Mechanical performance of aquatic rowing and flying

Aquatic flight, performed by rowing or flapping fins, wings or limbs, is a primary locomotor mechanism for many animals. We used a computer simulation to compare the mechanical performance of rowing and flapping appendages across a range of speeds. Flapping appendages proved to be more mechanically efficient than rowing appendages at all swimming speeds, suggesting that animals that frequently engage in locomotor behaviours that require energy conservation should employ a flapping stroke. The lower efficiency of rowing appendages across all speeds begs the question of why rowing occurs at all. One answer lies in the ability of rowing fins to generate more thrust than flapping fins during the power stroke. Large forces are necessary for manoeuvring behaviours such as accelerations, turning and braking, which suggests that rowing should be found in slow-swimming animals that frequently manoeuvre. The predictions of the model are supported by observed patterns of behavioural variation among rowing and flapping vertebrates.     

Kinematics, dynamics, and energetics of rowing and flapping propulsion in fishes

The shape and motion of the pectoral fins vary considerablyamong fishes that swim in the labriform mode. Pectoral fin motionin fishes is highly variable, but one conspicuous axis of thisvariation is the rowing-flapping axis. At one extreme of thisaxis, paddle-shaped fins row back and forth in a plane thatis parallel to fish motion, while at the other extreme, wing-shapedfins flap up and down in a plane that is perpendicular to fishmotion. We have used two fish, the threespine stickleback (Gasterosteusaculeatus) and the bird wrasse (Gomphosus varius), that fallnear the extremes of the rowing-flapping axis to study the dynamic,energetic, and ecological and evolutionary consequences of thiskinematic variation. Our work confirms some traditionally heldassumptions about rowing and flapping dynamics and energeticsbut reject others. A computer simulation experiment of virtualrowing and flapping appendages makes several predictions aboutdifferences in maneuvering performance and swimming energeticsbetween rowing and flapping, which, in turn, make predictionsabout the behavior and ecological distribution of fishes thatvary along the rowing-flapping axis. Both laboratory and fieldstudies of labrid swimming ability and distribution supportthese predictions.     

The rowing-to-flapping transition: ontogenetic changes in gill-plate kinematics in the nymphal mayfly Centroptilum triangulifer (Ephemeroptera, Baetidae)

Comparative studies encompassing a wide range of aquatic animals have shown that rowing is exclusively used at low Reynolds numbers ( Re  < 1), whereas flapping is predominantly used at Re  > 100, although few studies have been undertaken to document the transition in individual species that traverse the intermediate Re regime using a single set of appendages. Thus, it is not generally known whether a gradual increase in Re within a system results in a gradual or sudden shift between rowing and flapping. In the present study, we document ventilatory kinematics of a nymphal mayfly Centroptilum triangulifer that develops using a serial array of seven pairs of abdominal gill plates and operates at Reynolds numbers in the range 2–22 during ontogeny. We found that some kinematic variables (stroke frequency and metachronal phase lag) did not change during ontogeny but that others changed substantially. Specifically, gill kinematics in small instars used strokes with large pitch and stroke-plane deviations, whereas larger instars used strokes with minimal pitch and minimal stroke-plane deviation. Gills in larger instars also acquired an intrinsic hinge that allowed passive asymmetric movement between half strokes. Net flow in small animals was directed ventrally and essentially parallel to the stroke plane (i.e. rowing), whereas net flow in large animals was directed dorsally and essentially transverse to the stroke plane (i.e. flapping). The change in whole-gill kinematics from rowing to flapping occurred across a narrow Re range (3–8), which suggests a possible hydrodynamic demarcation between rowing and flapping.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 540–555.     

A comparison of swimming structures and kinematics in three species of crustacean larvae

Crustacean larvae swim with paired rowing appendages that rotate around the body of the animal. The number of paired rowing appendages varies from one species of larvae to another. In addition, the size of the crustacean larvae is different between species and increases as they grow. The nature of the fluid forces changes as size increases, so the morphology and mechanics of swimming in these animals will change during increases in size. This article demonstrates the changing kinematics of locomotion between three species of crustacean larvae, which swim with one (Artemia franciscana), two (Carcinus maenas) or five (Homarus americanus) pairs of propulsive limbs. The relative change in the surface area and volume ratios of the locomotor structures are also demonstrated.     

