共查询到20条相似文献,搜索用时 687 毫秒
1.
Wendy A. Wilson M. Justin O’Riain Robyn S. Hetem Andrea Fuller Linda G. Fick 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(7):1099-1110
The body temperature (T
b) of Cape ground squirrels (Xerus inauris, Sciuridae) living in their natural environment during winter has not yet been investigated. In this study we measured abdominal
T
b of eight free-ranging Cape ground squirrels over 27 consecutive days during the austral winter. Mean daily T
b was relatively stable at 37.0 ± 0.2°C (range 33.4 to 40.2°C) despite a marked variation in globe temperature (T
g) (range −7 to 37°C). Lactating females (n = 2) consistently had a significantly higher mean T
b (0.7°C) than non-lactating females (n = 3) and males. There was a pronounced nychthemeral rhythm with a mean active phase T
b of 38.1 ± 0.1°C and a mean inactive phase T
b of 36.3 ± 0.3°C for non-lactating individuals. Mean daily amplitude of T
b rhythm was 3.8 ± 0.2°C. T
b during the active phase closely followed T
g and mean active phase T
b was significantly correlated with mean active phase T
g (r
2 = 0.3–0.9; P < 0.01). There was no evidence for daily torpor or pronounced hypothermia during the inactive phase, and mean minimum inactive
phase T
b was 35.7 ± 0.3°C for non-lactating individuals. Several alternatives (including nocturnal huddling, an aseasonal breeding
pattern and abundant winter food resources) as to why Cape ground squirrels do not employ nocturnal hypothermia are discussed. 相似文献
2.
Kart Gür M Refinetti R Gür H 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2009,179(2):155-164
We studied daily rhythmicity of body temperature (T
b) before and during hibernation in Anatolian ground squirrels (Spermophilus xanthoprymnus) under natural and laboratory conditions using surgically implanted temperature loggers. Under both conditions, robust daily
T
b rhythmicity with parameters comparable to those of other ground squirrel species was observed before but not during hibernation.
Euthermic animals had robust daily T
b rhythms with a mean of 37.0°C and a range of excursion of approximately 4°C. No T
b rhythm was detected during torpor bouts, either because T
b rhythmicity was absent or because the daily range of excursion was smaller than 0.2°C. The general patterns of hibernation
that we observed in Anatolian ground squirrels were similar to those previously observed by other investigators in other species
of ground squirrels. 相似文献
3.
El Ouezzani S Janati IA Magoul R Pévet P Saboureau M 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(2):299-309
The jerboa (Jaculus orientalis) has been described in the past as a hibernator, but no reliable data exist on the daily and seasonal rhythmicity of body
temperature (T
b). In this study, T
b patterns were determined in different groups of jerboas (isolated males and females, castrated males and grouped animals)
maintained in captivity during autumn and winter, and submitted to natural variations of light and ambient temperature (T
a). T
b and T
a variations were recorded with surgically implanted iButton temperature loggers at 30-min intervals for two consecutive years.
About half (6/13) of isolated female jerboas hibernated with a T
b < 33°C, with hibernation bouts interspersed with short periods of normothermy from November to February. Hibernation bout
durations were longer (4–5 days) than those of normothermia phases (1–4 days). During hibernation, the minimum T
b was low (T
bmin ~10.7°C). In contrast, one of the 12 isolated males showed short hibernation bouts of ca. 2 days late in the hibernation
season, February–March. The males had T
bmin values of 15.1°C. In contrast to predictions, no castrated males hibernated. When jerboas were grouped, females and males
exhibited concomitant torpor bouts. In males, the longest bouts were observed during the late hibernation season. These data
suggest complex regulation of hibernation in jerboas. 相似文献
4.
