Energetics of bluetongue lizards (<Emphasis Type="Italic">Tiliqua scincoides</Emphasis>) in a seasonal tropical environment

We studied the physiological ecology of bluetongue lizards (Tiliqua scincoides) on the Adelaide River floodplain in tropical Australia to determine the seasonal patterns of energy expenditure and to determine the mechanisms by which seasonal differences were achieved. Field metabolic rates (FMR) were significantly lower in the dry season (37.6 kJ kg(-1) day(-1); n=9) than in the wet (127.3 kJ kg(-1) day(-1); n=7). Water flux was also lower in the dry season (6.8 ml kg(-1) day(-1); n=9) than in the wet (39.4 ml kg(-1) day(-1); n=7). Measurements of body temperatures (T(b)) and movements of free-ranging animals, and standard metabolic rate (SMR) of recently caught animals, allowed a detailed analysis of energy budgets for wet and dry seasons. In the dry, bluetongue lizards expended 90 kJ kg(-1) day(-1) less energy than in the wet season. Unlike some other lizards of the wet-dry tropics, SMR did not differ between seasons. About 5% of the seasonal difference in FMR was due to lower night time T(b) during the dry season, and about 7% was due to lower diurnal T(b). The remaining 88% of the decrease in energy expended in the dry season was due to a substantial decrease in other costs that may include reproduction, growth, digestion and activity. If we assume the animals fed daily and the costs of digestion are taken into account, the estimates are: 14% of the savings result from lower T(b) at night, 20% from lower T(b) in the day, and 66% result from decreased activity. It is therefore apparent that, unlike some agamid and varanid lizards that use a combination of behavioural and physiological mechanisms to conserve energy when food and water are limited, bluetongue lizards primarily use behavioural mechanisms to achieve a dramatic reduction in energy expenditure in the dry season.     

Daily Energy Expenditure and the Cost of Activity in Mammals

Among 17 species of mammals, field metabolic rates exclusiveof thermoregulatory and productive costs (designated FMR*) averaged2.65 x standard metabolism (SMR). Daily activity costswere calculatedby subtraction from FMR* of the daily energy expenditure associatedwith SMR and assimilation of nutrients. Total expenditure foractivity was of a similar magnitude to that for daily standardmetabolism. Calculations indicate that expenditures by mammalsfor locomotion probably account for less than half of dailyactivity costs. Expenditures by mammals engaged in other kindsof activities are also reviewed. During their daily activityperiods, terrestrial mammals expend energy at a rate of about4.1 x SMR. The utility of energetic increments for activityin time-energy budgets, thermal energy budgets, and analysesof the economics of foraging are discussed.     

Increased energy expenditure but decreased stress responsiveness during molt

Baseline and stress-induced corticosterone (CORT), heart rate (fH), and energy expenditure were measured in eight captive European starlings Sturnus vulgaris during and following a prebasic molt. The fH and oxygen consumption (V O2 ) were measured simultaneously across a range of heart rates, and energy expenditure (kJ/d) was then calculated from data. Energy expenditure and fH were strongly and positively correlated in each individual. Baseline fH and energy expenditure were significantly higher during molt. Molting starlings expended 32% more energy over 24 h than nonmolting birds, with the most significant increase (60%) occurring at night, indicating a substantial energetic cost to molt. Furthermore, the cardiac and metabolic responses to stress during molt were different than during nonmolt. Birds were subjected to four different 30-min acute stressors. The fH and CORT responses to these stressors were generally lower during molt. Although restraint caused a 64% increase in daily energy expenditure during nonmolt, no other stressor caused a significant increase in energy expenditure. Overall, our data suggest that molt is not only energetically expensive but that it also alters multiple stress response pathways. Furthermore, most acute stressors do not appear to require a significant increase in energy expenditure.     

