Showing papers in "Integrative and Comparative Biology in 2002"

Stress in Fishes: A Diversity of Responses with Particular Reference to Changes in Circulating Corticosteroids

Abstract: Physical, chemical and perceived stressors can all evoke non-specific responses in fish, which are considered adaptive to enable the fish to cope with the disturbance and maintain its homeostatic state. If the stressor is overly severe or long-lasting to the point that the fish is not capable of regaining homeostasis, then the responses themselves may become maladaptive and threaten the fish's health and well-being. Physiological responses to stress are grouped as primary, which include endocrine changes such as in measurable levels of circulating catecholamines and corticosteroids, and secondary, which include changes in features related to metabolism, hydromineral balance, and cardiovascular, respiratory and immune functions. In some instances, the endocrine responses are directly responsible for these secondary responses resulting in changes in concentration of blood constituents, including metabolites and major ions, and, at the cellular level, the expression of heat-shock or stress proteins. Tertiary or whole-animal changes in performance, such as in growth, disease resistance and behavior, can result from the primary and secondary responses and possibly affect survivorship.Fishes display a wide variation in their physiological responses to stress, which is clearly evident in the plasma corticosteroid changes, chiefly cortisol in actinopterygian fishes, that occur following a stressful event. The characteristic elevation in circulating cortisol during the first hour after an acute disturbance can vary by more than two orders of magnitude among species and genetic history appears to account for much of this interspecific variation. An appreciation of the factors that affect the magnitude, duration and recovery of cortisol and other physiological changes caused by stress in fishes is important for proper interpretation of experimental data and design of effective biological monitoring programs.

Thermal Physiology and Vertical Zonation of Intertidal Animals: Optima, Limits, and Costs of Living

Abstract: Temperature's pervasive effects on physiological systems are reflected in the suite of temperature-adaptive differences observed among species from different thermal niches, such as species with different vertical distributions (zonations) along the subtidal to intertidal gradient. Among the physiological traits that exhibit adaptive variation related to vertical zonation are whole organism thermal tolerance, heart function, mitochondrial respiration, membrane static order (fluidity), action potential generation, protein synthesis, heat-shock protein expression, and protein thermal stability. For some, but not all, of these thermally sensitive traits acclimatization leads to adaptive shifts in thermal optima and limits. The costs associated with repairing thermal damage and adapting systems through acclimatization may contribute importantly to energy budgets. These costs arise from such sources as: (i) activation and operation of the heat-shock response, (ii) replacement of denatured proteins that have been removed through proteolysis, (iii) restructuring of cellular membranes ("homeoviscous" adaptation), and (iv) pervasive shifts in gene expression (as gauged by using DNA microarray techniques). The vertical zonation observed in rocky intertidal habitats thus may reflect two distinct yet closely related aspects of thermal physiology: (i) intrinsic interspecific differences in temperature sensitivities of physiological systems, which establish thermal optima and tolerance limits for species; and (ii) 'cost of living' considerations arising from sub-lethal perturbation of these physiological systems, which may establish an energetics-based limitation to the maximal height at which a species can occur. Quantifying the energetic costs arising from heat stress represents an important challenge for future investigations.

Mechanisms of Adhesion in Geckos

Abstract: SYNOPSIS. The extraordinary adhesive capabilities of geckos have challenged explanation for millennia, since Aristotle first recorded his observations. We have discovered many of the secrets of gecko adhesion, yet the millions of dry, adhesive setae on the toes of geckos continue to generate puzzling new questions and valuable answers. Each epidermally-derived, keratinous seta ends in hundreds of 200 nm spatular tips, permitting intimate contact with rough and smooth surfaces alike. Prior studies suggested that adhesive force in gecko setae was directly proportional to the water droplet contact angle ( u) , an indicator of the free surface energy of a substrate. In contrast, new theory suggests that adhesion energy between a gecko seta and a surface (WGS) is in fact proportional to , and only for u . 608. A reanalysis of prior ˇ(1 1 cosu) data, in combination with our recent study, support the van der Waals hypothesis of gecko adhesion, and contradict surface hydrophobicity as a predictor of adhesion force. Previously, we and our collaborators measured the force production of a single seta. Initial efforts to attach a seta failed because of improper 3D orientation. However, by simulating the dynamics of gecko limbs during climbing (based on force plate data) we discovered that, in single setae, a small normal preload, combined with a 5 mm displacement yielded a very large adhesive force of 200 microNewton (mN), 10 times that predicted by whole-animal measurements. 6.5 million setae of a single tokay gecko attached maximally could generate 130 kg force. This raises the question of how geckos manage to detach their feet in just 15 ms. We discovered that simply increasing the angle that the setal shaft makes with the substrate to 30 8 causes detachment. Understanding how simultaneous attachment and release of millions of setae are controlled will require an approach that integrates levels ranging from molecules to lizards.

Adhesion a la moule.

