoregulation during roosting, we measured the thermoregulatory response and energetics of captive
pregnant and lactating female and male long-eared bats (Nyctophilus geoffroyi 8.9 g and N. gouldi 11.5 g) during overnight exposure to a constant ambient temperature (T
a) of 15°C. Bats were captured 1–1.5 h after sunset and measurements began at 21:22±0:36 h. All N. geoffroyi entered torpor commencing at 23:47±01:01 h. For N. gouldi, 10/10 males, 9/10 pregnant females and 7/8 lactating females entered torpor commencing at 01:10±01:40 h. The minimum T
b of torpid bats was 15.6±1.1°C and torpid metabolic rate (TMR) was reduced to 0.05±0.02 ml O2 g−1 h−1. Sex or reproductive condition of either species did not affect the timing of entry into torpor (F=1.5, df=2, 19, P=0.24), minimum TMR (F=0.21, df=4, 40, P=0.93) or minimum T
b (F=0.76, df=5, 41, P=0.58). Moreover, sex or reproductive condition did not affect the allometric relationship between minimum resting metabolic
rate and body mass (F=1.1, df=4, 37, P=0.37). Our study shows that under identical thermal conditions, thermal physiology of pregnant and lactating female and male
bats are indistinguishable. This suggests that the observed reluctance by reproductive females to enter torpor in the field
is predominantly because of ecological rather than physiological differences, which reflect the fact that females roost gregariously
whereas male bats typically roost solitarily. 相似文献
4.
Shawna A. Karpovich Øivind Tøien C. Loren Buck Brian M. Barnes 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2009,179(6):691-700
Arctic ground squirrels overwintering in northern Alaska experience average soil temperature of −10°C. To examine energetic
costs of arousing from hibernation under arctic compared to temperate conditions, captive ground squirrels were maintained
in ambient temperatures (T
a) of 2, −5 and −12°C. Rates of oxygen consumption and carbon dioxide production were used to estimate metabolic rate and fuel
use during the three phases of arousal episodes: rewarming, euthermia, and recooling. Respiratory quotient comparisons suggest
exclusive use of lipid during rewarming and mixed fuel use during euthermia. Animals rewarming from torpor at T
a −12°C took longer, consumed more oxygen, and attained higher peak rates of oxygen consumption when compared to 2°C. T
a had no significant effect on cost or duration of the euthermic phase. Animals recooled faster at −12°C than at 2°C, but total
oxygen consumption was not different. T
a had no significant effect on the total cost of arousal episodes when all three phases are included. Arousal episodes account
for 86% of estimated costs of a complete hibernation cycle including torpor when at 2°C and only 23% at −12°C. Thus, due to
the higher costs of steady-state metabolism during torpor, proportional metabolic costs of arousal episodes at T
a characteristic of the Arctic are diminished compared to relative costs of arousals in more temperate conditions. 相似文献
5.
Lovegrove G Körtner G Geiser F 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(1):11-18
The costs of arousal from induced torpor were measured in the striped-faced dunnart (Sminthopsis macroura; ca. 25 g) under two experimental ambient temperature cycles. The sinusoidal-type temperature cycles were designed to evaluate
the effects of passive, ambient temperature heating during arousal from torpor in these insectivorous marsupials. It was hypothesised
that diel ambient temperature cycles may offer significant energy savings during arousal in animals that employ daily torpor
in summer as a response to unpredictable food availability. The cost of arousal in animals in which passive, exogenous heating
occurred was significantly lower than that in animals not exposed to an ambient temperature cycle. The total cost of all three
phases of torpor (entry, maintenance and arousal) was almost halved when animals were exposed to an ambient heating cycle
from 15 °C to 25 °C over a 24-h period. In all animals, irrespective of the experimental ambient temperature cycle employed,
the minimum torpor body temperature was 17–18 °C. The body temperature (Tb) of animals exposed to exogenous heating increased from the torpor Tb minimum to a mean value of 22.59 °C before endogenous heat production commenced. This relatively small increase in Tb of ca. 5 °C through `free' passive heating was sufficient to account for the significant ca. three-fold decrease in the cost
of arousal and may represent an important energetic aid to free-ranging animals.
Accepted: 4 October 1998 相似文献
6.
