Fluctuating selection on basal metabolic rate

BMR (Basal metabolic rate) is an important trait in animal life history as it represents a significant part of animal energy budgets. BMR has also been shown to be positively related to sustainable work rate and maximal thermoregulatory capacity. To this date, most of the studies have focused on the causes of interspecific and intraspecific variation in BMR, and fairly little is known about the fitness consequences of different metabolic strategies. In this study, we show that winter BMR affects local survival in a population of wild blue tits (Cyanistes caeruleus), but that the selection direction differs between years. We argue that this fluctuating selection is probably a consequence of varying winter climate with a positive relation between survival and BMR during cold and harsh conditions, but a negative relation during mild winters. This fluctuating selection can not only explain the pronounced variation in BMR in wild populations, but will also give us new insights into how energy turnover rates can shape the life‐history strategies of animals. Furthermore, the study shows that the process of global warming may cause directional selection for a general reduction in BMR, affecting the general life‐history strategy on the population level.     

Age at first reproduction and probability of reproductive failure in women

Life history theory predicts a trade-off between fitness benefits and costs of delaying age at first reproduction (AFR). In many human populations, maternal AFR has been increasingly delayed beyond sexual maturity over the past decades, raising a question of whether any fitness benefits accrued outweigh costs incurred. To investigate the cost–benefit trade-off concerning AFR in women, we construct a theoretical model and test its predictions using pedigree data from historical Finnish mothers. The model predicts that the probability of reproductive failure (no offspring produced reaching breeding) will increase with AFR if the benefit with delaying in terms of improvement to offspring quality (i.e., breeding probability) cannot offset the cost from decline in offspring quantity. The data show that offspring quantity declined significantly with delayed reproduction, while offspring quality remained initially constant before declining when AFR was delayed beyond 30. Consistent with the theoretical model's predictions, reproductive failure probability increased markedly with delaying AFR after 30, independently of maternal socioeconomic status. Our study is the first to investigate the associations between delay in AFR after sexual maturity and changes in not only offspring quantity but also offspring quality and suggest a significant evolutionary disadvantage of delayed AFR beyond 30 for lineage persistence in a predemographic transition society.     

Nonshivering thermogenesis capacity versus basal metabolic rate in laboratory mice

I wanted to follow the correlation between level of basal metabolic rate (BMR) and maximum response to injection of noradrenaline (MMR_NA) in two lines of laboratory mice subjected to divergent, artificial selection toward high BMR (HBMR) and low BMR (LBMR). HBMR animals had heavier visceral organs (heart, liver, kidney, intestine), but their regulatory NST (MMR_NA–BMR) was lower and interscapular brown adipose tissue (IBAT) lighter than in LBMR mice. Obligatory part of nonshivering thermogenesis (NST) (in other words BMR) depended on visceral organ mass, whereas regulatory NST correlates with mass of IBAT. BMR was not correlated with total NST capacity, but phenotypic correlation between obligatory and regulatory NST was negative. This suggests possibility of substitution of obligatory NST to thermoregulation in a place of the regulatory NST. Then total thermoregulatory energy expenditures do not change.     

Allometric estimation of metabolic rate from heart rate in penguins

Studies of the relationship between heart rate (f(H)) and rate of oxygen consumption (V(.) (O(2))), which are then used to predict field metabolic rate, frequently fail to incorporate body mass as a predictive variable. This is a potentially important omission in the study of animals whose body mass fluctuates substantially during their annual cycle. In an attempt further to improve estimates of field metabolic rate from f(H), we re-evaluated data on M(b), f(H) and V(.) (O(2)) from previous studies of macaroni penguins (Eudyptes chrysolophus) and king penguins (Aptenodytes patagonicus) and derived a new relationship to integrate these three quantities. This relationship is at least as accurate and precise as previously determined relationships. We applied this same principle to published data on 11 of the 20 recognised penguin taxa to derive a relationship to predict V(.) (O(2)) from f(H) and M(b) in penguins of any species. This result has interesting implications in terms of reducing the logistical burden in studies of field metabolic rate.     

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), ...     

