Showing papers in "Philosophical Transactions of the Royal Society B in 1993"
TL;DR: Although the evidence that fat storage is costly is convincing, key empirical data are lacking and the sorts of data which need to be gathered are indicated and ways in which this might be done are suggested.
Abstract: Avian fat storage is associated with both benefits and costs. Although the benefits of maintaining higher energetic reserves have long been considered, the associated costs have received far less attention. Spatial and temporal patterns of fat storage, together with experimental data, indicate that birds are capable of actively regulating their energetic reserves at levels below physiological or environmental maxima. This regulation implies that fat storage entails a cost. Evidence of potential costs are reviewed and discussed under the following headings: mass-dependent metabolism, mass-dependent predation risk, mass-dependent risk of injury, mass-dependent foraging, pathological costs and reproductive costs. Although the evidence that fat storage is costly is convincing, key empirical data are lacking. We indicate the sorts of data which need to be gathered and suggest ways in which this might be done. We go on to discuss the interaction of these costs and their relevance to between-individual patterns of fat storage and the interpretation of ‘condition indices’. Because many of the purported costs of fat storage are dependent upon changes in body mass, or wing loading, our review is also relevant to other phenomena which may involve mass-dependent costs, such as gonadal hypertrophy, transport of food items and primary moult.
690 citations
TL;DR: In this article, the optimal trade-off between food and predation was investigated in a single-antenna setting, where an animal must reach a fixed state, its fitness depending on when this is attained, and the animal must survive to a fixed time.
Abstract: When animals can choose from a range of feeding options, often those options with a higher energetic gain carry a higher risk of predation. This paper analyses the optimal trade-off between food and predation. We are primarily interested in how an animal’s decisions and its state change over time. Our models are very general. They can be applied to growth decisions, such as choice of habitat, in which case we might consider how the state variable size changes over an animal’s lifetime. Equally our models are applicable to short-term foraging decisions, such as vigilance level, in which case we might consider how energy reserves vary over a day. We concentrate on two cases: (i) the animal must reach a fixed state, its fitness depending on when this is attained; (ii) the animal must survive to a fixed time, its fitness depending on its final state. In case (i) minimization of m ortality per unit increase of state is optimal under certain baseline conditions. In case (ii) behaviour is constant over time under baseline conditions (the 9Risk-spreading Theorem’). We analyse how these patterns are modified by complicating factors, e.g. time penalties, premature termination of the food supply, stochasticity in food supply or in metabolic expenditure, and state-dependence in the ability to obtain food, in metabolic expenditure and in predation risk. From this analysis we obtain a variety of possible explanations for why an animal should reduce its intake rate over time (i.e. show satiation). We show how earlier work can be viewed as special cases of our results.
628 citations
TL;DR: Animal communication systems have evolved so that individuals can make decisions based upon the behaviour, physiology or morphology of others, which should allow predictions about the kinds and forms of signals used by animals signalling under known conditions to be made.
Abstract: Animal communication systems have evolved so that individuals can make decisions based upon the behaviour, physiology or morphology of others. Receiving mechanisms probably evolve to increase the efficiency and reliability of information reception whereas signals probably evolve to increase the efficiency of communication and reliability of manipulation of the receiving individual to the benefit of the emitter. The minimum requirement for clear reception suggests that any study of the evolution and design of communication systems must consider the factors that affect the quality of the received and processed signal. Critical information is needed about how the signal is generated and emitted, how it fares during transmission through air, water or substrate, how it is received and processed by the receiver's sensory and cognitive systems, and the factors which affect the fitness consequences of alternative ways of reacting to the information contained in the signal. These should allow predictions about the kinds and forms of signals used by animals signalling under known conditions. Phylogenetic history, and the geological time a clade spends in different signalling environments, will also affect signal evolution, and hence the success of predictions about signal design. We need to use methods of many different biological fields to understand the design and evolution of signals and signalling systems.
594 citations
TL;DR: A new framework which integrates functional, mechanistic, ontogenetic and comparative aspects of nutrition is presented and tested in experiments with insects, showing how comparative analyses of a range of species can be used to investigate the influence of non-nutritional, ecological factors on the location of the targets.
Abstract: We have presented and tested in experiments with insects a new framework which integrates functional, mechanistic, ontogenetic and comparative aspects of nutrition. The framework firstly identifies local optim a (nutritional, intake and growth ‘targets’) within a multi-dimensional nutritional space, where each functionally relevant nutrient forms a single dimension. The positions of these targets are located experimentally through studies of feeding behaviour and physiology and their functional significance is tested using independent performance criteria. Functional rules employed by animals to either reach these targets or, if that is not possible, find a point of best compromise, are then investigated by reference to the geometry of arrays of intake and growth across a range of foods. Changes in the position of the targets with ontogeny are considered, as are the nature of underlying homeostatic mechanisms. We also show how comparative analyses of a range of species can be used to investigate the influence of non-nutritional, ecological factors on the location of the targets.
428 citations
TL;DR: There are many methods for inferring terrestrial palaeoclimates from palaeontological data, including the size and species diversity of ectothermic vertebrates, the locomotor and dental adaptations of mammals, characteristics of leaf shape, size, and epidermis, wood anatomy, and the climatic preferences of nearest living relatives of fossil taxa.
Abstract: There are many methods for inferring terrestrial palaeoclimates from palaeontological data, including the size and species diversity of ectothermic vertebrates, the locomotor and dental adaptations of mammals, characteristics of leaf shape, size, and epidermis, wood anatomy, and the climatic preferences of nearest living relatives of fossil taxa. Estimates of palaeotemperature have also been based on stable oxygen isotope ratios in shells and bones. Interpretation of any of these data relies in some way on uniformitarian assumptions, although at different levels depending on the method.
