Seasonal variation in the metabolism-temperature relation of House Sparrows (Passer domesticus) in KwaZulu-Natal,South Africa

Many birds exhibit considerable phenotypic flexibility in metabolism to maintain thermoregulation or to conserve energy. This flexibility usually includes seasonal variation in metabolic rate. Seasonal changes in physiology and behavior of birds are considered to be a part of their adaptive strategy for survival and reproductive success. House Sparrows (Passer domesticus) are small passerines from Europe that have been successfully introduced to many parts of the world, and thus may be expected to exhibit high phenotypic flexibility in metabolic rate. Mass specific Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR) were significantly higher in winter compared with summer, although there was no significant difference between body mass in summer and winter. A similar, narrow thermal neutral zone (25–28 °C) was observed in both seasons. Winter elevation of metabolic rate in House Sparrows was presumably related to metabolic or morphological adjustments to meet the extra energy demands of cold winters. Overall, House Sparrows showed seasonal metabolic acclimatization similar to other temperate wintering passerines. The improved cold tolerance was associated with a significant increase in VO₂ in winter relative to summer. In addition, some summer birds died at 5 °C, whereas winter birds did not, further showing seasonal variation in cold tolerance. The increase in BMR of 120% in winter, compared to summer, is by far the highest recorded seasonal change so far in birds.     

Sources and significance of variation in basal,summit and maximal metabolic rates in birds

The rates at which birds use energy may have profound effects on fitness, thereby influencing physiology, behavior, ecology and evolution. Comparisons of standardized metabolic rates (e.g., lower and upper limits of metabolic power output) present a method for elucidating the effects of ecological and evolutionary factors on the interface between physiology and life history in birds. In this paper we review variation in avian metabolic rates [basal metabolic rate (BMR; minimum normothermic metabolic rate), ...     

Physiological variation in Amethyst Sunbirds (Chalcomitra amethystina) over an altitudinal gradient in summer

Amethyst Sunbirds (Chalcomitra amethystina) occur over an altitudinal gradient within KwaZulu-Natal, South Africa, from the Drakensberg mountain range to the coast. Sunbirds were caught in summer (November–December 2006) at three altitudinal locations within KwaZulu-Natal; Underberg (1553 m above sea level (asl)), Howick (1075 m asl) and Oribi Gorge (541 m asl). Summer oxygen consumption (VO₂) was measured pre-acclimation at 5 and 25 °C. After post-acclimation to 25 °C and 660 m for 6 weeks, VO₂ measurements were taken at 8 different temperatures (15, 5, 10, 20, 30, 28, 25 and 33 °C). Summer resting metabolic rates (RMR) differed significantly between altitudinal subpopulations of Amethyst Sunbirds. Summer basal metabolic rate was observed to decrease as altitude decreased. Differences between pre-acclimation RMR (representing natural acclimatization to summer conditions in the field) and post-acclimation RMR (to 25 °C at 660 m asl for 6 weeks) were large. In particular, Sunbirds from the Underberg subpopulation increased RMR by 80.9% at 5 °C and 85.2% at 25 °C post-acclimation. This summer research complemented an earlier study on altitudinal variation in Amethyst Sunbirds in winter. It again emphasized the need to acknowledge altitudinal differences between subpopulations and not just use species means, as species means do not fully incorporate the effect of phenotypic plasticity/flexibility.     

Effects of short-term acclimation on thermoregulatory responses of the rock kestrel, Falco rupicolus

The effects of a short-term acclimation period on basal metabolic rate (BMR) and resting metabolic rate (RMR) were measured in captive-bred Rock Kestrels (Falco rupicolus). Birds were exposed to winter conditions (pre-acclimation) in a semi-natural environment before they were acclimated for a period of 3 weeks at a constant temperature of 25 °C and a constant light:dark cycle (12:12 h) (post-acclimation). After acclimation the kestrels showed changes in RMR, BMR and the width of the thermoneutral zone. There was inter- and intra-individual phenotypic plasticity in BMR and RMR both pre- and post-acclimation. However, more inter-individual variation was seen after acclimation. This study concurs with recent suggestions that phenotypic plasticity in BMR is prevalent in avian physiology, and thus a single-species-specific BMR value may not be representative. Furthermore, comparative avian studies of BMR need to account for phenotypic plasticity.     

