Balancing requirements for stability and maneuverability in cetaceans

The morphological designs of animals represent a balance betweenstability for efficient locomotion and instability associatedwith maneuverability. Morphologies that deviate from designsassociated with stability are highly maneuverable. Major featuresaffecting maneuverability are positions of control surfacesand flexibility of the body. Within odontocete cetaceans (i.e.,toothed whales), variation in body design affects stabilityand turning performance. Position of control surfaces (i.e.,flippers, fin, flukes, peduncle) provides a generally stabledesign with respect to an arrow model. Destabilizing forcesgenerated during swimming are balanced by dynamic stabilizationdue to the phase relationships of various body components. Cetaceanswith flexible bodies and mobile flippers are able to turn tightlyat low turning rates, whereas fast-swimming cetaceans with lessflexibility and relatively immobile flippers sacrifice smallturn radii for higher turning rates. In cetaceans, body andcontrol surface mobility and placement appear to be associatedwith prey type and habitat. Flexibility and slow, precise maneuveringare found in cetaceans that inhabit more complex habitats, whereashigh-speed maneuvers are used by cetaceans in the pelagic environment.     

Stability versus maneuverability in aquatic locomotion

The dictionary definition of stability as "Firmly established,not easily to be changed" immediately indicates the conflictbetween stability and maneuverability in aquatic locomotion.The present paper addresses several issues resulting from theseopposing requirements. Classical stability theory for bodiesmoving in fluids is based on developments in submarine and airshipmotions. These have lateral symmetry, in common with most animals.This enables the separation of the equations of motion intotwo sets of 3 each. The vertical (longitudinal) set, which includesmotions in the axial (surge), normal (heave) and pitching directions,can thus be separated from the lateral-horizontal plane whichincludes yaw, roll and sideslip motions. This has been founduseful in the past for longitudinal stability studies basedon coasting configurations but is not applicable to the analysisof turning, fast starts and vigorous swimming, where the lateralsymmetry of the fish body is broken by bending motions. Thepresent paper will also examine some of the aspects of the stabilityvs. maneuverability tradeoff for these asymmetric motions. Ananalysis of the conditions under which the separation of equationsof motions into vertical and horizontal planes is justified,and a definition of the equations to be used in cases wherethis separation is not accurate enough is presented.     

Terrestrial Intermittent Exercise: Common Issues for Human Athletics and Comparative Animal Locomotion

The earliest studies of intermittent exercise physiology notedthat moving intermittently (i.e., alternating brief movementswith brief pauses) could transform a heavy workload into a submaximalone that can be tolerated and sustained. The brief pauses thatcharacterize intermittent locomotion permit at least partialrecovery from prior activity. This research provided the foundationfor the development of interval training and more recently forthe re-evaluation of steady-state paradigms for comparativeanimal locomotion. In this paper I review key concepts underlyingthe performance of repeated activity. I provide examples fromhuman athletics and training and comparative animal locomotion.To explore the limits of intermittent exercise performance,I examine the performance limits for continuous exercise andthe rate and extent of the recovery of performance capacityfollowing activity. While it is evident that altering locomotorbehavior (i.e., moving intermittently) can alter the capacityof an animal to perform work, mathematical models of intermittentexercise could predict strategies (i.e., exercise intensity,exercise duration, and pause duration) that will increase performancelimits for intermittent activity.     

Mechanics of torque generation during quadrupedal arboreal locomotion

Quadrupedal animals moving on arboreal substrates face unique challenges to maintain stability. The torque generated by the limbs around the long axis of a branch during locomotion may clarify how the animals remain stable on arboreal supports. We sought to determine what strategy gray short-tailed opossums (Monodelphis domestica) use to exert torque and avoid toppling. The opossums moved across a branch trackway about half the diameter of their bodies. Part of the trackway was instrumented to measure substrate reaction forces and torque around the long axis of the branch. Kinematic analysis was used to estimate the center of pressure of the manus and pes; from center of pressure and vertical and mediolateral forces, the torque generated by substrate reaction forces versus muscular effort could be determined. Forelimbs generated significantly greater torque than hindlimbs, which is probably explained by the greater weight-bearing role of the forelimbs. Fore- and hindlimbs generated torque in opposite directions because contralateral fore- and hindlimbs typically contacted the branch. Torque generated by muscular effort, however, was often in the same direction in both fore- and hindlimbs. The muscle-generated torque is likely the result of mediolateral movement of the center of mass caused by mediolateral undulation of the torso. These results bear an important implication for the study of arboreal locomotion: center of mass dynamics are at least as important as static positions. M. domestica is a good representative for a primitive mammal, and comparisons with arboreal specialists will shed light on how proficient arboreal locomotion evolved.     