Summary The body temperature (T
b) of free-living alpine marmots rose with activity; the higher the effective environmental temperature (T
e), the higher the rise. Maximum T
bof 40° C was reached at the time of greatest activity in late afternoon or evening. The activity pattern was strongly influenced by the microclimate. Up to an T
eof 25° C the animals spent more time above ground and were more active the higher T
ewas, but above 25° C this trend was reversed, and the animals withdrew increasingly into their burrows. On warm days the activity pattern was therefore bimodal and above ground presence was reduced, in contrast to cool days. Hence behavioural thermoregulation limits the available time for above ground activity on days with high T
ein this strictly diurnal species. We suggest that the alpine marmots' preference for south oriented slopes is due to the better conditions for hibernation there, the microclimate during summer is more favourable on northerly slopes. Thermoregulatory constraints could also keep alpine marmots away from lower elevations. 相似文献
5.
The hibernating marsupial mountain pygmy-possum (Burramys parvus, 40 g) has to raise its slow-growing offspring during a short alpine summer. Only females provide parental care, while after
mating males emigrate to marginal habitats often at lower altitudes which can sustain only low possum densities. We predicted
that the hibernation strategies in mountain pygmy-possums are distinct from those of similar-sized placental hibernators,
because of the developmental constraints in marsupials and because hibernation differs between the sexes. Using temperature-sensitive
radio transmitters, we studied the hibernation patterns of free-living male and female mountain pygmy-possums living in a
north- and a south-facing boulder field (Kosciusko National Park) for two consecutive winters. Individual possums commenced
hibernation several months before the snow season. As in other hibernators, torpor in the mountain pygmy-possum was interrupted
by periodic arousals which occurred most often during the late afternoon. Torpor bouts initially lasted a few days when the
hibernacula temperature (T
hib) ranged from 4 to 7°C. As the hibernation season progressed, torpor bouts became longer and possum body temperatures (T
b) approached 2°C. The T
bs of females were significantly lower and torpor bouts were longer in the second half of the hibernation season than in males.
Between torpor bouts, both sexes were often active and left hibernacula for periods of up to 5 days. Especially during the
first months of the hibernation season, possums also frequently changed hibernacula sites probably in an attempt to select
a site with a more suitable microclimate. Emergence from hibernation was closely coupled with the disappearance of snow from
the possum habitat (September 1995, October 1996) and the limited fat stores probably dictate an opportunistic spring emergence.
However, in 1995, spring was early and males emerged significantly earlier than females. In 1996, when snow melt was delayed,
this difference vanished. Testes are regressed in males during hibernation and the time needed for testes growth and spermatogenesis
favours an earlier emergence for males which was probably achieved by their preference for the more sun exposed north-facing
boulder field. A sexual dimorphism in hibernation strategies and spring emergence therefore enables mountain pygmy-possums
to cope with their harsh alpine environment.
Received: 22 May 1997 / Accepted: 21 August 1997 相似文献
6.
Rae L. Russell Philip H. O’Neill L. Elaine Epperson Sandra L. Martin 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(8):1165-1172
Mammalian hibernation is characterized by profound reductions in body temperature (T
b) and metabolic, heart and respiratory rates. These reductions are characteristic of torpor, which is temporally confined
to winter. Hibernators including ground squirrels are heterothermic in winter, cycling between multiday periods of torpor
with low T
b and brief periods of rewarming. In contrast, ground squirrels remain homeothermic during summer, like non-hibernating mammals.
The transition between the homeothermic and heterothermic phases of the circannual rhythm of hibernation is often overlooked
in hibernation studies. Here, we examined the use of torpor throughout the fall transition in laboratory-housed 13-lined ground
squirrels by recording core body temperature with an implanted data logger. As is typical of laboratory-based hibernation
studies, animals were kept in standard housing prior to being moved into a cold, dark room to simulate natural hibernation
conditions. Significantly, the vast majority of both male and female ground squirrels expressed torpor in the fall while still
housed conventionally and prior to cold exposure. The expression of torpor was not predicted by body weight or age, rather
it appears to be preprogrammed in a time-dependent manner that is independent of, yet enhanced by, environmental cues. The
timing and duration of these torpor bouts occurring prior to cold exposure were also remarkably sporadic. Thus, it is not
possible to know with certainty which animals are torpor-naive before cold exposure in the absence of continuous measurement
of body temperature. We conclude that fall animals encompass variable points in the transition between summer and winter phases
of the circannual cycle of hibernation, thereby confounding studies in which they are used as non-hibernating controls. Conversely,
these fall transition animals offer unique opportunities to define the molecular changes that accompany and enable hibernation. 相似文献
7.