Thermal history can affect the short-term thermal acclimation of basal metabolic rate in the passerine Zonotrichia capensis

The obligatory cost of living for endotherms is measured by basal metabolic rate (BMR), a variable that is known to change after thermal acclimation. However, the relative timing between variation in ambient temperature and BMR is not well understood. In this study, we addressed this problem in the sparrow Zonotrichia capensis, studying whether previous thermal history affects the response of BMR to a new acclimation temperature. We found that after 4 weeks of acclimation either to 30 or 15 °C birds exhibited significant differences in BMR from pre-acclimation levels. Nevertheless, after a re-acclimation to the opposite treatment for six additional weeks, in the group previously acclimated to warm conditions the change in BMR was significantly greater than in the group previously acclimated to cold. We also found differences in the mass of the small intestine between groups but constancy in the mass of liver, kidney and heart masses at the end of the experiments. Our results indicate that the thermal history affects metabolic adjustments and highlights the importance of considering this when evaluating the plasticity of metabolic traits in small birds.     

东北地区黑线仓鼠的代谢产热特征及其体温调节

为探讨寒冷地区黑线仓鼠 (Cricetulusbarabensis)的代谢产热特征及体温调节 ,本文采用封闭式流体压力呼吸仪对其代谢率、热传导和体温等热生物学指标进行了测定。结果显示 :在环境温度为 5～ 35℃的范围内 ,黑线仓鼠的体温基本维持恒定 ,平均体温为 36 33± 0 2 3℃ ;热中性区为 2 5～ 32 5℃ ;基础代谢率为 3 4 9±0 36mlO2 / (g·h) ;环境温度 (Ta)在 5～ 2 5℃范围内 ,代谢率 (MR)与Ta 呈负相关 ,回归方程为 :MR [mlO2 / (g·h) ]=9 6 0 - 0 2 2Ta (℃ ) ,在此范围内 ,黑线仓鼠的热传导率 (C)最低 ,平均为 0 2 8± 0 0 1mlO2 /(g·h·℃ ) ;代谢预期比和热传导预期比 (F值 )为 1 6 8。黑线仓鼠的基本热生物学特征为 :较高的BMR和热传导率 ,相对较低的体温和较宽的热中性区。这些特征可能限制了其在极端寒冷和干旱环境中的分布和生存.     

Seasonal regulations of resting metabolic rate and thermogenesis in striped hamster (Cricetulus barabensis)

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Resting metabolic rate (RMR), nonshivering thermogenesis (NST) and mitochondria cytochrome c oxydase (COX) activity of brown adipose tissue (BAT), as well as weight of skin and fur were measured in striped hamsters (Cricetulus barabensis) that were live-trapped in the summer, autumn, winter and spring.     

Seasonal effects on metabolism and thermoregulation abilities of the Red-winged Starling (Onychognathus morio)

Basal metabolic rate (BMR) of birds is beginning to be viewed as a highly flexible physiological trait influenced by environmental fluctuations, and in particular changes in ambient temperatures (T_a). Southern Africa is characterized by an unpredictable environment with daily and seasonal variation. This study sought to evaluate the effects of seasonal changes in T_a on mass-specific resting metabolic rate (RMR), BMR and body temperature (T_b) of Red-winged Starlings (Onychognathus morio). They have a broad distribution, from Ethiopia to the Cape in South Africa and are medium-sized frugivorous birds. Metabolic rate (VO₂) and T_b were measured in wild caught Red-winged Starlings after a period of summer and winter acclimatization in outdoor aviaries. RMR and BMR were significantly higher in winter than summer. Body mass of Starlings was significantly higher in winter compared with summer. The increased RMR and BMR in winter indicate improved ability to cope with cold and maintenance of a high T_b. These results show that the metabolism of Red-winged Starlings are not constant, but exhibit a pronounced seasonal phenotypic flexibility with maintenance of a high T_b.     