Resting metabolic expenditure as a potential source of variation in growth rates of the sagebrush lizard

Along an elevational gradient on SW Utah, sagebrush lizards (Sceloporus graciosus) exhibit an unexpected pattern of growth. Lizards from a high elevation population grow faster than lizards from two populations at lower elevations despite shorter daily and seasonal activity. Results from a common environment study of growth suggest that the differences in growth are not due to adaptation to local environmental conditions. In this study, I test the hypothesis that higher growth rates in lizards from high elevation may be attributable to reduced resting metabolic expenditure compared to that of lizards from populations at two lower elevations. Resting metabolic rates were measured for individuals from each of the study populations across different times of day and over a broad range of temperatures. Under the same laboratory conditions, field-caught lizards from the high elevation population exhibited lower metabolic rates when compared to lizards from lower elevations. Daily resting metabolic expenditures were calculated using the observed metabolic rates coupled with estimates of daily activity. Daily resting metabolic expenditure was 50% greater for individuals from the two lower elevation populations, which could result in 12.5% more energy that could be potentially allocated to growth for lizards from high elevation. Such energetic savings may be able to explain differences in the patterns of growth observed in nature.     

The cost of disturbance: a waste of time and energy?

Quantifying the effect of disturbance is a central issue in conservation. Using time and energy budgets, we obtain a range of ways to assess the importance of disturbance. One measure is the time that must be spent foraging in order to balance the energy budget. From this we derive critical levels of wastage (rate of disturbance multiplied by duration of disturbance) at which the animal runs out of time or reaches a limit on energy expenditure. In the case of the time constraint, the critical wastage is the net rate of energetic gain while foraging divided by the rate of energetic expenditure during a disturbance. The associated critical rate of disturbance is the net rate of energetic gain while foraging divided by the energy spent during a disturbance. The model is illustrated using data from the African wild dog, which suffers disturbance from lions and kleptoparasitism from hyenas. Findings suggest that disturbance imposes significant costs on wild dog time and energy budgets. We show how alternative environments can be evaluated in terms of their effective rate of gain, which is the net rate of gain from foraging minus the rate of energy expenditure as a result of disturbance.     

The energetics of reproduction and parental care in the terrestrial isopod Porcellio laevis

Parental care is a behavioral strategy that contributes to increased fitness of progeny. Among terrestrial arthropods, many isopods provide extensive parental care. Few studies have quantified the underlying cost of parental care in terms of energy. We used the terrestrial woodlouse Porcellio laevis (Latreille) as a study model to examine how energetic acquisition and expenditure in females is affected during the incubation period and how parental care affects energy balance in this species. We determined the basic reproductive biology (i.e. fecundity, reproductive output, egg volume, egg loss), energy expenditure (i.e. metabolic rate), and energy acquisition (i.e. food consumption, digestibility) of ovigerous females in different stages of embryonic development. Non-ovigerous females were used as the control group. Our results show that P. laevis displays variability in life-history traits compared with populations from other zones around the world. Ovigerous females exhibited a lower ingestion rate and lower digestibility than control females, thus indicating a lower capacity for energy acquisition. Furthermore, energy expenditure was higher in ovigerous females when compared to non-ovigerous females. In particular, females in early embryonic development stored 5.1-fold less daily energy than females without eggs.

The results presented here show that the parental care provided by female P. laevis is energetically costly. Overall, our work brings us much closer to understanding the proximate mechanisms of the costs of parental care in terrestrial isopods. Both proximal mechanisms and consequences of providing care on future reproduction, should be considered in explaining the evolution of parental care.     

Differences in maintenance energy expenditure by two estuarine shrimp (Palaemonetes pugio and P. vulgaris) that may permit partitioning of habitats by salinity

