Normothermic Periods Research Articles

Second generation sequencing and morphological faecal analysis reveal unexpected foraging behaviour by Myotis nattereri (Chiroptera, Vespertilionidae) in winter.

BackgroundTemperate winters produce extreme energetic challenges for small insectivorous mammals. Some bat species inhabiting locations with mild temperate winters forage during brief inter-torpor normothermic periods of activity. However, the winter diet of bats in mild temperate locations is studied infrequently. Although microscopic analyses of faeces have traditionally been used to characterise bat diet, recently the coupling of PCR with second generation sequencing has offered the potential to further advance our understanding of animal dietary composition and foraging behaviour by allowing identification of a much greater proportion of prey items often with increased taxonomic resolution. We used morphological analysis and Illumina-based second generation sequencing to study the winter diet of Natterer’s bat (Myotis nattereri) and compared the results obtained from these two approaches. For the first time, we demonstrate the applicability of the Illumina MiSeq platform as a data generation source for bat dietary analyses.ResultsFaecal pellets collected from a hibernation site in southern England during two winters (December-March 2009–10 and 2010–11), indicated that M. nattereri forages throughout winter at least in a location with a mild winter climate. Through morphological analysis, arthropod fragments from seven taxonomic orders were identified. A high proportion of these was non-volant (67.9% of faecal pellets) and unexpectedly included many lepidopteran larvae. Molecular analysis identified 43 prey species from six taxonomic orders and confirmed the frequent presence of lepidopteran species that overwinter as larvae.ConclusionsThe winter diet of M. nattereri is substantially different from other times of the year confirming that this species has a wide and adaptable dietary niche. Comparison of DNA derived from the prey to an extensive reference dataset of potential prey barcode sequences permitted fine scale taxonomic resolution of prey species. The high occurrence of non-volant prey suggests that gleaning allows prey capture at low ambient temperatures when the abundance of flying insects may be substantially reduced. Interesting questions arise as to how M. nattereri might successfully locate and capture some of the non-volant prey species encountered in its faeces. The consumption of lepidopteran larvae such as cutworms suggests that M. nattereri eats agricultural pest species.

Continuous EEG in therapeutic hypothermia after cardiac arrest: Prognostic and clinical value

We read with interest the study by Crepeau et al.1 who reviewed EEG in cardiac arrest survivors. They found that when EEG was performed during hypothermic and early normothermic periods, it might yield useful prognostic information.

Hibernation and daily torpor in Australian mammals

Torpor is the most effective means for energy conservation available to mammals and is characterized by substantial reductions in body temperature (T b ) and metabolic rate (MR). Most Australian terrestrial mammals are small with high mass-specific energy requirements and, although it is widely believed that torpor is not needed in a ‘warm’ country like Australia, a large number of species are heterothermic (i.e. capable of changing T b , in contrast to homeothermic mammals with a constant high T b ). These heterothermic species (estimated >43% of terrestrial Australian native mammals) employ periods of daily torpor or prolonged multi-day torpor (hibernation) to conserve energy. Daily torpor is used by dasyurids (e.g. dunnarts, antechinus, quolls), myrmecobiids (numbat), tarsipedids (honey-possum), petaurid possums (e.g. sugar glider), rodents (but only known in the introduced house mouse), and small megabats (blossom-bats). During daily torpor, T b is reduced from ~35oC during the active or normothermic phase to ~10-25oC during torpor, and the torpor MR (TMR) is ~30% of the basal metabolic rate (BMR). Daily torpor is often, but not exclusively, used during the rest phase and, between bouts of torpor, animals usually forage and feed. Recent evidence shows that free-ranging arid zone dasyurids may employ daily torpor on every day in winter and that torpor may last twice as long as in captivity (often up to around 20 hours), which will reduce energy expenditure and thereby food requirements by up to 80%. Hibernation or prolonged torpor has been observed in the Monotremes (echidna), marsupials (pygmy-possums and feathertail glider) and insectivorous bats (e.g. long-eared bats). During prolonged torpor, which often, but not exclusively, is expressed in winter, T b is usually reduced to a minimum of ~0-10oC, and torpor bouts may last for several days or weeks, but in all species periodic arousals with brief normothermic periods (hours) between bouts of torpor have been observed. The TMR during hibernation is extremely low and can be as little as 1-5% of the BMR; daily energy expenditure can be reduced to only 3% of that in active individuals permitting survival on stored body fat for months without the need to feed. Daily and prolonged torpor in many Australian mammals appear to be opportunistic and not only important for survival of adverse seasonal conditions, but apparently also for dealing with unpredictable events such as droughts and perhaps fires and floods. As torpor substantially reduces energy requirements its use will in turn reduce the need for foraging and consequently exposure to predators. Predator avoidance by employing torpor and minimising foraging may be one of the reasons why none of the known heterothermic Australian species has gone extinct. In contrast many of the similar-sized perceived homeothermic species, such as rodents and bandicoots, have suffered high rates of extinction possibly because they must forage long and frequently to meet large energetic demands and thus are more vulnerable to predation by introduced foxes and cats.