Getting to the core: Internal body temperatures help reveal the ecological function and thermal implications of the lions’ mane 下载免费PDF全文
Paul Trethowan Andrea Fuller Anna Haw Tom Hart Andrew Markham Andrew Loveridge Robyn Hetem Byron du Preez David W. Macdonald 《Ecology and evolution》2017,7(1):253-262
It has been proposed that there is a thermal cost of the mane to male lions, potentially leading to increased body surface temperatures (Ts), increased sperm abnormalities, and to lower food intake during hot summer months. To test whether a mane imposes thermal costs on males, we measured core body temperature (Tb) continuously for approximately 1 year in 18 free‐living lions. There was no difference in the 24‐hr maximum Tb of males (n = 12) and females (n = 6), and males had a 24‐hr mean Tb that was 0.2 ± 0.1°C lower than females after correcting for seasonal effects. Although feeding on a particular day increased 24‐hr mean and 24‐hr maximum Tb, this phenomenon was true of both male and female lions, and females had higher 24‐hr mean and 24‐hr maximum Tb than males, on both days when lions did not feed, and on days when lions did feed. Twenty‐four‐hour Tb was not influenced by mane length or color, and 24‐hr mean Tb was negatively correlated with mane length. These data contradict the suggestion that there exists a thermal cost to male lions in possessing a long dark mane, but do not preclude the possibility that males compensate for a mane with increased heat loss. The increased insulation caused by a mane does not necessarily have to impair heat loss by males, which in hot environments is primarily through respiratory evaporative cooling, nor does in necessarily lead to increased heat gain, as lions are nocturnal and seek shade during the day. The mane may even act as a heat shield by increasing insulation. However, dominant male lions frequent water points more than twice as often as females, raising the possibility that male lions are increasing water uptake to facilitate increased evaporative cooling. The question of whether male lions with manes compensate for a thermal cost to the mane remains unresolved, but male lions with access to water do not have higher Tb than females or males with smaller manes. 相似文献
8.
Free-living ground squirrel species are sexually dimorphic in hibernation phenology. The underlying causes of these differences are not yet known. Androgens, testosterone (T) in particular, inhibit hibernation. To determine the influence of endogenous androgens on annual timing of hibernation we first measured circulating levels of T and dehydroepiandrosterone (DHEA), an adrenal androgen implicated in non-mating season aggression in other species, in free-living male arctic ground squirrels (Urocitellus parryii, AGS). We also manipulated endogenous androgen levels by surgical castration, and consequently compared body temperature records from intact (n = 24) and castrated (n = 9) males to elucidate the influence of endogenous androgens on annual body temperature cycles. The highest T levels (0.53 ± 0.10 ng/mL) were in reproductively mature male AGS in spring; whereas, both immature males in spring and all males in late summer had T levels an order of magnitude lower (0.07 ± 0.01 and 0.06 ± 0.00 ng/mL, respectively). DHEA levels were higher in males during the late summer compared to reproductively mature males in spring (120.6 ± 18.9 and 35.9 ± 2.3 pg/mL, respectively). Eliminating gonadal androgens via castration resulted in males delaying euthermy by extending heterothermy significantly in spring (Apr 22 ± 2.9) than reproductive males (Mar 28 ± 3.9) but did not change the timing of hibernation onset (castrate: Oct 12 ± 1.0 vs. intact: Oct 3 ± 3.1). We conclude that while androgens play a significant role in spring hibernation phenology of males, their role in fall hibernation onset is unclear. 相似文献
9.