The estuarine shrimp Palaemonetes pugio and P. vulgaris co-occur across a broad range in salinity. Field surveys and laboratory lethality tests suggest that low salinity conditions favor P. pugio over P. vulgaris. This study compared energetic expenditures across a range in salinity (0.5-35 ppt) to test the hypothesis that P. pugio experiences lower maintenance-energy requirements than P. vulgaris in low-salinity habitats. Standard metabolic rate (SMR) was measured as the minimum oxygen consumption rate at 25 degrees C to estimate daily maintenance-energy expenditure. SMR was greatest at 0.5 and least at 10 ppt (irrespective of species), and greater for P. vulgaris than for P. pugio. At low salinity (1.5-3 ppt), SMR was lower for P. pugio than for P. vulgaris. Energy expenditure did not coincide with the pattern predicted based upon osmoregulatory costs alone; no reduction was observed near the reported hemolymph concentration for P. vulgaris, although a minimum was observed near the hemolymph isoionic concentration for P. pugio. A local minimum in SMR by P. pugio between 1.5 and 3 ppt contrasted with relatively high SMR of P. vulgaris across this range. It appears that low-salinity habitats are energetically more favorable for P. pugio than for P. vulgaris. The results suggest an adaptive mechanism allowing P. pugio to occupy environments that present its competitor, P. vulgaris, with greater energetic challenges. While long-term exposure to very low salinity may be detrimental to both species, energetic traits of P. pugio may confer it with greater success than P. vulgaris in habitats in which salinity periodically fluctuates to low values.     

Effects of chronic oral rimonabant administration on energy budgets of diet-induced obese C57BL/6 mice

The endocannabinoids have been recognized as an important system involved in the regulation of energy balance. Rimonabant (SR141716), a selective inverse agonist of cannabinoid receptor 1 (CB1), has been shown to cause weight loss. However, its suppressive impact on food intake is transient, indicating a likely additional effect on energy expenditure. To examine the effects of rimonabant on components of energy balance, we administered rimonabant or its vehicle to diet-induced obese (DIO) C57BL/6 mice once daily for 30 days, by oral gavage. Rimonabant induced a persistent weight reduction and a significant decrease in body fatness across all depots. In addition to transiently reduced food intake, rimonabant-treated mice exhibited decreased apparent energy absorption efficiency (AEAE), reduced metabolizable energy intake (MEI), and increased daily energy expenditure (DEE) on days 4-6 of treatment. However, these effects on the energy budget had disappeared by days 22-24 of treatment. No chronic group differences in resting metabolic rate (RMR) or respiratory quotient (RQ) (P > 0.05) were detected. Rimonabant treatment significantly increased daily physical activity (PA) levels both acutely and chronically. The increase in PA was attributed to elevated activity during the light phase but not during the dark phase. Taken together, these data suggested that rimonabant caused a negative energy balance by acting on both energy intake and expenditure. In the short term, the effect included both reduced intake and elevated PA but the chronic effect was only on increased PA expenditure.     

High costs of female choice in a lekking lizard

Although the cost of mate choice is an essential component of the evolution and maintenance of sexual selection, the energetic cost of female choice has not previously been assessed directly. Here we report that females can incur high energetic costs as a result of discriminating among potential mates. We used heart rate biologging to quantify energetic expenditure in lek-mating female Galápagos marine iguanas (Amblyrhynchus cristatus). Receptive females spent 78.9+/-23.2 kJ of energy on mate choice over a 30-day period, which is equivalent to approximately (3/4) of one day's energy budget. Females that spent more time on the territories of high-quality, high-activity males displayed greater energetic expenditure on mate choice, lost more mass, and showed a trend towards producing smaller follicles. Choosy females also appear to face a reduced probability of survival if El Ni?o conditions occur in the year following breeding. These findings indicate that female choice can carry significant costs, and suggest that the benefits that lek-mating females gain through mating with a preferred male may be higher than previously predicted.     

