Showing papers in "The Journal of Experimental Biology in 1987"

Maximum Lift Production During Takeoff in Flying Animals

Abstract: Maximum lift production during takeoff in still air was determined for a wide variety of insects and a small sample of birds and bats, and was compared with variation in morphology, taxonomy and wingbeat type. Maximum lift per unit flight muscle mass was remarkably similar between taxonomic groups (54–63 N kg−1), except for animals using clap-and-fling wingbeats, where muscle mass-specific lift increased by about 25 % (72–86 N kg−1). Muscle mass-specific lift was independent of body mass, wing loading, disk loading and aspect ratio. Birds and bats yielded results indistinguishable from insects using conventional wingbeats. Interspecific differences in short-duration powered flight and takeoff ability are shown to be caused primarily by differences in flight muscle ratio, which ranges from 0.115 to 0.560 among species studied to date. These results contradict theoretical predictions that maximum mass-specific power output and lift production should decrease with increasing body mass and wing disk loading.

Energy Partitioning in Fish: The Activityrelated Cost of Osmoregulation in a Euryhaline Cichlid

Abstract: SUMMARY We have investigated how the maintenance, net cost of swimming and total (maintenance + net cost of swimming) metabolic rates of red, hybrid tilapia {Oreochromis mossambicus $ XO. hornorum cf) responded to different acclimation salinities, and if these responses correlated with changes in ion-osmoregulation (= osmoregulation) costs. Three groups of fish were acclimated to either fresh water (FW, 0%o), isosmotic sea water (ISW, 12%o) or full strength sea water (SW, 35 %o) and oxygen consumption was measured while they swam at 10, 20, 30 and 40cms" 1 . Maintenance oxygen consumption (estimated by extrapolation), for an average fish (63g), increased among groups in the following order: FW

Course-control, metabolism and wing interference during ultralong tethered flight in Drosophila melanogaster

Abstract: Tethered flight in a 3-day-old female Drosophila was sustained for 32.2 h with only short interruptions during uptake of sucrose solution. The course-control reactions derived from the difference of the wingbeat amplitudes on either side have been used to simulate the rotatory displacement of the surrounding landmarks during a comparable turn in free flight. Stabilization of a target in the preferred area of the visual field requires continuous visual attention. A rate of about 5 course-correcting manoeuvres per second was maintained throughout the experiment. Drosophila seems to be able to cover long distances in search of a favourable habitat. Flight-specific carbohydrate consumption is equivalent to a metabolic power input per body weight of about 18 W N−1. The tethered fly produces about 40 % of the lift required to sustain hovering flight. The resulting mechanochemical efficiency of about 0.04-0.07 is within the expected order of magnitude for flying insects. Expenditure of reserve substances may account for the difference between the comparatively low power input of about 7 WN−1 derived from carbohydrate uptake in the first hours of flight (Wigglesworth, 1949), and the actual metabolic turnover of about 21WN−1 derived from oxygen consumption during this period (Laurie-Ahlberg et al . 1985). Weis-Fogh's ‘clap and fling’, a widespread lift-generating process exploiting the aerodynamic wing interference at the dorsal end of the wingbeat, was in action throughout the flight. However, there were two significant modifications (as first conceived by Ellington, 1980): (1) during ‘clap’, there is a progress of wing contact from the leading to the trailing edge, which is likely to ‘squeeze’ a thrust-generating jet of air to the rear; (2) during ‘fling’, there is a progress of wing separation in the same direction, which is described as a ‘peel’ resembling the progressive separation of two plastic foils pulled apart against forces of mutual attraction. The wings of the test fly survived about 23 million such peels without damage. Increasing airspeed decreases the intensity of ‘clap and fling’ in Drosophila : results obtained in the wind tunnel show the transition to a ‘near clap and fling’, lacking mutual wing contact.

