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1.
This study investigated the sensitivity of managed boreal forests to climate change, with consequent needs to adapt the management to climate change. Model simulations representing the Finnish territory between 60 and 70 degrees N showed that climate change may substantially change the dynamics of managed boreal forests in northern Europe. This is especially probable at the northern and southern edges of this forest zone. In the north, forest growth may increase, but the special features of northern forests may be diminished. In the south, climate change may create a suboptimal environment for Norway spruce. Dominance of Scots pine may increase on less fertile sites currently occupied by Norway spruce. Birches may compete with Scots pine even in these sites and the dominance of birches may increase. These changes may reduce the total forest growth locally but, over the whole of Finland, total forest growth may increase by 44%, with an increase of 82% in the potential cutting drain. The choice of appropriate species and reduced rotation length may sustain the productivity of forest land under climate change.  相似文献   

2.
How does interferon inhibit tumour growth?   总被引:1,自引:0,他引:1  
Interferon can inhibit tumour growth in experimental animals and in some patients with benign and malignant tumours. There is experimental evidence to suggest that several mechanisms may be involved: a direct effect on the tumor or an indirect effect via the host, or both. Thus, interferon may slow the rate of tumour cell multiplication and this may lead to cell death. Interferon may induce changes in the cell surface rendering tumour cells more sensitive to host defence mechanisms. Interferon may induce reversion in the phenotype of tumour cells. Interferon may stimulate specific and non-specific humoral and cellular host mechanisms. The relative importance of these different effects of interferon may vary depending on the host and the particular tumour.  相似文献   

3.
Non-replication and inconsistency had been common features in the search for common variants of candidate genes affecting the risk of complex diseases. They may continue to require attention in the current era, when massive hypothesis-free testing of genetic variants is feasible. An empirical evaluation of the early experience with genome-wide association (GWA) studies suggests several examples where proposed associations have failed to be replicated by subsequent investigations. Non-replication and inconsistency is defined here in the framework of cumulative meta-analysis. Ideally, associations exist, GWA finds them, and subsequent investigations should replicate them. However, a number of other possibilities need to be considered. No common genetic variants may associate with the phenotype of interest and GWA may find nothing; or associations may exist, but GWA may miss them. Associations that do not exist may be falsely selected by the GWA and subsequent studies may appropriately refute them or falsely replicate them. Finally, GWA may find true associations that are nevertheless falsely non-replicated in the subsequent studies; or associations may be genuinely inconsistent across study populations. A list of options is presented for consideration in each of these scenarios.  相似文献   

4.
Partnership   总被引:1,自引:0,他引:1  
Individuals are called partners when it is in their best interest to help each other, if by doing so they increase the probability of being together in the future when, for similar reasons, they will continue to help each other. Kinsmen or individuals who often face (hedonic) situations in which helping is the dominating strategy are committed to help each other. Partnership may develop among them since the loss of the other means the loss of a guaranteed helper. Thus, they may be willing to take additional risks to help each other. Partnership may occur among unrelated individuals and with no hedonic situations. Partnership creates bonds between partners which may be much stronger than those between kinsmen; an individual may take more risks for his partner than he will ever take for a kin. Partnership may evolve without the sophistication and memory required for reciprocation altruism. Although kin selection, partnership and reciprocation are likely to appear fused as the causes for altruism, we argue that it may be possible to distinguish between them in some situations. We show that as the partners get older partnership may become less important to them. We also show that like cooperation, and for analogous reasons, malice may evolve among partners so that each will be willing to take additional risks in order to eliminate the other.  相似文献   

5.
Reactive oxygen species and airway inflammation   总被引:23,自引:0,他引:23  
Reactive oxygen species may be generated by several inflammatory cells which participate in airway inflammation and their production may be increased in asthma. Oxygen metabolites may contribute to the epithelial damage which is characteristic of asthmatic airways and may activate cells such as mast cells in the airway mucosa. Reactive oxygen species may cause bronchoconstriction, mucus secretion, have effects on airway vasculature, and may increase airway responsiveness. The role of reactive oxygen species in airway disease has been largely neglected, but appears to be an important area for future study. It is also possible that antioxidant defenses may be defective in asthma. If reactive oxygen species participate in the inflammatory response in airway disease, then radical scavengers or antioxidants could play a useful role in therapy.  相似文献   