Diuretic treatment affects the length of torpor bouts in hibernating European ground squirrels (Spermophilus citellus)

During the hibernation season, hibernating mammals show a sequence of torpor bouts that are interrupted by periodic arousals and brief normothermic periods. The functional significance of periodic arousals is still uncertain. We hypothesized that the imbalances in water economy may play a role in the timing of periodic arousals in hibernating species. We applied furosemide, a diuretic drug, to assess whether hibernating European ground squirrels respond to elevated urine production by shortening their torpor bouts. Urine production in the treated squirrels increased and led to more frequent arousals, presumably to restore water balance by recovery of lost water from blood and tissues. The length of the subsequent normothermic phase was not affected by the diuretic treatment. Body mass change correlated primarily with the amount of voided urine. Although our study did not identify the underlying mechanism, our results support the view that water economy, and water loss may play a role in the timing of periodic arousals.

Nafamostat prevents hypothermia and improves survival time after administration of lipopolysaccharide in a mouse surgical model

Lipopolysaccharide (LPS) is an endotoxin known to induce disseminated intravascular coagulation and multiple organ failure followed by septic shock in animals. Nafamostat is a synthetic protease inhibitor with anticoagulant effects. This study investigated the effect of systemic administration of nafamostat on thermogenic homeostasis and survival time in a mouse surgical model. Male C57Bl/6 mice were anesthetized with sevoflurane and implanted with intraabdominal telemetry transmitters. Following the surgery, three groups of animals were administered Escherichia coli LPS (0127: B8) subcutaneously at doses of 0.3, 1.0, or 3.0 mg kg(-1), and one group received saline without LPS. Three other groups received 3 mg.kg(-1) LPS with 1, 3, or 10 mg kg(-1) of nafamostat. In another group 10 mg kg(-1)1 of nafamostat only was administered. The times to the onset of hypothermia (body temperature < 30 degrees C) and death were determined. L LPS significantly shortened the duration of both normothermia and survival, and nafamostat prolonged the normothermic periods that were reduced b 3 mg.kg(-1) LPS. Survival time was significantly correlated with the duration of normothermia (n = 48; r (2) = 0.779; P < 0.000001). The results demonstrated the effect of systemic administration of nafamostat against LPS-induced hypothermia. Nafamostat prevented hypothermia, and the consequent normal thermoregulation may have prolonged the survival period.

Heterothermy in free-ranging male Egyptian Free-tailed bats ( Tadarida aegyptiaca) in a subtropical climate

Bats, like many other small endotherms, often use facultative reductions in metabolic rate and body temperature (Tb) to decrease their daily energy expenditure (Lyman 1970). The lower energy requirements associated with heterothermy offset the high massspecific rates of heat loss of most microchiropterans, allowing them to maintain energy balance even in environments where the availability of food fluctuates temporally and/or spatially. Heterothermic responses in bats and other mammals are thought to be broadly divisible into two categories, namely daily torpor and hibernation, which are distinguishable primarily on the basis of bout length (Geiser and Ruf 1995). Daily torpor typically involves periods of reduced Tb lasting less than 24 hours, whereas hibernation involves multi-day bouts that may last as long as several months (Geiser and Ruf 1995). Hibernation is widespread in temperate-zone bat species that experience low environmental temperatures and reduced food availability during winter (Lyman et al. 1982; Arlettaz et al. 2000; Humphries et al. 2002). Bats often hibernate in thermally stable microsites such as caves and buildings during winter, which allows them to maintain more-or-less constant Tb between interbout normothermic periods (Lyman et al. 1982; Arlettaz et al. 2000; Humphries et al. 2002; Boyles and Willis 2009). In contrast, daily

