Synchronization of circannual cycles: a cold spring delays the cycles of thirteen-lined ground squirrels

Summary Ground squirrels, show circannual cycles with periods normally less than a year when kept under laboratory conditions. The way in which environmental factors synchronize these cycles with the geophysical year under natural conditions is not known. We tested the possibility that cold temperatures can cause long-term phase delays in circannual cycles of thirteen-lined ground squirrels.Two groups of animals were kept in the cold (4 °C) for either 8.5 or 13 months, after which they were returned to the warm (21 °C) and kept there until they had completed at least one additional cycle. A third group was kept in the warm for the entire experiment. Most of the males in the cold room groups became arrested in the spring phase of their cycles while they were in cold. When returned to the warm, these males resumed cycling. When animals showed prolonged spring phases, their cycles were phase-delayed and continued to reflect this delay even after they were returned to the warm. Both body weight cycles and molt cycles were delayed. In contrast to the males in the cold room, none of the females in the cold room groups and none of the warm room animals of either sex showed this response.Our results demonstrate that cold temperatures can phase-delay both body weight and molt cycles and that the spring phase is a critical stage in this effect. We suggest that spring temperatures are largely responsible for the seasonal synchronization of circannual cycles in ground squirrels and are, therefore, a possible Zeitgeber for these cycles.     

Circannual cycles in golden-mantled ground squirrels: fall and spring cold pulses

Summary Endogenous circannual rhythms of male golden-mantled ground squirrels (Spermophilus lateralis) exposed to low ambient temperature (6 °C) at various times were compared to the rhythms of a control group kept in a warm room (21 °C) throughout. A 20-week pulse of cold in the spring delayed the subsequent peak body weight and molt offset. However, in the second year after the spring cold pulse, a delay in the rhythm was evident only using peak weight as a phase marker. A 20-week cold pulse in the fall resulted in an earlier peak body weight and earlier onset of pigmented scrotum and descended testes, but there was no evidence from subsequent years that rhythms had been phase advanced. A third of the animals kept continuously at 6 °C remained with pigmented scrotum, descended testes and low body weight for more than a year. Circannual periodicities of animals that continued to display rhythms in the cold room were not significantly longer than those of controls in the warm room. The results suggest that low temperature in the fall can alter the expression of circannual rhythms without much affecting their phasing, while low temperature in the spring produces phase delays which last longer but have not been proved to be persistent.Abbreviation PRC phase response curve     

Circannual cycles in golden-mantled ground squirrels: Experiments with food deprivation and effects of temperature on periodicity

Summary Female golden-mantled ground squirrels,Spermophilus lateralis, kept in a cool room (9.5 °C), were food deprived and their hibernation thereby extended by 11 weeks on average compared to undeprived control animals in the same room. The deprived group was then refed. Despite their prolonged hibernation, peak weights and onset of hibernation in the subsequent season were only 2–4 weeks later than in the undeprived controls and this effect was only marginally significant. However, the periods of circannual cycles of both the deprived and undeprived groups in the cool room were significantly longer than those of another group of female ground squirrels kept in a warm room (21 °C). It is argued that warm temperatures are capable of terminating the winter phase of circannual cycles, namely that of hibernation and declining body weight. If animals are kept continuously in a cool environment this phase ends spontaneously. Even many weeks of food deprivation are only capable of extending this phase by a relatively small amount, if at all.The author thanks Kirsteen Lang for invaluable help at every phase of this work, Linda Jones and others at the Environmental Sciences Centre, Kananaskis, for heir cooperation, and Janice Farintosh, John Ting and Yasmin Shah for collecting data. Support came from the Natural Sciences and Engineering Research Council of Canada.     

Influence of acclimation temperature on the shivering behavior of the butterfly Danaus plexippus (L.)