Phylogenetic differences of mammalian basal metabolic rate are not explained by mitochondrial basal proton leak

Metabolic rates of mammals presumably increased during the evolution of endothermy, but molecular and cellular mechanisms underlying basal metabolic rate (BMR) are still not understood. It has been established that mitochondrial basal proton leak contributes significantly to BMR. Comparative studies among a diversity of eutherian mammals showed that BMR correlates with body mass and proton leak. Here, we studied BMR and mitochondrial basal proton leak in liver of various marsupial species. Surprisingly, we found that the mitochondrial proton leak was greater in marsupials than in eutherians, although marsupials have lower BMRs. To verify our finding, we kept similar-sized individuals of a marsupial opossum (Monodelphis domestica) and a eutherian rodent (Mesocricetus auratus) species under identical conditions, and directly compared BMR and basal proton leak. We confirmed an approximately 40 per cent lower mass specific BMR in the opossum although its proton leak was significantly higher (approx. 60%). We demonstrate that the increase in BMR during eutherian evolution is not based on a general increase in the mitochondrial proton leak, although there is a similar allometric relationship of proton leak and BMR within mammalian groups. The difference in proton leak between endothermic groups may assist in elucidating distinct metabolic and habitat requirements that have evolved during mammalian divergence.     

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.     

A high standard metabolic rate constrains juvenile growth

The allocation of energy to various components of an individual's energy budget is often viewed as a competitive process. As such, a tradeoff may exist between production (growth) and maintenance metabolism. One view of a potential tradeoff, termed “the principle of allocation”, suggests that individuals with lower maintenance metabolic expenditures may have higher growth rates. To determine whether such a tradeoff exists, I analyzed the relationship between growth rate and maintenance metabolism of 225 juvenile snapping turtles housed in the laboratory. I measured growth from hatching to 6 months of age, and then measured oxygen consumption and calculated standard metabolic rate. Mean growth rate was 0.19 g d⁻ and mean standard metabolic rate (SMR) was 1.41 kJ d⁻. Maintenance metabolism and growth were negatively correlated after both were adjusted for body mass. The results support the “principle of allocation” theory: individuals with higher standard metabolic rates tended to have low growth rates.     

基础代谢产热的分子机制

本文综述了基础代谢的功能,发生,产热的途径以及各产热途径对基础代谢率（basal metabolic rate,BMR)的贡献,基础条件下整个机体的能量消耗用来维持两种功能：服务功能和细胞维持功能,基础代谢的产生是由体内的解偶联反应引起的,产热过程涉及到细胞内的非线粒体呼吸,质子漏和ATP周转反应,产生的热量分别占BMR的10％,20－30％和60％－70％。ATP周转反应包括Na^ -K^ 泵,Ca^2 泵,肌肉收缩,蛋白质周转,糖异生和尿素合成等,各产热反应对细胞呼吸的贡献只有组织特异性,却没有种属特异性,因而它们对BMR的贡献不仅与自身活性有关,还与体内各器官的相对重量有关。     

A killer appetite: metabolic consequences of carnivory in marine mammals

Among terrestrial mammals, the morphology of the gastrointestinal tract reflects the metabolic demands of the animal and individual requirements for processing, distributing, and absorbing nutrients. To determine if gastrointestinal tract morphology is similarly correlated with metabolic requirements in marine mammals, we examined the relationship between basal metabolic rate (BMR) and small intestinal length in pinnipeds and cetaceans. Oxygen consumption was measured for resting bottlenose dolphins and Weddell seals, and the results combined with data for four additional species of carnivorous marine mammal. Data for small intestinal length were obtained from previously published reports. Similar analyses were conducted for five species of carnivorous terrestrial mammal, for which BMR and intestinal length were known. The results indicate that the BMRs of Weddell seals and dolphins resting on the water surface are 1.6 and 2.3 times the predicted levels for similarly sized domestic terrestrial mammals, respectively. Small intestinal lengths for carnivorous marine mammals depend on body size and are comparatively longer than those of terrestrial carnivores. The relationship between basal metabolic rate (kcal day(-1)) and small intestinal length (m) for both marine and terrestrial carnivores was, BMR=142.5 intestinal length(1.20) (r(2)=0.83). We suggest that elevated metabolic rates among marine mammal carnivores are associated with comparatively large alimentary tracts that are presumably required for supporting the energetic demands of an aquatic lifestyle and for feeding on vertebrate and invertebrate prey.     

Countergradient variation in growth rate: compensation for length of the growing season among Atlantic silversides from different latitudes

Summary How do organisms adapt to the differences in temperature and length of the growing season that occur with latitude? Among Atlantic silversides (Menidia menidia) along the east coast of North America, the length of the first growing season declines by a factor of about 2.5 with increasing latitude. Yet body size at the end of the first growing season does not decline. High-latitude fish must, therefore, grow faster within the growing season than do low-latitude fish. This geographical pattern has a genetic basis. Laboratory experiments on fish from six different locations revealed a latitudinal gradient in the capacity for growth (i.e., maximum growth potential). In two subsequent experiments using fish from Nova Scotia (NS), New York (NY) and South Carolina (SC) that had been separately reared in a common environment for several generations, differences in growth rate among populations were highly significant. The rank order was NS>NY>SC, but the difference among populations depended on temperature. High-latitude fish outperformed those from low latitudes primarily at the high temperatures that low-latitude fish would be expected to experience most often in nature. These results suggest that instead of being adapted for growth at low temperatures, fish from high latitudes are adapted for rapid elevation of growth rate during the brief interval of the year when high temperatures occur. Selection on growth rate results from sizedependent winter mortality: the importance to winter survival of being large increases with latitude but the length of the growing season simultaneously decreases. The end result is countergradient variation in growth rate, a phenomenon that may be much more widespread than currently recognized.     