Daily and seasonal cycles of body temperature and aspects of heterothermy in the hedgehog Erinaceus europaeus 总被引:1,自引:1,他引:0
P. A. Fowler P. A. Racey 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1990,160(3):299-307
Summary Intra-abdominal temperature-sensitive radio transmitters were used to collect more than 350 sets of body temperature (T
b
) data from 23 captive adult hedgehogs over a 3-year period. Each data set comprised measurements made every 1/2 h for 24-h periods. Between 20 and 60 such data sets were recorded every calendar month, and a total of 17400 measurements of T
b
were collected. The hedgehogs were exposed to natural environmental conditions at 57°N in NE Scotland. Hedgehogs showed seasonal changes in mean daily euthermic T
b
,with a July maximum of 35.9±0.2°C, a September minimum of 34.7±0.9°C, and a marked circadian T
b
cycle that correlates closely with photoperiod. Maximal T
b
occurred within 2 h of midnight and this pattern of nocturnal maximum and diurnal minimum T
b
was most marked between April and September. The circadian T
b
cycle was least correlated with photoperiod during winter. Hibernal T
b
during winter correlated with ambient temperature (T
a
),it was maximal in September (17.7±1.0°C) and minimal in December (5.2±0.9°C). Apart from the tracking of T
a
and T
b
during hibernal bouts, with a time-lag of 4–6 h, circadian rhythmicity of hibernal T
b
was not evident. However, the T
b
of hibernating hedgehogs rose significantly when T
a
fell below — 5°C, although the animals did not neccessarily arouse. Although hibernal bouts occurred between September and April, 89.5% of such bouts were recorded between November and February. The mean time of entry into hibernation was 01:45±5.1 h GMT while the mean time of the start of spontaneous arousal from hibernation was 11:53±4.8 h GMT. Therefore, during hibernation hedgehogs were either fully aroused at night, when euthermic hedgehogs have maximalT
b
,or in deep hibernation around midday, when euthermic hedgehogs have minimal T
b
.Since wild hedgehogs will feed during spontaneous arousal from hibernation, these timings are probably adaptive, and suggest that entry into, and arousal from, hibernation may be extensions of circadian cyclicity. Spontaneous bouts of transient shallow torpor (TST) were recorded throughout the year, with nearly 80% of observations occurring during August and September, at the start of the hibernal period. TST bouts lasted for 4.9±2.9 h, with T
b
falling to 25.8±3.1 °C. Only 20% of TST bouts immediately preceded hibernation and their duration did not correlate with T
a
or body mass. TST bouts started at 06:51±4.7 h GMT, significantly later than entry into hibernation, and ended at 13:04±5.4 h GMT. The function of TST bouts is unclear, but they may be preparation for the hibernation season or a further energy conservation strategy. When arousing from hibernation hedgehogs warmed at a rate of 1.9±0.4°C·h-1, and when entering hibernation cooled at 7.9±1.9°C·h-1. Warming rates were slightly higher during mid-winter when T
b
and body mass were minimal, but cooling rates were 44% higher at the end of the hibernal period compared to the start. Cooling and warming rates were strikingly similar to those measured in hedgehogs at 31°N. These results demonstrate that thermoregulation in the hedgehog is closely regulated and changes on a seasonal basis, in meeting with requirements of surviving food shortages and low temperature during winter.Abbreviations
T
a
ambient temperature
-
T
b
body temperature
-
CSD
circular standard deviation
-
SWS
slow wave sleep
-
TST
transient shallow torpor 相似文献
10.
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
11.
M. A. Chappell 《Oecologia》1981,49(3):397-403
Summary Body temperatures (T
b) and daily activity patterns of free-living arctic ground squirrells (Spermophilus undulatus) were determined via telemetry at a field site in northern Alaska. Simultaneous measurements were made of ambient temperature (T
a), wind speed (V), and incident solar radiation. The operative environmental temperature (T
e) for ground squirrels was obtained from fur-covered, thin metal taxidermic models of the animals. Standard operative temperature (T
es), a comparative index of heat flow, was calculated from T
e, V, and laboratory measurements of thermal conductivity.During the period of the study (August), S. undulatus were active for about 14 h per day (06.00 to 20.00 h). T
b was high throughout the daily cycle, averaging 38–39°C. Circadian variations in T
b were slight; average T
b values dropped <1°C at night. Daytime T
b fluctuations were not closely correlated to activity or to changes in environmental conditions. Air temperatures during the study were low, usually between 10 and 15°C during the day. However, T
es in exposed areas was normally higher, even though skies were generally overcast. During periods of sunshine, T
es may be as high as 34°C. The absence of nocturnal activity may result from increased costs of thermoregulation at night, which sharply reduces foraging efficiency. The high and stable body temperatures of S. undulatus probably result from thermoneutral daytime T
es, low activity levels, and the use of well-insulated nests. 相似文献
12.