359 citations
TL;DR: It is suggested that some of the difficulty in understanding preference evolution might derive from defining a preference only by those extant stimuli that elicit the preference, and that signal diversity might arise from alternative means for eliciting the same preference.
Abstract: The evolution of female mating preferences is an important key to understanding the evolution of signal diversity. Several hypotheses for preference evolution invoke different processes but all can produce the same end results: thus comparisons of extant traits and preferences within and among populations have made little progress in discriminating among competing hypotheses. Some of these hypotheses, however, do make different predictions as to the historical sequence of trait-preference evolution, and thus can be discriminated with appropriate phylogenetic analyses. We explore this approach in an analysis of the evolution of calls and call preferences in a monophyletic group of frogs, the Physalaemus pustulosus species group. In this clade there are pre-existing preferences for four call traits. These data reject hypotheses that invoke coevolution (good genes, runaway sexual selection) and females evolving preferences to choose males providing better resources, and instead support the hypothesis of sensory exploitation that suggests that males evolve traits that match pre-existing biases in the female’s sensory system. We suggest that some of the difficulty in understanding preference evolution might derive from defining a preference only by those extant stimuli that elicit the preference. Our results suggest that preferences might be more general, and that signal diversity might arise from alternative means for eliciting the same preference. Furthermore, we discuss some difficulties with utilizing both population-based comparisons and phylogenetic approaches and suggest that the greatest progress will be made by addressing the problem of preference evolution at several levels of analysis.
326 citations
TL;DR: Two abilities of signal receivers that can be seen as adaptations increasing the efficiency of territory defence will be discussed: identifying neighbouring individuals and ranging (i.e. determining the distance to) signallers.
Abstract: Territorial systems are characterized by the relative longevity and stability of interactions between neighbouring individuals. Two abilities of signal receivers that can be seen as adaptations increasing the efficiency of territory defence will be discussed: identifying neighbouring individuals and ranging (i.e. determining the distance to) signallers. The costs involved in such discriminations will also be outlined. Although signalling has been traditionally considered as occurring between two individuals (signaller and receiver), long-range signals will be received by many individuals. In territorial systems a group of neighbours could be considered as a communication network: consisting as its simplest of a signaller and a number of receivers. The scope for low cost, low-risk information gathering in such networks by eavesdropping will be discussed with particular reference to territorial songbirds and electric fish.
292 citations
TL;DR: The aerodynamic properties of a bird's tail, and the forces produced by it, can be predicted by using slender lifting surface theory as mentioned in this paper, which shows that unlike conventional wings, which generate lift proportional to their area, the lift generated by the tail is proportional to the square of its maximum continuous span.
Abstract: The aerodynamic properties of a bird’s tail, and the forces produced by it, can be predicted by using slender lifting surface theory. The results of the model show that unlike conventional wings, which generate lift proportional to their area, the lift generated by the tail is proportional to the square of its maximum continuous span. Lift is unaffected by substantial variations in tail shape provided that the tail initially expands in width along the direction of flow. Behind the point of maximum width of the tail the flow is dominated by the wake of the forward section. Any area behind this point therefore causes only drag, not lift. The centre of lift is at the centre of area of the part of the tail in front of the point of maximum width. The moment arm of the tail, about its apex, is therefore more than twice the moment arm of a conventional wing about its leading edge. The drag of the tail is a combination of induced drag proportional to lift, and profile drag proportional to surface area. Induced drag can be halved by drooping the outer tail feathers to generate leading edge suction. This may be used for control, particularly in slow flight when both wings and tail are generating maximum lift. The slender lifting surface model is very accurate at angles of attack below about 15°. At higher angles of attack vortex formation at the leading edge can stabilize the flow over the tail and thereby generate increased lift by a detached vortex mechanism. Asymmetry in the orientation of the leading edges with relation to the freestream (either in roll, yaw or caused by asymmetry in the planform) is amplified in the flow field and leads to large rolling and yawing forces that could be used for control in turning manoeuvres. The slender lifting surface model can be used to examine the effect of variations in tail shape and tail spread on the aerodynamic performance of the tail. A forked tail that has a triangular planform when spread to just over 120° gives the best aerodynamic performance and this may be close to a universal optimum, in terms of aerodynamic efficiency, for a means to control pitch and yaw. However, natural selection may act to optimise the performance of the tail when it is not widely spread. The tail is normally only widely spread during manoeuvres, or at low speeds, selection may act to improve the efficiency of the tail when it is spread to only a relatively narrow angle - for example to maximize the bird’s overall lift to drag ratio - the optimum shape at any angle of spread is that which gives a straight trailing edge to the tail. This will always give a slightly forked planform, but fork depth will depend on how widely the tail is spread when selection acts, and this depends on the criteria for optimization under natural selection. A forked tail is more sensitive to changes in angle of attack and angle of spread, than other tail types. Forked tails are more susceptible to damage than other tail morphologies, and suffer a greater loss of performance following damage. Forked tails also confer less inherent stability than any other type of tail. Aerodynamic performance may not be an im portant optimization criterion for birds that fly in a cluttered environment, or do not fly very much. Natural selection, under these conditions, may favour tails of other shapes. The aerodynamic costs of sexually selected elongated tails can be predicted from the model. These predictions can be used to distinguish between the various models for the evolution of elongated tails. Elongated graduated tails and pintails could have evolved either through a Fisherian or H andicap mechanism. The evolution of long forked tails can be initially favoured by natural selection, the pattern of feather elongation seen in sexually selected forked tails is predicted by the Fisher hypothesis (Fisher 1930) but not by any of the other theories of sexual selection.