A trade-off between current and future sex allocation revealed by maternal energy budget in a small mammal

Sex-allocation theories generally assume differential fitness costs of raising sons and daughters. Yet, experimental confirmation of such costs is scarce and potential mechanisms are rarely addressed. While the most universal measure of physiological costs is energy expenditure, only one study has related the maternal energy budget to experimentally controlled offspring sex. Here, we experimentally test this in the bank vole (Myodes glareolus) by simultaneously manipulating the litter's size and sex ratio immediately after birth. Two weeks after manipulation, when mothers were at the peak of lactation and were pregnant with concurrent litters, we assessed their energy budget. We found that maternal food consumption and daily energy expenditure increased with the size of the litters being lactated. Importantly, the effects of offspring sex on energy budget depended on the characteristics of the simultaneously gestating litters. Specifically, the mothers nursing all-male litters and concurrently pregnant with male-biased litters had the highest energy expenditure. These had consequences for the next generation, as size of female offspring from the concurrent pregnancy of these mothers was compromised. Our study attests a higher cost of sons, consequently leading to a lower investment in them, and reveals the significance of offspring sex in moulding the trade-off between current and future maternal investment.     

The energetic consequences of behavioral variation in a marine carnivore

Intraspecific variability in foraging behavior has been documented across a range of taxonomic groups, yet the energetic consequences of this variation are not well understood for many species. Understanding the effect of behavioral variation on energy expenditure and acquisition is particularly crucial for mammalian carnivores because they have high energy requirements that place considerable pressure on prey populations. To determine the influence of behavior on energy expenditure and balance, we combined simultaneous measurements of at‐sea field metabolic rate (FMR) and foraging behavior in a marine carnivore that exhibits intraspecific behavioral variation, the California sea lion (Zalophus californianus). Sea lions exhibited variability in at‐sea FMR, with some individuals expending energy at a maximum of twice the rate of others. This variation was in part attributable to differences in diving behavior that may have been reflective of diet; however, this was only true for sea lions using a foraging strategy consisting of epipelagic (<200 m within the water column) and benthic dives. In contrast, sea lions that used a deep‐diving foraging strategy all had similar values of at‐sea FMR that were unrelated to diving behavior. Energy intake did not differ between foraging strategies and was unrelated to energy expenditure. Our findings suggest that energy expenditure in California sea lions may be influenced by interactions between diet and oxygen conservation strategies. There were no apparent energetic trade‐offs between foraging strategies, although there was preliminary evidence that foraging strategies may differ in their variability in energy balance. The energetic consequences of behavioral variation may influence the reproductive success of female sea lions and result in differential impacts of individuals on prey populations. These findings highlight the importance of quantifying the relationships between energy expenditure and foraging behavior in other carnivores for studies addressing fundamental and applied physiological and ecological questions.     

Temperature effects on bioenergetics of growth, assimilaton efficiency and thyroid activity in juvenile varand lizards

When varanid lizards, Varanus niloticus, were allowed to select their preferred body temperature (c. 34°C) they exhibited swifter growth, larger food intake and superior efficiency of conversion when compared with animals restricted to a maximum body temperature of 24°C. At the higher temperature the animals also exhibited a higher metabolic rate and increased thyroid activity, while those at the lower temperature lostproportionately more energy via respiration. A complete energy budget over a period of 6 weeks is presented.     

Corticosterone, locomotor performance, and metabolism in side-blotched lizards (Uta stansburiana)

Elevated levels of circulating corticosterone commonly occur in response to stressors in wild vertebrates. A rise in corticosterone, usually in animals of subordinate rank, results in a variety of effects on behavior and physiology. Behavioral and physiological responses to short-term increases in corticosterone are well studied. In contrast, the effects of chronic elevated levels of corticosterone are poorly understood, particularly in lizards. Here, we examined the long-term effects of exogenous corticosterone on locomotor performance, resting and active metabolic rate, and hematocrit in male side-blotched lizards Uta stansburiana. Corticosterone implantation resulted in higher levels of stamina relative to sham-surgery controls. In addition, lizards with elevated corticosterone exhibited lower resting metabolic rates relative to controls. Corticosterone had no effect on peak activity metabolism but did result in faster recovery times following exhaustive exercise. We suggest that elevated levels of corticosterone in response to dominance interactions promote enhanced locomotor abilities, perhaps as a flight response to avoid agonistic interactions. Furthermore, stressed lizards are characterized by lower resting metabolic rates, which may serve as strategy to conserve energy stores and enhance survival.     