Plants versus animals: do they deal with stress in different ways?

Both plants and animals respond to stress by using adaptationsthat help them evade, tolerate, or recover from stress. In asynthetic paper A. D. Bradshaw (1972) noted that basic biologicaldifferences between plants and animals will have diverse evolutionaryconsequences, including those influencing how they deal withstress. For instance, Bradshaw argued that animals, becausethey have relatively well-developed sensory and locomotor capacities,can often use behavior and movement to evade or ameliorate environmentalstresses. In contrast, he predicted that plants will have toemphasize increased physiological tolerance or phenotypic plasticity,and also that plants should suffer stronger selection and showmore marked differentiation along environmental gradients. Herewe briefly review the importance of behavior in mitigating stress,the behavioral capacities of animals and plants, and examplesof plant responses that are functionally similar to behaviorsof animals. Next, we try to test some of Bradshaw's predictions.Unfortunately, critical data often proved non-comparable: plantand animal biologists often study different stressors (e.g.,water versus heat) and measure different traits (photosynthesisversus locomotion). Nevertheless, we were able to test someof Bradshaw's predictions and some related ones of our own.As Bradshaw predicted, the phenology of plants is more responsiveto climate shifts than is that of animals and the micro-distributionsof non-mobile, intertidal invertebrates ("plant" equivalents)are more sensitive to temperature than are those of mobile invertebrates.However, mortality selection is actually weaker for plants thanfor animals. We hope that our review not only redraws attentionto some fascinating issues Bradshaw raised, but also encouragesadditional tests of his predictions. Such tests should be informative.     

Control of Locomotion in a Lower Vertebrate, the Lamprey: Brainstem Command Systems and Spinal Cord Regeneration

SYNOPSIS. The lamprey, a lower vertebrate, has recently becomea very useful model system for studying motor control, includingthe organization of neural networks, and for examining the relationbetween kinematic patterns and underlying neural mechanisms.This aquatic animal displays a number of interesting locomotorbehaviors, including flexure reflexes, forward locomotion, backwardlocomotion, turning, withdrawal, and equilibrium reflexes. Avaluable property of the lamprey preparation is that the nervoussystem survives under in vitro conditions for several days andgenerates well-coordinated locomotor activity that underliessome of the above behaviors. Thus, the neural control of basiclocomotor behaviors can be studied in an isolated nervous systemin which the ionic or pharmacological make-up of the bath canbe altered and in which stable conditions are provided for intracellularrecordings. In addition, recent data indicate that the lampreypreparation is a valuable model system for studies of axonalregeneration and recovery of locomotor function following spinalcord injury. This article will focus on three aspects of locomotorbehavior in the lamprey: kinematics and motor activity of locomotorbehaviors, descending control of locomotion, and regenerationof descending brainstem command pathways that initiate locomotion.     

MUCUS PRODUCTION AND PHYSIOLOGICAL ENERGETICS IN PATELLA VULGATA L.

Most energy budgets for marine gastropods lack a measured mucusterm. This is a major omission since mucus is widespread inmolluscan physiological processes. In this paper we outlinemethods for estimating mucus production in the intertidal gastropod,Patella vulgata L. This species uses mucus primarily for adhesionand locomotion. Pedal mucus production rates were measured inaerial environments of 70% relative humidity (RH) and 100% RHand in seawater. Animals in 70% RH did not move, while thosein 100% RH and seawater were mobile. Animals in 100% RH showedthe highest mucus production rate. Those in seawater secretedabout 75% of the mucus produced in 100% RH and those in 70%RH only about 40% of that produced in 100% RH. Significant logarithmicrelationships between mucus production rate and whole dry weightof animal, and mucus production rate and shell length were foundin all cases. The mucus term in the energy budget was calculated as 23% ofingestion both for individuals and for a specific population.This is much higher than the estimate of 4% of Wright &Hartnoll (1981). We have recalculated an energy budget for Patellavulgata to include the substantial mucus term. The recalculatedbudget is structurally different from the original budget. Thissuggests conclusions drawn from budgets not including a measuredmucus term should be regarded with caution. (Received 12 September 1989; accepted 13 December 1989)     

Hip actuations can be used to control bifurcations and chaos in a passive dynamic walking model

We explored how hip joint actuation can be used to control locomotive bifurcations and chaos in a passive dynamic walking model that negotiated a slightly sloped surface (gamma<0.019 rad). With no hip actuation, our passive dynamic walking model was capable of producing a chaotic locomotive pattern when the ramp angle was 0.01839 rad相似文献   