The Wake of a Kestrel (Falco Tinnunculus) in Flapping Flight

Abstract: The structure of the wake behind a kestrel in medium-speed flight down a 36 m length of corridor was analysed qualitatively and quantitatively by stereophotogrammetry of multiple flash photographs of the motion of small soap-covered helium bubbles. The wake consists of a pair of continuous, undulating trailing vortices. The upstroke is therefore aerodynamically active and the circulation appears to remain constant along the wing whose geometry is altered during the course of the wingstroke. It is argued that the flight kinematics, and so the wake structure, of the kestrel may be typical of flapping flight at medium speeds and a flight model based on this wake geometry is presented. Rough estimates of the rate of momentum generated in the wake balance the weight almost exactly and a direct estimate of the induced power requirement from the wake measurements is obtained. The significance of these results for the various alternative aerodynamic descriptions and energetic predictions of models of flapping animal flight is briefly assessed

Functional design of horse hoof keratin: the modulation of mechanical properties through hydration effects.

Abstract: Tensile moduli and J-integral fracture toughness values were determined for horse hoof-wall keratin at four hydration levels. The stiffness of hoof-wall was influenced by water content to a greater degree than is the stiffness of other mammalian hard keratins. Young's modulus increased from 410 MPa at 100% relative hydration (RH) to 14.6 GPa at 0% RH. Fracture toughness was maximal (22.8 kJ m-2) at an intermediate hydration (75% RH), which represents a two-fold increase over both fully hydrated and dehydrated material. Maximum fracture toughness occurred at a hydration level which is within the range that has been found in vivo in the hoof wall. These results lead to the hypothesis that the density of secondary bonding sites within the hoof-wall keratin matrix proteins provides the hoof organ with the means to modulate tissue properties, even though this epidermal tissue functions after the cells have died.

Locomotion Energetics of the Ghost Crab: II. Mechanics of the Centre of Mass During Walking and Running

Abstract: Terrestrial locomotion involving appendages has evolved independently in vertebrates and arthropods. Differences in the mechanical design of the locomotor apparatus could impose constraints on the energetics of locomotion. The mechanical energy fluctuations of the centre of mass of an arthropod, the ghost crab Ocypode quadrata (Fabricius), were examined by integrating the ground reaction forces exerted during sideways locomotion. Crabs used a pendulum-type energy exchange mechanism during walking, analogous to an egg rolling end over end, with the same effectiveness as birds and mammals. Moreover, ghost crabs were found to have two running gaits. A switch from a slow to a fast run occurred at the same speed and stride frequency predicted for the trot-gallop transition of a quadrupedal mammal of the same body mass. In addition, the mass-specific mechanical energy developed over a unit distance was independent of speed and was within the limits measured for birds and mammals. Despite the obvious differences in mechanical design between crabs and mammals, energy-conserving mechanisms and the efficiency of locomotion were remarkably similar. These similarities may result from the fact that the muscles that generate forces during terrestrial locomotion have relatively conservative mechanical and energetic properties.

Flight of auks (alcidae) and other northern seabirds compared with southern procellariiformes: ornithodolite observations

Abstract: Airspeeds in flapping and flap-gliding flight were measured at Foula, Shetland for three species of auks (Alcidae), three gulls (Landae), two skuas (Stercorariidae), the fulmar (Procellariidae), the gannet (Sulidae) and the shag (Phalacrocoracidae). The airspeed distributions were consistent with calculated speeds for minimum power and maximum range, except that observed speeds in the shag were unexpectedly low in relation to the calculated speeds. This is attributed to scale effects that cause the shag to have insufficient muscle power to fly much faster than its minimum power speed. The wing adaptations seen in different species are considered as deviations from a ‘procellariiform standard’, which produce separate effects on flapping and gliding speeds. Procellariiformes and the gannet flap-glide in cruising flight, but birds that swim with their wings do not, because their gliding speeds are too high in relation to their flapping speeds. Other species in the sample also do not flap-glide, but the reason is that their gliding speeds are too low in relation to their flapping speeds.

The use of peripheral nerve grafts to enhance neuronal survival, promote growth and permit terminal reconnections in the central nervous system of adult rats.

