bluuebunny/crossref_metadata_2025_split huggingface dataset:
ISLAND POPULATIONS OF RODENTS: THEIR ORGANIZATION AND FUNCTIONING
Authors: GLIWICZ JOANNA 
Published: January 2008

Summary1. Data from 14 confined populations living under natural conditions (mainly on small islands) and from a few laboratory populations have been used.2. Several differences between a typical, confined rodent population (i.e. living under natural conditions in a well isolated, homogeneous and relatively small area) and an open one have been determined.3. Island populations are characterized by:(a) Attainment and maintenance of high densities not observed at all, or recorded only periodically, in open populations of comparable species.(b) Stability of population numbers, expressed either by very slight fluctuations or by a very regular cycle with only small differences between peaks of consecutive years.(c) Lack of emigration resulting from any or all of the barriers surrounding the confined population, from homogeneity of the habitat enclosed by these barriers, or from a lower tendency to dispersal of individuals forming such populations.(d) Decreased reproduction.(e) Low losses of independent individuals.(f) Mortality of sucklings changing with the population density.(g) An age structure that is probably more differentiated and more regularly changing in an annual and long‐term cycle.(h) Different spatial organization based on smaller home ranges, that are differently arranged in relation to one another from those in open populations; the arrangement of home ranges allows the population to squeeze in a greater number of individuals with possibly the lowest number of interactions between individuals.4. In confined populations there must be different mechanisms for the regulation of numbers from those in open populations: (I) in the latter the regulation occurs by the outflow of the surplus of independent individuals, i.e. through the dispersal and high mortality of migrants; (2) in confined populations the inflow of independent individuals is regulated by controlled reproduction and early mortality of offspring. Both mechanisms are induced by social pressure but in the second case (regulation of inflow) a much stronger social organization is indispensable Only those species that are capable of the formation of such an organization can survive as confined populations.5. Knowledge of phenomena occurring in confined populations is useful for predicting the fate of populations of different species which become isolated as a result of human activity in transforming and subdividing the natural environment.
CUTICULAR LIPIDS OF TERRESTRIAL PLANTS AND ARTHROPODS: A COMPARISON OF THEIR STRUCTURE, COMPOSITION, AND WATERPROOFING FUNCTION
Authors: HADLEY N. F. 
Published: January 2008

Summary1. Lipids deposited on the surface or embedded within the cuticle of terrestrial plants and arthropods are primarily responsible for the observed low rates of water loss through the cuticle.2. These lipids are a mixture of long‐chain compounds which include hydrocarbons (saturated, unsaturated, branched), wax esters, free fatty acids, alcohols, ketones, aldehydes, and cyclic compounds.3. The cuticle of both plants and arthropods is a continuous, non‐cellular multilayered membrane which overlies the epidermal cells.4. In arthropods, horizontal division of the cuticle into layers is clearly visible. In plants, the layers comprising the cuticle are not sharply demarcated.5. The substance responsible for the structural integrity of the plant cuticle (cutin) is composed of cross‐esterified fatty acids; structural integrity in arthropod cuticle is provided by a chitin‐protein complex.6. Cuticular lipids are probably formed near the surface in both plants and arthropods; however, specific sites of synthesis are known for only a few species and little is known about their transport from these sites to the surface. The elaborate pore canal and wax canal system of arthropod cuticle is absent from plants.7. The physical structure and arrangement of the lipid deposits on the cuticular surface that are so important in controlling water movement depend on both quantity and chemical composition, and are, in turn, specific to each species in relation to its environment.8. Different lipid components are not equally efficient in reducing transpiration. Maximum waterproofing effectiveness is provided by long‐chain, saturated, non‐polar molecules containing few methyl branches.9. Plants and arthropods can, within genetic constraints, alter the composition of their cuticular waxes to improve impermeability when conditions require increased water conservation.10. None of the models proposed to explain the change in arthropod cuticular permeability which occurs at a species‐specific temperature (‘transition temperature’) in many species is supported by the experimental data now available.
THE MOLECULAR AND CELLULAR BASIS OF PREIMPLANTATION MOUSE DEVELOPMENT
Authors: JOHNSON MARTIN H. 
Published: January 2008