OSMOTIC PROPERTIES OF AN INFAUNAL ESTUARINE BIVALVE SOLEN CYLINDRACEUS (HANLEY)

Solen cylindraceus is an infaunal euryhaline osmoconformer witha wide salinity tolerance range, 13-45. Under conditions inwhich the animal is removed from its burrow, osmotic equilibrationis rapid (1-12 h). When the animal remains undisturbed in itsburrow, equilibration is retarded (72-204 h). It is suggestedthat the observed decrease in the rate of change of haemolymphosmolarity in animals in their burrows is linked to the behaviouralresponse of the animal and to the stability of the interstitialsalinity. Doubt is also cast upon the usefulness of in vitroexperimentation in osmotic studies of estuarine intertidal burrowinganimals. (Received 22 December 1987; accepted 15 February 1988)     

In Search of Food: Exploring the Evolutionary Link Between cGMP-Dependent Protein Kinase (PKG) and Behaviour

Despite an immense amount of variation in organisms throughoutthe animal kingdom many of their genes show substantial conservationin DNA sequence and protein function. Here we explore the potentialfor a conserved evolutionary relationship between genes andtheir behavioural phenotypes. We investigate the evolutionaryhistory of cGMP-dependent protein kinase (PKG) and its possibleconserved function in food-related behaviours. First identifiedfor its role in the foraging behaviour of fruit flies, the PKGencoded by the foraging gene has since been associated withthe maturation of behaviour (from nurse to forager) in honeybees and the roaming and dwelling food-related locomotion innematodes. These parallels encouraged us to construct proteinphylogenies using 32 PKG sequences that include 19 species.Our analyses suggest five possible evolutionary histories thatcan explain the apparent conserved link between PKG and behaviourin fruit flies, honey bees and nematodes. Three of these raisethe hypothesis that PKG influences the food-related behavioursof a wide variety of animals including vertebrates. Moreover,it appears that the PKG gene was duplicated some time betweenthe evolution of nematodes and a common ancestor of vertebratesand insects whereby current evidence suggests only the for-likePKG might be associated with food-related behaviour.     

Predator-prey dynamics and movement in fractal environments

Previous research suggests that local interactions and limited animal mobility can affect population dynamics. However, the spatial structure of the environment can further limit the mobility of animals. For example, an animal confined to a river valley or to a particular plant cannot move with equal ease in all directions. We show that spatial architecture could influence the population dynamics of predator-prey systems using individual-based computer simulations parameterized with allometric relationships from the literature. Spatial forms (representing geographical features or plant architecture) of differing fractal dimension were generated, and simulated predators and prey were introduced into these computer environments. We claim that the alteration in interaction rates and population dynamics found in these simulations can be explained as a consequence of the anomalously slow rates of movement associated with fractal spaces and the diffusion-limited nature of predator-prey interactions. As a result, functional responses and numerical responses are substantially reduced in fractal environments, and the overall stability of the system is determined by the interaction between individual mobility and spatial architecture.     

THE EVOLUTION OF BIPEDAL RUNNING IN LIZARDS SUGGESTS A CONSEQUENTIAL ORIGIN MAY BE EXPLOITED IN LATER LINEAGES

The origin of bipedal locomotion in lizards is unclear. Modeling studies have suggested that bipedalism may be an exaptation, a byproduct of features originally designed to increase maneuverability, which were only later exploited. Measurement of the body center of mass (BCOM) in 124 species of lizards confirms a significant rearward shift among bipedal lineages. Further racetrack trials showed a significant acceleration threshold between bipedal and quadrupedal runs. These suggest good general support for a passive bipedal model, in which the combination of these features lead to passive lifting of the front of the body. However, variation in morphology could only account for 56% of the variation in acceleration thresholds, suggesting that dynamics have a significant influence on bipedalism. Deviation from the passive bipedal model was compared with node age, supporting an increase in the influence of dynamics over time. Together, these results show that bipedalism may have first arisen as a consequence of acceleration and a rearward shift in the BCOM, but subsequent linages have exploited this consequence to become bipedal more often, suggesting that bipedalism in lizards may convey some advantage. Exploitation of bipedalism was also associated with increased rates of phenotypic diversity, suggesting exploiting bipedalism may promote adaptive radiation.     