Hibernation by a free-ranging subtropical bat (Nyctophilus bifax)

Knowledge about torpor in free-ranging subtropical bats is scarce and it is widely believed that low and stable ambient temperatures are necessary for prolonged torpor. We present temperature-telemetry data from free-ranging male (n = 4) and female (n = 4) subtropical vespertilionid bats, Nyctophilus bifax (approximately 10 g), exposed to pronounced daily fluctuations of ambient temperature. All bats used torpor on every day in winter and both males and females exhibited multi-day torpor bouts of up to 5.4 days. Although females were larger than males, patterns of torpor were similar in both sexes. Torpor use was correlated with prevailing weather conditions and, on days when bats remained torpid, maximum ambient temperature was significantly lower than on days when bats aroused. Moreover, the duration of interbout normothermic periods at night increased with increasing average nightly ambient temperature. Skin temperature of torpid bats varied by 10.2 +/- 3.6 degrees C day(-1) (n = 8, N = 47) and daily minimum skin temperature was positively correlated with the daily minimum ambient temperature. Our study shows that prolonged torpor is an important component of the winter ecology of a subtropical bat and that torpor and activity patterns of N. bifax predominantly reflect prevailing weather conditions.

THE TEMPORAL ORGANIZATION OF DAILY TORPOR AND HIBERNATION: CIRCADIAN AND CIRCANNUAL RHYTHMS

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)

Hibernation in Free-Living Mountain Pygmy-Possums, Burramys Parvus (Marsupialia, Burramyidae)

The long-term pattern of hibernation was studied in free-living mountain pygmy-possums, Burramys parvus, using temperature-sensitive radio-collars. Most males and females began to hibernate in early June within one week of their release. Hibernation was interrupted by spontaneous arousals that were followed by short normothermic periods and re-entry into torpor. The duration of multiday torpor bouts averaged 8 . 0 days (range 3-17 days) and arousal periods averaged 19 . 1 h. Single-day torpor bouts were observed occasionally. The duration of torpor bouts lengthened with the progress of the hibernation season and normothermic periods became shorter. The pattern of hibernation in free-living B. parvus was similar to that of captive individuals maintained under temperature regimes that were similar to those in the wild.

Hibernation in the mountain pygmy possum Burramys parvus (Marsupialia)

Mountain pygmy possums Burramys parvus (40 g) disappear from their Mt. Kosciusko boulder fields from May to October/November and it is assumed that they hibernate during this time. However, laboratory studies did not observe the characteristic hibernation pattern of placentals, which, throughout the hibernation season, show long bouts of torpor (several days to weeks) that are interrupted by short (&lt; 1 day) normothermic periods. We investigated the pattern of hibernation in juvenile (N = 8) and adult (N = 8) male and female B. parvus in the laboratory at an air temperature that was similar to that in the field during winter. Adults commenced hibernation earlier and hibernated longer (about seven months) than juveniles (about five months). All adult individuals hibernated whereas only six of the eight juveniles did so. Hibernating animals showed distinct seasonal changes in the duration of torpor bouts. Torpor bouts were short (about five days) at the beginning, long (12–20 days) during the middle, and short again at the end of the hibernation season. Normothermic periods were usually shorter than one day. The pattern of the seasonal change of torpor bout duration differed between juveniles and adults and between sexes. Body temperature during mid‐hibernation was regulated at about 2 ° c in females and 3 ° C in males and the metabolic rate was similar to that of hibernating placentals.

Effect of hypothermia on high-energy phosphate stores and contractile function in supported isolated, blood perfused heart.

Contractile function, high-energy phosphate stores and tissular water, Na and K contents were investigated in order to study the specific effect of hypothermia in heart preservation. Isolated dog hearts were perfused with fresh oxygenated blood from a support animal. Experimental conditions were: (a) 30-min normothermia; (b) 3-hour normothermia; (c) 2-hour hypothermia (13°C) between normothermic periods. Ventricular function curves were drawn in isovolumic conditions during the normothermic periods. Enzymatic determinations of tissular PC, ATP, ADP, and AMP were performed on serial samples (20–60 mg) obtained by a drill biopsy technique. High-energy phosphate stores were not modified by hypothermia. After the hypothermic episode the mechanical function of the heart was impaired, and the water, Na and K contents were definitely modified.