Summary Most of the monarch butterflies kept at 4–5° C for a few days shivered when released at a test temperature of 15–16° C, whereas fewer of the butterflies kept at 23–24° C did so. Cold-acclimated butterflies shivered more readily, as indicated by the length of the interval between release at the test temperature and the onset of shivering, and they shivered for longer periods of time. The effects of cold acclimation were reversible, but in only 1 out of 3 replicates was the warm acclimation clearly reversed. Cool animals shivered at room temperature, indicating that body temperature and not ambient temperature is important in releasing the behavior. It is suggested that the acclimation involves alteration in the central neurons controlling the activity of muscles involved in shivering.I thank Miss Janice Ruppert and Mr. C. J. Doughty for their valuable technical assistance. The co-operation of the administrators of New Brighton Beach State Park in permitting me to collect in the park is appreciated.     

Changes in selected aspects of immune function in the leopard frog, Rana pipiens, associated with exposure to cold

The effect of exposure to low temperatures (5 °C) on lymphocyte proliferation, leukocyte populations, and serum complement levels was examined in the northern leopard frog, Rana pipiens. Proliferation of T lymphocytes in response to phytohemagglutinin stimulation was significantly decreased in frogs kept for 2, 3, and 5 months at 5 °C compared to that of animals kept at 22 °C. A significant increase in the average percentage of neutrophils and a decrease in the mean percentage of eosinophils was observed in the blood of frogs held for 5 months in the cold compared to animals held at 22 °C for the same length of time. Mean serum complement activity after 1 month at 5 °C was significantly reduced in comparison to animals held at 22 °C and was not detectable after 5 months in the cold. Recovery of complement levels at room temperature (22 °C) was also examined after cold exposure. Complement levels were significantly higher than controls (at 22 °C) in frogs returned to 22 °C for 7 and 14 days after 5 months in the cold. After frogs were held at 5 °C for 1 month, serum complement levels increased significantly within 2 days after returning to 22 °C and continued to rise 5 and 9 days after warming. Injections with Aeromonas hydrophila following a 5-week exposure to 5 °C failed to cause death or observable symptoms of disease in frogs that were returned to 22 °C. Accepted: 20 November 1996     

Fatty acid composition and extreme temperature tolerance following exposure to fluctuating temperatures in a soil arthropod

Ectotherms commonly adjust their lipid composition to ambient temperature to counteract detrimental thermal effects on lipid fluidity. However, the extent of lipid remodeling and the associated fitness consequences under continuous temperature fluctuations are not well-described. The objective of this study was to investigate the effect of repeated temperature fluctuations on fatty acid composition and thermal tolerance. We exposed the springtail Orchesella cincta to two constant temperatures of 5 and 20 °C, and a continuously fluctuating treatment between 5 and 20 °C every 2 days. Fatty acid composition differed significantly between constant low and high temperatures. As expected, animals were most cold tolerant in the low temperature treatment, while heat tolerance was highest under high temperature. Under fluctuating temperatures, fatty acid composition changed with temperature initially, but later in the experiment fatty acid composition stabilized and closely resembled that found under constant warm temperatures. Consistent with this, heat tolerance in the fluctuating temperature treatment was comparable to the constant warm treatment. Cold tolerance in the fluctuating temperature treatment was intermediate compared to animals acclimated to constant cold or warmth, despite the fact that fatty acid composition was adjusted to warm conditions. This unexpected finding suggests that in animals acclimated to fluctuating temperatures an additional underlying mechanism is involved in the cold shock response. Other aspects of homeoviscous adaptation may protect animals during extreme cold. This paper forms a next step to fully understand the functioning of ectotherms in more thermally variable environments.     

