共查询到20条相似文献,搜索用时 644 毫秒
1.
Tøien Ø Blake J Edgar DM Grahn DA Heller HC Barnes BM 《Science (New York, N.Y.)》2011,331(6019):906-909
Black bears hibernate for 5 to 7 months a year and, during this time, do not eat, drink, urinate, or defecate. We measured metabolic rate and body temperature in hibernating black bears and found that they suppress metabolism to 25% of basal rates while regulating body temperature from 30° to 36°C, in multiday cycles. Heart rates were reduced from 55 to as few as 9 beats per minute, with profound sinus arrhythmia. After returning to normal body temperature and emerging from dens, bears maintained a reduced metabolic rate for up to 3 weeks. The pronounced reduction and delayed recovery of metabolic rate in hibernating bears suggest that the majority of metabolic suppression during hibernation is independent of lowered body temperature. 相似文献
2.
It has been suggested that sexual reproduction is maintained because it reduces the load imposed by recurrent deleterious mutations. If rates of deleterious mutation per diploid genome per generation (U) exceed 1, and mutations interact synergistically, then sexuals can overcome their inherent twofold disadvantage. We have tested this hypothesis by estimating genomic point mutation rates for protein-coding genes in a range of animal taxa. We find a positive linear relationship between U and generation time. In species with short generation times, U is predicted to be far below 1, suggesting that sex is not maintained by its capacity to purge the genome of deleterious mutations. 相似文献
3.
All organisms face the problem of how to fuel ontogenetic growth. We present a model, empirically grounded in data from birds and mammals, that correctly predicts how growing animals allocate food energy between synthesis of new biomass and maintenance of existing biomass. Previous energy budget models have typically had their bases in rates of either food consumption or metabolic energy expenditure. Our model provides a framework that reconciles these two approaches and highlights the fundamental principles that determine rates of food assimilation and rates of energy allocation to maintenance, biosynthesis, activity, and storage. The model predicts that growth and assimilation rates for all animals should cluster closely around two universal curves. Data for mammals and birds of diverse body sizes and taxa support these predictions. 相似文献
4.
Defense strategies against hypoxia and hypothermia 总被引:47,自引:0,他引:47
P W Hochachka 《Science (New York, N.Y.)》1986,231(4735):234-241
Because aerobic metabolic rates decrease in hypoxia-sensitive cells under oxygen-limiting conditions, the demand for glucose or glycogen for anaerobic glycolysis may rise drastically as a means of making up for the energetic shortfall. However, ion and electrical potentials typically cannot be sustained because of energy insufficiency and high membrane permeabilities; therefore metabolic and membrane functions in effect become decoupled. In hypoxia-tolerant animals, these problems are resolved through a number of biochemical and physiological mechanisms; of these metabolic arrest and stabilized membrane functions are the most effective strategies for extending tolerance to hypoxia. Metabolic arrest is achieved by means of a reversed or negative Pasteur effect (reduced or unchanging glycolytic flux at reduced O2 availability); and coupling of metabolic and membrane function is achievable, in spite of the lower energy turnover rates, by maintaining membranes of low permeability (probably via reduced densities of ion-specific channels). The possibility of combining metabolic arrest with channel arrest has been recognized as an intervention strategy. To date, the success of this strategy has been minimal, mainly because depression of metabolism through cold is the usual arrest mechanism used, and hypothermia in itself perturbs controlled cell function in most endotherms. 相似文献
5.
Webster M 《Science (New York, N.Y.)》2007,317(5837):499-502
Morphological variation within species is a raw material subject to natural selection. However, temporal change in morphological diversity has usually been studied in terms of variation among rather than within species. The distribution of polymorphic traits in cladistic character-taxon matrices reveals that the frequency and extent of morphological variation in 982 trilobite species are greatest early in the evolution of the group: Stratigraphically old and/or phylogenetically basal taxa are significantly more variable than younger and/or more derived taxa. Through its influence on evolutionary tempo, high intraspecific variation may have played a major role in the pronounced Cambrian diversification of trilobites. 相似文献
6.