238 citations
TL;DR: In this article, the authors present optimization criteria for energy-selected and time-selected flight strategies for birds migrating over land using either of two basic flight strategies, i.e. flapping or gliding/soaring flight.
Abstract: Birds migrating over land use either of two basic flight strategies, i.e. flapping or gliding/soaring flight. In soaring flight the birds gain altitude mainly by circling in thermals, i.e. rising air, and then they glide off until another thermal is encountered. Powered flapping flight is energetically much more expensive than gliding flight. This leaves us with the question why do not most birds adopt the soaring strategy rather than flapping flight on migration? I present optimization criteria, based on flight mechanical theory, for (i) energy-selected migration and (ii) time-selected migration, for flapping and soaring flight migration, respectively. These are evaluated in relation to general body size and rate of climb in thermals. I also consider the effects of wing morphology and horizontal winds. The general conclusion is that minimization of transport costs probably cannot be the only critical selective factor. In time-selected migration the size range of birds for which flapping flight is advantageous over thermal soaring flight, is significantly larger than in energy-selected migration, and this is in better agreement with what is found in real birds. Therefore, resulting migration speed probably constitutes an important selective force in bird migration. I also evaluate criteria for mixed strategies, i.e. when birds should use soaring flight when thermals are available and proceed by flapping flight otherwise. Finally, I also discuss some other factors, e.g. sensitivity to crosswinds, abundance of thermals and topography, which may affect the evolution of migration strategy.
229 citations
TL;DR: It is argued that there is no reason to dismiss species recognition as a possible cause of evolutionary change in moth sex pheromones and Mendelian genes controlling differences in mate choice and in the production of mate recognition signals have been found.
Abstract: Sex pheromone communication in moths is a well investigated case of mate-finding by chemical signals, but the evolutionary causes of the great complexity and diversity of these signals are still not generally agreed on. In the present paper, I argue that there is no reason to dismiss species recognition as a possible cause of evolutionary change in moth sex pheromones. Admittedly, selection for species recognition cannot explain all of the diversity in sex pheromones and the data supporting this contention are weak, but the alternative causes suggested, invoking mate choice between conspecifics as the mechanism of sexual selection, has so far no empirical support. Finding and analysing genes responsible for mate choice is important to corroborate any theory of sexual selection and speciation. In this respect genetic dissection of moth pheromone communication has provided important progress. Mendelian genes controlling differences in mate choice and in the production of mate recognition signals have been found. Polymorphic pheromone systems give the population biologists unique possibilities to study mate choice and selection at the genotype level in nature.
220 citations
TL;DR: It is suggested that STDS should be considered as a potentially powerful factor in future studies of mate choice and sperm competition, and a number of testable predictions about the consequences of STDS for avian reproductive biology are raised.
Abstract: Sexually transmitted diseases (STDS) span two current areas of sexual selection theory, namely the roles of multiple mating in determining individual reproductive success, and of parasites in mate choice, yet have been relatively neglected in the ecological literature. I reviewed the occurrence of STDS in populations of commercially kept birds and found widespread evidence for the existence of pathogenic STDS in such populations. STDs may have important consequences for the evolution of behaviour, reproductive physiology and some secondary sexual characteristics. Where STDS are costly they are hypothesized to affect the evolution of mating systems, and, via selection for hostility in the female reproductive tract, to explain high levels of sperm mortality after insemination. The potential for coevolutionary cycling is large, as some STDS may coevolve with female and male reproductive physiology, which may themselves coevolve. Although little information currently exists concerning the occurrence of STDS in wild birds, techniques for their identification are well established. This study raises a number of testable predictions about the consequences of STDS for avian reproductive biology, and I suggest that STDS should be considered as a potentially powerful factor in future studies of mate choice and sperm competition.
TL;DR: The role of heat-shock proteins (hsps) in thermotolerance was examined in the budding yeast Saccharomyces cerevisiae and in the fruit fly Drosophila melanogaster, suggesting that the primary function of hsp 104 is to rescue proteins from denaturation rather than to degrade them once they have been denatured.
Abstract: The role of heat-shock proteins (hsps) in thermotolerance was examined in the budding yeast Saccharomyces cerevisiae and in the fruit fly Drosophila melanogaster. In yeast cells, the major protein responsible for thermotolerance is hsp 100. In cells carrying mutations in the hsp 100 gene, HSP 104, growth is normal at both high and low temperatures, but the ability of cells to survive extreme temperatures is severely impaired. The loss of thermotolerance is apparently due to the absence of the hsp 104 protein itself because, with the exception of the hsp 104 protein, no differences in protein profiles were observed between mutant and wild-type cells. Aggregates found in mutant cells at high temperatures suggest that the cause of death may be the accumulation of denatured proteins. No differences in the rates of protein degradation were observed between mutant and wild-type cells. This, and genetic analysis of cells carrying multiple hsp 70 and hsp 104 mutations, suggests that the primary function of hsp 104 is to rescue proteins from denaturation rather than to degrade them once they have been denatured. Drosophila cells do not produce a protein in the hsp 100 class in response to high temperatures. In this organism, hsp 70 appears to be the primary protein involved in thermotolerance. Thus, the relative importance of different hsps in thermotolerance changes from organism to organism.