Abstract: Mussels owe their sessile way of life in the turbulent intertidal zone to adaptive adjustments in the process and biochemistry of permanent attachment. These have understandably attracted scientific interest given that the attachment is rapid, versatile, tough and not subverted by the presence of water. The adhesive pads of mussel byssus contain at least six different proteins all of which possess the peculiar amino acid 3, 4-dihydroxyphenylalanine (DOPA) at concentrations ranging from 0.1 to 30 mol %. Studies of protein distribution in the plaque indicate that proteins with the highest levels of DOPA, such as mefp-3 (20 mol %) and mefp-5 (30 mol %), appear to predominate at or near the interface between the plaque and substratum. Although the presence of DOPA in proteins has traditionally been associated with cross-linking via chelate-mediated or covalent coupling, recent experiments with natural and synthetic DOPA-containing polypeptides suggest that cross-link formation is not the only fate for DOPA. Intact DOPA, particularly near the interface, may be essential for good chemisorption to polar surfaces. Uniformly high DOPA oxidation to cross-links leads to interfacial failure but high cohesive strength, while low DOPA oxidation results in better adhesion at the expense of cohesion. Defining the adaptations involved in balancing these two extremes is crucial to understanding marine adhesion.

Endocrine Responses to Unpredictable Environmental Events: Stress or Anti-Stress Hormones?

Abstract: SYNOPSIS. In addition to seasonal changes in morphology, physiology and behavior that occur in predictable annual cycles, there are facultative responses to unpredictable events known as labile ( i.e., short-lived) perturbation factors (LPFs). These rapid behavioral and physiological changes have been termed the ‘‘emergency’’ life history stage (ELHS) and serve to enhance life-time fitness. Glucocorticosteroids interacting with other hormones in the hypothalamo-pituitary-adrenal (HPA) cascade, initiate and orchestrate the ELHS within minutes to hours. Components of the ELHS include: redirection of behavior from a normal life history stage to increased foraging, irruptive-type migration during the day, enhanced restfulness at night, elevated gluconeogenesis and recovery once the perturbation passes. These physiological and behavioral changes allow an individual to avoid potential deleterious effects of stress that may result from chronically elevated levels of circulating glucocorticosteroids over days and weeks. In other words, acute rises in glucocorticosteroids following perturbations of the environment may actually avoid chronic stress and serve primarily as ‘‘anti-stress’’ hormones. Several field studies in diverse habitats indicate that free-living populations have elevated circulating levels of corticosteroids when in an ELHS. However, expression of an ELHS may not always be advantageous and there is accumulating evidence from birds that the adrenocortical responses to LPFs are modulated both on seasonal and individual levels. These data suggest that glucocorticosteroid secretions in response to LPFs not only trigger physiological and behavioral responses but also allow flexibility so that the response is integrated in relation to time of year (normal LHS) as well as individual differences owing to body condition, disease and social status.

An Integrative Study of Insect Adhesion: Mechanics and Wet Adhesion of Pretarsal Pads in Ants

Abstract: SYNOPSIS. Many animals that locomote by legs possess adhesive pads. Such organs are rapidly releasable and adhesive forces can be controlled during walking and running. This capacity results from the interaction of adhesive with complex mechanical systems. Here we present an integrative study of the mechanics and adhesion of smooth attachment pads (arolia) in Asian Weaver ants (Oecophylla smaragdina). Arolia can be unfolded and folded back with each step. They are extended either actively by contraction of the claw flexor muscle or passively when legs are pulled toward the body. Regulation of arolium use and surface attachment includes purely mechanical control inherent in the arrangement of the claw flexor system. Predictions derived from a ‘wet’ adhesion mechanism were tested by measuring attachment forces on a smooth surface using a centrifuge technique. Consistent with the behavior of a viscid secretion, frictional forces per unit contact area linearly increased with sliding velocity and the increment strongly decreased with temperature. We studied the nature and dimensions of the adhesive liquid film using Interference Reflection Microscopy (IRM). Analysis of ‘footprint’ droplets showed that they are hydrophobic and form low contact angles. In vivo IRM of insect pads in contact with glass, however, revealed that the adhesive liquid film not only consists of a hydrophobic fluid, but also of a volatile, hydrophilic phase. IRM allows estimation of the height of the liquid film and its viscosity. Preliminary data indicate that the adhesive secretion alone is insufficient to explain the observed friction and that rubbery deformation of the pad cuticle is involved.

Fungal endophytes: common host plant symbionts but uncommon mutualists.

Abstract: Fungal endophytes are extremely common and highly diverse microorganisms that live within plant tissues, but usually remain asymptomatic. Endophytes traditionally have been considered plant mutualists, mainly by reducing herbivory via production of mycotoxins, such as alkaloids. However, the vast majority of endophytes, especially horizontally-transmitted ones commonly found in woody plants, apparently have little or no effect on herbivores. For the systemic, vertically-transmitted endophytes of grasses, mutualistic interactions via increased resistance to herbivores and pathogens are more common, as predicted by evolutionary theory. However, even in these obligate symbioses, endophytes are often neutral or even pathogenic to the host grass, depending on endophyte and plant genotype and environmental conditions.We present a graphical model based upon variation in nitrogen flux in the host plant. Nitrogen is a common currency in endophyte/host and plant/herbivore interactions in terms of limitations to host plant growth, enhanced uptake by endophytes, demand for synthesis of nitrogen-rich alkaloids, and herbivore preference and performance. Our graphical model predicts that low alkaloid-producing endophytes should persist in populations when soil nutrients and herbivory are low. Alternatively, high alkaloid endophytes are favored under increasing herbivory and increasing soil nitrogen, at least to some point. At very high soil nitrogen levels, uninfected plants may be favored over either type of infected plants. These predictions are supported by patterns of infection and alkaloid production in nature, as well by a manipulative field experiment. However, plant genotype and other environmental factors, such as available water, interact with the presence of the endophyte to influence host plant performance.