SummaryThe formation of a mouse blastocyst involves the use of genetic information derived from the expression both of maternal genes in the preovulatory oocyte and of embryonic genes from the mid‐2‐cell stage onwards. Evidence is reviewed suggesting that maternal RNA transcripts made up to 20 days prior to ovulation are available for use after fertilization, that no significant KNA synthesis occurs between germinal vesicle breakdown and the mid‐2‐cell stage and that during this interval of transcriptional inactivity production of protein is regulated at a post‐transcriptional level. Embryonic genes first become active at the mid‐2‐cell stage and at, or shortly after, this time most maternal mRNA is inactivated. Thereafter, the available evidence suggests that although embryonic mRNA has considerable stability, much of it is translated immediately after it is transcribed. This tight linkage of mRNA transcription and utilization appears to be crucial for certain key events in development.The cellular interactions operating during early development are described. It is suggested that asymmetry of cell contacts in the 8‐cell embryo imparts a mosaic structure to the embryo, and that this mosaicism is conserved and elaborated with division to the 16‐ and 32‐cell stages. The mechanisms are discussed by which mosaicism is induced and through which the two cell lineages of the blastocyst are founded.Temporal events in preimplantation development show a periodicity of about 27 h. It is proposed that within each period differentiative events are cumulative but reversible, and that the boundaries between each developmental period constitute points of commitment at which reversal of development becomes no longer possible.
INSECT HORMONES IN DEVELOPMENT
Authors: RICHARDS G. 
Published: January 2008

SummaryAdvances in studies of prothoracicotropic hormone (ecdysiotropin), ecdysteroids and juvenile hormones in the past decade are considered:1. Until recently there has been little progress with prothoracicotropic hormone. The development of a sensitive bioassay for the hormone promises to produce rapid advances.2. Current methods of hormone analysis are described, with detection limits. The application of these methods in studies of hormones at different stages and in different tissues of insects have revealed a far greater complexity in hormone titres than was predicted from classical studies.3. Very few studies employ chemical characterization of hormones and some assays do not distinguish biologically inactive metabolites of the hormones from the active hormones. Many studies have thus failed to reveal the numerous rapid fluctuations in hormone titre necessary for insect development.4. While ecdysteroids act, via a receptor, on specific chromosome sites, the cellular mode of action of juvenile hormone in larval development is still unknown. Recent evidence suggests that juvenile hormone acts prior to the time at which its effects are realized by ecdysteroids.5. Insect hormones produce dramatic changes in gene activity and their co‐ordinate control of specific protein synthesis has been the basis for a number of ‘model systems’ of gene control in higher eukaryotes.
PHOTOCONTROL OF STOMATAL MOVEMENTS
Authors: PEMADASA M. A. 
Published: January 2008