6.
Divergent natural selection, adaptive divergence and gene flow may interact in a number of ways. Recent studies have focused on the balance between selection and gene flow in natural populations, and empirical work has shown that gene flow can constrain adaptive divergence, and that divergent selection can constrain gene flow. A caveat is that phenotypic diversification may be under the direct influence of environmental factors (i.e. it may be due to phenotypic plasticity), in addition to partial genetic influence. In this case, phenotypic divergence may occur between populations despite high gene flow that imposes a constraint on genetic divergence. Plasticity may dampen the effects of natural selection by allowing individuals to rapidly adapt phenotypically to new conditions, thus slowing adaptive genetic divergence. On the other hand, plasticity may promote future adaptive divergence by allowing populations to persist in novel environments. Plasticity may promote gene flow between selective regimes by allowing dispersers to adapt to alternate conditions, or high gene flow may result in the selection for increased plasticity. Here I expand frameworks for understanding relationships among selection, adaptation and gene flow to include the effects of phenotypic plasticity in natural populations, and highlight its importance in evolutionary diversification.  相似文献   

7.
Laboratory dialysis, one of the most widely used techniques in biological research is truly a ' gateway technology' . The analogy is to that of a ' gate' of a building through which everybody has to pass, even though they may wish to go to different departments. Similarly, researchers may be working in altogether different areas but all may need to use laboratory dialysis at one stage or the other during the course of their research. Biochemists may use it to purify enzymes, an immunologist may use it to purify monoclonal antibodies from culture supernatants, a chemist may use it as a step in the crystallography process or for purification of ionic liquids, a biotechnologist may use it to study the effectiveness of enzyme immobilization and a drug discovery scientist may use it for determining drug-protein interaction. The present article reviews patents in the field of laboratory dialysis from inception till date, focusing on the various developmental and innovation related milestones during evolution of the technique. It captures the full panorama of a very interesting technique which continues to be as relevant today as it was in 1866 when the term ' dialysis' was first coined.  相似文献   

8.
Arms races between and within species.   总被引:35,自引:0,他引:35  
An adaptation in one lineage (e.g. predators) may change the selection pressure on another lineage (e.g. prey), giving rise to a counter-adaptation. If this occurs reciprocally, an unstable runaway escalation or 'arms race' may result. We discuss various factors which might give one side an advantage in an arms race. For example, a lineage under strong selection may out-evolve a weakly selected one (' the life-dinner principle'). We then classify arms races in two independent ways. They may be symmetric or asymmetric, and they may be interspecific or intraspecific. Our example of an asymmetric interspecific arms race is that between brood parasites and their hosts. The arms race concept may help to reduce the mystery of why cuckoo hosts are so good at detecting cuckoo eggs, but so bad at detecting cuckoo nestlings. The evolutionary contest between queen and worker ants over relative parental investment is a good example of an intraspecific asymmetric arms race. Such cases raise special problems because the participants share the same gene pool. Interspecific symmetric arms races are unlikely to be important, because competitors tend to diverge rather than escalate competitive adaptations. Intraspecific symmetric arms races, exemplified by adaptations for male-male competition, may underlie Cope's Rule and even the extinction of lineages. Finally we consider ways in which arms races can end. One lineage may drive the other to extinction; one may reach an optimum, thereby preventing the other from doing so; a particularly interesting possibility, exemplified by flower-bee coevolution, is that both sides may reach a mutual local optimum; lastly, arms races may have no stable and but may cycle continuously. We do not wish necessarily to suggest that all, or even most, evolutionary change results from arms races, but we do suggest that the arms race concept may help to resolve three long-standing questions in evolutionary theory.  相似文献   

9.
Plasticity-mediated changes in interaction dynamics and structure may scale up and affect the ecological network in which the plastic species are embedded. Despite their potential relevance for understanding the effects of plasticity on ecological communities, these effects have seldom been analysed. We argue here that, by boosting the magnitude of intra-individual phenotypic variation, plasticity may have three possible direct effects on the interactions that the plastic species maintains with other species in the community: may expand the interaction niche, may cause a shift from one interaction niche to another or may even cause the colonization of a new niche. The combined action of these three factors can scale to the community level and eventually expresses itself as a modification in the topology and functionality of the entire ecological network. We propose that this causal pathway can be more widespread than previously thought and may explain how interaction niches evolve quickly in response to rapid changes in environmental conditions. The implication of this idea is not solely eco-evolutionary but may also help to understand how ecological interactions rewire and evolve in response to global change.  相似文献   

