The Theory of Speciation VIA the Founder Principle

The founder principle has been used to explain many instances of rapid speciation. Advances from theoretical population genetics are incorporated into Mayr''s original founder-effect genetic-revolution model to yield a newer model called the genetic transilience. The basic theoretical edifice lies upon the fact that founder event can sometimes lead to an accumulation of inbreeding and an induction of gametic disequilibrium. This, in turn, causes alleles to be selected more for their homozygous fitness effects and for their effects on a more stable genetic background. Selection occurring in multi-locus systems controlling integrated developmental, physiological, behavioral, etc., traits is particularly sensitive to these founder effects. If sufficient genetic variability exists in the founder population, such multilocus genetic systems can respond to drift and the altered selective forces by undergoing a rapid shift to a new adaptive peak known as the genetic transilience. A genetic transilience is, therefore, most likely to occur when the founder event causes a rapid accumulation of inbreeding without a severe reduction in genetic variability. The implications of this model are then examined for three aspects of the founder-effect genetic-transilience model: the attributes of the ancestral population, the nature of the sampling process used to generate the founders and the attributes of the founder population. The model is used to explain several features of the evolution of the Hawaiian Drosophila, and experimental designs are outlined to test the major predictions of the theory. Hence, this theory of speciation can be tested in the laboratory, using systems and techniques that already exist—a rare attribute of most models of speciation.     

The Role of Theory in Ecology

Theory can have many different kinds of use in illuminatingecological research. The examples sketched in this paper include:the uses and short-comings of population models currently usedin setting catch quotas for whales and for fisheries; the richarray of behaviour displayed by nonlinear equations and itsrelevance to understanding natural and managed populations;models for the interaction between populations (particularlythe regulation of natural populations by diseases); and somegeneral patterns of community organization. The paper concludeswith some remarks on the contrasts between public pieties about"The Scientific Method" and the way scientists actually work,from Darwin's day to our own.     

The Role of the Membrane in Transporter Folding and Activity

The synthesis, folding, and function of membrane transport proteins are critical factors for defining cellular physiology. Since the stability of these proteins evolved amidst the lipid bilayer, it is no surprise that we are finding that many of these membrane proteins demonstrate coupling of their structure or activity in some way to the membrane. More and more transporter structures are being determined with some information about the surrounding membrane, and computational modeling is providing further molecular details about these solvation structures. Thus, the field is moving towards identifying which molecular mechanisms - lipid interactions, membrane perturbations, differential solvation, and bulk membrane effects - are involved in linking membrane energetics to transporter stability and function. In this review, we present an overview of these mechanisms and the growing evidence that the lipid bilayer is a major determinant of the fold, form, and function of membrane transport proteins in membranes.     

吞咽障碍治疗仪的作用原理及效果

介绍了吞咽障碍严重损害人类健康,吞咽障碍治疗仪是通过电刺激方式来促进受损神经复苏,加强吞咽肌群的运动,提高病人吞咽能力,从而达到治疗目的,取得了良好的效果。     

The Role of Astrocytic Glycogen in Supporting the Energetics of Neuronal Activity

Energy homeostasis in the brain is maintained by oxidative metabolism of glucose, primarily to fulfil the energy demand associated with ionic movements in neurons and astrocytes. In this contribution we review the experimental evidence that grounds a specific role of glycogen metabolism in supporting the functional energetic needs of astrocytes during the removal of extracellular potassium. Based on theoretical considerations, we further discuss the hypothesis that the mobilization of glycogen in astrocytes serves the purpose to enhance the availability of glucose for neuronal glycolytic and oxidative metabolism at the onset of stimulation. Finally, we provide an evolutionary perspective for explaining the selection of glycogen as carbohydrate reserve in the energy-sensing machinery of cell metabolism.     

The Role of Reactive Oxygen Species in the Antitumor Activity of Bleomycin

Calf thymus DNA was incubated with bleomycin and FeCl₃, in the presence of isolated rat liver microsomal NADH-cytochrome b₅ reductase, cytochrome b₅ and NADH which catalyze redox cycling of the bleomycin-Fe-complex. Furthermore, isolated rat liver nuclei were incubated with bleomycin, FeCl₃ and NADH, a system in which redox cycling of bleomycin-Fe leads to DNA damage. In both systems free bases from DNA were released. Furthermore, 8-hydroxy-guanine was also found in the supernatant. On the other hand, 8-hydroxy-deoxyguanosine was detected in DNA of cell nuclei indicating that hydroxylation of the guanine molecule occurred in intact DNA. The release of bases correlated with the release of malondialydehyde as well as with NADH and oxygen consumption. These results indicate that NADH-cytochrome b₅ reductase catalyzes redox cycling of the bleomycin-Fe-complex which results in the formation of reactive oxygen species which oxidize deoxyribose as well as bases of DNA. Both mechanisms may contribute to the cytotoxic and cytostatic effects of bleomycin observed in intact cells.     