Information regarding passerine heterothermy and torpor is scant, although many species are small and must cope with a fluctuating
food supply and presumably would benefit from energy savings afforded by torpor. We studied whether insectivorous Dusky Woodswallows
(Artamus cyanopterus; ∼35 g) enter spontaneous torpor (food ad libitum) when held outdoors as a pair in autumn/winter. Woodswallows displayed
pronounced and regular daily fluctuations in body temperature (T
b) over the entire study period. The mean T
b ranged from ∼39°C to 40°C (photophase, day time) and ∼33°C to 36°C (scotophase, night time). However, on 88% of bird nights,
nocturnal T
b minima fell to < 35°C. The lowest T
b observed in air was 29.2°C. However, when a bird fell into water its T
b dropped further to ∼22°C; this T
b was regulated for several hours and the bird survived. Our observations suggest that heterothermy is a normal part of the
daily thermal regime for woodswallows to minimise energy expenditure. Spontaneous nocturnal torpor in captive woodswallows
suggests that torpor in the wild may be more pronounced than recorded here because free-living birds are likely challenged
by both low food availability and adverse weather. 相似文献
7.
Mariska Batavia George Nguyen Kristine Harman Irving Zucker 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2013,183(2):269-277
Turkish hamsters (Mesocricetus brandti) are a model organism for studies of hibernation, yet a detailed account of their torpor characteristics has not been undertaken. This study employed continuous telemetric monitoring of body temperature (T b) in hibernating male and female Turkish hamsters at ambient temperatures (T as) of 5 and 13 °C to precisely characterize torpor bout depth, duration, and frequency, as well as rates of entry into and arousal from torpor. Hamsters generated brief intervals of short (<12 h), shallow test bouts (T b > 20 °C), followed by deep torpor bouts lasting 4–6 days at T a = 5 °C and 2–3 days at T a = 13 °C. Females at T a = 5 °C had longer bouts than males, but maintained higher torpor T b; there were no sex differences at T a = 13 °C. Neither body mass loss nor food intake differed between the two T as. Hamsters entered torpor primarily during the scotophase (subjective night), but timing of arousals was highly variable. Hamsters at both T as generated short, shallow torpor bouts between deep bouts, suggesting that this species may be capable of both hibernation and daily torpor. 相似文献
8.
Lisa Warnecke Fritz Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(3):437-445
Limited information is available on basking behaviour in torpid mammals and its energetic consequences. We investigated the
effects of physiological and behavioural strategies on the energetics of the fat-tailed dunnart (Sminthopsis crassicaudata). Metabolic rate and body temperature during torpor, basking and rest were measured over 24 h in response to simulated environmental
conditions: (a) constant ambient temperature (T
a) of 15°C, (b) constant T
a of 15°C with access to a radiant heat lamp, (c) a T
a cycle (range 15–31°C), and (d) a T
a cycle with access to a radiant heat lamp. When a radiant heat source was provided, all dunnarts (n = 16) basked during all measurements, which resulted in energy savings of up to 74% during rest. Overall, torpor was used
on 59% of measurements with a maximum duration of 16.2 h and reductions in metabolic rate of 90% compared to normothermic
values. Torpid dunnarts actively moved from a shaded area to position themselves under the heat lamp with body temperatures
as low as 17.5°C and thereby reduced rewarming costs by 66%. We demonstrated, for the first time in the laboratory, that torpid
animals actively move to a heat source to bask, and that this behaviour results in considerable energy savings. Our finding
supports the view that basking during normothermia and rewarming from torpor substantially reduces energetic requirements,
which may be important for the survival of small dasyurids living on limited resources in the Australian arid zone. 相似文献
9.
10.