Moult and basal metabolic costs in males of two subspecies of stonechats: the European Saxicola torquata rubicula and the East African S. t. axillaris

The circannual patterns in resting metabolic rate (RMR) of males of two subspecies of stonechats, the European Saxicola torquata rubicula and the East African S. t. axillaris, are compared. As the birds from the two subspecies were raised and kept under comparable laboratory conditions, differences in metabolic rate between the two subspecies had to be genetically determined. RMR peaked during moult in both subspecies. During the rest of the year RMR was fairly constant in both subspecies and assumed to reflect basal metabolic rate (BMR). African stonechats had a 22% lower mass specific BMR than European stonechats, which is thought to reflect a genetical physiological adaptation to the differences in environmental circumstances they experience in the field. A low BMR makes an animal more susceptible to cold. Hence, the relatively high plumage mass in the African compared to the European stonechat may be functionally linked to its relatively low BMR. Moult costs, calculated from the plumage masses and the differences in RMR inside and outside the moult period, tended to be higher in the European compared to the African stonechats. These data and an interspecific comparison of moult costs over various species of birds support the earlier notion by Lindström et al. (1993) that moult costs are more closely linked with BMR than with body mass or rate of moult. The relation between moult costs and BMR and the fact that the efficiency of moult is extremely low (3.8 and 6.4% for European and African stonechats, respectively) suggest that the maintenance of specific tissues necessary for moult is a large cost factor. Alternatively, impaired insulation during moult may necessitate an increased metabolic capacity which may be associated with an increased RMR.     

Phytoplankton growth rate as a function of cell size: an experimental test in Lake Biwa

It is well known that algal growth rates decrease with increasing cell size. Most of these findings were, however, obtained under laboratory conditions. It is not clear if these allometric relationships are also applicable to in situ conditions. In the present study, the relationship between growth rates and cell size of algal species was examined seasonally in Lake Biwa by in situ dilution bioassays. The bioassays revealed that the highest growth rate of each species throughout the experiments was negatively correlated with cell size consistent with known allometric relationships. At each incubation experiment, however, growth rates were not necessarily correlated with cell size. This was true even when both macro- and micronutrients were added, although a substantial number of species responded to nutrient enrichment. These results showed that nutrient supplies affected algal species differently regardless of cell size and that factors other than nutrient supplies limited the growth rate of some algal species. Due to such species-specific differences in limiting factors, at any given time in situ growth rates of algae are not determined exclusively by cell size. Received: August 24, 2000 / Accepted: March 2, 2001     

Thermal sensitivity of growth rate in hatchling Sceloporus lizards: environmental,behavioral and genetic aspects

Summary To investigate the physiological, behavioral, and genetic contributions to growth rate, we studied the thermal sensitivity of growth rate in hatchlings of the iguanid lizards Sceloporus occidentalis and S. graciosus in the laboratory. We used a cycling thermal regime patterned after thermal environments found in nature. Growth rates increased with duration of access to radiant heat. Thus, variation in the thermal environment can cause phenotypic variation in growth rate and hence body size. The two species differed in both the magnitude and thermal sensitivity of growth rate, and these differences were associated with differences in behavioral thermoregulation. Thus, growth is determined interactively by both behavior and physiology. We found evidence of among-family variation in the growth rates of S. occidentalis, suggesting that growth rate has the genetic potential to evolve. In S. occidentalis, both growth rate and egg size affected body size of hatchlings at several weeks of age. In turn, hatchling size may affect fitness: for example, larger S. occidentalis hatchlings had higher sprint speeds and may therefore be more adept at capturing prey or evading predators. Our results demonstrate that growth rate has genetic, behavioral, and physiological components, and that the resulting effects on body size may have important consequences for ecological performance e.g., sprint speed.     