Summary1. Opening in light is a feature common to the majority of functional stomata, but the current argument is against the traditional view that light is the principal environmental promoter of opening, because stomata can open in the dark in response to CO2removal and/or temperature increase. In this review, evidence is provided that light is more efficient and effective than other physical factors in both producing and maintaining wide opening. However, light acts on stomata both directly and indirectly, in conjunction with changes in, for example, CO2balance, water regime and temperature of the leaf tissue.2. Three general categories of light effects on stomata are recognized: (a) photosynthetic effects driven by metabolic processes, induced or enhanced by light, (b) hydrophotic effects mediating through light‐induced changes in epidermal turgor, and (c) photothermal effects arising from light‐dependent changes in leaf temperature.3. Photosynthetic effects involve both CO2depletion, and starch mobilization, malate synthesis, H+extrusion, and accumulation of K+and C1‐in guard cells; these processes are triggered by light of different qualities: (a) Both blue and red light are involved in photosynthetic CO2fixation, utilizing energy from photosynthetic light reaction(s), which provides C precursors for synthesis of stornatal starch. (b) Blue light, but not red, enhances starch mobilization, PEP carboxylase activity and respiration. Accordingly, blue light is postulated to enhance hydrolysis of stornatal starch providing C3precursors for malate synthesisviaPEP‐fixation of endogenous CO2; the active extrusion of H+, derived from malate, is coupled with K+influx to guard cells. Malate and C1‐are competitive anions, for K+, and one begins to play a progressively more important role as the other becomes limiting; in intact leaves, however, malate plays a more decisive role. These processes are driven by the energy from blue‐light‐enhanced respiration. (c) Both photosynthetic fixation and PEP carboxylation act as CO2sensors, but the exact role of CO2in the stornatal mechanism has yet to be determined.4. Hydrophotic and photothermal effects facilitate guard cell expansion by releasing epidermal pressure through enhanced evaporative water loss, and are, therefore, indirect effects of light; photothermal effects may also contribute to metabolic processes outlined in paragraph 3.5. Stomatal closure in the dark accompanies starch synthesis, malate reduction, efflux of K+and C1‐from guard cells, and accumulation of CO2in substomatal cavities. Malate may be converted to starchviaC2compounds. Guard cells release K+and C1‐ into apoplastic space, from which they are removed by neighbouring cells. The entry of K+into neighbouring cells is supposed to be coupled with H+extrusion. These processes are dependent on respiratory energy.6. The differential abaxial and adaxial stomatal light responses are related to inherent metabolic differences between the two epidermes, but the biochemical basis is not known.
ARTHROPODS THAT PREY ON VERTEBRATES
Authors: McCORMICK SHARON , POLIS GARY A. 
Published: January 2008

Summary1. Many arthropods are predators of vertebrates: four orders of the class arachnida, six orders of insecta, five orders of crustacea and one order of chilopoda include species that have been reported to eat vertebrates. At the population level, some arthropods are responsible for significant mortality among some vertebrates.2. Arthropods are well equipped for this type of predation; many are larger than vertebrates (approximately 20% of the vertebrate fauna of eastern North America is less than 10 cm in length), they may hunt in social groups and many have toxins or other adaptations that increase predatory efficiency.3. Several arthropod predators and vertebrates may be involved in cross predation, the species eating each other. The switch in the role of predator and prey occurs during ‘ontogenetic reversal’ as the vertebrate grows from small and vulnerable to large and predaceous. Cross predation decreases the future risk for one's self or offspring.4. The opportunity for arthropod predation on vertebrates exists in many communities, but a review of some food webs catalogued by Cohen (1978) indicates that this particular link may be easily overlooked. Some arthropods should be investigated as potential predators of vertebrates.5. The information available from the analysis of feeding interactions in a community should be an important link between field and theoretical ecology; however, most food webs are probably underestimates of the complexity that is commonplace.
SELENIUM: TOXICITY AND TOLERANCE IN HIGHER PLANTS
Authors: Brown T. A. , Shrift A. 
Published: January 2008

Summary1. Different plant species show considerable variation in their selenium content. Primary indicators, also termed selenium accumulators, many of which are members of the genus Astragalus, are highly tolerant of selenium; they are known to contain tissue levels of several thousand µg selenium/g. Secondary indicators, tolerant to low concentrations of the element, may absorb up to 1000 µg selenium/g. Non‐accumulators are poisoned by selenium.2. The toxicity of selenate (SeO4‐) and selenite (SeO3‐) to most plants can be attributed to a combination of three factors. Firstly, selenate and selenite are readily absorbed from the soil by roots and translocated to other parts of the plant. Secondly, metabolic reactions convert these anions into organic forms of selenium. Thirdly, the organic selenium metabolites, which act as analogues of essential sulphur compounds, interfere with cellular biochemical reactions.3. Incorporation into proteins of the amino acid analogues selenocysteine and selenomethionine, in place of the equivalent sulphur amino acids, is considered to be the underlying cause of selenium toxicity. The physical and chemical differences between selenium and sulphur will result in small, but significant, changes in the biological properties of a selenium‐substituted protein.4. Selenium‐tolerant accumulator plants differ in at least two respects from sensitive species. Large quantities of Se‐methylselenocysteine and selenocystathionine, two non‐protein selenoamino acids rarely detected in non‐accumulators, have been isolated from the tissues of selenium accumulators. In addition, selenium is kept from entering proteins so that the selenium levels in proteins of accumulator plants is significantly lower than the levels in selenium‐sensitive plants.5. Exclusion of selenium from the proteins of accumulators is thought to be the basis of selenium tolerance. Discrimination against selenocysteine during protein synthesis seems to prevent incorporation of this selenoamino acid into proteins of accumulators. Furthermore, synthesis of Se‐methylselenocysteine and selenocystathionine, which results in diversion of selenium away from the synthesis of selenomethionine, will restrict the amount of this compound available for protein synthesis.6. Selenium accumulation among unrelated plant genera is a striking example of convergent evolution. The possibility that accumulation of this element is associated with a nutritional requirement for selenium, although explored in the past, is still in need of further clarification.
CHEMO‐ORIENTATION
Authors: BELL WILLAM J. , TOBIN THOMAS R. 
Published: January 2008