W. Bartels B. S. Law F. Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(3):233-239
Little is known about torpor in the tropics or torpor in megachiropteran species. We investigated thermoregulation, energetics
and patterns of torpor in the northern blossom-bat Macroglossus minimus (16 g) to test whether physiological variables may explain why its range is limited to tropical regions. Normothermic bats
showed a large variation in body temperature (T
b) (33 to 37 °C) over a wide range of ambient temperatures (T
as) and a relatively low basal metabolic rate (1.29 ml O2 g−1 h−1). Bats entered torpor frequently in the laboratory at T
as between 14 and 25 °C. Entry into torpor always occurred when lights were switched on in the morning, independent of T
a. MRs during torpor were reduced to about 20–40% of normothermic bats and T
bs were regulated at a minimum of 23.1 ± 1.4 °C. The duration of torpor bouts increased with decreasing T
a in non-thermoregulating bats, but generally terminated after 8 h in thermoregulating torpid bats. Both the mean minimum T
b and MR of torpid M. minimus were higher than that predicted for a 16-g daily heterotherm and the T
b was also about 5 °C higher than that of the common blossom-bat Syconycteris australis, which has a more subtropical distribution. These observations suggest that variables associated with torpor are affected
by T
a and that the restriction to tropical areas in M. minimus to some extent may be due to their ability to enter only very shallow daily torpor.
Accepted: 22 September 1997 相似文献
11.
Geiser F Westman W McAllan BM Brigham RM 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2006,176(2):107-116
Altricial mammals and birds become endothermic at about half the size of adults and presumably would benefit energetically
from entering torpor at that time. Because little is known about torpor during development in endotherms, we investigated
whether after the establishment of endothermic thermoregulation (i.e. the ability to maintain a high body temperature during
cold exposure), Sminthopsis macroura, a small (∼25 g) insectivorous marsupial, is capable of entering torpor and whether torpor patterns change with growth. Endothermic
thermoregulation was established when the nest young reached a body mass of ∼10 g, and they were capable of entering torpor
early during development at ∼10–12 g, lending some support to the view that torpor is a phylogenetically old mammalian trait.
Torpor bout length shortened significantly and the minimum metabolic rate during torpor increased as juveniles approached
adult size, and consequently total daily energy expenditure increased steeply with age. Relationships between total daily
energy expenditure and body mass during development of S. macroura (slope ∼1.3) differed substantially from the relationship between basal metabolism and body mass in adult endotherms (slope
∼0.75) suggesting that the energy expenditure–size relationship during the development differs substantially from that in
adults under thermo-neutral conditions. Our study shows that while torpor can substantially reduce energy expenditure during
development of endotherms and hence is likely important for survival during energy bottlenecks, it also may enhance somatic
growth when food is limited. We therefore hypothesize that torpor during the development in endotherms is far more widespread
than is currently appreciated. 相似文献
12.
D. J. Hosken P. C. Withers 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):71-80
The thermal and metabolic physiology of Chalinolobus gouldii, an Australian vespertilionid bat, was studied in the laboratory using flow-through respirometry. Chalinolobus gouldii exhibits a clear pattern of euthermic thermoregulation, typical of endotherms with respect to body temperature and rate of
oxygen consumption. The basal metabolic rate of euthermic Chalinolobus gouldii is approximately 86% of that predicted for a 17.5-g mammal and falls into the range of mass-specific basal metabolic rates
ascribed to vespertilionid bats. However, like most vespertilionid bats, Chalinolobus gouldii displays extreme thermolability. It is able to enter into torpor and spontaneously arouse at ambient temperatures as low
as 5 °C. Torpid bats thermoconform at moderate ambient temperature, with body temperature ≈ ambient temperature, and have
a low rate of oxygen consumption determined primarily by Q
10 effects. At low ambient temperature (< 10 °C), torpid C. gouldii begin to regulate their body temperature by increased metabolic heat production; they tend to maintain a higher body temperature
at low ambient temperature than do many northern hemisphere hibernating bats. Use of torpor leads to significant energy savings.
The evaporative water loss of euthermic bats is relatively high, which seems unusual for a bat whose range includes extremely
arid areas of Australia, and is reduced during torpor. The thermal conductance of euthermic C. gouldii is less than that predicted for a mammal of its size. The thermal conductance is considerably lower for torpid bats at intermediate
body temperature and ambient temperature, but increases to euthermic values for torpid bats when thermoregulating at low ambient
temperature.
Accepted: 22 August 1996 相似文献
13.