Seasonal effects on thermoregulatory responses of the Rock Kestrel, Falco rupicolis

Thermoregulatory responses are known to differ seasonally in endotherms and this is often dependent on the environment and region they are resident. Holarctic animals are exposed to severe winters and substantial seasonal variation in ambient temperature. In contrast, those in the Afrotropics have less severe winters, but greater variation in temperature, rainfall and net primary production. These environmental factors place different selection pressures on physiological responses in endotherms. In this study, metabolic rate (VO₂) and body temperature (T_b) were measured in captive bred Rock Kestrels (Falco rupicolus) from the Afrotropics after a period of summer and winter acclimatisation. Resting metabolic rate was significantly lower after the winter acclimatisation period than after the summer acclimatisation period, and there was a shift in the thermoneutral zone from 20–33 °C in summer to 15–30 °C in winter. However, no significant difference in basal metabolic rate between summer and winter was found. The results show that Rock Kestrels reduce energy expenditure at low ambient temperatures in winter as expected in an Afrotropical species.     

Seasonal acclimatization of metabolism in Eurasian tree sparrows (Passer montanus)

Acclimatization to winter conditions is an essential prerequisite for survival of small passerines of the northern temperate zone. Changes in photoperiod, ambient temperature and food availability trigger seasonal acclimatization in physiology and behavior of many birds. In the present study, seasonal adjustments in several physiological, hormonal, and biochemical markers were examined in wild-captured Eurasian tree sparrows (Passer montanus) from the Heilongjiang Province in China. In winter sparrows had higher body mass and basal metabolic rate (BMR). Consistently, the dry mass of liver, heart, gizzard, small intestine, large intestine and total digestive tract were higher in winter than in that in summer. The contents of mitochondrial protein in liver, and state-4 respiration and cytochrome c oxidase (COX) activity in liver and muscle increased significantly in winter. Circulating level of serum triiodothyronine (T₃) was significantly higher in winter than in summer. Together, these data suggest that tree sparrows mainly coped with cold by enhancing thermogenic capacities through increased organ masses and heightened activity of respiratory enzymes activities. The results support the view that prominent winter increases in BMR are manifestations of winter acclimatization in tree sparrows and that seasonal variation in metabolism in sparrows is similar to that in other small temperate-wintering birds.     

内蒙古草原小毛足鼠的活动性、代谢特征和体温的似昼夜节律

小毛足鼠(Phodopus roborovskii)是分布在内蒙古草原沙地的一种小型哺乳动物,关于其生物学和生态学特征,尤其是生理学特征还知之甚少。似昼夜节律是动物行为学和生理生态学中备受关注的一个领域。在室内条件下通过体内埋置无线电传感器连续监测小毛足鼠的体温、用自动监测系统连续监测活动性和TSE LabMaster呼吸代谢测定系统连续测定了其代谢率的昼夜节律性。结果发现:小毛足鼠在夜间的平均体温是(37.27±0.39)℃,昼间的平均体温是(36.11±0.18)℃;在夜间的平均代谢率是(4.65±1.10)mLO2·g-1·h-1,昼间的平均代谢率是(3.09±0.42)mLO2·g-1·h-1;在夜间的平均活动率为(237±145)次/0.1h,昼间的平均活动率为(38±5)次/0.1h。小毛足鼠的代谢率、活动性和体温的峰值相位主要集中在夜间,属典型的夜行性动物。实验结果从行为学特性和生理学特征等新的角度支持了野外观察小毛足鼠是夜行性动物的推断。综合活动性、代谢率和体温三方面同步变化的特征,为小毛足鼠的似昼夜节律变化提供了新的机理性解释。研究也表明小毛足鼠是研究野生动物似昼夜节律变化机理的好模型。     

黑线仓鼠繁殖输出与基础代谢率的关系

为了解黑线仓鼠繁殖输出与基础代谢率(BMR)的关系,阐明最大持续能量收支(SusMR)的限制水平, 揭示哺乳期能量收支对策,本文测定了哺乳期黑线仓鼠的体重、摄食量、BMR 和身体组成,以及哺乳期的胎仔数、胎仔重和泌乳能量支出(MEO)。结果显示,黑线仓鼠哺乳期体重降低了15.0 ± 0.8% , 摄食量显著增加, 哺乳高峰期平均摄食量为13.9 ± 0.3 g /d, 摄入能为222.1 ± 5.3 kJ/ d, 比哺乳初期增加121% , 比对照组高288% ;哺乳高峰期MEO 为62.4 ± 2.3 kJ/ d, 哺乳末期BMR 为49.7 ± 1.1 kJ/ d; 断乳时平均胎仔数4.7 ± 0.2、窝胎仔重50.5 ±1.6 g; 哺乳末期BMR 比对照组增加48% ,BMR 与消化系统各器官的相关性高于对照组; BMR 与胎仔数、胎仔重、乳腺重量和MEO 显著正相关。结果表明:初次繁殖的黑线仓鼠哺乳期SusMR 限制为4.47 ×BMR, 在自身维持和繁殖输出之间采取了“权衡分配”的原则,通过体重降低以减少BMR 的增加幅度, 从而有利于繁殖输出。     