《农业科学学报》2017,(1)
The objectives of this study were to determine how the distribution of photosynthetically active radiation(PAR) in a maize canopy affected basal intemode strength and stalk lodging.The distributions of PAR within the canopies of two maize cultivars(Zhongdan 909 and Xinyu 41) were altered by removing whole leaves or half leaves in different canopy layers.The results showed that removing whole leaves or half leaves above the three-ear-leaves(R_(AE) and R_(AE/2)) at flowering significantly increased PAR at the ear and interception of PAR(IPAR) from the earto middle of the ear and soil surface.These changes increased the structural carbohydrate content and rind penetration strength(RPS) of the third basal intemode by 5.4-11.6%and reduced lodging by 4.2-7.8%.Removal of the first three leaves below the three-ear-leaves(R_(BE)) before flowering significantly reduced IPAR from the ear to half way below the ear.This reduced the structural carbohydrate content and the RPS of the third basal intemode by 9.1-17.4%and increased lodging by 7.0-11.2%.Removal of the three lowest green leaves(R_B) in the canopy before flowering increased PAR at the bottom of the canopy,but had no effect on the structural carbohydrate content of the basal intemode,the RPS,and the lodging rate.Overall,the results indicated that the key factors affecting the basal intemode strength formation and lodging were PAR at the ear and IPAR from the ear to halfway below the ear.Increasing PAR at the ear and IPAR from the ear to halfway below the ear could enhance lodging resistance by increasing the structural carbohydrate content and mechanical strength of the basal intemode. 相似文献
7.
《Science (New York, N.Y.)》1985,230(4726):687
The "turritid gastropod" referred to on page 713 (column 2, line 22) of the article "Hydrothermal vent animals: Distribution and biology" by J. Frederick Grassle (23 Aug.) should have been a "turrid gastropod." The first reference 26 on page 716 (column 2, line 14) should have been to R. A. Lutz and D. C. Rhoads, Eos 64, 1017 (1983). The statement at the end of page 716 that vent animals have metabolic rates that are orders of magnitude higher than relatives in other parts of the deep sea cannot be substantiated because, although many deep-sea organisms have low metabolic rates, benthic decapod crustacea and echinoderms from areas away from hydrothermal vents in the deep sea have metabolic rates similar to those of vent species when measured at the same temperature. This is further discussed in a forthcoming issue of the Bulletin of the Biological Society of Washington. 相似文献
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A key unresolved question in population ecology concerns the relationship between a population's size and its growth rate. We estimated this relationship for 1780 time series of mammals, birds, fish, and insects. We found that rates of population growth are high at low population densities but, contrary to previous predictions, decline rapidly with increasing population size and then flatten out, for all four taxa. This produces a strongly concave relationship between a population's growth rate and its size. These findings have fundamental implications for our understanding of animals' lives, suggesting in particular that many animals in these taxa will be found living at densities above the carrying capacity of their environments. 相似文献
10.
Escherichia coli aspartate transcarbamylase: the relation between structure and function 总被引:17,自引:0,他引:17
The x-ray structures of the allosteric enzyme aspartate transcarbamylase from Escherichia coli have been solved and refined for both allosteric forms. The T form was determined in the presence of the heterotropic inhibitor cytidine triphosphate, CTP, while the R form was determined in the presence of the bisubstrate analog N-phosphonacetyl-L-aspartate. These two x-ray structures provide the starting point for an understanding of how allosteric enzymes are able to control the rates of metabolic pathways. Insights into the mechanisms of both catalysis and homotropic cooperativity have been obtained by using site-directed mutagenesis to probe residues thought to be critical to the function of the enzyme based on these x-ray structures. 相似文献
11.
Puromycin fails to alter minimal oxygen consumption of rats treated with thyroxine, provided the rectal temperatures of these rats are maintained at 37.8 degrees to 38.1 degrees C. The previously reported puromycin-induced decline in basal metabolic rate of thyroxine-treated rats may have been due to the hypothermia produced by this drug. 相似文献
12.
Deep-sea hydrothermal vent communities exhibit an array of reproductive strategies. Although a few vent species undergo planktotrophic, high-dispersal modes of development, most exhibit relatively low dispersal, but probably free-swimming nonplanktotrophic development. This predominance of nonplanktotrophy may be largely a reflection of phylogenetic constraints on the vent colonizing taxa; intervent dispersal among these forms may be facilitated by reduced developmental rates in the cold abyssal waters away from the vents. It is proposed that for those vent species with nonplanktotrophic development, larval dispersal is a stepwise process with oceanic ridge axes serving as discrete dispersal corridors. 相似文献
13.