Abstract: During both development and regeneration, the survival of neurones and the growth of axons are controlled by inherent neuronal properties, conditions in the axonal environment, and the establishment of appropriately timed and specific functional contacts. To study the effects of extrinsic influences on the survival, growth and connectivity of axotomized neurones in the mature mammalian CNS, we replaced the optic nerve in adult rats with segments of autologous peripheral nerve (PN) and used morphometric techniques, neuroanatomical tracer substances and immunological cell markers to examine retinal ganglion cells (RGCs), their axons in the PN grafts and their terminals in the superior colliculi (SC) of these animals. We observed that: (1) the survival of axotomized RGCs was enhanced by the PN grafts; (2) in the PN-grafted eyes, approximately 20% of the surviving RGCs regrew their axons into the grafts and (3) some of the RGC axons that regenerated along the PN grafts bridging the eye and the tectum re-entered the SC, arborized and made synaptic contacts with tectal neurones. It is not known if the terminal connections established between RGCs and cells in the SC are appropriate, functional or capable of influencing the long-term survival of their cells of origin.

Swimming in the California sea lion: morphometrics, drag and energetics.

Abstract: During swimming, the California sea lion, Zalophus californianus (Lesson), generates thrust forces solely by means of its pectoral flippers. This study examines the drag, energetic cost and efficiency associated with this method of locomotion. Sea lions are highly streamlined, with a fineness ratio of 5.5 and maximum girth at 40% of body length. This profile leads to reduced drag and swimming power requirements. Films of gliding animals showed the drag coefficient (based on wetted surface area) to be 0.0042 at a Reynolds number of 2.0 X 10(6). This value is comparable to that found for other aquatic vertebrates and suggests that the sea lion9s morphology helps to delay turbulent separation and maintain laminar flow over the forward portion of its body. Swimming metabolism was measured in a water flume at velocities up to 1.3 ms-1. Effective swimming speeds up to 2.7 ms-1 were attained by increasing each animal9s drag. Oxygen consumption rose exponentially with velocity and for two animals was best described as VO2 = 6.27e0.48U, where VO2 is in mlO2 min-1 kg-1 and U is in ms-1. Minimum cost of transport for these animals was 0.12 ml O2 kg-1 m-1 at a relative speed of 1.4 body lengths s-1. This is 2.5 times that predicted for a fish of similar size. Swimming efficiencies were determined from these results using power output values calculated from the measured drag coefficient and standard hydrodynamic equations. At the highest velocity, aerobic efficiency reached a maximum of 15% while mechanical efficiency of the foreflippers was 80%. The results demonstrate that foreflipper propulsion is a highly efficient and comparatively inexpensive method of locomotion in aquatic mammals.

The Sulphide-Binding Protein in the Blood of the Vestimentiferan Tube-Worm, Riftia Pachyptila, is the Extracellular Haemoglobin

Abstract: The sulphide-binding protein that occurs in high concentrations in the vascular blood and coelomic fluid of the hydrothermal vent tube-worm Riftia pachyptila Jones is the haemoglobin. Sulphide binding does not occur at the oxygen-binding sites of the haem, but may occur via thiol-disulphide exchange at the interchain disulphide bridges on the macromolecule. We have confirmed the report that vascular blood is heterogeneous for two haemoglobins (FI and FII) that are different in M r, but we conclude that the coelomic fluid is homogeneous for the lower M r haemoglobin FII, in the intact, living animal. These two haemoglobins occur naturally in the living animals, and FII is not a dissociation product of the higher M r FI. The sulphide-binding capacities of the two haemoglobin species differ by about a factor of two. Consequently, the vascular blood and the coelomic fluid also have different sulphide-binding capacities. These differences in sulphide-binding capacity may have important ramifications for the physiology of this unusual animal.

Role of glycolysis in adenylate depletion and repletion during work and recovery in teleost white muscle

Abstract: Measurements of metabolite concentrations before and immediately after swimming of trout to exhaustion indicate that all three potential endogenous fuels of anaerobic metabolism [glycogen, phosphocreatine (PCr) and adenosine triphosphate (ATP)] are utilized during anaerobic white muscle work. Lactate, H+, creatine Pi, NH4+ and inosine monophosphate (IMP) are formed in the process. Glycolysis is considered to be functionally (if loosely) coupled to adenylate depletion by setting up conditions favouring AMP-deaminase-catalysed formation of IMP and NH3. During recovery under these experimental conditions, glycolysis appears to outcompete oxidative metabolism as an ADP acceptor; therefore, in this kind of white muscle, glycolysis is also linked to IMP reconversion to AMP and thus to adenylate replenishment. The net process generates H+, which is why ATP replenishment must be completed before PCr concentrations can be returned to pre-exercise values.