《Chronobiology international》2013,30(2):103-128
Mammals and birds have evolved the ability to maintain a high and constant body temperature Tb over a wide range of ambient temperatures Ta using endogenous heat production. In many, especially small endotherms, cost for thermoregulatory heat production can exceed available energy; to overcome these energetic bottlenecks, they enter a state of torpor (a regulated reduction of Tb and metabolic rate). Since the occurrence of torpor in many species is a seasonal event and occurs at certain times of the day, we review whether circadian and circannual rhythms, important in the timing of biological events in active animals, also play an important role during torpor when Tb is reduced substantially and may even fall below 0°C. The two distinct patterns of torpor, hibernation (prolonged torpor) and daily torpor, differ substantially in their interaction with the circadian system. Daily torpor appears to be integrated into the normal circadian rhythm of activity and rest, although torpor is not restricted only to the normal rest phase of an animal. In contrast, hibernation can last for several days or even weeks, although torpor never spans the entire hibernation season, but is interrupted by periodic arousals and brief normothermic periods. Clearly, a day is no longer divided in activity and rest, and at first glance the role of the circadian system appears negligible. However, in several hibernators, arousals not only follow a regular pattern consistent with a circadian rhythm, but also are entrainable by external stimuli such as photoperiod and Ta. The extent of the interaction between the circadian and circannual system and hibernation varies among species. Biological rhythms of hibernators for which food availability appears to be predictable seasonally and that hibernate in deep and sealed burrows show little sensitivity to external stimuli during hibernation and hence little entrainability of arousal events. In contrast, opportunistic hibernators, which some times use arousals for foraging and hibernate in open and accessible hibernacula, are susceptible to external zeitgebers. In opportunistic hibernators, the circadian system plays a major role in maintaining synchrony between the normal day-night cycle and occasional foraging. Although the daily routine of activity and rest is abandoned during hibernation, the circadian system appears to remain functional, and there is little evidence it is significantly affected by low Tb. (Chronobiology International, 17(2), 103–128, 2000) 相似文献
14.
Heterothermy in the southern African hedgehog, <Emphasis Type="Italic">Atelerix frontalis</Emphasis>
Hallam SL Mzilikazi N 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(3):437-445
Most research on mammalian heterothermic responses in southern Africa tends to be laboratory based and biased towards rodents
and smaller members of the Afrotheria. In this study, we continuously measured body temperature of southern African hedgehogs
(Atelerix frontalis) between April and August 2009 (−10°C < T
a < 43°C), kept under semi-captive conditions. A. frontalis showed a high propensity for torpor with animals spending up to 84% of the measurement period torpid. During this study,
A. frontalis displayed the lowest T
b min (ca 1°C) yet recorded in an Afrotropical placental heterotherm. Bout lengths of between 0.7 h (40 min) and 116.3 h (4.8 days)
were recorded. Differences in bout length were observed between lighter individuals compared with an individual exhibiting
a higher body mass at the onset of winter, with low M
b individuals exhibiting daily torpor whereas a heavier individual exhibited torpor bouts that were indicative of hibernation.
Our results suggest that heterothermic responses are an important feature in the energy balance equation of this species and
that body mass at the onset of winter may determine the patterns of heterothermy utilised in this species. 相似文献
15.
P. I. Webb J. D. Skinner 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(5):325-330
We determined the effect of food availability (presence/absence) and ambient temperature (25/10°C) on daily energy expenditure
and the use of activity and torpor in summer-acclimated captiveGraphiurus murinus. Daily energy expenditure declined logarithmically with duration of food deprivation at a mean rate of 11 and 31% per day
at 25 and 10°C, respectively. The incidence of torpor in the presence of food at 25°C was low (one in seven individuals) and
increased on a single day's exposure to 10°C and with duration of food deprivation. Use of torpor was highest during the day,
varied between individuals, and torpor bouts of greater than 24h duration were not noted. With food deprivation, individuals
at 25°C initially responded by reducing activity but remained euthermic while the same individuals at 10°C responded by increasing
their use of torpor during the light period; this difference in response probably reflects a difference in the relative energetic
benefits of torpor at different temperatures. 相似文献
16.