Implications of the feeding current structure of Euchaeta rimana, a carnivorous pelagic copepod, on the spatial orientation of their prey

Many marine planktonic organisms create water currents to entrainand capture food items. Rheotactic prey entrained within thesefeeding currents often exibit escape reactions. If the directionof escape is away from the feeding current, the prey may successfullydeter predation. If the escape is towards the center of thefeeding current, the prey will be re-entrained towards its predatorand remain at risk of predation. The direction of escape isdependent on (i) the ability of the prey to escape in a directiondifferent than its pre-escape orientation and (ii) the orientationcaused by the interaction of the prey's body with the movingfluid. In this study, the change in orientation of Acartia hudsonicanauplii as a result of entrainment within the feeding currentof Euchaeta rimana, a planktonic predatory copepod, was examined,When escaping in still water, A.hudsonica nauplii were ableto vary their pre-escape direction by only 10. This allowsonly a limited ability to escape in a direction different thantheir pre-escape orientation. Analyses of the feeding currentof E.rimana show the flow speed to be most rapid in the centralregion with an exponential decrease in speed distally. In contrast,flow vorticity is minimal in the center of the feeding currentand maximal at 1.75 mm along the antennae. As a result, thedegree of rotation of the prey towards the center of the feedingcurrent shows a strong dependency on the prey's location withinthe feeding current. The feeding current of E.rimana rotatedthe prey 14 when near the center of the flow field and up to160 when located more distal in the feeding current Since theprey's escape abilities cannot compensate for the rotation dueto the flow, this mechanism will maintain the escaping preywithin the feeding current of their predator. Therefore, thefeeding current facilitates predatory copepods in capturingprey by (i) increasing the amount of water which passes overtheir sensors and through their feeding appendages and (ii)controlling the spatial orientation of their prey prior to escape.     

Perceptive performance and feeding behavior of calanoid copepods

The goal of this study was to determine variables associatedwith calanoid feeding behavior, and thus, to improve our understandingof the basics of calanoid feeding rates. These variables includedperiods and frequency of appendage motion, rates of cell clearance,distance at which a copepod first reacts to a cell which iseventually captured, and rate of water flow through the areacovered by the motions of a copepod's feeding appendages. Theeffects of these variables on feeding rates were determinedfor copepodids and adult females of the calanoid copepod Eucalanuspileatus at phytoplankton concentrations covering the rangeencountered by this species on the south-eastern shelf of theUSA. Our results indicate that the distance at which E.pileatusperceives phytoplankton cells increases {small tilde}2-foldas food concentrations decrease from 1.0 to 0.1 mm³ l^–1.These results lead us to hypothesize that this is due to increasedsensitivity of chemosensors on the copepods' feeding appendages.This 2-fold increase in perceptive distance amounts to a near4-fold increase in perceived volume which is close to the 6-foldincrease in volume swept clear (VSC) from 1.0 to 0.1 mm³ l^–1of Thalassiosira weissflogii. We assume that the increases inVSC by planktonic copepods, when food levels are below satiation,are largely a function of the sensory performance of the individualcopepod.     

Neuromuscular Organization for "Wing" Control in a Mollusc (Clione limacina) and a Bird (Columba livia): Parallels in Design

Flapping as a means of locomotion is shared by divergent groupsranging from pteropod molluscs to birds. The pteropod, Clionelimacina, exhibits two modes of locomotion, slow and fast swimming.The motor units which control swimming consist of small motoneuronsand relatively nonfatigable muscle fibers, while those involvedin fast swimming consistof large motoneurons and relativelyfatigable fibers (Satterlie et al., 1990).The pectoralis muscleof the pigeon, Columba livia, consists of two populations ofmuscle fibers distinguished by histochemistry and size. Cinematographicand electromyographic experiments suggest that the large fibersare used for takeoff and landing and the small fibers for levelflight (Dial et al., 1988). We have employed a suite of experimentaltechniques similar to those used for studies of the neuromuscularsystem of Clione to analyze a limited sample of motor unitsfrom the pectoralis of Columba. The peak tetanic tension andcontractile fatigue resistance during electrical stimulationof single alpha axons, functionally isolated from nerve filaments,was studied in 30 motor units. All units but one generated peaktetanic tensions which were less than 0.22% of whole muscletension. A high proportion (75%) of units demonstrated fatigueresistance, reflective of the demands of sustained flappingflight. These preliminary data suggest that the peripheral neuromuscularsystems of Clione and Columba share some common components forthe execution of at least two distinct modes of flapping locomotion.     