13.
Thomas Waßmer Franziska Wollnik 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):270-279
Body temperature (T
b) of seven European hamsters maintained at constant ambient temperature (T
a = 8 °C) and constant photoperiod (LD 8:16) was recorded throughout the hibernating season using intraperitoneal temperature-sensitive
HF transmitters. The animals spent about 30% of the hibernation season in hypothermia and 70% in inter-bout normothermy. Three
types of hypothermia, namely deep hibernation bouts (DHBs), short hibernation bouts (SHBs), and short and shallow hibernation
bouts (SSHBs), were distinguished by differences in bout duration and minimal body temperature (T
m). A gradual development of SSHBs from the diel minimum of T
b during normothermy could be seen in individual hamsters, suggesting a stepwise decrease of the homeostatic setpoint of T
b regulation during the early hibernation season. Entry into hibernation followed a 24-h rhythm occurring at preferred times
of the day in all three types of hypothermia. DHBs and SHBs were initiated approximately 4 h before SSHBs, indicating a general
difference in the physiological initiation of SSHBs on the one hand and DHBs and SHBs on the other. Arousals from SHBs and
SSHBs also followed a 24-h rhythm, whereas spontaneous arousals from DHBs were widely scattered across day and night. Statistical
analyses of bout length and the interval between arousals revealed evidence for a free-running circadian rhythm underlying
the timing of arousals. The results clearly demonstrate that entries into hypothermia are linked to the light/dark-cycle.
However, the role of the circadian system in the timing of arousals from DHBs remains unclear.
Accepted: 11 December 1996 相似文献
14.
The optimal depot fat composition for hibernation by golden-mantled ground squirrels (Spermophilus lateralis) 总被引:3,自引:3,他引:0
C. L. Frank K. B. Storey 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1995,164(7):536-542
Golden-mantled ground squirrels (Spermophilus lateralis) are herbivores that hibernate during winter. Although little is known about the nutritional/physiological constraints on hibernation, numerous studies have demonstrated that increasing the amount of linoleic acid (a polyunsaturated fatty acid) in the diet enhances hibernation. This is probably because high linoleic acid diets reduce the melting points of the depot fats produced for hibernation which makes them more metabolizable at low body temperatures. This suggests that a major limitation on hibernation may be obtaining enough linoleic acid in the diet for proper hibernation. In all previous studies, however, the amount of linoleic acid in the diets of free-ranging animals was either not considered, or the range of dietary linoleic acid contents in the experiments was less than that of natural diets. It is thus not known whether the amount of linoleic acid available to hibernators under natural conditions actually limits their torpor patterns. A series of laboratory feeding and hibernation experiments were conducted with S. lateralis and artificial diets with different linoleic acid contents that were either below or above the linoleic acid content of the natural diet. The results demonstrated that when dietary linoleic acid contents are either below or above natural levels, hibernation ability is greatly reduced. Hibernation ability was reduced when the squirrels were maintained on a high linoleic acid diet probably by the production of toxic lipid peroxides in brown adipose tissues. The results indicate that there is an optimal level of dietary linoleic acid for proper hibernation, and this is equal to that of the natural diet. The amount of linoleic acid available in the diet thus does not limit hibernation under normal natural conditions.Abbreviations BAT
brown adipose tissue
- bm
body mass
- FA
fatty acid
- PUFA
polyunsaturated fatty acid
-
T
a
ambient temperature
-
T
b
body temperature
- WAT
white adipose tissue 相似文献
15.