Hydric Conditions During Incubation Influence Locomotor Performance of Hatchling Snapping Turtles

Abstract: Locomotor performance of hatchling snapping turtles ( Chelydra serpentina ) was assessed while turtles were running on land and swimming in water. Hatchlings from eggs incubated on a relatively wet substrate were faster than hatchlings from eggs incubated on a drier medium, both in absolute distance and in body lengths moved per unit time. The superior performance of turtles from the wet substrate was not due to differences in hydration of tissues, because differences in performance persisted after turtles from both groups had been fully hydrated. The superior performance of turtles from the wet substrate may stem from a greater aerobic capacity, because these animals accumulated lactate more slowly during locomotion than did turtles from eggs incubated on the dry substrate. These observations may provide a physiological basis for the improved survival of larger hatchlings of many species of reptiles.

Immune reactivity in the nervous system: modulation of T-lymphocyte activation by glial cells.

Abstract: The vertebrate central nervous system (CNS) has been traditionally thought to be inaccessible for the passenger lymphocytes of the immune system. This does not seem to be the case: activated T-lymphocytes can readily cross the endothelial blood-brain barrier (BBB) and some glial cells, notably the astrocytes, seem to be programmed to act as most efficient and complex partners for antigen-specific T-lymphocytes. We used myelin basic protein (MBP) specific permanent rat T-lymphocyte lines as probes to assess the immune status of the CNS. These cells, upon activation in vitro, are able to transfer lethal, experimentally induced autoimmune-encephalomyelitis (EAE) to normal syngeneic recipients. Activated T-lymphocytes, but not resting ones, can break through the BBB irrespective of their antigen specificity. Immune surveillance of the CNS thus seems to be executed by activated T-lymphocytes. Having crossed the BBB, the activated T-cells interact with local glial cells by releasing factors, including interferon-gamma, which induced astrocytes to synthesize and express, on their membranes, class II major histocompatibility antigens (Ia determinants), which are critically required for immunogenic presentation of antigens to T-cells. Indeed, Ia-induced astrocytes of the CNS (and the Schwann cells of peripheral nerves) are efficient antigen presenter cells, which are able strongly to up-regulate antigen-reactive T-lymphocytes. In addition, it has recently been shown that at least some astrocytes are able to down-regulate immune cells. Some, but not all, astrocytes are capable of suppressing activation of T-cells. This suppression can be modulated by interferon-gamma, and is sensitive to irradiation. The question of whether suppression is mediated by direct cell-to-cell contact or via soluble mediators (e.g. apolipoprotein E) is under investigation. Astrocytes have been found to be most subtle regulators of immuno-competent T-cells. Most probably they are centrally involved in physiological immune reactivity of the CNS, and it will be tempting to learn how far glial cells are involved in transmitting regulatory signals between the immune and nervous systems.

Regulation of blood oxygen transport and red cell pHi after exhaustive activity in rainbow trout (Salmo gairdneri) and starry flounder (Platichthys stellatus)

Abstract: In vitro, exogenous adrenaline reduced the Bohr and Root shifts caused by elevated PaCO2 and depressed plasma pH in rainbow trout blood, but not in starry flounder blood. In vivo immediately after exercise, plasma adrenaline (Ad) and noradrenaline (NAd) increased about 12-fold in rainbow trout. Associated with this catecholamine mobilization was a significant haemoconcentration, red blood cell (RBC) swelling and a reduction in RBC [NTP]; the latter was larger than that explained by cell swelling alone, indicating metabolic degradation of nucleoside triphosphate (NTP). RBC intracellular pH (pHi) fell only slightly after exercise (0.07 units) at 0 h, but was restored by 0.5 h in the face of a large plasma acidosis (0.4 units). [O2]/[Hb] fell significantly, but this decline may have been due in part to the significant reduction in PaO2. The reduction in [O2]/[Hb] was less than predicted from in vitro O2-dissociation curves at low (0.5 nmol l-1) catecholamine levels, but similar to that predicted at high (90 nmol l-1) catecholamine levels. In flounder, resting Ad and NAd levels were about 10 times those in trout and did not change significantly after exercise. As a consequence, there was no reduction in RBC [NTP], and RBC pHi fell significantly (0.10 units) after exercise in the face of a large plasma acidosis (0.4 units) and remained depressed until 4 h, although RBC swelling did occur. These factors in addition to the increased PaCO2 may have contributed to the reduction in arterial [O2]/[Hb], in the face of a constant PaO2. However, [O2]/[Hb] was restored to resting levels prior to the correction of RBC pHi and PaCO2. This, in conjunction with the observation that catecholamines did not affect the in vitro blood--O2 dissociation curve, suggests that additional factors may be involved in regulating O2 transport after exercise in flounder.