Thermal adaptability of large white pigs in the tropical environment

Twenty-four Large White weaners-twelve males and twelve females, were randomly divided into three groups of eight (four males and four females per two separate pens) and were assigned to three groups of two pens each for the males and the females weaners.One group of two pens was without wallow facility (control), one other group was provided with wallows (wet) and the third group was in air-conditioned room (cold). Twice a day, the respiratory rate and the rectal temperatures were measured early in the mornings at 8.00–9.00 hrs (A.M.) and late in the early evenings at 16.00–18.00 hrs.The mean respiratory frequency (A.M) ranged from 7 to 9; 6–12 and 8–13 breaths per minute for the cold, wet and control respectively while the mean respiratory frequency (P.M.) ranged from 6 to 9, 10 to 17 and 13 to 19 breaths per minute for the cold, wet and control respectively.The mean rectal temperatures (A.M.) ranged very slightly from 38.54° to 39.12°C; 38.50° to 39.05°C and 38.61°C to 39°C for the cold, wet as control respectively while the mean rectal temperatures (P.M.) ranged from 39.00° to 39.22°C; 38.97° to 39.29°C and 39.28° to 39.55°C for the cold, wet and control respectively.The animals were maintained for another seven to ten weeks and were slaughtered. The slaughter characteristics did not indicate an appreciable thermal stress except for the reproductive organs which showed weight increase indicating reduced efficiency of the thermally stressed animals as is the case in the tropical environment.     

Inducing sporulation in Alternaria solani I. Effect of water treatment

The sporulation was induced when fully grown cultures were given dip or spray treatment with distilled water (cold or hot) and thereafter, kept partially covered at different temperatures. Cultures dipped in cold water (4° C) for 4 minutes or sprayed with cold water (4° C) or hot water (58° C) and thereafter incubated at room temperature (13–26° C) in diffused sunlight, produced maximum number of spores within 60 hours. Incubating water treated cultures in diffused sunlight or complete darkness and age and scraping of the cultures had a considerable effect upon intensity of sporulation. The cultures yield a number of subsequent crops of spores when scraped and given dip treatment with cold or hot water, after obtaining each crop of spores.     

Die überwinterung als adaptive leistung,Geprüft an verschiedenen karyotypen der inversionspolymorphen art Drosophila subobscura

Adult flies of Drosophila subobscura were kept in a refrigerator for 72 days. The animals belonged to a second generation derived from a cross between two homokaryotypic stocks. One of these was homozygous for the Standard (St) gene arrangement of the U-chromosome, the other one for the gene arrangement U₁₊₂, which differs from the U_St by two inversions. Both gene arrangements are abundant in natural populations of Northern and Central Europe.According to Mendelian expectations the karyotypes U_St/St, U_St/1+2 and U_1+2/1+2 should show up in the second generation in conformity with the proportion 1 : 2 : 1. A random sample of 70 adults taken before confining the animals to the refrigerator contained 11 : 43 : 16 specimens of the above mentioned karyotypes respectively. Karoytypic proportions observed after keeping the flies in the cold were therefore compared not only with the hypothetical 1 : 2 : 1 proportion but also with the 11 : 43 : 16 proportion of that prior sample. There was however no significant deviation from the latter proportion. For both males and females the result remained the same, independent of whether or not they had copulated. Animals which had been kept and normally fed for the same duration at 18°C showed no significant deviation from the initial karyotype proportion, either. Thus the attempt to show through karyotype proportions an adaptation to long periods of cold was entirely unsuccessful.In a second run I buried eggs, the three larval stages, and pupae as well as adults into the forest soil in autumn for exposure to the winter cold. A sample was removed 125 days later, the remaining 180 days after having been dug in. As in the first run the flies showed no significant changes in karyotype proportions. While death rate seemed to be homogeneous, the three karyotypes nevertheless showed some differences in viability.In laboratory tests, those male and female specimens which had not copulated withstood the cold better. The highest mortality rate occurred among sexually mixed groups. Further, a shorter life span and lower fertility rate were found in animals kept at 18°C than in those kept in the refrigerator.Among the animals that had been dug into the forest soil only those survived, which had started the cold period as immature stages. They developed very slowly. These ecological findings suggest that Drosophila subobscura hibernates in its immature stages rather than as adult flies.Very young larvae were found to have the best chance of survival. This observation led to a third experiment: I exposed young larvae to a cold shock treatment. Thereby a first hint was obtained concerning the presumed differences in adaptive capacities of different karyotypes. After a cold shock the development of the homokaryotypes, from the egg to the larval stage, was faster and in one case there even emerged more homokaryotype than heterokaryotype larvae.     