The influence of surface wettability on the adhesion strength of settled spores of the green alga enteromorpha and the diatom amphora.

Abstract: In this paper we report on the effect of surface wettability on surface selection and adhesion properties of settled (adhered) spores of the biofouling marine alga Enteromorpha and cells of the diatom Amphora, through the use of patterned self-assembled monolayers (SAMs). The SAMs were formed from alkanethiols terminated with methyl (CH(3)) or hydroxyl (OH) groups, or mixtures of the two, creating a discontinuous gradient of wettability as measured by advancing water contact angle. In the case of Enteromorpha, primary adhesion, as measured by the transition from a motile spore to a settled, sessile organism, is strongly promoted by the hydrophobic surfaces. On the other hand, adhesion strength of the settled spores, as measured by resistance to detachment in a turbulent flow cell, is greatest on a hydrophilic surface. In the case of Amphora, there is little influence of surface wettability on the primary adhesion of this organism, but motility is inhibited at contact angles ≥60° and the cells are more strongly adhered to hydrophobic surfaces. Adhesion strength of Enteromorpha spores is also influenced by group size, spores in groups being more resistant to detachment than single spores.

Host Specificity in Ectomycorrhizal Communities: What Do the Exceptions Tell Us?

Abstract: Classic ectomycorrhizal symbioses are mutualisms that involve the exchange of fixed carbon for mineral nutrients between plant roots and fungi. They are unique in the way they contain features of both intimate and diffuse symbioses. The degree of host specificity varies, particularly among the fungi. Here we examine two exceptional cases of specificity to see what they tell us about the advantages of specificity, how it is initiated, and the potential role that it plays in complex ecosystems. The first case involves non-photosynthetic epiparasitic plants, which contrary to virtually all other plants, exhibit high levels of specificity toward their fungal hosts. The second case involves suilloid fungi; this is the largest monophyletic group of ectomycorrhizal fungi that is essentially restricted to associations with a single plant family. In both cases, new symbioses are initiated by dormant propagules that are stimulated to germinate by chemical cues from the host. This reduces the cost of wasting propagules on non-hosts. The advantages of specificity remain unclear in both cases, but we argue that increased benefit to the specialist may result from specialized physiological adaptations. We reexamine the idea that specialist fungi may help their hosts compete in complex ecosystems by reducing facultative epiparasitism by other plants, and suggest an alternative hypothesis for the observed pattern.

Maneuvering and Stability Performance of a Robotic Tuna

Abstract: The Draper Laboratory Vorticity Control Unmanned Undersea Vehicle (VCUUV) is the first mission-scale, autonomous underwater vehicle that uses vorticity control propulsion and maneuvering. Built as a research platform with which to study the energetics and maneuvering performance of fish-swimming propulsion, the VCUUV is a self-contained free swimming research vehicle which follows the morphology and kinematics of a yellowfin tuna. The forward half of the vehicle is comprised of a rigid hull which houses batteries, electronics, ballast and hydraulic power unit. The aft section is a freely flooded articulated robot tail which is terminated with a lunate caudal fin. Utilizing experimentally optimized body and tail kinematics from the MIT RoboTuna, the VCUUV has demonstrated stable steady swimming speeds up to 1.2 m/sec and aggressive maneuvering trajectories with turning rates up to 75 degrees per second. This paper summarizes the vehicle maneuvering and stability performance observed in field trials and compares the results to predicted performance using theoretical and empirical techniques.

Causes and Consequences of Thermal Tolerance Limits in Rocky Intertidal Porcelain Crabs, Genus Petrolisthes

Abstract: Vertical zonation of intertidal organisms, from the shallow subtidal to the supralittoral zones, is a ubiquitous feature of temperate and tropical rocky shores. Organisms that live higher on the shore experience larger daily and seasonal fluctuations in microhabitat conditions, due to their greater exposure to terrestrial conditions during emersion. Comparative analyses of the adaptive linkage between physiological tolerance limits and vertical distribution are the most powerful when the study species are closely related and occur in discrete vertical zones throughout the intertidal range. Here, I summarize work on the physiological tolerance limits of rocky intertidal zone porcelain crab species of the genus Petrolisthes to emersion-related heat stress. In the eastern Pacific, Petrolisthes species live throughout temperate and tropical regions, and are found in discrete vertical intertidal zones in each region. Whole organism thermal tolerance limits of Petrolisthes species, and thermal limits of heart and nerve function reflect microhabitat conditions. Species living higher in the intertidal zone are more eurythermal than low-intertidal congeners, tropical species have the highest thermal limits, and the differences in thermal tolerance between low- and high-intertidal species is greatest for temperate crabs. Acclimation of thermal limits of high-intertidal species is restricted as compared to low-intertidal species. Thus, because thermal limits of high-intertidal species are near current habitat temperature maxima, global warming could most strongly impact intertidal species.