TL;DR: The role of those stress proteins functioning as molecular chaperones, both within the normal cell and in the cell subjected to metabolic stress are discussed.
Abstract: In response to either elevated temperatures or several other metabolic insults, cells from all organisms respond by increasing the expression of so-called heat shock proteins (hsp or stress proteins). In general, the stress response appears to represent a universal cellular defence mechanism. The increased expression and accumulation of the stress proteins provides the cell with an added degree of protection. Studies over the past few years have revealed a role for some of the stress proteins as being intimately involved in protein maturation. Members of the hsp 70 family, distributed throughout various intracellular compartments, interact transiently with other proteins undergoing synthesis, translocation, or higher ordered assembly. Although not yet proven, it has been suggested that members of the hsp 70 family function to slow down or retard the premature folding of proteins in the course of synthesis and translocation. Yet another family of stress proteins, the hsp 60 or GroEL proteins (chaperonins), appear to function as catalysts of protein folding. Here I discuss the role of those stress proteins functioning as molecular chaperones, both within the normal cell and in the cell subjected to metabolic stress.
TL;DR: The principle conclusion of the study is that the pattern of mixing between age and sexual activity classes have a very major influence on the predicted pattern of HIV spread and the demographic impact of AIDS.
Abstract: The paper describes the development and analysis of a mathematical model of the spread and demographic impact of HIV in heterosexual communities in developing countries. The model extends previous work in this area by the representation of patterns of mixing between and within different age and sexual activity classes in a two sex structure. Summary parameters are derived to represent different mixing patterns, ranging from assortative via random to disassortative, as are methods to ensure that particular mixing patterns between different age and sexual classes (stratified on the basis of rates of sexual partner change) meet constraints that balance the supply and demand for sexual partners as AIDS induced mortality influences the demographic structure of a population. Analyses of model behaviour rely on numerical methods due to the complexity of the mathematical framework, and sensitivity analyses are conducted to assess the significance of different assumptions and different parameter assignments. Simulated patterns of HIV spread across the two sexes and various age classes are compared with observed patterns in Uganda. The principle conclusion of the study is that the pattern of mixing between age and sexual activity classes, combined with the assumptions made to balance supply and demand between the sexes have a very major influence on the predicted pattern of HIV spread and the demographic impact of AIDS. The paper ends with a discussion of future needs in model development and data acquisition.
TL;DR: A conceptual framework in which to consider the information that is emerging about the proteins called molecular chaperones is proposed, and some definitions that may be useful in this new field of biochemistry are suggested.
Abstract: This introductory article proposes a conceptual framework in which to consider the information that is emerging about the proteins called molecular chaperones, and suggests some definitions that may be useful in this new field of biochemistry. Molecular chaperones are currently defined in functional terms as a class of unrelated families of protein that assist the correct non-covalent assembly of other polypeptide-containing structures in vivo, but which are not components of these assembled structures when they are performing their normal biological functions. The term assembly in this definition embraces not only the folding of newly synthesized polypeptides and any association into oligomers that may occur, but also includes any changes in the degree of either folding or association that may take place when proteins carry out their functions, are transported across membranes, or are repaired or destroyed after stresses such as heat shock. Known molecular chaperones do not convey steric information essential for correct assembly, but appear to act by binding to interactive protein surfaces that are transiently exposed during various cellular processes; this binding inhibits incorrect interactions that may otherwise produce non-functional structures. Thus the concept of molecular chaperones does not contradict the principle of protein self-assembly, but qualifies it by suggesting that in vivo self-assembly requires assistance by other protein molecules.
TL;DR: The fundamental evolutionary instability of recognition mechanisms perhaps explains why biological signals are so variable in form, and why, in experiments, animals sometimes show greater responses to novel forms of signals than they do to familiar forms.
Abstract: Mechanisms concerned with the recognition of biological signals act as important agents of selection on the appearance or \`form' of signals. Recognition of a given signal form can be achieved by many equally efficient alternative mechanisms. These alternative mechanisms will be selectively neutral and subject to change by genetic drift, thus preventing the fixation of a signal form that is optimal in releasing the receiver's behaviour. Because signal form is a multidimensional trait with an almost infinite potential to vary, it is expected that some novel forms of signals always exist that elicit responses more readily than any of those signals that the receiver has experienced during its evolutionary history. The existence of such \`hidden preferences' is illustrated in simple models of recognition mechanisms based on artificial neural networks. The fundamental evolutionary instability of recognition mechanisms perhaps explains why biological signals are so variable in form, and why, in experiments, animals sometimes show greater responses to novel forms of signals than they do to familiar forms.
TL;DR: The symplasmic pathway seems not to be interrupted by structural developments which make the endodermis an apoplasmic barrier of high resistance, and evidence that stelar tissues contain an H $^{+}$ -translocating ATPase whose activity can be influenced by physiological factors is pointed out.