Freeze or dehydrate: only two options for the survival of subzero temperatures in the arctic enchytraeid<Emphasis Type="Italic"> Fridericia ratzeli</Emphasis>

Hygrophilic soil animals, like enchytraeids, overwintering in frozen soil are unlikely to base their cold tolerance on supercooling of body fluids. It seems more likely that they will either freeze due to inoculative freezing, or dehydrate and adjust their body fluid melting point to ambient temperature as has been shown for earthworm cocoons and Collembola. In the present study we tested this hypothesis by exposing field-collected adult Fridericia ratzeli from Disko, West Greenland, to freezing temperatures under various moisture regimes. When cooled at –1 °C min^–1 under dry conditions F. ratzeli had a mean temperature of crystallisation (T_c) of –5.8 °C. However, when exposed to temperatures above standard T_c for 22 h, at –4 °C, most individuals (90%, n= 30) remained unfrozen. Slow cooling from –1 °C to –6 °C in vials where the air was in equilibrium with the vapour pressure of ice resulted in freezing in about 65% of the individuals. These individuals maintained a normal body water content of 2.7–3.0 mg mg^–1 dry weight and had body fluid melting points of about –0.5 °C with little or no change due to freezing. About 35% of the individuals dehydrated drastically to below 1.1 mg mg^–1 dry weight at –6 °C, and consequently had lowered their body fluid melting point to ca. –6 °C at this time. Survival was high in both frozen and dehydrated animals at –6 °C, about 60%. Approximately 25% of the animals (both frozen and dehydrated individuals) had elevated glucose concentrations, but the mean glucose concentration was not increased to any great extent in any group due to cold exposure. The desiccating potential of ice was simulated using aqueous NaCl solutions at 0 °C. Water loss and survival in this experiment were in good agreement with results from freezing experiments. The influence of soil moisture on survival and tendency to dehydrate was also evaluated. However, soil moisture ranging between 0.74 g g^–1 and 1.15 g g^–1 dry soil did not result in any significant differences in survival or frequency of dehydrated animals even though the apparent wetness and structure of the soil was clearly different in these moisture contents.Abbreviations DW dry weight - FW fresh weight - MP melting point - RH relative humidity - Tc crystallisation temperatures - WC water contentCommunicated by I.D. Hume     

Photoperiodic regulation of body mass, food intake, hibernation, and reproduction in intact and castrated male European hamsters,Cricetus cricetus

A group of sexually active male European hamsters were raised either in short-photoperiod conditions (SP; LD 8:16) or in long-photoperiod conditions (LP; LD 16:8) from their capture at the end of the hibernation period. Another group of hamsters was castrated in April and gonadectomized animals were maintained in SP and cold (7 degrees C) or in a succession of SP and LP plus cold. Another group, castrated in May or in September and raised in LP conditions, was transferred in September to SP conditions and cold. 1. Normal hamsters raised in continuous SP or LP apparently did not show signs of rhythmic behavior, except possibly in gonadal activity. 2. Body weight increased continuously, plasma testosterone levels oscillated between 1.5 and 2.5 ng/ml, and animals raised in SP and in cold did not enter hibernation. 3. Similar results were also found in castrated animals kept in SP conditions and cold. 4. The sequence LP-SP induced a decrease in food intake and body weight and a decrease in plasma testosterone levels and triggered entry into hibernation in both intact and castrated animals. 5. After 6 months continuously in SP and with exposure to cold spontaneous recrudescence in food intake and body weight occurred and hibernation ended in both intact and castrated animals. 6. In normal animals a spontaneous increase in plasma testosterone levels was observed. 7. In both normal and gonadectomized animals the phase of refractoriness could be broken by exposure to LP conditions. 8. The critical photoperiod lies between 15 and 15.5 h. These results demonstrate that the European hamster is a photoperiodic species.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of increased catecholamine levels in blood plasma during cold-adaptation and intramuscular infusion on thresholds of thermoregulatory reactions in guinea-pigs