P. J. Young 《Oecologia》1990,83(4):504-511
Summary The patterns of torpor and euthermy during hibernation was documented for 28 free-ranging Columbian ground squirrels (Spermophilus columbianus) fitted with temperature-sensitive radio transmitter collars. Adult males began hibernation earlier, were euthermic for a greater proportion of the hibernating season and emerged earlier than other age and sex classes. The patterns of hibernation of adult females did not differ significantly from those of juveniles. Emergence from the hibernaculum was preceded by a long (3–12 d) euthermic interval in adult males but not in adult females or juveniles. Changes in soil temperature did not appear to initiate emergence. The greater time spent euthermic by adult males is interpreted as a significantly greater energy cost of hibernation for adult males than for other age and sex classes. The benefits offsetting these costs may be increased reproductive potential in spring and avoidance of predation in late summer. 相似文献
16.
H. V. Carey N. S. Sills 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(4):254-261
The ability to actively transport nutrients is maintained in intestinal tissues of hibernating ground squirrels compared with their active counterparts, and shows apparent upregulation in hibernators when transport rates are normalized to tissue mass. To identify the mechanisms responsible for the preservation of transport function during the extended fast of hibernation, we studiedd-glucose uptake into jejunal brush border membrane vesicles prepared from active and hibernating 13-lined ground squirrels. Hibernators were without food and showing regular bouts of torpor for at least 6 weeks before sacrifice. Electron micrographs indicated similar microvillus heights of jejunal enterocytes in the two activity states, whereas microvillus density was slightly greater in the hibernators. Glucose uptake into brush border membrane vesicles was inversely related to medium osmolarity, indicating negligible binding of substrate to brush border membrane vesicles surfaces, and intravesicular spaces were similar in hibernating and active squirrels. Glucose uptake showed strong Na+ dependency in both groups, with equivalent overshoot values in the presence of Na+. Kinetic analysis revealed a significant increase in the maximal velocity of transport (J
max) in hibernators (55.9±5.6 nmol·min-1·mg-1) compared with active squirrels (36.7±5.1 nmol·min-1·mg-1,P<0.05), with no change inK
m. Thus, the structure and absorptive capacity of the intestinal brush border persists in fasted hibernators, and the increase inJ
max for glucose uptake during hibernation likely contributes to the enhanced Na+-dependent glucose absorption previously observed at the tissue level.Abbreviations
BBM
brush border membrane(s)
-
BBMV
brush border membranes vesicles
-
SGLT1
Na+-glucose transporter
-
3-OMG
3-orthomethylglucose
-
J
max
maximal velocity of transport
-
K
m
transporter affinity for substrate
-
T
b
body temperature 相似文献
17.
Comparison of hibernation, estivation and daily torpor in the edible dormouse, Glis glis 总被引:2,自引:0,他引:2
Wilz M Heldmaier G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(7):511-521
Three major forms of dormancy in mammals have been classified: hibernation in endotherms is characterised by reduced metabolic
rate (MR) and body temperature (T
b) near ambient temperature (T
a) over prolonged times in the winter. Estivation is a similar form of dormancy in a dry and hot environment during summertime.
Daily torpor is defined as reduced MR and T
b lower than 32 °C, limited to a duration of less than 24 h. The edible dormouse (Glis glis) is capable for all three distinct forms of dormancy. During periods of food restriction and/or low T
a, daily torpor is displayed throughout the year, alternating with hibernation and estivation in winter and summer respectively.
We recorded T
b, O2-consumption and CO2-production in unrestrained dormice at different T
a's for periods of up to several months. Cooling rate and rate of metabolic depression during entrance into the torpid state
was identical in all three forms of dormancy. The same was true for thermal conductance, maximum heat production, duration
of arousal and cost of an arousal. The only difference between hibernation and daily torpor was found in the bout duration.