Seasonal regulations of energetics, serum concentrations of leptin, and uncoupling protein 1 content of brown adipose tissue in root voles (Microtus oeconomus) from the Qinghai-Tibetan plateau

Survival of small mammals in winter requires proper adjustments in physiology, behavior and morphology. The present study was designed to examine the changes in serum leptin concentration and the molecular basis of thermogenesis in seasonally acclimatized root voles (Microtus oeconomus) from the Qinghai-Tibetan plateau. In January root voles had lower body mass and body fat mass coupled with higher nonshivering thermogenesis (NST) capacity. Consistently, cytochrome c oxidase activity and mitochondrial uncoupling protein-1 (UCP1) protein contents in brown adipose tissues were higher in January as compared to that in July. Circulating level of serum leptin was significantly lower in winter and higher in July. Correlation analysis showed that serum leptin levels were positively related with body mass and body fat mass while negatively correlated with UCP1 protein contents. Together, these data provided further evidence for our previous findings that root voles from the Qinghai-Tibetan plateau mainly depend on higher NST coupled with lower body mass to enhance winter survival. Further, fat deposition was significantly mobilized in cold winter and leptin was potentially involved in the regulation of body mass and thermogenesis in root voles. Serum leptin might act as a starvation signal in winter and satiety signal in summer.     

食物限制对黑线仓鼠能量代谢和产热的影响

为阐明动物应对食物短缺的能量学对策与其自身的代谢水平的关系,测定了不同限食程度下黑线仓鼠的体重、基础代谢率和非颤抖性产热。结果发现,限食使基础代谢率、非颤抖性产热、褐色脂肪组织细胞色素c氧化酶活性降低。90% 限食驯化4 周后,存活率为80% ,60% 限食驯化4 周后,存活率为30% 。低温驯化使黑线仓鼠基础代谢率和非颤抖性产热显著增加,使80% 限食动物的体重和存活率显著降低。高基础代谢率组的摄食量比低基础代谢率组多23.8% ,80% 限食后两组体重降低的幅度和存活率差异不显著。结果表明:高水平的代谢率使黑线仓鼠对食物资源短缺的敏感性增加;支持“代谢率转换假说”,符合“具有储食习性的动物对食物短缺的生理耐受性较低” 的预测。     

Temperature-dependent rate of clutch production in a tropical lizard (Paroedura picta: Gekkonidae): Intraspecific test of the metabolic theory of ecology

Recently, a general model based on scaling of metabolic rate and reaction kinetics that predicts dependence of various biological rates on temperature and body size has been proposed as a core of the “Metabolic Theory of Ecology” (MTE). However, its thermal component has been rarely explicitly tested and its usefulness for prediction of thermal effect on key life-history traits such as reproductive rate and hence fitness is still questionable. Here, we tested its applicability to temperature-dependent rate of clutch production in a tropical gecko. The thermal effects on reproductive rates in reptiles are only poorly known and difficult to estimate, because most species lay clutches largely infrequently. Females of the Madagascar ground gecko (Paroedura picta) lay clutches in unusually short intervals, which allowed us to use this species as a model for estimation of dependence of rate of clutch production on temperature. We kept adult females at three constant temperatures (24, 27, 30 °C) and recorded their reproductive characteristics. Increasing temperature positively influences rate of clutch production, but in a manner not predicted by a simple model of reaction kinetics. The results in P. picta suggest that predictions of fitness consequences of shifts in thermal environment can be more complicated than expected under the general relationship of the MTE.     