Experimental enhancement of corticosterone levels positively affects subsequent male survival

Corticosterone is an important hormone of the stress response that regulates physiological processes and modifies animal behavior. While it positively acts on locomotor activity, it may negatively affect reproduction and social activity. This suggests that corticosterone may promote behaviors that increase survival at the cost of reproduction. In this study, we experimentally investigate the link between corticosterone levels and survival in adult common lizards (Lacerta vivipara) by comparing corticosterone-treated with placebo-treated lizards. We experimentally show that corticosterone enhances energy expenditure, daily activity, food intake, and it modifies the behavioral time budget. Enhanced appetite of corticosterone-treated individuals compensated for increased energy expenditure and corticosterone-treated males showed increased survival. This suggests that corticosterone may promote behaviors that reduce stress and it shows that corticosterone per se does not reduce but directly or indirectly increases longer-term survival. This suggests that the production of corticosterone as a response to a stressor may be an adaptive mechanism that even controls survival.     

随机限食和重喂食小鼠能量收支和生长发育的可塑性

为阐明能量收支和生长发育的可塑性对动物适应食物资源变化的作用和意义,将断乳后的雄性KM小鼠40只随机限食4周,再重喂食4周。采用封闭式流体压力呼吸计测定基础代谢率(BMR)。限食使摄食量显著增加,BMR和活动行为降低,胴体和生殖腺重量显著降低。重喂食后上述指标均恢复到对照组水平,表现出显著的可塑性变化。结果表明,KM小鼠能通过摄食量、BMR、活动行为和身体组成的可塑性调节以适应难以预测的食物资源变化。     

Meeting the energy demands of reproduction in female koalas,<Emphasis Type="Italic"> Phascolarctos cinereus</Emphasis>: evidence for energetic compensation

Koalas are generally considered to be limited by their ability to acquire energy from their diet of Eucalyptus foliage and have the lowest mass-specific peak lactational energy output measured in any mammal to date. This study considered the energetics and sources of energy utilised for reproduction in free-ranging female koalas. Energy requirements and foliage intake were greater in both lactating and non-lactating females in winter than summer, presumably due to demands of thermoregulation. Koalas met the peak energy requirements of lactation primarily by a 36% increase in their intake of foliage. Metabolic energy expenditure (field metabolic rate, 1778 kJ.day^–1 for a 6.25-kg female at the time of peak lactation) was not elevated during lactation. This was due to compensation for part of their lactational demands by reduction of another, non-reproductive, component of their energy budget. The observed energetic compensation was probably due primarily to substitution of the waste heat from the metabolic costs of milk production and increased heat increment of feeding for thermoregulatory energy expenditure. There may also have been energetic compensation by reduction of some aspect of maintenance metabolism. Such energetic compensation, together with the strategy of spreading lactation over a long period, minimises the magnitude of lactational energy demands on koalas, and thus the increase in daily food intake required during lactation. As the nutritional requirements of females at peak lactation are the highest of any members of the population, low reproductive requirements effectively increase the types and amount of habitat able to support koala populations.Abbreviations FMR field metabolic rate - HIF heat increment of feeding - RMR resting metabolic rate - _O2 rate of oxygen consumptionCommunicated by I.D. Hume     