Scaling of Soaring Seabirds and Implications for Flight Abilities of Giant Pterosaurs

The flight ability of animals is restricted by the scaling effects imposed by physical and physiological factors. In comparisons of the power available from muscle and the mechanical power required to fly, it is predicted that the margin between the powers should decrease with body size and that flying animals have a maximum body size. However, predicting the absolute value of this upper limit has proven difficult because wing morphology and flight styles varies among species. Albatrosses and petrels have long, narrow, aerodynamically efficient wings and are considered soaring birds. Here, using animal-borne accelerometers, we show that soaring seabirds have two modes of flapping frequencies under natural conditions: vigorous flapping during takeoff and sporadic flapping during cruising flight. In these species, high and low flapping frequencies were found to scale with body mass (mass ^−0.30 and mass ^−0.18) in a manner similar to the predictions from biomechanical flight models (mass ^−1/3 and mass ^−1/6). These scaling relationships predicted that the maximum limits on the body size of soaring animals are a body mass of 41 kg and a wingspan of 5.1 m. Albatross-like animals larger than the limit will not be able to flap fast enough to stay aloft under unfavourable wind conditions. Our result therefore casts doubt on the flying ability of large, extinct pterosaurs. The largest extant soarer, the wandering albatross, weighs about 12 kg, which might be a pragmatic limit to maintain a safety margin for sustainable flight and to survive in a variable environment.     

Cyanide-Insensitive Respiration in Thermogenic Flowers of Victoria and Nelumbo

The thermogenic carpellary appendages of the flowers of Victoriacruziana d'Orb. and the thermogenic staminal appendages of Nelumbolutea (Willd.) Pers. possess the cyanide-insensitive, ‘alternative’respiratory pathway. The presence of this pathway was demonstratedin tissue slices as well as in mitochondria. The thermogenicactivity was accompanied by ultrastructural changes in the Victoriamitochondria. Before anthesis, mitochondria with well-developedcristae were present in appendage tissue in large numbers. Duringanthesis, lamelliform cristae appeared in a different orientation. Key words: Victoria, Nelumbo, flowers, thermogenicity, mitochondria     

The scaling and structure of aquatic animal wakes

Animal generated water movements are visualized and quantifiedusing two-dimensional particle image velocimetry (PIV). Theresulting vector flow fields allow for the study of the distributionof velocity, vorticity and vortices. Structural and temporalaspects of animal-induced flows covering a range of Reynolds(Re) numbers between less than 1 to more than 10⁴ are presented. Maps of flow induced by continuous foraging and intermittentescape responses of tethered nauplius and copepodid stages ofthe marine copepod Temora longicornis offer insight in viscosity-dominatedflow regimes. Fast escape responses of the equally sized largestnauplius stage and the smallest copepodid stage are compared.The nauplius moves by generating a viscous flow pattern withhigh velocities and vorticity; the copepodid moves by usinginertial effects to produce a vortex ring with a rearward jetthrough the center. Larvae and small adult fish (zebra danio) use a burst-and-coast-swimmingmode at Re numbers up to 6,000, shedding a vortex ring withthe associated jet at the tail during the burst phase. Flowpatterns during the coasting phase differ between the smalllarvae and larger adults due to the changes in importance ofviscosity. A 12 cm long mullet swimming in a continuous mode generatesa chain of vortex rings with a backward undulating jet throughthe centers of the rings at Re numbers of 4 x 10⁴ in inertia-dominatedregimes. Our empirical results provide realistic insight in the scaleeffects determining the morphology of the interactions betweenanimals and water.     