10.
This paper discusses the need for a more integrated approach to modelling changes in climate and crops, and some of the challenges posed by this. While changes in atmospheric composition are expected to exert an increasing radiative forcing of climate change leading to further warming of global mean temperatures and shifts in precipitation patterns, these are not the only climatic processes which may influence crop production. Changes in the physical characteristics of the land cover may also affect climate; these may arise directly from land use activities and may also result from the large-scale responses of crops to seasonal, interannual and decadal changes in the atmospheric state. Climate models used to drive crop models may, therefore, need to consider changes in the land surface, either as imposed boundary conditions or as feedbacks from an interactive climate-vegetation model. Crops may also respond directly to changes in atmospheric composition, such as the concentrations of carbon dioxide (CO2), ozone (03) and compounds of sulphur and nitrogen, so crop models should consider these processes as well as climate change. Changes in these, and the responses of the crops, may be intimately linked with meteorological processes so crop and climate models should consider synergies between climate and atmospheric chemistry. Some crop responses may occur at scales too small to significantly influence meteorology, so may not need to be included as feedbacks within climate models. However, the volume of data required to drive the appropriate crop models may be very large, especially if short-time-scale variability is important. Implementation of crop models within climate models would minimize the need to transfer large quantities of data between separate modelling systems. It should also be noted that crop responses to climate change may interact with other impacts of climate change, such as hydrological changes. For example, the availability of water for irrigation may be affected by changes in runoff as a direct consequence of climate change, and may also be affected by climate-related changes in demand for water for other uses. It is, therefore, necessary to consider the interactions between the responses of several impacts sectors to climate change. Overall, there is a strong case for a much closer coupling between models of climate, crops and hydrology, but this in itself poses challenges arising from issues of scale and errors in the models. A strategy is proposed whereby the pursuit of a fully coupled climate-chemistry-crop-hydrology model is paralleled by continued use of separate climate and land surface models but with a focus on consistency between the models.  相似文献   

11.
Schultz W 《Neuron》2011,69(4):603-617
How do addictive drugs hijack the brain's reward system? This review speculates how normal, physiological reward processes may be affected by addictive drugs. Addictive drugs affect acute responses and plasticity in dopamine neurons and postsynaptic structures. These effects reduce reward discrimination, increase the effects of reward prediction error signals, and enhance neuronal responses to reward-predicting stimuli, which may contribute to compulsion. Addictive drugs steepen neuronal temporal reward discounting and create temporal myopia that impairs the control of drug taking. Tonically enhanced dopamine levels may disturb working memory mechanisms necessary for assessing background rewards and thus may generate inaccurate neuronal reward predictions. Drug-induced working memory deficits may impair neuronal risk signaling, promote risky behaviors, and facilitate preaddictive drug use. Malfunctioning adaptive reward coding may lead to overvaluation of drug rewards. Many of these malfunctions may result in inadequate neuronal decision mechanisms and lead to choices biased toward drug rewards.  相似文献   

12.
This paper reviews hypotheses about roles of angiogenesis in the pathogenesis of inflammatory disease in two organs, the synovial joint and the lung. Neovascularisation is a fundamental process for growth and tissue repair after injury. Nevertheless, it may contribute to a variety of chronic inflammatory diseases, including rheumatoid arthritis, osteoarthritis, asthma, and pulmonary fibrosis. Inflammation can promote angiogenesis, and new vessels may enhance tissue inflammation. Angiogenesis in inflammatory disease may also contribute to tissue growth, disordered tissue perfusion, abnormal ossification, and enhanced responses to normal or pathological stimuli. Angiogenesis inhibitors may reduce inflammation and may also help to restore appropriate tissue structure and function.  相似文献   

13.
Altered diurnal secretory patterns, i.e. altered phase and/or amplitude of melatonin have been reported in sleep and affective disorders. The alteration may depend on environmental factors which in vulnerable individuals may cause sleep and/or affective disorders. Early stress in conjunction with development of resistance to corticotropin-releasing hormone may be linked to the low melatonin syndrome in subgroups of depressed patients. Also the seasonal variation in melatonin as well as serotonin may be linked to the seasonal pattern seen in subgroups of affective disorders. Melatonin may be used as a combined marker for proneness to develop affective disorders especially in latent carriers of bipolar disorders.  相似文献   

14.
Neoplasms can produce a variety of remote effects on the host; these are referred to as paraneoplastic syndromes. The syndromes may affect any of the systems of the body, may precede or follow the diagnosis of the underlying neoplasm, and may or may not parallel the course of the neoplasm in severity. The diagnosis of and therapy for these syndromes can be challenging to a physician, but successful therapy may bring about worthwhile relief for the patient. In addition, the syndromes and the substances that cause them are sometimes useful in diagnosing and in following the course of certain neoplasms. Perhaps of greater importance, study of these remote effects of neoplasia may shed light on the nature of the neoplastic process itself.  相似文献   