Dipteran insect flight dynamics. Part 1 Longitudinal motion about hover

This paper presents a reduced-order model of longitudinal hovering flight dynamics for dipteran insects. The quasi-steady wing aerodynamics model is extended by including perturbation states from equilibrium and paired with rigid body equations of motion to create a nonlinear simulation of a Drosophila-like insect. Frequency-based system identification tools are used to identify the transfer functions from biologically inspired control inputs to rigid body states. Stability derivatives and a state space linear system describing the dynamics are also identified. The vehicle control requirements are quantified with respect to traditional human pilot handling qualities specification. The heave dynamics are found to be decoupled from the pitch/fore/aft dynamics. The haltere-on system revealed a stabilized system with a slow (heave) and fast subsidence mode, and a stable oscillatory mode. The haltere-off (bare airframe) system revealed a slow (heave) and fast subsidence mode and an unstable oscillatory mode, a modal structure in agreement with CFD studies. The analysis indicates that passive aerodynamic mechanisms contribute to stability, which may help explain how insects are able to achieve stable locomotion on a very small computational budget.     

Developmental stability and predation success in an insect predator-prey system

I investigated the relationships among developmental stability(as measured by individual bilateral asymmetry values), twomeasures of locomotory performance and predation success inan insect predator-prey system. In this system yellow dungfliesScathophaga stercoraria preyed upon houseflies Musca domesticainlaboratory-controlled conditions. There was no relationshipbetween locomotion and absolute asymmetry or mean size of twomorphological traits (fourth longitudinal wing vein, forelegtibia) in either species. Analysis of single predation trialsindicated that locomotion performance and trait size are notassociated with the probability of predation. However, Muscathat were captured had tibia that were more asymmetric thanMusca that survived. Similarly, Scathophaga that were successfulpredators had more symmetric forelegs than unsuccessful predators.There was no relationship between predation and wing vein asymmetry,which may indicate the importance of terrestrial-based predatoryavoidance tactics in this system. There were no relationshipsbetween morphology or locomotion with predation latency, preyhandling times, or the number of times a prey "escaped" froma predator. The mechanisms behind the relationship between tibiaasymmetry and predation success are discussed. This is the firstexperiment to reveal direct evidence for selection for symmetric,developmentally stable individuals through differential predation     

Young flying squirrels (Pteromys volans) dispersing in fragmented forests

Dispersal is a key determinant of the population dynamics ofspecies. Thus, a better understanding of how dispersal is affectedby the landscape structure and how animals make decisions aboutmoving across different landscapes is needed. We studied thedispersal of 60 radio-collared juvenile Siberian flying squirrels(Pteromys volans) in southern Finland. The effect of landscapestructure on selected dispersal direction, dispersal distance,and straightness of dispersal path was studied. Flying squirrelswere capable of dispersing over long distances in fragmentedforest landscapes. The patches used as temporary roosting sitesduring dispersal were of a lower quality than were those usedas finally occupied patches. The patches used were larger thanwere patches on average in the study areas. There was a veryclear directional bias in the dispersal path (i.e., it was nearlya straight line), which remained over a large scale, but wide-openareas obstructed the straightness of the path. As the distancesbetween crossed patches increased, short-distance disperserswere found further away from their natal home range. However,there were no differences in the landscape that could explainthe differences between individuals in decisions to remain philopatricor to become short- or long-distance dispersers. In addition,whereas short-distance dispersers dispersed in random directions,long-distance dispersers started to disperse in directions dominatedby preferred habitat. Thus, there were behavioral differencesbetween dispersers. Our results supported the hypotheses statingthat individuals decide to disperse long or short distancesbefore the onset of dispersal.     

The Foregut of Gecarcinus lateralis as an Organ of Salt and Water Balance

The permeability of the foregut of the land crab, Gecarcinuslateralis, to tritiated water (THO), Na²², and Cl³⁶ was studiedin vitro during the intermolt period and after ecdysis. In crabswith eyestalks, the foregut is permeable to water and ions inthe direction hemolymph-to-lumen and lumen-to-hemolymph, bothduring the intermolt period and after ecdysis. However, theforegut of animals without eyestalks is impermeable after ecdysis. The movement of THO always follows the movement of Na²² acrossthe wall of the foregut, while the movement of Cl³⁶ may or maynot be correlated with the movement of Na²² and THO. Comparisonof the ratio of water to ions in the hemolymph with the ratiocalculated from radioisotope flux indicates that Na⁺ and waterare probably moving isosmotically, although not necessarilyaccompanied by Cl^– When an extract of the thoracic ganglionic mass of G. lateralisis added to the "hemolymph side" of the foregut in vitro, thereis immediately a large increase in permeability to water andsalts. This occurs in the foregut of crabs with eyestalks duringintermolt and also in eyestalkless crabs after ecdysis. Thus, not only is the foregut of Gecarcinus lateralis permeableto water and salts in both directions, but also the extent ofits permeability is under neuroendocrine control. As a consequence,the animal may be able to move water and salts into the foregutor out of it into the hemolymph as needed. This may be an importantadaptation for a terrestrial crab that must conserve water,especially at the critical time of ecdysis.     