Effects of concentration on the feeding of a marine copepod in algal monocultures and mixtures

High-speed microcinematography was used to examine the feedingbehavior of the marine copepod Eucalanus elongatus in a rangeof concentrations of algal monocultures and mixtures. Two celltypes were offered, the 13-µm diatom Thalassiosira weissflogii,which is primarily accumulated passively by low amplitude flappingof the second maxillae, and the 20 450-µm diatom Rhizosoleniaalata, which is actively captured by detection of and orientedresponse to individual cells. E. elongatus rapidly switchedback and forth between these two capture modes in mixtures ofboth diatoms, and flapped the second maxillae at low amplitudesregardless of the absolute or relative abundance of small andlarge cells. However, copepods in both monocultures and mixturesaltered the duration and/or rate of flapping of the feedingappendages with changes in algal concentration, with maximumactivity levels occurring at intermediate concentrations. Themarked reduction in feeding motions observed at the lowest algalconcentrations supports results from traditional grazing studiesand optimal foraging models, and may conserve energy duringprolonged perods of low food availability in continental slopewaters.     

Aerodynamics and Energetics of Intermittent Flight in Birds

Hypotheses explaining the use of intermittent bounding and undulatingflight modes in birds are considered. Existing theoretical modelsof intermittent flight have assumed that the animal flies ata constant speed throughout. They predict that mean mechanicalpower in undulating (flap-gliding) flight is reduced comparedto steady flight over a broad range of speeds, but is reducedin bounding flight only at very high flight speeds. Lift generatedby the bird's body or tail has a small effect on power, butis insufficient to explain observations of bounding at intermediateflight speeds. Measurements on starlings Sturnus vulgaris inundulating flight in a wind tunnel show that flight speed variesby around ±1 m/sec during a flap-glide cycle. Dynamicenergy is used to quantify flight performance, and reveals thatthe geometry of the flight path depends upon wingbeat kinematics,and that neither flapping nor gliding phases are at constantspeed and angle to the horizontal. The bird gains both kineticand potential energy during the flapping phases. A new theoreticalmodel indicates that such speed variation can give significantsavings in mechanical power in both bounding and undulatingflight. Alternative hypotheses for intermittent flight includea gearing mechanism, based on duty factor, mediating musclepower or force output against aerodynamic requirements. Thiscould explain the use of bounding flight in hovering and climbingin small passerines. Both bounding and undulating confer otheradaptive benefits; undulating may be primitive in birds, butbounding may have evolved in response to flight performanceoptimization, or to factors such as unpredictability in responseto predation.     

Flight modes in migrating European bee-eaters: heart rate may indicate low metabolic rate during soaring and gliding

Background

Many avian species soar and glide over land. Evidence from large birds (m _b>0.9 kg) suggests that soaring-gliding is considerably cheaper in terms of energy than flapping flight, and costs about two to three times the basal metabolic rate (BMR). Yet, soaring-gliding is considered unfavorable for small birds because migration speed in small birds during soaring-gliding is believed to be lower than that of flapping flight. Nevertheless, several small bird species routinely soar and glide.

Methodology/Principal Findings

To estimate the energetic cost of soaring-gliding flight in small birds, we measured heart beat frequencies of free-ranging migrating European bee-eaters (Merops apiaster, m _b∼55 g) using radio telemetry, and established the relationship between heart beat frequency and metabolic rate (by indirect calorimetry) in the laboratory. Heart beat frequency during sustained soaring-gliding was 2.2 to 2.5 times lower than during flapping flight, but similar to, and not significantly different from, that measured in resting birds. We estimated that soaring-gliding metabolic rate of European bee-eaters is about twice their basal metabolic rate (BMR), which is similar to the value estimated in the black-browed albatross Thalassarche (previously Diomedea) melanophrys, m _b∼4 kg). We found that soaring-gliding migration speed is not significantly different from flapping migration speed.

Conclusions/Significance

We found no evidence that soaring-gliding speed is slower than flapping flight in bee-eaters, contradicting earlier estimates that implied a migration speed penalty for using soaring-gliding rather than flapping flight. Moreover, we suggest that small birds soar and glide during migration, breeding, dispersal, and other stages in their annual cycle because it may entail a low energy cost of transport. We propose that the energy cost of soaring-gliding may be proportional to BMR regardless of bird size, as theoretically deduced by earlier studies.     