A daily torpor bout lasted 3–21 h, a hibernation bout 39–768 h. As a consequence of prolonged duration, MR, T
b and also the T
b − T
a gradient decreased to lower values during hibernation bouts when compared to daily torpor bouts. Our findings suggest that
all three forms of dormancy are based on the same physiological mechanism of thermal and metabolic regulation.
Accepted: 27 June 2000 相似文献
18.
Endothermic mosasaurs? Possible thermoregulation of Late Cretaceous mosasaurs (Reptilia,Squamata) indicated by stable oxygen isotopes in fossil bioapatite in comparison with coeval marine fish and pelagic seabirds 下载免费PDF全文
The thermoregulatory style of Late Cretaceous mosasaurs has become a highly controversial subject in vertebrate palaeontology. These extinct marine reptiles have previously been described as poikilothermic, endothermic or gigantothermic. Here we analyse three genera of mosasaurs from the Mooreville Chalk in Alabama (USA) of differing body mass, and compare their δ18OPO4 derived body temperatures (Tb) with those of coeval poikilothermic fish (Enchodus) and endothermic pelagic seabirds (Ichthyornis). Results show that all mosasaurs, Clidastes (Tb = 33.1°C), Platecarpus (Tb = 36.3°C), and Tylosaurus (Tb = 34.3°C), had elevated average body temperatures in relation to those of the fish (Tb = 28.3°C) and were closer to those of Ichthyornis (Tb = 38.6°C). The temperatures calculated for Enchodus compare well with previously reported temperature estimates for the Mooreville Chalk and the Tb of Ichthyornis compares well with temperatures that have been reported for modern seabirds, suggesting that this method provides accurate results. Finally, although there are small differences of body temperature among mosasaur genera, these are independent of size, and thus inferred body mass, suggesting that mosasaurs were not gigantotherms, but rather endotherms. 相似文献
19.
Using continuous video recording, we identified predation as the main cause of nest failure of understorey‐nesting birds in an intact evergreen forest in northeastern Thailand. Our dataset of 87 predation events is the largest recorded in the tropics. The main predators were macaques (n = 38; 43.7%), nocturnal snakes (n = 19; 21.8%), non‐raptorial birds (n = 12; 13.8%), raptors (n = 6; 6.9%), squirrels (n = 5; 5.7%) and tree shrews (n = 4; 4.6%). The two most important predators, Pig‐tailed Macaque Macaca nemistrina and Green Cat Snake Boiga cinerea, showed no preference for nest type, nest stage or nest height and we found no difference in their relative predation rates among years. Predation was predominantly diurnal (73.6%), suggesting that visual cues may be important for predators at this site. 相似文献
20.
N. J. Adams B. Pinshow L. Z. Gannes H. Biebach 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(3):195-199
We examined the relationship between body temperature (Tb) of free flying pigeons and ambient water vapor pressure and temperature. Core or near core Tb of pigeons were measured using thermistors inserted into the cloaca and connected to small transmitters mounted on the tail
feathers of free flying tippler pigeons (Columba livia). Wet and dry bulb temperatures were measured using modified transmitters mounted onto free-flying pigeons. These allowed
calculation of relative humidity and hence water vapor pressure at flight altitudes. Mean Tb during flight was 42.0 ± 1.3 °C (n = 16). Paired comparisons of a subset of this data indicated that average in-flight Tb increased significantly by 1.2 ± 0.7 °C (n = 7) over that of birds at rest (t = −4.22, P < 0.05, n = 7) within the first 15 min of takeoff. In addition, there was a small but significant increase in Tb with increasing ambient air (Ta) when individuals on replicate flights (n = 35) were considered. Inclusion of water vapor pressure into the regression model did not improve the correlation between
body temperature and ambient conditions. Flight Tb also increased a small (0.5 °C) but significant amount (t = 2.827, P < 0.05, n = 8) from the beginning to the end of a flight. The small response of Tb to changing flight conditions presumably reflects the efficiency of convection as a heat loss mechanism during sustained
regular flight. The increase in Tb on landing that occurred in some birds was a probable consequence of a sudden reduction in convective heat loss.
Accepted: 2 February 1999 相似文献