Quantifying dynamic stability and maneuverability in legged locomotion.

Abstract: Animals can swerve, dodge, dive, climb, turn and stop abruptly. Their stability and maneuverability are remarkable, but a challenge to quantify. Formal stability analysis can allow for quantitative comparisons within and among species. Stability analysis used in concert with a template (a simple, general model that serves as a guide for control) can lead to testable hypotheses of function. Neural control models postulated without knowledge of the animal's mechanical (musculo-skeletal) system can be counterproductive and even destabilizing. Perturbations actively corrected by reflex feedback in one direction can result in perturbations in other directions because the system is coupled dynamically. The passive rate of recovery from a perturbation in one direction differs from rates in other directions. We hypothesize that animals might exert less neural control in directions that rapidly recover via passive dynamics (e.g., in body orientation and rotation). By contrast, animals are likely to exert more neural control in directions that recover slowly or not at all via passive dynamics (e.g., forward velocity and heading). Neural control best enhances stability when it works with the natural, passive dynamics of the mechanical system. Measuring maneuverability is more challenging and new, general metrics are needed. Templates reveal that simple analyses of summed forces and quantification of the center of pressure can lead to valuable hypotheses, whereas kinematic descriptions may be inadequate. The study of stability and maneuverability has direct relevance to the behavior and ecology of animals, but is also critical if animal design is to be understood. Animals appear to be grossly over-built for steady-state, straight-ahead locomotion, as they appear to possess too many neurons, muscles, joints and even too many appendages. The next step in animal locomotion is to subject animals to perturbations and reveal the function of all their parts.

Flexible Wings and Fins: Bending by Inertial or Fluid-Dynamic Forces?

Abstract: SYNOPSIS. Flapping flight and swimming in many organisms is accompanied by significant bending of flexible wings and fins. The instantaneous shape of wings and fins has, in turn, a profound effect on the fluid dynamic forces they can generate, with non-monotonic relationships between the pattern of deformation waves passing along the wing and the thrust developed. Many of these deformations arise, in part, from the passive mechanics of oscillating a flexible air- or hydrofoil. At the same time, however, their instantaneous shape may well emerge from details of the fluid loading. This issue—the extent to which there is feedback between the instantaneous wing shape and the fluid dynamic loading—is core to understanding flight control. We ask to what extent surface shape of wings and fins is controlled by structural mechanics versus fluid dynamic loading. To address this issue, we use a combination of computational and analytic methods to explore how bending stresses arising from inertial-elastic mechanisms compare to those stresses that arise from fluid pressure forces. Our analyses suggest that for certain combinations of wing stiffness, wing motions, and fluid density, fluid pressure stresses play a relatively minor role in determining wing shape. Nearly all of these combinations correspond to wings moving in air. The exciting feature provided by this analysis is that, for high Reynolds number motions where linear potential flow equations provide reasonable estimates of lift and thrust, we can finally examine how wing structure affects flight performance. Armed with this approach, we then show how modest levels of passive elasticity can affect thrust for a given level of energy input in the form of an inertial oscillation of a compliant foil.

Mechanics of adhesion through a fibrillar microstructure.

Abstract: SYNOPSIS. Many organisms have evolved a fibrillated interface for contact and adhesion as shown by several of the papers in this issue. For example, in the Gecko, this structure appears to give them the ability to adhere and separate from a variety of surfaces by relying only on weak van der Waals forces. Despite the low intrinsic energy of separating surfaces held together by van der Waals forces, these organisms are able to achieve remarkably strong adhesion. To help understand adhesion in such a case, we consider a simple model of a fibrillar interface. For it, we examine the mechanics of contact and adhesion to a substrate. It appears that this structure allows the organism, at the same time, to achieve good, ‘universal’ contact and adhesion. Due to buckling, a carpet of fibrils behaves like a plastic solid under compressive loading, allowing intimate contact in the presence of some roughness. As an adhesive, we conjecture that energy in the fibrils is lost upon decohesion and unloading. This mechanism can add considerably to the intrinsic work of fracture, resulting in good adhesion even with only van der Waals forces. Analysis of the mechanics of adhesion through such a fibrillar interface provides rules for the design of the microstructure for desired performance as an adhesive.