Summary1. A new classification system for chemo‐orientation mechanisms is suggested, based on delineating (a) internal and external orientation information available to an organism, (b) mode of information processing, (c) type of motor output pattern, and (d) guidance systems that modulate or direct motor output.2. Cross‐phyletic comparison of chemo‐orientation indicates that morphology, to a greater extent than phylogeny, determines the kind of chemo‐orientation mechanisms available to an organism. Analogies are drawn between single‐celled organisms with surface chemical receptor sites and higher organisms with elaborate chemosensory organs and nervous systems.
ENVIRONMENTAL EFFECTS ON ANIMALS USED IN BIOMEDICAL RESEARCH
Authors: CLOUGH G. 
Published: January 2008

SummaryI. Reliability of the results of bio‐medical research clearly depends upon the animals used showing as standard responses as is possible.2. The majority of animals used in this field are small, homoiothermic mammals which have sensitive and strong homeostatic mechanisms. If a change in ambient conditions is of sufficient magnitude to unbalance homeostasis, then the neuroendocrine system is stimulated so as to restore it, and this can interfere with the response to test conditions or agents.3. The homeostatic effectors involved are diverse and can include both physiological and behavioural changes in the animal. These can affect metabolic rate, body temperature, activity, food consumption, hormone concentration, wake/sleep patterns, maturation, posture, lactation and many other bodily functions. Any of these changes is potentially capable of influencing experimental results.4. The evidence presented shows how environmental factors may affect the outcome of experiments in the fields of animal behaviour, cancer research, immunology, pathology, pharmacology, psychology, reproduction, teratology and toxicology; particular attention is paid to the effects of ambient temperature, relative humidity, air movement and quality, light and sound.5. While a constant, reproducible environment would be ideal, there is little possibility of controlling all the variables; nevertheless all investigators should minimize those environmental variables that have been shown to be important.6. To enable other investigators to repeat experiments or carry out comparative studies, environmental conditions pertaining during an experiment should be adequately described in any publications.
THE MECHANISM OF α‐ADRENERGIC AGONIST ACTION IN LIVER
Authors: REINHART PETER H. , TAYLOR WAYNE M. , BYGRAVE FYFE L. 
Published: January 2008