Daily torpor in the gray mouse lemur (Microcebus murinus) in Madagascar: energetic consequences and biological significance 总被引:5,自引:0,他引:5
J. Schmid 《Oecologia》2000,123(2):175-183
Patterns and energetic consequences of spontaneous daily torpor were measured in the gray mouse lemur (Microcebus murinus) under natural conditions of ambient temperature and photoperiod in a dry deciduous forest in western Madagascar. Over a
period of two consecutive dry seasons, oxygen consumption (VO2) and body temperature (T
b) were measured on ten individuals kept in outdoor enclosures. In all animals, spontaneous daily torpor occurred on a daily
basis with torpor bouts lasting from 3.6 to 17.6 h, with a mean torpor bout duration of 9.3 h. On average, body temperatures
in torpor were 17.3±4.9°C with a recorded minimum value of 7.8°C. Torpor was not restricted to the mouse lemurs’ diurnal resting
phase: entries occurred throughout the night and arousals mainly around midday, coinciding with the daily ambient temperature
maximum. Arousal from torpor was a two-phase process with a first passive, exogenous heating where the T
b of animals increased from the torpor T
b minimum to a mean value of 27.1°C before the second, endogenous heat production commenced to further raise T
b to normothermic values. Metabolic rate during torpor (28.6±13.2 ml O2 h–1) was significantly reduced by about 76% compared to resting metabolic rate (132.6±50.5 ml O2 h–1). On average, for all M. murinus individuals measured, hypometabolism during daily torpor reduced daily energy expenditure by about 38%. In conclusion, all
these energy-conserving mechanisms of the nocturnal mouse lemurs, with passive exogenous heating during arousal from torpor,
low minimum torpor T
bs, and extended torpor bouts into the activity phase, comprise an important and highly adapted mechanism to minimize energetic
costs in response to unfavorable environmental conditions and may play a crucial role for individual fitness.
Received: 8 July 1999 / Accepted: 3 December 1999 相似文献
17.
Chung D Lloyd GP Thomas RH Guglielmo CG Staples JF 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(5):699-711
We examined respiration and lipid composition of liver mitochondria purified from a hibernator (Ictidomys tridecemlineatus) in different stages of a torpor bout. Between interbout euthermia (body temperature, T
b, 37°C) and early entrance (T
b 30°C), state 3 and state 4 respirations, fueled by 6 mM succinate, fell by over 50%. Mitochondrial respiration did not decline
any further in the late entrance and torpor stages (T
b 15 and 5°C, respectively). Succinate dehydrogenase (SDH) activity declined in a similar pattern as mitochondrial respiration,
and there was a significant positive correlation between state 3 respiration and SDH activity. However, unlike during arousal
from torpor, oxaloacetate was not a major factor in inhibition of SDH. Analysis of mitochondrial lipids showed little change
in neutral lipids or phospholipid classes, except for a transient decrease in phosphatidylethanolamine content in early entrance.
In the transition from interbout euthermia to early entrance, we found transient increases in some saturated phospholipid
fatty acids (16:0, 18:0) and decreases in some unsaturates (18:2, 20:4). These changes resulted in transient increases in
total saturates and the ratio of saturates to unsaturates, and transient decreases in total unsaturates, total polyunsaturates,
total n-6, the ratio of monounsaturates to polyunsaturates, and unsaturation index. None of these changes persisted into late
entrance or torpor, nor did they correlate with mitochondrial respiration. We conclude that mitochondrial metabolic suppression
during entrance into a torpor bout occurs very early and is likely related to acute regulation of electron transport chain
enzymes rather than changes in membrane phospholipid composition. 相似文献
18.
Reduction of metabolism during hibernation and daily torpor in mammals and birds: temperature effect or physiological inhibition? 总被引:6,自引:6,他引:0
Fritz Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1988,158(1):25-37
Summary The present study addresses the controversy of whether the reduction in energy metabolism during torpor in endotherms is strictly a physical effect of temperature (Q10) or whether it involves an additional metabolic inhibition. Basal metabolic rates (BMR; measured as oxygen consumption,
), metabolic rates during torpor, and the corresponding body temperatures (T
b) in 68 mammalian and avian species were assembled from the literature (n=58) or determined in the present study (n=10). The Q10 for change in
between normothermia and torpor decreased from a mean of 4.1 to 2.8 with decreasingT
b from 30 to <10°C in hibernators (species that show prolonged torpor). In daily heterotherms (species that show shallow, daily torpor) the Q10 remained at a constant value of 2.2 asT
b decreased. In hibernators with aT
b<10°C, the Q10 was inversely related to body mass. The increase of mass-specific metabolic rate with decreasing body mass, observed during normothermia (BMR), was not observed during torpor in hibernators and the slope relating metabolic rate and mass was almost zero. In daily heterotherms, which had a smaller Q10 than the hibernators, no inverse relationship between the Q10 and body mass was observed, and consequently the metabolic rate during torpor at the sameT
b was greater than that of hibernators. These findings show that the reduction in metabolism during torpor of daily heterotherms and large hibernators can be explained largely by temperature effects, whereas a metabolic inhibition in addition to temperature effects may be used by small hibernators to reduce energy expenditure during torpor.Abbreviation
BMR
basal metabolic rate 相似文献
19.