Mutualistic Fermentative Digestion in the Gastrointestinal Tract: Diversity and Evolution

Abstract: All animals, including humans, are adapted to life in a microbial world. Anaerobic habitats have existed continuously throughout the history of the earth, the gastrointestinal tract being a contemporary microniche. Since microorganisms colonize and grow rapidly under the favorable conditions in the gut they could compete for nutrients with the host. This microbial challenge has modified the course of evolution in animals, resulting in selection of complex animal-microbe relationships that vary tremendously, ranging from competition to cooperation. The ecological and evolutionary interactions between herbivorous dinosaurs and the first mammalian herbivores and their food plants are reconstructed using knowledge gained during the study of modern living vertebrates, especially foregut and hindgut fermenting mammals. The ruminant is well adapted to achieve maximal digestion of roughage using the physiological mechanism at the reticulo-omasal orifice which selectively retains large particles in the reticulo-rumen. However, the most obvious feature of all ruminants is the regurgitation, rechewing and reswallowing of foregut digesta termed rumination. Foregut fermenting mammals also share interesting and unique features in two enzymes, stomach lysozyme and pancreatic ribonuclease which accompany and are adaptations to this mode of digestion. The microbial community inhabiting the gastrointestinal tract is represented by all major groups of microbes (bacteria, archaea, ciliate protozoa, anaerobic fungi and bacteriophage) and characterized by its high population density, wide diversity and complexity of interactions. The development and application of molecular ecology techniques promises to link distribution and identity of gastrointestinal microbes in their natural environment with their genetic potential and in situ activities.

Understanding vertebrate brain evolution

Abstract: SYNOPSIS. Four major questions can be asked about vertebrate brain evolution: 1) What major changes have occurred in neural organization and function? 2) When did these changes occur? 3) By what mechanisms did these changes occur? 4) Why did these changes occur? Comparative neurobiologists have been very successful in recognizing major changes in brain structure. They have also made progress in understanding the functional significance of these changes, although this understanding is primarily limited to sensory centers, rather than integrative or motor centers, because of the relative ease of manipulating the relevant stimuli. Although neuropaleontology continues to provide important insights into when changes occurred, this approach is generally limited to recognizing variation in overall brain size, and sometimes brain regions, as interpreted from the surface of an endocranial cast. In recent years, most new information regarding when neural changes occurred has been based on cladistical analysis of neural features in extant taxa. Historically, neurobiologists have made little progress in understanding how and why brains evolve. The emerging field of evolutionary developmental biology appears to be the most promising approach for revealing how changes in development and its processes produce neural changes, including the emergence of novel features. Why neural changes have occurred is the most difficult question and one that has been the most ignored, in large part because its investigation requires a broad interdisciplinary approach involving both behavior and ecology.

The structure and adhesive mechanism of octopus suckers.

Abstract: SYNOPSIS. Octopus suckers consist of a tightly packed three-dimensional array of muscle with three major muscle fiber orientations: 1) radial muscles that traverse the wall; 2) circular muscles arranged circumferentially around the sucker; and 3) meridional muscles oriented perpendicular to the circular and radial muscles. The sucker also includes inner and outer fibrous connective tissue layers and an array of crossed connective tissue fibers embedded in the musculature. Adhesion results from reducing the pressure inside the sucker cavity. This can be achieved by the three-dimensional array of muscle functioning as a muscularhydrostat. Contraction of the radial muscles thins the wall, thereby increasing the enclosed volume of the sucker. If the sucker is sealed to a surface the cohesiveness of water resists this expansion. Thus, the pressure of the enclosed water decreases instead. The meridional and circular muscles antagonize the radial muscles. The crossed connective tissue fibers may store elastic energy, providing an economical mechanism for maintaining attachment for extended periods. Measurements using miniature flush-mounted pressure transducers show that suckers can generate hydrostatic pressures below 0 kPa on wettable surfaces but cannot do so on non-wettable surfaces. Thus, cavitation, the failure of water in tension, may limit the attachment force of suckers. As depth increases, however, cavitation will cease to be limiting because ambient pressure increases with depth while the cavitation threshold is unchanged. Structural differences between suckers will then determine the attachment force.

Physiological ecology of rocky intertidal organisms: a synergy of concepts.

Abstract: SYNOPSIS. The rocky intertidal zone is among the most physically harsh environments on earth. Marine invertebrates and algae living in this habitat are alternatively pounded by waves and exposed to thermal extremes during low tide periods (Denny and Wethey, 2001). Additionally, they must deal with strong selective pressures related to predation and competition for space (Connell, 1961). As a result, the steep physical gradient and spatially condensed community has made the rocky intertidal zone an ideal ‘‘natural laboratory’’ to study the coupled role of physical and biological factors in determining the abundance and distribution of organisms in nature (Connell, 1961; Paine, 1966, 1994). Early intertidal studies favored a major role of physiological adaptations to temperature and desiccation stress in determining patterns of vertical distribution (zonation) commonly found for intertidal organisms on rocky shores. It was shown that lethal limits of marine organisms correlated positively with the position of organisms along the physical gradient from the benign low-intertidal to the stressful high-intertidal zone, especially if differences in microhabitat and wave-exposure were taken into account (Gowanloch and Hayes, 1926; Orton, 1929; Broekhuysen, 1940; Evans, 1948). Zones characterized by indicator species appeared to correlate with shifts in the length of exposure to air, further supporting the potential role of physical factors in limiting distribution (Doty, 1946). The sharp distinction between some zones led Doty (1946) to conclude ‘‘Since the algae and their zones are sometimes, but rarely, intermixed and or arranged in these different orders, ..., itseems unlikely that competition can be a factor in controlling vertical distribution.’’ However, it was also noticed that physical conditions in the field rarely exceed lethal physiological limits (Broekhuysen, 1940; Evans, 1948). These observations left unresolved the role of chronic sublethal stress or biological factors, e.g., competition and predation, in setting distribution limits in the rocky intertidal zone (Wolcott, 1973). Connell (1961) then demonstrated that interspecific competition between the two barnacles Semibalanus (previously Balanus) balanoides and Chthalamus stellatus was responsible for setting the lower limits of the vertical distribution range of the higher occurring C. stellatus. The influence of biological factors was further demonstrated by Paine, who showed that the lower limits of mussels beds of the species Mytilus californianus could be extended through the removal of the predatory seastar Pisaster ochraceus (Paine, 1974). Although these papers established the influence