Abstract: The structural features of the pathways followed by solutes and water are described. The porous nature of the cell walls comprising the apoplasm is described and the difficulties in verifying the passage of water through different parts of the apoplasm are discussed. The endodermis is of ubiquitous occurrence and has two invariant characteristics, a girdle-like wall thickening, the Casparian band, and the attachment of the plasma membrane to the band. Suggestions are made concerning the constraints placed on the passage of materials in the stele by these structures. The hypodermis is also a very common structure which shares a number of properties seen in the endodermis. The implications of an apoplasmic barrier in the hypodermis are discussed. The plasmodesmata are the key structural feature of the symplasmic pathway and recent information makes it clear that the size of the pores in the neck region can vary with the physiological state and position of tissues. The symplasmic pathway seems not to be interrupted by structural developments which make the endodermis an apoplasmic barrier of high resistance. Recent information from transpiring plants indicates that the turgor pressure in cortical cells increases centripetally: there is, therefore an outwardly directed hydrostatic pressure gradient. The implications of these new findings for water and solute flows in the symplast are considered. The final step in the radial transfer of materials is their release into the xylem. There is evidence that stelar tissues contain an H $^{+}$ -translocating ATPase whose activity can be influenced by physiological factors. It is pointed out that there may be major changes in the concentration of K $^{+}$ in xylem sap during a day-night cycle which may influence the polarization of the cell membranes of xylem parenchyma and the opening of ion-channels. The xylem elements themselves are not always fully conductive, even when their final diameter has been reached. The protoplasts and cross walls may be more persistent than is usually assumed, especially in soil-grown roots. Because of the low activity of Ca $^{2+}$ in the cytoplasm and the discontinuity of compartments within cells which contain abundant free Ca $^{2+}$ , this ion probably moves radially primarily by diffusion in the apoplasm. The transfer of Ca $^{+2}$ across the endodermis is shown to depend on the activity of Ca $^{2+}$ ATPase in the plasma membrane of the stelar side of the endodermis, emphasising once again the epithelial nature of this cell layer.
TL;DR: In this article, a mathematical model of the motion of arthropod filiform hairs in general, and of spider trichobothria specifically, in oscillating air flows is presented.
Abstract: This study is concerned with the mathematical modelling of the motion of arthropod filiform hairs in general, and of spider trichobothria specifically, in oscillating air flows. Analysis of the behaviour of hair motion is based on numerical calculations of the equation for conservation of hair angular momentum. In this equation the air-induced drag and virtual mass forces driving the hair about the point of attachment to the substrate are both significant and require a correct prescription of the air velocity. Two biologically significant cases are considered. In one the air oscillates parallel to the axis of the cylindrical substrate supporting the hair. In the other the air oscillates normal to that axis. It is shown that the relative orientation between the respective directions of the air motion and the substrate axis has a marked effect on the magnitudes of hair displacement, velocity and acceleration but not on the resonance frequency of the hair. It is also shown that the variation of velocity with distance from the substrate depends on the value of the parameter Re $\_s$ St $\_s$ , the product of the Reynolds number and the Strouhal number characterizing the motion of air past the substrate. In the case of air motion parallel to the substrate axis the analytical result derived by Stokes (1851), for a fluid oscillating along a flat surface of infinite extent, applies if Re $\_s$ St $\_s$ > 10 or, equivalently, if fD $^2$ /v > 20/ $\pi$ where f is the air oscillation frequency, D the substrate diameter and v the kinematic viscosity of the air. In contrast, in the case of air motion perpendicular to the substrate axis Stokes' (1851) analysis never applies due to a substrate curvature dependence of the velocity profile for all biologically significant values of Re $\_s$ St $\_s$ . Present theoretical considerations point to a new method for simultaneously determining R, the damping constant, and S, the torsional restoring constant of a filiform hair from measurements of the phase difference between hair displacement and air velocity as a function of the air oscillation frequency. For the filiform hairs of crickets we find from the data available that S = O(10 $^{-11}$ ) N m rad $^{-1}$ and R = O(10 $^{-13}$ ) N m s rad $^{-1}$ . All major qualitative aspects of known hair motion in response to air motion are correctly predicted by the numerical model.
TL;DR: It seems likely that the sperm whale is obtaining 77% of its food by swimming through luminous shoals of slow-swimming, neutrally bouyant squids and only about 23% by chasing faster swimming, larger cephalopods.
Abstract: Stomach contents from 17 sperm whales, 15 males and two females, caught during commercial activities in 1981-1984 in the Azores region were identified and measured. A total of 28 738 cephalopods and 16 fish were represented in the collections. In addition, there were tunicates in two whales and man-made products in three whales. None of the stomachs were empty. Flesh was present in 94.1% and indigestible fragments alone, including mandibles (beaks) of cephalopods, were present in 5.9% of the stomachs. Twelve species of cephalopod were represented by flesh and 40 species were represented by lower beaks. The cephalopod families contributing food to the whales in this region are, in order of their contribution by estimated mass, the Octopoteuthidae (39.8%), the Histioteuthidae (32.7%), the Architeuthidae (12.1%), the Lepidoteuthidae (4.5%), the Ommastrephidae (3.4%), the Pholidoteuthidae (2.1%), the Cycloteuthidae (1.9%), the Cranchiidae (1.7%) and eight other families each contributing less than 1% by mass. Presence of Gonatus beaks in the stomachs show which whales have migrated southwards to the Azores just prior to capture and the presence of a large Megalocranchia species possibly shows which whales have migrated from higher latitudes off Iceland. However, the presence of Teuthowenia maculata shows which whales came north from the West coast of Africa, just prior to capture. The modal mass of cephalopods consumed is 400-450 g which represents 0.00001 of the whales' body mass. 77.5% of the species eaten have luminous organs and 82% of the species are neutrally buoyant. It seems likely that the sperm whale is obtaining 77% of its food by swimming through luminous shoals of slow-swimming, neutrally bouyant squids and only about 23% by chasing faster swimming, larger cephalopods. Cephalopods not previously recorded from the North Atlantic are Onychoteuthis borealijaponicus, and Histioteuthis bonnellii corpuscula. Histioteuthis?miranda may have been collected by the whales much further south than the Azores. Species not recorded previously in the diet of sperm whales in the North Atlantic are Ommastrephes bartrami, Gonatus steenstrupi, Histioteuthis?miranda, H. bonnellii corpuscula, H. meleagroteuthis, Discoteuthis laciniosa, Mastigoteuthis species, Chiroteuthis species,?Helicocranchia, Liocranchia reinhardti, and?Liguriella.