Exploring individual quality: basal metabolic rate and reproductive performance in storm-petrels

Despite evidence that some individuals achieve both superiorreproductive performance and high survivorship, the factorsunderlying variation in individual quality are not well understood.The compensation and increased-intake hypotheses predict thatbasal metabolic rate (BMR) influences reproductive performance;if so, variation in BMR may be related to differences in individualquality. We evaluated whether BMR measured during the incubationperiod provides a proximate explanation for variation in individualquality by measuring the BMRs and reproductive performance ofLeach's storm-petrels (Oceanodroma leucorhoa) breeding on KentIsland, New Brunswick, Canada, during 2000 and 2001. We statisticallycontrolled for internal (body mass, breeding age, sex) and external(year, date, time of day) effects on BMR. We found that maleswith relatively low BMRs hatched their eggs earlier in the seasonand that their chicks' wing growth rates were faster comparedto males with relatively high BMRs. Conversely, BMR was notrelated to egg volume, hatching date, or chick growth rate forfemales or to lifetime (23 years) hatching success for eithersex. Thus, for males but not for females, our results supportthe compensation hypothesis. This hypothesis predicts that animalswith low BMRs will achieve better reproductive performance thananimals with high BMRs because they have lower self-maintenancecosts and therefore can apportion more energy to reproduction.These results provide evidence that intraspecific variationin reproductive performance is related to BMR and suggest thatBMR may influence individual quality in males.     

Vitamin C improves basal metabolic rate and lipid profile in alloxan-induced diabetes mellitus in rats

Diabetes mellitus (DM) is a multi-factorial disease which is characterized by hyperglycaemia, lipoprotein abnormalities and oxidative stress. This study evaluated effect of oral vitamin C administration on basal metabolic rate and lipid profile of alloxan-induced diabetic rats. Vitamin C was administered at 200 mg/kg body wt. by gavage for four weeks to diabetic rats after which the resting metabolic rate and plasma lipid profile was determined. The results showed that vitamin C administration significantly (P<0.01) reduced the resting metabolic rate in diabetic rats; and also lowered plasma triglyceride, total cholesterol and low-density lipoprotein cholesterol. These results suggest that the administration of vitamin C in this model of established diabetes mellitus might be beneficial for the restoration of basal metabolic rate and improvement of lipid profile. This may at least in part reduce the risk of cardiovascular events seen in diabetes mellitus.     

Age at first reproduction in male fallow deer: age-specific versus dominance-specific behaviors

The argument that an optimal age at first reproduction evolveswhere the benefits of reproduction outweigh the costs impliesthat where conditions change, age at first reproduction shouldalso change. We studied six captive populations of fallow deer(Dama dama) that differed in the age structure of males, maledensity, and sex ratio. We examined responses of males to changesin competition by simulating the presence of additional malesby providing visual, olfactory, and auditory stimuli. Our resultssuggest that dominance rank was the most important factor indetermining the level of reproductive behaviors exhibited. Theparticipation in reproduction increased with dominance status,and this association held for males that are usually sociallyimmature (3-5 years old). Hence, age apart from dominance wasrelatively unimportant in affecting the reproductive behavior.Male density was positively correlated with the time spent walkingand standing The female-to-male ratio was positively relatedto male-female interactions, but negatively related to male-maleinteractions. In response to the simulations, males older than3 years increased the rate of reproductive behaviors, but youngermales did not change or decreased the rate. We conclude thatonly males up to 3 years of age refrained from reproductionunder competition by mature males. However, past 3 years ofage, investment in reproduction is a function of dominance ratherthan a function bf age. This implies that 4- and 5-year-oldmales do not seems to defer reproduction until socially maturebut that their participation is a correlate of the achievabledominance rank.     

Seasonal variation in metabolic rate of a medium-sized frugivore, the Knysna Turaco (Tauraco corythaix)

Many seasonal thermoregulation studies have been conducted on Holarctic birds that live in predictable, highly seasonal climates with severe winters. However, relatively few studies have been conducted on their southern hemisphere Afrotropical counterparts that encounter less predictable climates with milder winters. These latter birds are expected to conserve energy in winter by downregulating their metabolic rates. Therefore in this study, metabolic rate was measured during summer and winter in Knysna Turaco, Tauraco corythaix (Musophagiformes, Musophagidae) (c. 310 g), a non-passerine, in order to test whether there is energy conservation in winter. No overall significant differences in resting metabolic rates over a range of ambient temperatures were observed between winter and summer. However, whole-organism basal metabolic rates were 18.5% higher (p=0.005) in winter than in summer (210.83±15.97 vs. 186.70±10.52 O₂ h⁻¹). Knysna Turacos had broad thermoneutral zones ranging from 20 to 28 °C in winter and 10 to 30 °C in summer. These results suggest that Knysna Turacos show seasonal thermoregulatory responses that represent cold defense rather than energy conservation, which is contrary to what was expected.