Fluid dynamics and microscale chemical movement in the chemosensory appendages of the lobster, Homarus americanus

Every chemosensory structure has a boundary layer surroundingit through which chemical signals must pass before contactingreceptor cells. Fluid motion in this boundary layer is slowand odor movement is mainly by diffusion. The boundary layerstructure depends upon external fluid velocities and the morphologyof the appendage. High-speed (10–200 Hz) electrochemicalrecordings from microchemical electrodes were used to quantifychemical transport in the microscale environment of three morphologicallydifferent chemosensory appendages of the lobster, Homarus americanus:lateral antennule, medial antennule and walking legs. Controlledpulses of the odor tracer (dopamine) were delivered to the threeappendages at three different flow speeds (0, 3, 6 cm/s). Theamplitudes of the pulses increased with increasing flow speed,indicating that boundary layer thickness decreased with increasingflow speed. Larger pulse amplitudes were measured in the walkinglegs than in the lateral or medial antennules at all flow speeds.In addition, larger amplitudes were recorded in the medial antennulethan the lateral antennule. Changes in pulse amplitude withincreasing flow speed were larger than changes in pulse duration.These results demonstrate that pulse amplitude is affected morethan pulse duration by boundary layer thickness and that themorphology of the receptor strucure helps determine the structureof signals arriving at receptor cells. This may explain whyanimals have adopted sampling strategies that reduce boundarylayer thickness.     

Aerodynamic Characteristics, Power Requirements and Camber Effects of the Pitching-Down Flapping Hovering

The pitching-down flapping is a new type of bionic flapping,which was invented by the author based on previous studieson the aerodynamic mechanisms of fruit fly(pitching-up)flapping.The motivation of this invention is to improve the aerodynamiccharacteristics of flapping Micro Air Vehicles(MAVs).In this paper the pitching-down flapping is briefly introduced.Themajor works include:(1)Computing the power requirements of pitching-down flapping in three modes(advanced,symmetrical,delayed),which were compared with those of pitching-up flapping;(2)Investigating the effects of translational accelerationtime,Δτ_t,and rotational time,Δτ_r,at the end of a stroke,and the angle of attack,α,in the middle of a stroke on the aerodynamiccharacteristics in symmetrical mode;(3)Investigating the effect of camber on pitching-down flapping.From the above works,conclusions can be drawn that:(1)Compared with the pitching-up flapping,the pitching-down flapping can greatly reduce thetime-averaged power requirements;(2)The increase in Δτt and the decrease in Δτ_r can increase both the lift and drag coefficients,but the time-averaged ratio of lift to drag changes a little.And α has significant effect on the aerodynamic characteristicsof the pitching-down flapping;(3)The positive camber can effectively increase the lift coefficient and the ratio of lift to drag.     

Light, temperature and nitrogen as interacting factors affecting diel vertical migrations of dinoflagellates in culture

Diel vertical migrations of the marine dinoflagellates Gonyaulaxpolyedra Stein and Ceratium furca (Ehr.) Clap, et Lachm. werefollowed in a laboratory tube (2.02 m x 0.25 m) under a 12:12hlight:dark cycle. The effects of temperature stratification,two levels of surface irradiance and nitrogen depletion on patternsof vertical migrations were examined. At temperatures between22–26°C with small temperature gradients, both speciesmigrated at a rate of 0.7 –1.0 m h^–1. Steeper thermoclines(ca. 0.8°C 0.1 m^–1) with temperatures below ca. 20°Ccaused a marked decrease in swimming speed which resulted inaccumulations of cells in these thermocline regions. Under conditionsof nutrient sufficiency both algae migrated into the surfacelayers at irradiance values of over 1000 µE m^–2s^–1. Increasing nitrogen depletion caused the downwardmigration of both algae to commence progressively earlier inthe day and before the end of the light period. The earlierdownward migrations enabled a more complete descent throughthe thermocline. Nitrogen depleted cells of Gonyaulax continuedto undertake vertical migrations but avoided high irradiancesthus forming subsurface maxima at irradiance levels close to150 µE m^–2 s^–1. Ceratium cells which exhaustedboth inorganic nitrogen and phosphorus ceased to migrate accompaniedby a large change in cellular fluorescence.     