The Role of Quartz in the Origin of Optical Activity on Earth

A thorough analysis of literature data on distribution of rightand left quartz in many locations on the surface of Earthindicates that quartz enantiomorph crystals are distributed inequal amounts in all locations. Therefore optically activequartz crystals of one or the other enantiomorph could not serveas the source of homochirality in the evolution of biosphere.Hence the calculation of a PVED based on published `small excessof left quartz crystals' on Earth lacks a sound physical basis.     

组氨酸残基在乙醇酸氧化酶活性中的作用

DEPC能显著抑制GAO的活性。其失活速度表现为假一级动力学特性,并和抑制剂浓度成线性正比关系。底物乙醇酸可保护GAO免受DEPC抑制,羟胺能使被抑制的酶重新复活。光谱测定表明,被抑制的酶只有组氨酸残基被修饰,而酪氨酸残基未被修饰,修饰前后酶的氨基含量均无变化。反应动力学表明,在35℃下,GAO中有一个pK为6.5的解离基团和催化活性有关,其解离⊿H为31610 J/mol。因此组氨酸残基为GAO催化活性的一个必需基团。     

The Role of Chitinase in the Antifungal Activity of Bacillussp. 739

Investigation of the crude extracellular chitinase of Bacillussp. 739, an antagonist of phytopathogenic fungi, discerned a relationship between the chitinase and antifungal activities of this bacterium. Purified chitinase lost its ability to inhibit the growth of micromycetes. The antagonistic (antifungal) activity of crude chitinase was found to be located in a low-molecular-weight fraction of the enzyme, which does not possess chitinase activity. Both crude and purified chitinase were able to lyse the cell walls of intact mycelium. Accordingly, it may be inferred that the antagonistic activity of Bacillussp. 739 against micromycetes is largely determined by low-molecular-weight nonenzymatic substances, whereas the role of chitinase is to utilize chitin, which is ubiquitously present in soil.     

The Phenomenon of Refusal in Muscular Activity. The Role of the Respiratory System

Among the factors leading to the refusal to continue muscular work, afferent impulsation carrying information about the efforts developed by the working muscles and about the respiratory function tension is noteworthy. Based on this information, the integral self-rating of the intensity of the physical load and its endurance is formed in the sensory CNS sphere, with one of the signals to stop the work being the feeling of shortness of breath. Under the cyclic working conditions, the so-called critical power load, which is high enough but does not lead to a refusal so far, enabling one to perform the maximum amount of useful work, appears to be the most effective. A question is posed as to the possibility of using an active choice of preferable load intensity by an individual in order to develop a method for determining the optimal work power according to the functional state of the body.     

The Role of Collagen Charge Clusters in the Modulation of Matrix Metalloproteinase Activity

Members of the matrix metalloproteinase (MMP) family selectively cleave collagens in vivo. Several substrate structural features that direct MMP collagenolysis have been identified. The present study evaluated the role of charged residue clusters in the regulation of MMP collagenolysis. A series of 10 triple-helical peptide (THP) substrates were constructed in which either Lys-Gly-Asp or Gly-Asp-Lys motifs replaced Gly-Pro-Hyp (where Hyp is 4-hydroxy-l-proline) repeats. The stabilities of THPs containing the two different motifs were analyzed, and kinetic parameters for substrate hydrolysis by six MMPs were determined. A general trend for virtually all enzymes was that, as Gly-Asp-Lys motifs were moved from the extreme N and C termini to the interior next to the cleavage site sequence, k_cat/K_m values increased. Additionally, all Gly-Asp-Lys THPs were as good or better substrates than the parent THP in which Gly-Asp-Lys was not present. In turn, the Lys-Gly-Asp THPs were also always better substrates than the parent THP, but the magnitude of the difference was considerably less compared with the Gly-Asp-Lys series. Of the MMPs tested, MMP-2 and MMP-9 most greatly favored the presence of charged residues with preference for the Gly-Asp-Lys series. Lys-Gly-(Asp/Glu) motifs are more commonly found near potential MMP cleavage sites than Gly-(Asp/Glu)-Lys motifs. As Lys-Gly-Asp is not as favored by MMPs as Gly-Asp-Lys, the Lys-Gly-Asp motif appears advantageous over the Gly-Asp-Lys motif by preventing unwanted MMP hydrolysis. More specifically, the lack of Gly-Asp-Lys clusters may diminish potential MMP-2 and MMP-9 collagenolytic activity. The present study indicates that MMPs have interactions spanning the P₂₃–P₂₃′ subsites of collagenous substrates.     