Summary1. Although the mechanism of action of a‐adrenergic agonists in liver tissue is somewhat complex, a number of experimental approaches can be usefully employed to identify the molecular details of the events that occur.2. Receptors specific for α1‐adrenergic agonists located on the plasma membranes of rat liver cells have been partially characterized using pharmacological agents, affinity labels and monoclonal antibodies. Much of this work has employed isolated plasma membrane fractions and does not take account of tissue‐related factors which may now be studied in the intact perfused rat liver, following the development of an appropriate assay system.3. Because a redistribution of cellular Ca2+ is central to the mechanism of action of a‐adrenergic agonists in liver, it is important to first gain an understanding of basic cellular Ca2+ regulation. Knowledge about the compartmentation of cellular calcium and about Ca2+‐translocation systems located in the mitochondria, plasma membrane and endoplasmic reticulum is now quite extensive. However, the role of mitochondria in the regulation of intracellular Ca2+ is still unclear; it now appears that the mitochondrial calcium content is much less than considered previously. This may have important implications for such a regulatory role.4. The sequence of Ca2+ movements that may occur when a‐adrenergic agonists interact with liver have been identified and are as follows: (a) Ca2+ is mobilized from an intracellular pool(s) (mitochondria plus endoplasmic reticulum and/or plasma membranes). (b) This elevates the cytoplasmic free Ca2+ concentration and leads to an efflux of the ion from the cell. (c) At this time, Ca2+‐sensitive metabolic events in the cytoplasm are activated and an increase in Ca2+‐cycling occurs across the plasma membrane. (d) Immediately after the hormone is withdrawn, there is a net influx of Ca2+ into the cell, and the intracellular Ca2+ pools and transmembrane fluxes are restored to the pre‐induced states. In this model, Ca2+ movements across the plasma membrane play a key role in regulating the cytoplasmic Ca2+ concentration.5. In the perfused rat liver it has been possible to define in quite precise terms the amounts and rates of Ca2+ mobilized in each of these stages.6. Although several proposals for ‘second messengers’ to link the hormone‐receptor interaction with initial Ca2+ mobilization have been made, at this time only polyphosphoinositide turnover appears to be a suitable candidate.
CUTANEOUS GAS EXCHANGE IN VERTEBRATES: DESIGN, PATTERNS, CONTROL AND IMPLICATIONS
Authors: FEDER MARTIN E. , BURGGREN WARREN W. 
Published: January 2008

Summary1. The exchange of oxygen and carbon dioxide between skin and environment is commonplace in the vertebrates. In many lower vertebrates, the skin is the major or even sole avenue for respiration.2. As implied by the physical laws governing diffusion of gases, the skin diffusion coefficient, surface area, gas diffusion distance and transcutaneous gas partial pressures may independently or jointly affect cutaneous respiration. In vertebrates, each of these variables has undergone modification that may be related to dependence upon cutaneous gas exchange.3. Both theoretical models and experimental data suggest that cutaneous gas exchange is limited by the rate of diffusion. However, changes in convection of the respiratory medium and of blood may partially compensate for diffusion limitation, and potentially function in the regulation of cutaneous gas exchange.4. Typically, the skin is one of several gas exchangers, although many salamanders and some species in other vertebrate groups breathe solely through the skin. The cutaneous contribution to overall gas exchange is often most important in small animals, at cool temperatures, at low levels of activity and in normoxic and normocapnic conditions. Branchial and pulmonary respiration increasingly predominate in other circumstances.5. Often, the skin figures more prominently in CO2, excretion than in O2, uptake.6. Cutaneous gas exchange emerges in vertebrates as a process perhaps less effective and more constrained than branchial or pulmonary exchange but also less energetically costly. Its utility is indicated by its wide and successful exploitation in vertebrates occupying a diverse array of habitats.
ISLAND BIOGEOGRAPHY AND PALAEOBIOLOGY: IN SEARCH FOR EVOLUTIONARY EQUILIBRIA
Authors: HOFFMAN ANTONI 
Published: January 2008

Summary1. The concept of evolutionary equilibrium has been derived from the theory of island biogeography via an ecological rationale for increase in species extinction rate and decrease in speciation rate with increasing diversity of the system.2. This concept is theoretically plausible at the species level and at a regional scale but, in spite of several empirical tests in the fossil record, it has thus far remained unsupported by empirical evidence. In order to test it conclusively, one has to analyze not only the pattern of species number through time but also its relationship to speciation and species extinction rates; independent evidence for perturbations must also be available.3. The concept of evolutionary equilibrium at the global scale must be extrapolated over higher levels of taxonomic hierarchy, for reliable species‐level data are unavailable at this scale. A theoretical justification for this concept cannot, then, be derived from the theory of island biogeography.4. The rates of family extinction and origination in the Phanerozoic show no evidence for diversity‐dependence, which undermines most quantitative models of biotic diversification based on the concept of global evolutionary equilibrium. Rigorous testing of these models cannot be done at the present state of knowledge because of the uncertainty about the empirical pattern (sampling and taxonomic biases, absolute time scale).