TL;DR: The general context of visual and olfactory signals in butterfly communication is discussed using specific examples, including Amauris, and models for the evolution of chemical signalling systems in these mimetic butterflies are compared and assessed.
Abstract: The two major signal functions for adult butterflies are protection against predators and intraspecific communication. Protective use of colour patterns (e.g. aposematism, crypsis) is mainly directed against visually hunting vertebrate predators. Mate location in butterflies is effected through behavioural adaptations of both sexes, and long-range visual searching by males. Recognition and selection of mates at close-range is largely controlled by species-specific male pheromone components, although other signals (e.g. colour, movement) play the initial role. Increased elaboration of pheromones for specific signalling has been hypothesized where the design of visual signals is constrained by defensive functions involving pattern convergence (co-mimicry). Male pheromones are also important for trait signalling, often being decisive in female mate choice. The general context of visual and olfactory signals in butterfly communication is discussed using specific examples, including Amauris. Their low divergence in colour patterns contrasts with great differentiation in the chemistry of their scent-organ volatiles. Models for the evolution of chemical signalling systems in these mimetic butterflies are compared and assessed. A more complete understanding of the evolution and function of butterfly signalling systems will require renewed effort in a number of areas. These include integrated studies on the use and significance of colours and scents, the measurement of colour, chemical analyses of pheromone bouquets, genetics, and receptor physiology. All of this work will need to be put in a better comparative framework through cladistic analysis of a wider variety of biologically contrasted butterfly groups, including previously studied case lacking a rigorous phylogenetic perspective.
TL;DR: A tracking radar and an optical range-finder, placed on a ship, were used to register the flight of eleven species of seabirds, in waters off the Antarctic Peninsula and in the Atlantic Ocean as discussed by the authors.
Abstract: A tracking radar and an optical range-finder, placed on a ship, were used to register the flight of eleven species of seabirds, in waters off the Antarctic Peninsula and in the Atlantic Ocean. Albatrosses under calm conditions used swell soaring, turning and twisting extensively within a width of 300-500 m laterally from the overall direction of movement. Their resulting travel speed was on average 10 m s $^{-1}$ . In windy conditions the albatrosses as well as giant petrels travelled faster, with resulting speeds up to 22.5 m s $^{-1}$ , by a combination of wave soaring and dynamic soaring. Shearwaters and the antarctic fulmar proceeded by flap-gliding, along tracks that were only slightly zigzag within 50-60 m from the resulting course of movement. The little shearwater flew faster, with an airspeed about 14 m s $^{-1}$ , than larger-sized shearwaters and fulmars, using continuous flapping flight to a higher degree than its larger relatives. South polar skuas and Wilson's storm-petrels were tracked on foraging flights, and flocks of imperial shags on commuting flights between feeding and breeding-roosting areas. The south polar skua was able to accelerate to airspeeds exceeding 20 m s $^{-1}$ in pursuit flights after shags. Wilson's storm-petrels showed significantly slower airspeeds in foraging flights as compared to non-foraging flights. Average airspeeds of most species fell between the minimum power and maximum range speeds estimated from aerodynamical theory. Species using gliding or flap-gliding flight showed a mean airspeed close to the gliding speed for best glide ratio. Optimal speeds in foraging flights, as expected for the south polar skuas and Wilson's storm-petrels, are unlikely to coincide with the minimum power and maximum range speeds. Albatrosses reached the fastest resulting travel speeds when moving at angles 120 degrees -150 degrees from the wind (partly following winds), with strong wind forces. They predominantly travelled with the wind from their left side which, in the southern hemisphere, would lead them away from low pressure centres and towards high pressure areas.
TL;DR: The reliability of signals which display symmetry, as is measured by the 'fluctuating asymmetry', is interpreted as a consequence of the investment required of signals that coordinate development.
Abstract: All signals, with the exception of very special ones such as human verbal communication, evolve to be reliable. Communication systems that have been considered as systems of conventional signalling are reinterpreted as reliable systems by indicating the investment which increases their reliability. Examples are given from decorative patterns and set specific signals, such as status signals. The general importance of reliability is further discussed for cases such as the chemical signals within the multicellular organism, in which there is no conflict between the communicating parties. The reliability of signals which display symmetry, as is measured by the `fluctuating asymmetry', is interpreted as a consequence of the investment required of signals that coordinate development.
TL;DR: Two families of molecular chaperone, the hsp 60-GroEL family and the TF55-TCP1 family, have been discovered in evolutionarily related cellular compartments as mentioned in this paper.
Abstract: Two families of molecular chaperone, the hsp 60-GroEL family and the TF55-TCP1 family, have been discovered in evolutionarily related cellular compartments. A member of one of these families, hsp 60, has been shown to play a global role in polypeptide chain folding in mitochondria. We review here studies of both hsp 60 and other family members, discussing their essential physiological roles and mechanism of action.
TL;DR: It is suggested that the evolutionary past may represent a constraint on the communication system, where conservative features of the sensory and nervous system would now appear to be maladaptive for intraspecific communication.