15.
植食性昆虫的学习行为一般具有习惯性反应、厌恶性学习、联系性学习、敏感性反应、嗜好性诱导几种类型,它们对害虫防治方法的效果具有重要影响。害虫通过嗜好性诱导对栖境中大面积单作农作物造成更大的危害,通过联系性学习可对诱虫植物的效果产生积极或消极的影响。害虫对驱避剂或杀虫剂等产生习惯性反应可降低其防治效果。害虫对寄主植物驱避抗性产生习惯性学习就会加重对作物的为害,产生厌恶性学习则有利于对作物的保护。利用害虫的联系性学习行为,释放前让不育雄虫学习自然交配场所的环境刺激,可增强通过释放不育雄虫控制害虫的防治效果。了解植食性昆虫学习行为对害虫治理的影响有助于研究和发展有效的栖境调控、行为调控等策略和方法。  相似文献   

16.
Valvular nasal obstruction may occur in the postoperative rhinoplasty patient. One may anticipate a dropping of the tip, from residual redundant or inelastic skin, in some older patients with long noses. Measures to correct (or avoid) this may be undertaken at the time of the primary rhinoplasty. However, an overcorrection may be necessary if there is much redundant skin. Discretion may indicate the need for a secondary procedure. Lateral wall valving is unusual-but it may occur in the long, high, thin nose (where a suggestion of this action may be observed preoperatively). Maintenance of continuous cartilage along the alar rim, at the time of alar cartilage resection, appears to be important in prevention of postoperative valvular obstruction in these few patients.  相似文献   

17.
Garfish, which are found in the Indo-Pacific Ocean areas, have a long, spear-like beak with two marrow jaws and small pointed teeth. They often make sudden leaps while swimming, particularly when attracted by bright lights. In Papua New Guinea people often fish from canoes using a light at night, and serious injuries may be caused by a fish jumping and its beak piercing part of the body. The surface wound may appear deceptively small and innocent, but if the wound is on the chest or abdomen the beak may have penetrated sufficiently deeply to cause internal injuries, and death may result. Patients may have to be admitted to hospital for removal of the beak, which may remain embedded in a limb.  相似文献   

18.
Hunting G-quadruplexes   总被引:3,自引:0,他引:3  
Huppert JL 《Biochimie》2008,90(8):1140-1148
Whilst DNA spends much of its time in the double-stranded form, frequently in storage, wrapped around histones and packaged as chromatin, it can also form other complex structures, which may play a role in natural regulation and gene control. These alternative structures therefore also present an interesting novel series of targets for artificial intervention, and so may lead to novel therapeutics. In this review, I describe the current understanding of how genomic and bioinformatics studies may be used to understand the roles that one such structure, the four-stranded guanine-rich G-quadruplex, may play in the genome, and outline how these may be considered as targets for intervention. I will also describe recent work looking at RNA G-quadruplexes, and the biological roles they may play.  相似文献   

19.
Chloroplasts may contract under natural conditions and give up water to the rest of the cell, thus indicating changes in metabolism or constitution. Such contractions may be produced experimentally. In Nitella the chloroplasts are ellipsoid bodies which, under natural conditions, may contract to spheres with a loss of volume. This may be brought about by lead acetate, ferric chloride, and digitonin: the contraction may occur while the cell is alive. The contraction in lead acetate is reversible (in lead nitrate little or no contraction occurs). In Spirogyra the chloroplast is a long, spirally coiled ribbon which may contract under natural conditions to a short nearly straight rod with a loss of volume. This can be brought about by inorganic salts and in other ways while the cell is still alive.  相似文献   

20.
Whiplash injury may extend far beyond the neck, and may involve even the soft tissues of the pelvis. For permanent recovery, all the injuries must be evaluated and treated together. When impact from the rear snaps the head back and then forward, posterior subluxations in the cervical spine cause anterior-posterior narrowing of the intervertebral foramina, which may result in injury to the cervical nerve roots. Impact at the front, causing hyperflexion followed by hyperextension, has a similar effect although usually not as severe. Resulting symptoms may not appear until two or three weeks later, when irritative lesions have developed because of hemorrhage or swelling. Mild or progressive degenerative changes may cause no symptoms but may predispose the affected area to injury following some slight trauma. Capsular ligaments of the lateral intervertebral joints are especially liable to whiplash injury which may give rise to scars and adhesions that compress spinal nerves. Sympathetic system involvement may cause reflex and referred pain. Detailed neurologic, roentgen and electromyographic studies may be necessary for proper evaluation of injuries. Seemingly psychosomatic pain or disability is likely to have some physical basis in whiplash injuries. In 33 patients with whiplash injury, some recently injured and some chronically disabled with persistent symptoms, good results were observed following hydromassage, hot packs, joint mobilization exercises and, in a few, cervical or pelvic traction.  相似文献   

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