Summary Catecholamines and some of their metabolites were determined in urine and blood plasma of guinea-pigs before, during and after acclimation to a cold or warm environment. During adaptation to 5°C the amounts of noradrenaline in plasma and 24-h urine samples continuously increased up to 600% compared with values obtained at an ambient temperature of 22°C. Higher levels of dihydroxyphenylglycol and 3-methoxy-4-hydroxyphenylglycol further indicated an increased turnover of noradrenaline during cold adaptation. Acclimation to an ambient temperature of 28°C reduced the peripheral release of noradrenaline in comparison to the release observed at 22°C. Cold-induced increases in metabolic rate and electrical muscle activity both occur at a considerably lower mean body temperature in cold-than in warm-adapted guinea-pigs. The shift of thermoregulatory cold defence reactions to a lower mean body temperature could also be observed in warm-adapted animals after intramuscular infusion of noradrenaline in amounts comparable to those released during cold adaptation.It is concluded that high peripheral sympathetic activity directly or indirectly inhibits noradrenergic neurons in the lower brain stem that modulate the thermoregulatory control system by means of their afferents to the hypothalamus. As a consequence of this peripheral influence the thermoregulatory set point is shifted to a lower mean body temperature.Abbreviations A adrenaline - CA cold adapted - CNS central nervous system - DHPG dihydroxyphenylglycol - EMA electrical muscle activity - HPLC high performance liquid chromatography - 5-HT 5-hydroxytryptamine (serotonine) - MHPG 3-methoxy-4-hydroxypheyylglycol - MR metabolic rate - NA noradrenaline - T _b mean body temperature - WA warm adapted     

Effect of cold exposure on the concentration of triglyceride in the liver of the rat

The aim of the present study was to examine an effect of cold exposure on the concentration of triglycerides (TG) in the rat's liver. The rats were divided into the following groups: control, fed with oil, treated with hydrocortisone, fed with oil and treated with hydrocortisone, treated with noradrenaline. The rats exposed to cold were kept in wire cages (one rat in one cage) in the cold room at temperature +2 degrees C. They had free access to food (pellet diet for rodents) and water. In the control group the exposure to cold increased mildly (though significantly) the TG concentration after 1 and 3 h and had no effect after 2 and 24 h. It did not affect the concentration of plasma free fatty acids (FFA). At room temperature feeding with oil (2 ml/100 g of body weight) alone, and combined with hydrocortisone treatment (5 mg/100 g of body weight) as well as treatment with noradrenaline (0.1 mg/100 g of body weight) had no effect on the liver TG concentration, although the concentration of plasma FFA was increased. Exposure to cold for 3 h increased markedly the liver TG concentration in each of those groups. It is concluded that exposure to cold elicits a mechanism, which in the presence of elevated plasma FFA concentration induces accumulation of TG in the liver.     

Does immune challenge affect torpor duration?

1. Hibernation may alter the relationship between pathogens and their hosts; low host temperatures can prevent pathogen replication. Therefore, manipulating the timing and duration of torpor bouts could allow animals to gain an advantage over pathogens.
2. Thirty-two Turkish Hamsters ( Mesocricetus brandti ) were placed in short-day, cold conditions. After 10 weeks, 20 animals were challenged with an antigen to simulate a pathogen infection. Ten of these animals were returned to the cold ('cold-challenged'). The other 10 animals were placed in warm conditions ('warm-challenged'). Twelve animals received saline injections and were returned to the cold ('cold-control'). Cold-challenged animals spent significantly more time in torpor than did cold-control animals.
3. After 6·5 weeks, all animals were housed in warm conditions and ceased torpor. Both cold-challenged and warm-challenged animals received a second injection of antigen. There was no correlation between time spent euthermic and level of secondary humoral response of cold-challenged animals. The secondary humoral response of the cold-challenged animals was significantly lower than that of warm-challenged animals.
4. In this study immune status influenced torpor duration, and torpor caused immunosuppression. Hibernators may manipulate body temperature in order to combat pathogens while their own immune systems are suppressed.     