Abstract: A number of insects use sound signals for the attraction of mates and in aggressive interactions between males. I discuss two constraints which may have shaped both the design of long-range signals, and the structure and physiology of the ear and nervous system of the receiver. Properties of the transmission channel for sound will impose limitations on long-range transfer of information, which may be compensated for by adapting either the signal or the behaviour of the sender or receiver. I describe properties of the nervous system which force the sender to produce more conspicuous signals. I suggest that the evolutionary past may represent a constraint on the communication system, where conservative features of the sensory and nervous system would now appear to be maladaptive for intraspecific communication.
TL;DR: In this article, a climate model is used to simulate the climate of the Late Permian, which employs more detailed prescriptions of land-ocean boundaries, topography, and inland lakes and seas than were used in previous climate simulations of supercontinents with idealized land-Ocean boundaries and no topography.
Abstract: A climate model is used to simulate the climate of the Late Permian. The climate model employs more detailed prescriptions of land-ocean boundaries, topography, and inland lakes and seas than were used in previous climate simulations of supercontinents with idealized land-ocean boundaries and no topography. The presence of mountains and plateaus and of inland seas and lakes produce large differences in the simulated climate compared to simulations that omit these features. Mountains and plateaus become focal points for enhanced precipitation and also help to intensify the monsoon circulations. Extensive inland seas and lakes exert a strong local damping of the seasonal range of temperature and also cause changes beyond the lakes region due to dynamical and hydrological effects. Using the climate-biome classification scheme of Walter, the simulated distribution of climates-biomes is compared to the observed distribution of Late Permian vegetation-biomes. Agreement is good in all but two areas.
TL;DR: Humphrey et al. as mentioned in this paper measured the hair and air motion of Cupiennius salei (Ctenidae) and found that hair length is not larger than boundary layer thickness at a hair's best frequency.
Abstract: Adults of the wandering spider Cupiennius salei (Ctenidae) have 936 ( $\pm$ 31 s.d.) trichobothria or filiform hairs on their legs and pedipalps. This is the largest number of these air movement detectors recorded for a spider. The trichobothria are 100-1400 $\mu$ m long and 5-15 $\mu$ m wide (diameter at base). Many of them are bent distally pointing towards the spider body. Their feathery surface increases drag forces and thus mechanical sensitivity by enlarging the effective hair diameter. Typically, trichobothria are arranged in clusters of 2-30 hairs which increase in length towards the leg tip. The trichobothria's mechanical directionality is either isotropic or it exhibits a preference for air flow parallel or perpendicular (from lateral) to the long leg axis. These differences are neither due to the distal bend of the hair nor to the bilateral symmetry of the cuticular cup at the hair base but to the spring supporting the hair. Different directional properties may be combined in the same cluster of hairs. Trichobothria are tuned to best frequency ranges between 40 and 600 Hz depending on hair length. Because, with increasing hair length, absolute mechanical sensitivity changes as well, the arrangement of hairs in a cluster provides for a fractionation of both the intensity and frequency range of a stimulus, in addition, in some cases, to that of stimulus direction. Boundary layer thickness above the spider leg in oscillating airflow varies between about 2600 $\mu$ m at 10 Hz and 600 $\mu$ m at 950 Hz. It is well within the range of hair lengths. In airflow perpendicular to the long leg axis particle velocity above the leg increases considerably as compared to the free field. The curved surface of the cuticular substrate has therefore to be taken into account when calculating hair motion. The experimentally measured properties of hair and air motion were also determined numerically using the theory developed in the companion paper (Humphrey et al. Phil. Trans. R. Soc. Lond. B 340, 423-444 (1993)). There is good agreement between the two. Short hairs are as good or better velocity sensors as long hairs but more sensitive acceleration sensors. In agreement with most of our measurements optimal hair length is not larger than boundary layer thickness at a hair's best frequency. Best frequencies of hair deflection and of ratio a (maximum hair tip displacement:air particle displacement) differ from each other. The highest measured value for ratio a was 1.6. In only 22 $\%$ of the cases hair tip displacement exceeded air particle displacement. Hair motion is insensitive to changes in hair mass as shown by the numerical comparison of a solid and a hollow hair.
TL;DR: The efficacy of dynamical systems theory as a means of determining the varied oscillatory behaviors inherent in a channel-based neural model is demonstrated and the maps of bifurcations provide a useful tool for determining how these behaviors depend upon model parameters and comparing the model to a real neuron.
Abstract: The anterior burster (AB) neuron of the lobster stomatogastric ganglion displays varied rhythmic behavior when treated with neuromodulators and channel-blocking toxins. We introduce a channel-based model for this neuron and show how bifurcation analysis can be used to investigate the response of this model to changes of its parameters. Two dimensional maps of the parameter space of the model were constructed using computational tools based on the theory of nonlinear dynamical systems. Changes in the intrinsic firing and oscillatory properties of the model AB neuron were correlated with the boundaries of Hopf and saddle-node bifurcations on these maps. Complex rhythmic patterns were observed, with a bounded region of the parameter plane producing bursting behavior of the model neuron. Experiments were performed by treating an isolated AB cell with 4-aminopyridine which selectively reduces g $\_{\text{A}}$ , the conductance of the transient potassium channel. The model accurately predicts the qualitative changes in the neuronal voltage oscillations that are observed over a range of reduction of g $\_{\text{A}}$ in the neuron. These results demonstrate the efficacy of dynamical systems theory as a means of determining the varied oscillatory behaviors inherent in a channel-based neural model. Further, the maps of bifurcations provide a useful tool for determining how these behaviors depend upon model parameters and comparing the model to a real neuron.