Brood discrimination, nest mate discrimination, and determinants of social behavior in facultatively quasisocial beetles (Nicrophorus spp.)

In this study we investigated ecological determinants of socialityin burying beetles (Nicrophorus spp.), potential conflicts ofinterest among reproductive females, and the effects of nestingfailure and costs of fighting on cooperation. Burying beetlesare known to form monogamous pairs when exploiting small vertebratecarcasses. More complex social behavior in this group is poorlyunderstood. We conducted experiments in which one or two females(N. defodiens, N. orbicollis) were provided small or large carcasseson which to breed. On large but not on small carcasses, twofemales often formed cooperative breeding associations (jointlyprepared a carcass and fed young). In N. defodiens, but notN. orbicollis, two females produced a larger brood than singlefemales on large carcasses. In both species, the reproductiveoutput per female was less for two than for one female. Thepresence of a second female did not decrease the preparationtime of a carcass (discovery of resource to egg hatch). Conflictwas evident between females. Trials employing females of similarsize were more likely to result in injury than trials usingfemales of dissimilar size (N. tomentosus, N. defodiens, N.orbicollis). In N. tomentosus, those associations that persistedthe longest resulted in the fewest injuries. After care of youngwas initiated, conflict among familiar nest mates was not observed.There was no evidence that breeding females could discriminatebetween brood; use of a genetic marker (N. orbicollis) demonstratedthat females fed related and unrelated young alike. Femalesof similar size (high potential cost of fighting for the dominantindividual) were not more likely to form cooperative breedingassociations than females of dissimilar size (low cost of fightingfor dominant). Females of a species subject to a high rate ofnest failure (N. defodiens) were more likely to cooperate thanfemales of a species with a low rate of nest failure (N. orbicollis).It is argued that limited reproductive opportunities, difficultyin controlling rivals' access to a large carcass, and the superabundantlarval food supply represented by a large carcass, but not kinselection, have contributed to the evolution of cooperativebehavior in this group. In addition, we hypothesize that beetlesmight initially tolerate consexual rivals on large carcasseswhen there is a high likelihood of nesting failure, therebyavoiding potentially costly conflicts.     

Vascular Continuity in the Primary and Secondary Stem Tissues of Bougainvillea (Nyctaginaceae)

An investigation of stem structure of Bougainvillea by serialsections and cine-photography shows that the medullary systemof the inner area of young stems is the sole vascular systemdirectly continuous into the lateral appendages (leaves, axillarybuds and axillary thorns) via complex nodal anastomoses. Thevascular system at the periphery of the primary bundles is notdirectly continuous into these appendages. In secondary growth,there is direct continuity between vascular bundles within asingle ring, in a tangential direction via either xylem aloneor both xylem and phloem, and between rings in a radial directionalways via xylem and phloem, even though the rings are derivativesof successive cambia. Bougainvillea, vascular system, phloem, xylem, anomalous secondary thickening     

Behavioral interactions between a cyclopoid copepod predator and its prey

Behavioral observations on the predatory interactions betweenMesocyclops edax and several different types and sizes of preyrevealed that prey size alone was less important than otherspecific morphological and behavioral characteristics of theprey in deterring successful predation by the copepod. The behavioralresponses of Bosmina and Asplanchna to an attacking copepodwere passive and consisted of a simple retraction of vulnerableswimming appendages which made the prey more difficult to grasp.Daphnia and Diaphanosoma on the other hand exhibited very activeswimming escape responses. Tropocyclops usually avoided M. edaxby fleeing before the larger predator could detect them. Thehard carapaces of Daphnia, Bosmina and Keratella were effectiveat reducing ingestion following capture by M. edax. The resultsof these behavioral observations were supported by enclosureexperiments in which the predator was offered a choice betweentwo prey simultaneously. Cyclopoid copepods are capable of successfullyattacking, capturing and ingesting prey organisms several timestheir own body length. Although size alone may influence thepreference of cyclopoid copepods on large and small individualsof the same or similar prey species, it is not a dependabledeterminant of the preference of cyclopoids on multispecificprey assemblages. ¹Present address: Department of Biology, Williams Hall No. 31,Lehigh University, Bethlehem, PA 18015, USA