布氏田鼠哺乳期低温经历抑制成年期神经再生

哺乳动物在出生前后所经历的环境条件对其成年后的行为和生理等具有重要影响。环境温度是影响动物后代表型的重要因素之一。本研究将分娩当天的布氏田鼠母体和幼仔在常温（23℃±1℃）或低温（4℃±1℃）饲养,断乳（21日龄）时转至常温环境,至第63日龄时再随机将两组动物各分为常温组和低温暴露组,期间检测体重、摄食量、静止代谢率、认知能力和神经细胞增殖和存活等,以验证哺乳期的低温经历可影响成年动物的代谢生理、行为表型和相关脑区神经再生的假说。结果发现：哺乳期低温经历导致成年布氏田鼠摄食量显著降低,与代谢有关的下丘脑以及学习记忆有关的海马区细胞增殖和存活数量减少。当动物在成年期面临冷暴露时,与哺乳期常温经历的动物相比,哺乳期低温经历的动物摄食量较低,在Y迷宫新异臂中的穿梭次数和停留时间显著降低,但海马和下丘脑部分核团的细 胞增殖以及海马CA的细胞存活明显升高。这表明哺乳期低温经历对布氏田鼠的能量代谢、行为和相关脑区的成体神经再生产生了持久的抑制效应,但成年后再次面对低温时,动物的代谢能力和代谢及学习记忆相关脑区的神经细胞可塑性优于哺乳期未曾经历低温的动物。     

Thermal acclimation induced compensation in biochemical constituents of the Indian freshwater leech,Poecilobdella viridis (Blanchard)

Poecilobdella viridis was used to study the variations in the biochemical parameters: body protein, glycogen and water, following warm (32.0° ± 0.5°C) and cold (10.0° ± 0.5°C) acclimation for 5, 10, 15 and 30 days. The percentage of glycogen decreased significantly (p < 0.05) during both warm and cold acclimation whereas the protein percentage increased significantly (p < 0.05). The percentage of water was significantly (p < 0.05). reduced during both acclimation processes. Ecophysiological significance of these alterations to leeches, in counteracting the ambient thermal fluxes, has been briefly discussed.     

温度和高脂食物对黑线仓鼠代谢产热和体脂累积的影响

能量代谢的适应性调节是小型哺乳动物应对环境季节性变化的主要策略之一。为探讨不同温度下动物在代谢产热能量支出与脂肪累积之间的权衡策略,以成年雄性黑线仓鼠为研究对象开展了3 个实验:实验1 将动物驯化于高脂和低脂食物;实验2 将动物暴露于低温(5℃)和暖温(30℃);实验3 将饲喂高脂食物的动物暴露于低温。以食物平衡法测定摄食量、摄入能和消化率,以开放式氧气分析仪测定代谢产热,以索氏抽提法测定脂肪含量。结果发现,取食高脂食物的黑线仓鼠摄食量显著减少,但脂肪累积显著增加;暖温下摄食量显著减少,但体脂含量显著增加,低温下摄食量显著升高,但体脂含量显著减少;饲喂高脂食物的黑线仓鼠在低温下摄入能显著增加,非颤抖性产热增强,但体脂含量显著降低。结果表明高脂食物对黑线仓鼠体脂累积的影响与环境温度有关,低温诱导脂肪动员,暖温促进脂肪贮存;低温下黑线仓鼠增加能量摄入不能完全补偿用于产热的能量支出,导致脂肪动员增加;暖温下代谢产热降低是脂肪累积的主要因素;与能量摄入相比代谢产热的能量支出在体脂累积的适应性变化中发挥更重要的作用。     

Changes in physiological and neuroendocrine properties during thermal adaptation of golden hamsters (Mesocricetus auratus)