Power Requirements of Swimming: Do New Methods Resolve Old Questions?

Abstract: A recurring question in the study of fish biomechanics and energetics is the mechanical power required for tail-swimming at the high speeds seen among aquatic vertebrates. The quest for answers has been driven by conceptual advances in fluid dynamics, starting with ideas on the boundary layer and drag initiated by Prandtl, and in measurement techniques starting with force balances focussing on drag and thrust. Drag (=thrust) from measurements on physical models, carcasses, kinematics as inputs to hydromechanical models, and physiological power sources vary from less than that expected for an equivalent rigid reference to over an order of magnitude greater. Estimates of drag and thrust using recent advances largely made possible by increased computing power have not resolved the discrepancy. Sources of drag and thrust are not separable in axial undulatory self propulsion, are open to interpretation and Froude efficiency is zero. Wakes are not easily interpreted, especially for thrust evaluation. We suggest the best measures of swimming performance are velocity and power consumption for which 2D inviscid simulations can give realistic predictions. Steady swimming power is several times that required for towing an equivalent flat plate at the same speed.

Overcoming the constraints of long range radio telemetry from animals: getting more useful data from smaller packages.

Abstract: SYNOPSIS. Many species carry out their most interesting activities where they cannot readily be observed or monitored. Marine mammals are extreme among this group, accomplishing their most astounding activities both distant from land and deep in the sea. Collection, storage and transmission of data about these activities are constrained by the energy requirements and size of the recording loggers and transmitters. The more bits of information collected, stored and transmitted, the more battery is required and the larger the tag must be. We therefore need to be selective about the information we collect, while maintaining detail and fidelity. To accomplish this in the study of marine mammals, we have designed ‘‘intelligent’’ data logger/ transmitters that provide context-driven data compression, data relay, and automated data base storage. We later combine these data with remotely sensed environmental information and other oceanographic data sets to recreate the environmental context for the animal’s activity, and we display the combined data using computer animation techniques. In this way, the system can provide near real time ‘‘observation’’ of animal behavior and physiology from the remotest parts of the globe.

Structural Design and Biomechanics of Friction-Based Releasable Attachment Devices in Insects

Abstract: Design of attachment devices in insects varies enormously in relation to different functional loads. Many systems, located on different parts of the body, involve surfaces with particular frictional properties. Such systems evolved to attach parts of the body to each other, or to attach an insect to the substratum by providing fast and reversible attachment/detachment. Among these systems, there are some that deal with predefined surfaces, and others, in which one surface remains unpredictable. The first type of system occurs, for example, in wing-locking devices and head-arresting systems and is called probabilistic fasteners. The second type is mainly represented by insect attachment pads of two alternative designs: hairy and smooth. The relationship between surface patterns and/or mechanical properties of materials of contact pairs results in two main working principles of the frictional devices: mechanical interlocking, or maximization of the contact area. We give an overview of the functional design of two main groups of friction-based attachment devices in insects: probabilistic fasteners and attachment pads.

Energetic Bottlenecks and Other Design Constraints in Avian Annual Cycles

Abstract: SYNOPSIS. The flexible phenotypes of birds and mammals often appear to represent adjustments to alleviate some energetic bottleneck or another. By increasing the size of the organs involved in digestion and assimilation of nutrients (gut and liver), an individual bird can increase its ability to process nutrients, for example to quickly store fuel for onward flight. Similarly, an increase in the exercise organs (pectoral muscles and heart) enables a bird to increase its metabolic power for sustained flight or for thermoregulation. Reflecting the stationary cost of organ maintenance, changes in the size of any part of the ‘‘metabolic machinery’’ will be reflected in Basal Metabolic Rate (BMR) unless changes in metabolic intensity also occur. Energetic bottlenecks appear to be set by the marginal value of organ size increases relative to particular peak requirements (including safety factors). These points are elaborated using the studies on long-distance migrating shorebirds, especially red knots Calidris canutus. Red knots encounter energy expenditure levels similar to experimentally determined ceiling levels of ca. 5 times BMR in other birds and mammals, both during the breeding season on High Arctic tundra (probably mainly a function of costs of thermoregulation) and during winter in temperate coastal wetlands (a function of the high costs of processing mollusks, prey poor in nutrients but rich in shell material and salt water). During migration, red knots phenotypically alternate between a ‘‘fueling [life-cycle] stage’’ and a ‘‘flight stage.’’ Fueling red knots in tropical areas may encounter heat load problems whilst still on the ground, but high flight altitudes during migratory flights seem to take care of overheating and unacceptably high rates of evaporative water loss. The allocation principles for the flexible phenotypes of red knots and other birds, the costs of their organ flexibility and the ways in which they ‘‘organize’’ all the fast phenotypic changes, are yet to be discovered.