R. Oelkrug G. Heldmaier C. W. Meyer 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(1):137-145
In eutherian mammals, uncoupling protein 1 (UCP1) mediated non-shivering thermogenesis from brown adipose tissue (BAT) provides
a mechanism through which arousal from torpor and hibernation is facilitated. In order to directly assess the magnitude by
which the presence or absence of UCP1 affects torpor patterns, rewarming and arousal rates within one species we compared
fasting induced torpor in wildtype (UCP1+/+) and UCP1-ablated mice (UCP−/−). Torpor was induced by depriving mice of food for up to 48 h and by a reduction of ambient temperature (T
a) from 30 to 18°C at four different time points after 18, 24, 30 and 36 h of food deprivation. In most cases, torpor bouts
occurred within 20 min after the switch in ambient temperature (30–18°C). Torpor bouts expressed during the light phase lasted
3–6 h while significantly longer bouts (up to 16 h) were observed when mice entered torpor during the dark phase. The degree
of hypometabolism (5–22 ml h−1) and hypothermia (19.5–26.7°C) was comparable in wildtype and UCP1-ablated mice, and both genotypes were able to regain normothermia.
In contrast to wildtype mice, UCP1-ablated mice did not display multiple torpor bouts per day and their peak rewarming rates
from torpor were reduced by 50% (UCP1+/+: 0.24 ± 0.08°C min−1; UCP1−/−: 0.12 ± 0.04°C min−1). UCP1-ablated mice therefore took significantly longer to rewarm from 25 to 32°C (39 vs. 70 min) and required 60% more energy
for this process. Our results demonstrate the energetic benefit of functional BAT for rapid arousal from torpor. They also
suggest that torpor entry and maintenance may be dependent on endogenous rhythms. 相似文献
20.
Kelm DH von Helversen O 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2007,177(6):667-677
Neotropical nectar-feeding bats (Glossophaginae) are highly specialized in the exploitation of floral nectar and have one
of the highest mass-specific metabolic rates among mammals. Nevertheless, they are distributed throughout the tropics and
subtropics over a wide elevational range, and thus encounter many extreme and energetically challenging environmental conditions.
Depressing their otherwise high metabolic rate, e.g., in situations of food restriction, might be an important adaptive physiological
strategy in these dietary specialists. We investigated the thermoregulatory behavior of captive 10-g nectar feeding bats (Glossophaga soricina; Chiroptera, Phyllostomidae) under variable ambient temperatures (T
a) and feeding regimes and predicted that bats would use torpor as an energy-conserving behavior under energetic constraints.
All tested animals entered torpor in response to energetic restrictions and the depth of torpor was dependent on the body
condition of the animals and hence on their degree of physiological constraints. Periods of torpor with body temperatures
(T
b) below 34°C were precisely adjusted to the photoperiod. The median length of diurnal torpor was 11.43 h. The lowest T
b measured was 21°C at a T
a of 19°C. Estimated energy savings due to torpor were considerable, with reductions in metabolic rate to as low as 5% of the
metabolic rate of normothermic bats at the same T
a. However, contrary to temperate zone bats that also employ diurnal torpor, G. soricina regulated their T
b to the highest possible levels given the present energetic supplies. To summarize, G. soricina is a precise thermoregulator, which strategically employs thermoregulatory behavior in order to decrease its energy expenditure
when under energetic restrictions. This adaptation may play a crucial role in the distribution and the assembly of communities
of nectar-feeding bats and may point to a general capacity for torpor in tropical bats. 相似文献