TL;DR: In this paper, the authors present a false view of the cell wall apoplast of leaves, showing that the flow of the transpiration stream is flow through leaky tubes, and is inadequately described by the Hagen-Poiseuille Law.
Abstract: Flow of the transpiration stream in the lumen apoplast of the xylem appears hydrodynamically orthodox in being approximately described by the Hagen-Poiseuille Law, and by Murray's Law for branching pipes. Flow may be followed in the major (supply) veins by labelling the stream with dye solutions. Progress of the dye in the stream into the minor (distribution) veins is obscured by surrounding tissues. Observations of the spread of fluorescent tracers from these veins in living leaves gave results that have been seriously misinterpreted to present a false view of the cell wall apoplast. Microscopy of the stabilized water-soluble fluorescent tracers moving out of the minor veins has revealed that: (i) the dye is separated from the water by filtration through cell membranes, and the water moves through the symplast; and (ii) the dye diffuses in the cell wall apoplast at rates 1/100 to 1/10 000 the rate of diffusion in water. As a consequence of (i), high concentrations of dye build up at sites called sumps. In grasses these sumps may be in the intercellular spaces outside the xylem. In dicotyledons these sumps are within the small tracheary elements. In fact, flow in the lumen apoplast is flow through leaky tubes, and is inadequately described by the Hagen-Poiseuille Law. Leaky tubes have a critical radius, below which (for a given pressure gradient) flow cannot occur. As a consequence of this, a wedge of xylem made up of vessels of different radii acts as a unit to concentrate dye tracers in a sump at its apex. Sumps may also be formed by evaporation of the water in the stream, especially at leaf margins. Investigations with the cryo-analytical scanning electron microscope of the natural ions of the transpiration stream reveal high concentrations of K, Cl, P and Ca in the stream in all the sizes of vessel and vein of sunflower leaves. These high concentrations appear to be produced, not by the mechanisms responsible for the formation of sumps of dyes, but by some other processes, probably occurring in the stem. The absence of sump formation by ions at the places where dyes form sumps is probably due to the more rapid penetration of the ions through the cell membranes. Reasons for the discrepancy between these measurements of salt concentrations in the stream and those obtained from sap expressed from leaves by pressure vessels are discussed. Implications of these facts for the design and interpretation of experiments with leaves are presented.
TL;DR: In this article, the authors re-examine some of the indirect methods that were used to support the formulation of this theory and conclude that because of ambiguities inherent in the interpretation of the results obtained by these approaches the evidence in support of the Cohesion Theory is not conclusive.
Abstract: According to the widely accepted Cohesion Theory, water is pulled by transpiration from the roots through the xylem to the leaves. It is believed that this process results in the development of large tensions (negative pressures) in the xylem. In this chapter we re-examine some of the indirect methods that were used to support the formulation of this theory. We conclude that because of ambiguities inherent in the interpretation of the results obtained by these approaches the evidence in support of the Cohesion Theory is not conclusive. Direct measurements of xylem pressure in herbaceous plants and tall trees have yielded values of tensions that are inconsistent with the Cohesion Theory. In the light of the data from the xylem pressure probe and nuclear magnetic resonance (NMR)-imaging, we believe that several forces may be responsible for long-distance water transport in plants. These include tension, osmotic pressure, capillary and air-water interfacial forces.
TL;DR: Data from bioassays of insects using artificial diets, and with transgenic plants, suggest that the in vitro assay of relative inhibitor effectiveness is consistent with the effects of different inhibitors on insect development and survival in vivo.
Abstract: Crops resistant to insect attack offer a different strategy of pest control to indiscriminate pesticide usage, which has undesirable effects on both the environment and humans. Transgenic plant technology can be a useful tool in producing resistant crops, by introducing entirely novel resistance genes into a plant species. Although most work in this area has focused on the use of genes encoding insecticidal Bacillus thuringiensis $\delta $ -endotoxins in transgenic plants, an alternative approach is to use plant genes which encode proteins with insecticidal properties. Protease inhibitors are involved in endogenous plant defence against insects. Over-expression of several inhibitors from constitutive promoters has been shown to afford protection in transgenic tobacco plants against attack by lepidopteran larvae. However, the degree of protection is not sufficiently high, and shows species- and inhibitor-specific effects. By assaying the interactions of protease inhibitors with insect gut proteases in vitro, the most effective inhibitor can be selected for a particular insect species. Data from bioassays of insects using artificial diets, and with transgenic plants, suggest that the in vitro assay of relative inhibitor effectiveness is consistent with the effects of different inhibitors on insect development and survival in vivo. Development of this techniology is considered. A different approach must be taken with sucking insect pests, as they do not rely on proteolysis for nutrition, and as Bt toxins effective against homopterans have not been reported to date. Bioassay in artificial diet was used to identify plant proteins with insecticidal effects on the rice brown planthopper (a model homopteran). The lectin from snowdrop (GNA) was found to be the most effective of the proteins tested. GNA was shown to be present in the phloem sap of a transgenic tobacco plant transformed with a chimeric gene construct, containing the rice sucrose synthase-1 gene promoter and the GNA coding sequence, by immunoassay of honeydew produced by aphids feeding on it. GNA is also insecticidal to the aphid Myzus persicae, which will feed on tobacco, and thus a bioassay of transgenic tobacco, to `prove' the technology, can be carried out. The effects of combining different resistance genes in the same transgenic plant to improve the effectiveness of protection are discussed, and exemplified.