Balancing Requirements for Stability and Maneuverability in Cetaceans

Abstract: The morphological designs of animals represent a balance between stability for efficient locomotion and instability associated with maneuverability. Morphologies that deviate from designs associated with stability are highly maneuverable. Major features affecting maneuverability are positions of control surfaces and flexibility of the body. Within odontocete cetaceans (i.e., toothed whales), variation in body design affects stability and turning performance. Position of control surfaces (i.e., flippers, fin, flukes, peduncle) provides a generally stable design with respect to an arrow model. Destabilizing forces generated during swimming are balanced by dynamic stabilization due to the phase relationships of various body components. Cetaceans with flexible bodies and mobile flippers are able to turn tightly at low turning rates, whereas fast-swimming cetaceans with less flexibility and relatively immobile flippers sacrifice small turn radii for higher turning rates. In cetaceans, body and control surface mobility and placement appear to be associated with prey type and habitat. Flexibility and slow, precise maneuvering are found in cetaceans that inhabit more complex habitats, whereas high-speed maneuvers are used by cetaceans in the pelagic environment.

Integrative Functional Morphology of the Gekkotan Adhesive System (Reptilia: Gekkota)

Abstract: Climbing assisted by adhesive subdigital pads in gekkotan lizards has been the subject of intrigue and study for centuries. Many hypotheses have been advanced to explain the mechanism of adhesion, and recently this phenomenon has been investigated at the level of individual setae. The ability to isolate, manipulate and record adhesive forces from individual setae has provided new insights, not only into the mechanism of attachment, but also into the physical orientation of these structures necessary to establish attachment, maximize adhesive force, and effect subsequent release. This, in turn, has enabled a reassessment of the overall morphology and mode of operation of the adhesive system. Digital hyperextension has often been noted as a behavioral characteristic associated with the deployment of the gekkotan adhesive system-this is now understandable in the context of setal attachment and release kinematics, and in the context of the evolution of this pattern of digital movement from the primitive pattern of saurian digital kinematics. The perpendicular and parallel preloads associated with setal attachment are now reconcilable with other morphological aspects of the gekkotan adhesive system-the lateral digital tendon complex and the vascular sinus network, respectively. Future investigations of the integrated adhesive system will help to further elucidate the interdependence of its structural and functional components.

Physiology on a landscape scale: plant-animal interactions.

Abstract: We explore in this paper how animals can be affected by variation in climate, topography, vegetation characteristics, and body size. We utilize new spatially explicit state-of-the-art models that incorporate principles from heat and mass transfer engineering, physiology, morphology, and behavior that have been modified to provide spatially explicit hypotheses using GIS. We demonstrate how temporal and spatial changes in microclimate resulting from differences in topography and vegetation cover alter animal energetics, and behavior. We explore the impacts of these energetic predictions on elk energetics in burned and unburned stands of conifer in winter in Yellowstone National Park, chuckwalla lizard distribution limits in North America, California Beechey Ground squirrel and Dusky Footed woodrat mass and energy requirements and activity patterns on the landscape, their predator prey interactions with a rattlesnake, Crotalus viridis, and shifts in that food web structure due to topographic and vegetative variation. We illustrate how different scales of data/observation provide different pieces of information that may collectively define the real distributions of a species. We then use sensitivity analyses of energetic models to evaluate hypotheses about the effects of changes in core temperature (fever) global climate (increased air temperature under a global warming scenario) and vegetation cover (deforestation) on winter survival of elk, the geographic distribution of chuckwallas and the activity overlap of predator and prey species within a subset of commonly observed species in a terrestrial food web. Variation in slope and aspect affect the spatial variance in solar radiation incident on the ground, hence ground surface temperature, at the same elevation, same hourly 2 m air temperatures, and wind speeds. We illustrate visually how spatial effects and landscape heterogeneity make statistical descriptions of animal responses problematic, since multiple distributions of their responses to climate, topography, and vegetation on the landscape can yield the same descriptive statistics, especially at high (30 m) resolution. This preliminary analysis suggests that the model has far-reaching implications for hypothesis testing in ecology at a variety of spatial and temporal scales.

Partner choice in nitrogen-fixation mutualisms of legumes and rhizobia.