Summary Golden hamsters raised at 22°C were adapted in the early summer for 3 weeks to either 28°C or 5°C. To achieve profound changes the photoperiod was also shortened from 14 h to 11 h during adaptation to cold. During the investigation body weight, food consumption, water intake, urine production, and osmolality, as well as secreted amounts of noradrenaline (NA) and dopamine (DA), were recorded in each animal before, during, and after the adaptation period. In another group of golden hamsters the brains were processed for immunocytochemical detection of arginine-vasopressin (AVP) and corticotropin releasing factor (CRF) in the third week of adaptation to a cold or warm environment. In warm-adapted animals food and water consumption and urine production remained unchanged or were only slightly reduced. NA and DA secretion were reduced by 50%. The AVP-immunoreactivity reflected an antidiuretic state in these animals. In fibers influencing the adrenal axis, AVP-immunoreactivity was weak compared to CRF fibers. Food and water consumption, urine production, and DA secretion increased two-fold during cold adaptation. Daily secreted amounts of NA increased nine-fold. AVP-immunoreactivity was weak in projections to the neurohypophysis. Fibers influencing the adrenal axis, however, displayed strong AVP-immunoreactivity in comparison to that of CRF. The immunocytochemically determined patterns of AVP and CRF distribution indicated an activation of the osmoregulative axis in the warm-adapted animals and of the adrenal axis in the cold-adapted golden hamsters.Abbreviations NA noradrenaline - DA dopamine - AVP argininevasopressin - CRF corticotropin releasing factor - SON supraoptic nucleus     

The persistence and transfer of voluntary hand-warming in natural and laboratory cold settings after 1 year

Hayduk (1980) used a classical conditioning-biofeedback overlap (CBO) design to teach six volunteers to warm their hands in an ambient temperature of –14°C. He found voluntarily warmed hands to be more dexterous, more sensitive, and less painful in the cold laboratory setting than unwarmed hands. The present paper reports a 1-year follow-up of five of Hayduk's original six volunteers. Ability to hand-warm was reevaluated, both at room temperature and at –14°C and was found to be essentially unchanged from post-training performance of the previous year. The effects of hand-warming on performance, sensation, and cold pain were remeasured in the cold laboratory and found to be essentially unchanged from the effects following training the previous year. Finally, the volunteers were asked to describe the degree to which they had used their hand-warming, and the circumstances under which they had used it, in natural settings throughout a Canadian winter. The volunteers reported only minimal use of hand-warming, primarily to reduce cold pain.     

Developmental and adult acclimation effects of ambient temperature on temperature regulation of mice selected for high and low levels of nest-building

Summary Genetic and environmental components of adaptation to cold inMus musculus were assessed in a study of the effects of selective breeding for behavioral temperature regulation (indexed by high and low levels of nest-building), rearing mice from birth in the cold, and cold acclimation of adult animals, on thermoregulatory traits. Mice from the eleventh selected generation of a high-nesting line maintained higher resting metabolic rates and body temperatures, while at the same time consuming less food when compared with mice from the low-nesting line (Table 1). High-nesting mice were also more discriminating in their temperature preference when placed on a thermal gradient. Thus, common genetic loci must influence a variety of energy conservation measures important for survival in the cold, including insulative nest-building, metabolic efficiency, and optimum microhabitat selection.Rearing mice at 5°C from birth until 70 days of age resulted in permanent increases in nonshivering thermogenesis, weight of interscapular brown adipose tissue, and core body temperature when compared to mice raised at 22°C (Table 1). These greater heat production capacities were accompanied by consumption of more food. Cold acclimation of adults at 5°C for 3 weeks similarly increased measures of thermogenic capacity (nonshivering thermogenesis and interscapular brown adipose tissue) as well as food consumption, when compared to the effects of warm acclimation, but differed from the effects of cold-rearing in that while resting metabolic rates were elevated, no significant differences in body temperature were found (Table 1).Sex differences were also noted for most of the thermoregulatory measures, with the lighter females scoring higher on thermal preference, resting metabolic rate, nonshivering thermogenesis, brown fat, and food consumption.In general, these results suggest that a more precise partitioning of the genetic and environmental factors which influence thermoregulatory traits in mammals could eventually result in a better understanding of the differences which exist between acclimated and acclimatized animals.