不同采伐强度对云冷杉天然林主要针叶树种生长的影响 总被引:1,自引:0,他引:1
以云冷杉天然速生丰产林的12块固定样地为研究对象,研究不同采伐强度(对照、20%、30%、40%)对全林及不同林层的主要针叶树种(红松、云杉、冷杉)的断面积生长率、蓄积生长率的影响。结果表明:采伐与对照相比,能显著促进林分生长,全林及各林层的断面积生长率和蓄积生长率均大于对照,全林及第Ⅰ、Ⅱ林层的断面积和蓄积生长率随采伐强度的增加先增后减,第Ⅲ林层的断面积和蓄积生长率随采伐强度的增加而增加。所有样地中,断面积和蓄积生长率由大到小的排序为:第Ⅲ林层、第Ⅱ林层、全林、第Ⅰ林层。在伐后6、9 a,不同采伐强度的全林和第Ⅰ、Ⅱ林层的断面积和蓄积生长率之间的差异性显著,而第Ⅲ林层的差异性不显著。采伐过的样地各林层生长率均大于对照样地同林层的生长率,其中采伐强度为30%的样地的第Ⅱ、Ⅲ林层的生长率与对照样地差异性显著。故采伐强度为30%的森林经营措施更有利于天然云冷杉林的伐后恢复生长。 相似文献
14.
Global maps of sulfate and methane in marine sediments reveal two provinces of subsurface metabolic activity: a sulfate-rich open-ocean province, and an ocean-margin province where sulfate is limited to shallow sediments. Methane is produced in both regions but is abundant only in sulfate-depleted sediments. Metabolic activity is greatest in narrow zones of sulfate-reducing methane oxidation along ocean margins. The metabolic rates of subseafloor life are orders of magnitude lower than those of life on Earth's surface. Most microorganisms in subseafloor sediments are either inactive or adapted for extraordinarily low metabolic activity. 相似文献
15.
通过室内培养,研究了异丙隆对大田土壤和大棚土壤基础呼吸和微生物生物量碳的动态影响。结果表明:异丙隆使用量在50mg/kg以下,对土壤基础呼吸和微生物生物量碳基本没有影响;在100 mg/kg以上,其抑制效应随使用量的增加而明显,但在培养期内基本恢复到正常水平;异丙隆对2种土壤的影响未表现出明显差异。 相似文献
16.
Synteny and collinearity in plant genomes 总被引:4,自引:0,他引:4
Correlated gene arrangements among taxa provide a valuable framework for inference of shared ancestry of genes and for the utilization of findings from model organisms to study less-well-understood systems. In angiosperms, comparisons of gene arrangements are complicated by recurring polyploidy and extensive genome rearrangement. New genome sequences and improved analytical approaches are clarifying angiosperm evolution and revealing patterns of differential gene loss after genome duplication and differential gene retention associated with evolution of some morphological complexity. Because of variability in DNA substitution rates among taxa and genes, deviation from collinearity might be a more reliable phylogenetic character. 相似文献
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Elephant beetles (Megasoma elephas; Scarabaeidae) weighing from 10 to 35 grams, respond homeothermically when ambient temperature is reduced below about 20 degrees C in the laboratory. This metabolic response is not associated with locomotion or any other overt activity. Warming is initiated when the body temperature reaches an apparent set point of 20 degrees to 22 degrees C. Unlike the case for euthermic birds and mammals, energy metabolism and body temperature in these beetles are conspicuously oscillatory, with a given cycle in oxygen consumption peaking before the corresponding cycle in body temperature. 相似文献
19.
河南省栎类和杨树林分断面积和蓄积生长模型构建 总被引:1,自引:0,他引:1
20.
We combined precise focal depths and fault plane solutions of more than 40 events from the 20 September 1999 Chi-Chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central Taiwan is a moderately dipping (20 degrees to 30 degrees ) thrust fault away from the deformation front. A second, subparallel seismic zone lies about 15 kilometers below the main thrust. These seismic zones differ from previous models, indicating that both the basal decollement and relic normal faults are aseismic. 相似文献