饥饿对中华倒刺鲃幼鱼代谢、个性和集群的影响

在自然界中,环境变化、季节更替和人为因素造成食物资源时空分布的不均一性,导致鱼类经常面临食物资源短缺的环境胁迫,对其能量代谢和行为造成一定影响。为考察食物资源短缺下暖水性鲤科鱼类能量代谢、个性与集群行为的应对策略及其可能的内在关联,选取中华倒刺鲃(Spinibarbus sinensis)幼鱼为实验对象,分别测定饥饿组(2周)和对照组(维持日粮)在处理前后实验鱼的标准代谢率(Standard metabolic rate,SMR)、个性行为(勇敢性、探索性和活跃性)以及实验处理后的集群行为(凝聚力和协调性)。研究发现:(1)饥饿组和对照组实验过程中实验鱼SMR均显著下降,但仅饥饿组实验鱼SMR具有重复性;(2)饥饿导致中华倒刺鲃幼鱼勇敢性、探索性、活跃性均显著增加;(3)饥饿导致群体成员间距离缩短,游泳速度及其同步性上升。研究表明:饥饿后的中华倒刺鲃不仅适应性降低SMR以减少能量消耗,而且呈现出更高的勇敢性、探索性和活跃性以利于获取食物资源;饥饿迫使中华倒刺鲃群体提高凝聚力和协调性,可能有助于提高群体的生存能力。     

Variation in stress and innate immunity in the tree lizard (<Emphasis Type="Italic">Urosaurus ornatus</Emphasis>) across an urban–rural gradient

The urban environment presents new and different challenges to wildlife, but also potential opportunities depending on the species. As urban encroachment onto native habitats continues, understanding the impact of this expansion on native species is vital to conservation. A key physiological indicator of environmental disturbance is the vertebrate stress response, involving increases in circulating glucocorticoids (i.e. corticosterone), which exert influence on numerous physiological parameters including energy storage, reproduction, and immunity. We examined how urbanization in Phoenix, Arizona influences corticosterone levels, blood parasitism, and innate immunity in populations of tree lizards (Urosaurus ornatus) to determine whether urbanization may be detrimental or beneficial to this species. Both baseline and stress-induced corticosterone concentrations were significantly lower in urban lizards relative to the rural ones, however, the magnitude of the increase in corticosterone with stress did not differ across populations. Urban lizards also had a lower ratio of heterophils to lymphocytes, but elevated overall leukocyte count, as compared to lizards from the natural site. Urban and rural lizards did not differ in their prevalence of the blood parasite, Plasmodium mexicanum. Taken together, these results suggest that urban tree lizards may have suppressed overall corticosterone concentrations possibly from down-regulation as a result of frequent exposure to stressors, or increased access to urban resources. Also, urban lizards may have bolstered immunocompetence possibly from increased immune challenges, such as wounding, in the urban environment, or from greater energetic reserves being available as a result of access to urban resources.     

Autumn-winter energetics of Holarctic tree squirrels:a review

Similarities in general size, geometry, lifestyle, and environment mean that certain energetic constraints are common and peculiar to Holarctic tree squirrels as a group. Holarctic tree squirrels are relatively small, diurnal mammals which, in association with their food niche, maintain activity throughout the autumn-winter period. Despite this, they exhibit no major morphological or physiological adaptations to minimize energy expenditure at low temperatures; on the contrary, both basal metabolism and conductance are higher than expected on the grounds of physical size. When they are active energy expenditure is therefore strongly influenced by effective ambient temperature for these species when active in their natural autumn-winter environments. Nest use allows near-basal metabolism at most natural ambient temperatures. The balance of economical inactivity against feeding rewards offset by cold exposure must therefore be a crucial aspect of the lifestyle of these squirrels.     

Optimisation of energetic and reproductive gains explains behavioural responses to environmental variation across seasons and years

Animals switch between inactive and active states, simultaneously impacting their energy intake, energy expenditure and predation risk, and collectively defining how they engage with environmental variation and trophic interactions. We assess daily activity responses to long‐term variation in temperature, resources and mating opportunities to examine whether individuals choose to be active or inactive according to an optimisation of the relative energetic and reproductive gains each state offers. We show that this simplified behavioural decision approach predicts most activity variation (R² = 0.83) expressed by free‐ranging red squirrels over 4 years, as quantified through accelerometer recordings (489 deployments; 5066 squirrel‐days). Recognising activity as a determinant of energetic status, the predictability of activity variation aggregated at a daily scale, and the clear signal that behaviour is environmentally forced through optimisation of gain, provides an integrated approach to examine behavioural variation as an intermediary between environmental variation and energetic, life‐history and ecological outcomes.