The Role of Metal Ions in the Hemagglutinating Activity of the Wax Bean Hemagglutinin

The phytohemagglutinin of the wax bean (Phaseolus vulgaris) could be resolved into an active and an inactive component when subjected to gel filtration on Sephadex G-100 in the presence of 8m urea and 0.001 m EDTA, pH 5.5. Subsequent chromatography of the active component on Sephadex G-100 at pH 7.5 in the absence of urea revealed the presence of an inactive fraction (F-1-A) and a fraction (F-1-B) which had 35% of the activity of the original hemagglutinin. The activity of fraction F-1-A could be restored to that of the native hemagglutinin by treatment with cupric ions, whereas the activity of fraction F-1-B could be fully restored by treatment with either cupric or calcium ions.     

The Protein Folding Problem: The Role of Theory

The protein folding problem was first articulated as question of how order arose from disorder in proteins: How did the various native structures of proteins arise from interatomic driving forces encoded within their amino acid sequences, and how did they fold so fast? These matters have now been largely resolved by theory and statistical mechanics combined with experiments. There are general principles. Chain randomness is overcome by solvation-based codes. And in the needle-in-a-haystack metaphor, native states are found efficiently because protein haystacks (conformational ensembles) are funnel-shaped. Order-disorder theory has now grown to encompass a large swath of protein physical science across biology.     

The Role of Oxygen in the Regulation of Nitrogenase Activity in Drought-Stressed Soybean Nodules

The aim of this study was to investigate the mechanism of nitrogenase inhibition in drought-stressed soybean (Glycine max L.) nodules to determine whether this stress was similar to other inhibitory treatments (e.g. detopping) known to cause an O2 limitation of nodule metabolism. Nodulated soybean plants were either detopped or subjected to mild, moderate, or severe drought stress by growth in different media and by withholding water for different periods. All treatments caused a decline in nitrogenase activity, and in the drought-stressed nodules, the decline was correlated with more negative nodule water potentials. Increases in rhizosphere O2 concentration stimulated nitrogenase activity much more in detopped plants than in drought-stressed plants, reflecting a greater degree of O2 limitation with the detopped treatment than with the drought-stressed treatment. These results indicated that drought stress differs from many other inhibitory treatments, such as detopping, in that its primary cause is not a decrease in nodule permeability and a greater O2 limitation of nodule metabolism. Rather, drought stress seems to cause a decrease in the maximum O2-sufficient rate of nodule respiration or nitrogenase activity, and the changes in nodule permeability reported to occur in drought-stressed nodules may be a response to elevated O2 concentrations in the infected cell that may occur as nodule respiration declines.     

Challenges of Activity Theory

One of the major distinctive features of the method of investigating nervous activity developed by I. P. Pavlov is, as we know, the synthetic formation, in the course of an experiment, of conditioned reflexes and of more complex systems of temporary connections.     

The Role of School Environment in Physical Activity among Brazilian Adolescents

Objective

To analyze the association of physical activity facilities and extracurricular sports activities in schools with physical activity among adolescents.

Methodology/Principal Findings

We used data collected for the National Survey of School Health in 2012. The national representative sample comprised 109,104 Brazilian students from 2,842 schools. We calculated the prevalence of participation in physical education classes, leisure-time physical activity, and total physical activity level. We also evaluated the following physical activity facilities: sports courts, running/athletics tracks, schoolyard with teacher-directed physical activities, swimming pools, locker rooms; and the offer of extracurricular sports activities. Schools with at least one physical activity facility had increased odds of participation in physical education (OR 1.59; 95% CI 1.20 to 2.10). However, in order to increase leisure-time physical activity (OR1.14; 95% CI 1.03 to 1.26) and total physical activity level (OR 1.15; 95% CI 1.06 to 1.24) at least four and two facilities, respectively, were necessary. Extracurricular sports activities in schools were positively associated with leisure-time physical activity and physical activity level. The number of sports courts and swimming pool in a school were associated with participation in physical education classes. Availability of sports courts, running/athletics tracks, and swimming pool in schools were associated with leisure-time physical activity. Total physical activity was associated with schools with sports courts, schoolyard with teacher-directed physical activities, and swimming pool.

Conclusions

School-level characteristics have important potential to increase the possibility of engagement in physical activity in and out of school, and therefore have a fundamental role in promoting these practices.     

Prospects for Using the Theory of Activity in Ethnopsychology

The question of the causes of differences in mental activity among different peoples has a long history. Each of the different branches of psychology deals with this question in its own way, but the basic factors that they identify are the same. Those analyzed in ethnopsychology, for instance, may be divided into several basic groups.