Spring-mass running: simple approximate solution and application to gait stability

The planar spring-mass model is frequently used to describe bouncing gaits (running, hopping, trotting, galloping) in animal and human locomotion and robotics. Although this model represents a rather simple mechanical system, an analytical solution predicting the center of mass trajectory during stance remains open. We derive an approximate solution in elementary functions assuming a small angular sweep and a small spring compression during stance. The predictive power and quality of this solution is investigated for model parameters relevant to human locomotion. The analysis shows that (i), for spring compressions of up to 20% (angle of attack > or = 60 degree, angular sweep < or = 60 degree) the approximate solution describes the stance dynamics of the center of mass within a 1% tolerance of spring compression and 0.6 degree tolerance of angular motion compared to numerical calculations, and (ii), despite its relative simplicity, the approximate solution accurately predicts stable locomotion well extending into the physiologically reasonable parameter domain. (iii) Furthermore, in a particular case, an explicit parametric dependency required for gait stability can be revealed extending an earlier, empirically found relationship. It is suggested that this approximation of the planar spring-mass dynamics may serve as an analytical tool for application in robotics and further research on legged locomotion.     

Chinchilla (Chinchilla lanigera) behavioral responses to a visual signal preceding handling

Zoos use ambassador animals in educational programs featuring close contact with humans. Chinchillas (Chinchilla lanigera) at the Saint Louis Zoo are retrieved for programs by a keeper wearing brown handling gloves, but green cleaning gloves are worn during normal husbandry when physical contact with the animal is only incidental. The chinchillas’ primary keeper anecdotally reported more reactivity and movement from chinchillas when approached with handling gloves. Animals’ behavioral reactions to the presence of humans often include locomotion and vigilance, but these responses may be attenuated by predictability. To investigate these behaviors, handling trials involving brief contact attempts with both cleaning and handling gloves were filmed. Results indicated that chinchillas responded to disturbances by moving, jumping, and adopting more alert body postures. Surprisingly, movement was recorded in longer durations when the keeper attempted to touch the animals with cleaning gloves. This higher arousal may indicate that the animal was not expecting to be handled, yet an attempt to do so was being made. This reaction provides evidence that potentially aversive events should be reliably and consistently signaled.     

Tendon elasticity and muscle function

Vertebrate animals exploit the elastic properties of their tendons in several different ways. Firstly, metabolic energy can be saved in locomotion if tendons stretch and then recoil, storing and returning elastic strain energy, as the animal loses and regains kinetic energy. Leg tendons save energy in this way when birds and mammals run, and an aponeurosis in the back is also important in galloping mammals. Tendons may have similar energy-saving roles in other modes of locomotion, for example in cetacean swimming. Secondly, tendons can recoil elastically much faster than muscles can shorten, enabling animals to jump further than they otherwise could. Thirdly, tendon elasticity affects the control of muscles, enhancing force control at the expense of position control.     

The cost of incline locomotion in ghost crabs (<Emphasis Type="Italic">Ocypode quadrata</Emphasis>) of different sizes

It is well established that the metabolic cost of horizontal locomotion decreases as a regular function of animal body mass, regardless of body form and phylogeny. How body size affects the cost of incline exercise remains much less clear. Studies on vertebrates have led to the hypotheses that the cost of vertical work is independent of body mass and that the added cost of locomoting on inclines is lower for small animals. Studies on vertebrates and a few invertebrates provide evidence both for and against these hypotheses. To gain further insight into the cost of incline exercise, we measured oxygen consumption of small (2.33 ± 0.07 g) and large (46.66 ± 5.33 g) ghost crabs (Ocypode quadrata) locomoting horizontally and up a 20° incline. The slope of the oxygen consumption versus speed relationship (= minimum cost of transport) was not significantly different for small crabs exercising horizontally and on an incline. However, the intercept for incline exercise was significantly higher, indicating that small crabs used more energy during incline exercise than during horizontal exercise. Incline had no effect on the slope or intercept of the oxygen consumption versus speed relationship for large crabs. Our results suggest that the cost of incline locomotion may be large for small animals and that the cost is not independent of body size. Our results add to the growing body of research indicating that body mass is but one factor that determines the cost of incline locomotion and efficiency of vertical work.