Abstract: Mutualistic interactions are widespread and obligatory for many organisms, yet their evolutionary persistence in the face of cheating is theoretically puzzling. Nutrient-acquisition symbioses between plants and soil microbes are critically important to plant evolution and ecosystem function, yet we know almost nothing about the evolutionary dynamics and mechanisms of persistence of these ancient mutualisms. Partner-choice and partner-fidelity are mechanisms for dealing with cheaters, and can theoretically allow mutualisms to persist despite cheaters.Many models of cooperative behavior assume pairwise interactions, while most plant-microbe nutrient-acquisition symbioses involve a single plant interacting with numerous microbes. Market models, in contrast, are well suited to mutualisms in which single plants attempt to conduct mutually beneficial resource exchange with multiple individuals. Market models assume that one partner chooses to trade with a subset of individuals selected from a market of potential partners. Hence, determining whether partner-choice occurs in plant-microbe mutualisms is critical to understanding the evolutionary persistence and dynamics of these symbioses. The nitrogen-fixation/carbon-fixation mutualism between leguminous plants and rhizobial bacteria is widespread, ancient, and important for ecosystem function and human nutrition. It also involves single plants interacting simultaneously with several to many bacterial partners, including ineffective ("cheating") strains. We review the existing literature and find that this mutualism displays several elements of partner-choice, and may match the requirements of the market paradigm. We conclude by identifying profitable questions for future research.

Using Functional Morphology to Examine the Ecology and Evolution of Specialization

Abstract: Researchers strive to understand what makes species different, and what allows them to survive in the time and space that they do. Many models have been advanced which encompass an array of ecological, evolutionary, mathematical, and logical principles. The goal has been to develop ecological theories that can, among other things, make specific and robust predictions about how and where organisms should live and what organisms should utilize. The role of functional morphology is often an under-appreciated parameter of these models. A more complete understanding of how anatomical features work to allow the organism to accomplish certain tasks has allowed us to revisit some of these ideas with a new perspective. We illustrate our view of this role for functional morphology in ecology by considering the issue of specialization: we attempt to align several definitions of specialization based upon shared ecological and evolutionary principles, and we summarize theoretical predictions regarding why an organism might specialize. Kinematic studies of prey capture in several types of fishes are explored with regard to the potential ecological and evolutionary consequences of specialization, most notably in the area of trade-offs. We suggest that a functional morphological perspective can increase our understanding of the ecological concepts of specialization and it consequences. The kinds of data that functional morphologists collect can help us to quantify organismal performance associated with specialization and the union of functional morphology with ecology can help us to better understand not just how but why organisms interact in the manner that they do.

Control of posture, depth, and swimming trajectories of fishes.

Abstract: Perturbations vary in period and amplitude, and responses to unavoidable perturbations depend on response time and scale. Disturbances due to unavoidable perturbations occur in three translational planes and three rotational axes during forwards and backwards swimming. Stability depends on hydrodynamic damping and correcting forces, which may be generated by propulsors (powered) or by control surfaces moving with the body (trimming). Hydrostatic forces affecting body orientation (posture) result in negative metacentric heights amplifying rolling disturbances. The ability to counteract perturbations and correct disturbances is greater for fishes with more slender bodies, which appears to affect habitat choices. Postural control problems are greatest at low speeds, and are avoided by some fishes by sitting on the bottom. In currents, body form and behavior affect lift, drag, weight, and friction and hence speeds to which posture can be controlled. Self-correcting and regulated damping and trimming mechanisms are most important in stabilizing swimming trajectories. Body resistance, fin trajectory, multiple propulsors, and long-based fins damp self-generated locomotor disturbances. Powered control using the tail evolved early in chordates, and is retained by most groups, although fishes, especially acanthopterygians, make greater use of appendages. As with most areas of stability, little is known of control costs. Costs and benefits of low-density inclusions and hydrodynamic mechanisms for depth control vary with habits and habitats. Control may make substantial contributions to energy budgets.

Water temperature, predation, and the neglected role of physiological rate effects in rocky intertidal communities.

Abstract: Ecologists and physiologists working on rocky shores have emphasized the effects of environmental stress on the distribution of intertidal organisms. Although consumer stress models suggest that physical extremes may often reduce predation and herbivory through negative impacts on the physiological performance of consumers, few field studies have rigorously tested how environmental variation affects feeding rates. I review and analyze field experiments that quantified per capita feeding rates of a keystone predator, the sea star Pisaster ochraceus, in relation to aerial heat stress, wave forces, and water temperature at three rocky intertidal sites on the Oregon coast. Predation rates during 14-day periods were unrelated to aerial temperature, but decreased significantly with decreasing water temperature. There was suggestive but inconclusive evidence that predation rates also declined with increasing wave forces. Data-logger records suggested that thermal stress was rare in the wave-exposed habitats that I studied; sea star body temperatures likely reached warm levels (>24°C) on only 9 dates in 3 yr. In contrast, wind-driven upwelling regularly generated 3 to 5°C fluctuations in water temperature, and field and laboratory results suggest that such changes significantly alter feeding rates of Pisaster. These physiological rate effects, near the center of an organism's thermal range, may not reduce growth or fitness, and thus are distinct from the effects of environmental stress. This study underscores the need to consider organismal responses both under "normal" conditions, as well as under extreme conditions. Examining both kinds of responses is necessary to understand how different components of environmental variation regulate physiological performance and the strength of species interactions in intertidal communities.