Thyroid hormones increase liver and muscle thermogenic capacity in the little buntings (Emberiza pusilla)

Thyroid hormones can increase energy expenditure and stimulate basal thermogenesis by lowering metabolic efficiency. In the present study, we examined the effects of thyroid hormones on basal heat production as well as on several physiological and biochemical measures indicative of thermogenic capacity to test our hypothesis that thyroid hormones stimulate increases in thermogenesis in little buntings. Little buntings that fed on thyroxine (T₄)–laced poultry food of 3 and 5 ppm concentrations showed increases in basal metabolic rate (BMR) during the 3-week acclimation. At the end, these buntings had lower body weights, higher levels of contents of mitochondrial protein, state 4 respiration and cytochrome c oxidase activity in liver and muscle, and higher concentrations of serum triiodothyronine (T₃) and T₄ compared to control buntings. These results support the argument that thyroid hormones play an important role in the regulation of thermogenic ability in buntings by stimulating mitochondrial respiration and enzyme activities associated with aerobic metabolism.     

Effects of photoperiod on energy budgets and thermogenesis in Mongolian gerbils (Meriones unguiculatus)

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To investigate the role of photoperiod on the regulation of energy budgets and thermogenesis in Mongolian gerbils, body mass (BM), body fat mass (BFM), basal metabolic rate (BMR), nonshivering thermogenesis (NST), gross energy intake (GEI), mitochondrial cytochrome c oxidase (COX) activity and uncoupling protein1 (UCP1) content of brown adipose tissue (BAT), and serum tri-iodothyronine (T₃), thyroxine (T₄) and leptin levels were measured.     

Seasonality in basal metabolic rate and thermal conductance in a long-distance migrant shorebird,the knot (Calidris canutus)

Knots Calidris canutus live highly seasonal lives, breeding solitarily on high arctic tundra and spending the non-breeding season in large social flocks in temperate to tropical estuaries. Their reproductive activities and physiological preparations for long flights are reflected in pronounced plumage and body mass changes, even in long-term captives of the islandica subspecies (breeding in north Greenland and northeast Canada and wintering in western Europe) studied in outdoor aviaries. The three to four fattening episodes in April-July in connection with the flights to and from the high arctic breeding grounds by free-living birds, are represented by a single period of high body mass, peaking between late May and early July in a sample of ten captive islandica knots studied over four years. There are consistent and synchronized annual variations in basal metabolic rate and thermal conductance in three islandica knots. Basal metabolic rate was highest during the summer body mass peak. Within the examined individuals, basal metabolic rate scales on body mass with an exponent of about 1.4, probably reflecting a general hypertrophy of metabolically expensive muscles and organs. Any potential effect of moult on basal metabolic rate was obscured by the large seasonal mass-associated variations. In breeding plumage, insulation (the inverse of thermal conductance) was a factor of 1.35 lower than in winter plumage. This was paralleled by the dry mass of contour feathers being a factor of 1.17 lower. In this subspecies the breeding season is indeed the period during which the costs of thermoregulation are lowest. In captive knots seasonal changes in basal metabolic rate and thermal conductance likely reflect an anticipatory programme adaptive to the variable demands made by the environment at different times of the year.     

Seasonal adjustments in body mass and thermogenesis in Mongolian gerbils (<Emphasis Type="Italic">Meriones unguiculatus</Emphasis>): the roles of short photoperiod and cold

Seasonal adjustments in body mass and thermogenesis are important for the survival of small mammals during acclimatization in the temperate zone. To determine the contributions of short photoperiod and cold temperatures to seasonal changes in thermogenesis and body mass in Mongolian gerbils (Meriones unguiculatus), body mass, basal metabolic rate (BMR), nonshivering thermogenesis (NST), energy intake and energy digestibility were determined in seasonally acclimatized and laboratory acclimated animals. Body mass showed significant seasonal changes and decreased to a minimum in winter. Both BMR and NST increased in winter, and these changes were mimicked by exposing animals to short photoperiod or cold temperatures in the animal house. Digestible energy intake also increased significantly in winter, and also during exposure of housed animals to both short photoperiod and cold. These results suggest that Mongolian gerbils overcome winter thermoregulatory challenges by increasing energy intake and thermogenesis, and decreasing body mass to reduce total energy requirements. Short photoperiod and cold can serve as effective environmental cues during seasonal acclimatization.