Selective and Reversible Blocking of the Lateral Line in Freshwater Fish

Abstract: Fish possess two separate systems for detection of low-level sound and water motions in the low-frequency range: the inner ear and the lateral line. The relative roles of these systems in normal fish behaviour is still not clear. There is, for instance, a lack of experimental evidence showing the involvement of the lateral line and the inner ear in detection of infrasound, in directional hearing in the near field, and in detection and attack of swimming prey below the surface. To provide a useful tool for such studies, we have developed a pharmacological method for selective and reversible blocking of the lateral line in the roach ( Rutilus rutilus ). By recording multi-unit activity from the lateral line nerve and microphonic potentials from the inner ear, we have shown that cobalt ions in the external water may completely block the mechanosensitivity of the lateral line without affecting the utricular microphonic activity. This inhibiting effect of Co 2+ is antagonized by Ca 2+ , making the ratio between these ions the important blocking factor. For practical work, we recommend 12–24h exposure to 0.1 mmol 1 −1 Co 2+ at a Ca 2+ concentration of less than 0.1 mmol 1 −1 . The fish showed no sign of general behavioural disorders even after 1 week in this solution, and the microphonic sensitivity of the inner ear was not reduced. The blocking effect of Co 2+ was clearly reversible, and the recovery was dependent upon both the duration of the Co 2+ exposure and the Ca 2+ concentration of the recovery solution.

Sensory Feedback During Active Movements of Stick Insects

Abstract: In the stick insect Carausius momsus, the role of the chordotonal organ was investigated using a new experimental arrangement which artificially closes the femur-tibia control system. The chordotonal organ was stimulated during voluntary movements by applying trapezoidal ramp stimuli in the closed-loop configuration. The results demonstrate that the feedback loop is used to control the end points of joint movement. In addition, it was found that the control system counteracts experimentally applied velocity changes imposed during the middle part of the movements. Acceleration-sensitive units are shown to contribute to the reaction. The results show that during active voluntary movements reflexes measured in the inactive animal are neither simply incorporated in a servo-system nor suppressed. Instead their characteristics are altered so that the voluntary movements are executed as intended by the animal. Thus reflexes cannot be considered as a fixed behavioural unit; rather their changing role must be analysed in the context of the behaviour studied.

Stretch Activation of a K+ Channel in Molluscan Heart Cells

Abstract: Heart ventricle cells of Lymnaea stagnalis contain a stretch-activated K + channel which exhibits two open states and three closed states. Over the range 0 to −25 mmHg (1 mmHg = 133.3 Pa), the probability that the channel is open is a steeply non-linear function of negative pressure. Pressure-dependent decreases in the mean times of the longest component of the closed-time distribution are observed in the same range and (because other mean times show no consistent or sufficiently large changes with pressure) are assumed to account for increases in the probability of being open. Channel activity characteristically occurs as bursts with a mean time of 3.6 ms. These bursts contain, on average, 1.7 closings; 78 % of the burst time is spent in the open state. It is concluded that the stretch-sensitive kinetic component is an interburst closed state. Note: To whom reprint requests should be sent.

The Physiology of Compensation by Locusts for Changes in Dietary Protein

Abstract: SUMMARY 1. Previous work has demonstrated that fifth-instar nymphs of Locusta migratoria L. respond to differences in levels of dietary protein by altering intermeal interval but not meal size (Simpson & Abisgold, 1985): insects fed a diet with 14% protein (p) eat the same sized meals more frequently than those fed a diet with 28% protein (P). The physiological basis for this compensatory response is investigated. 2. Insects fed the P-diet had a significantly larger increase in blood osmolality during and after a meal than did those fed the p-diet. 3. Unexpectedly, this difference in blood osmolality did not result in a variation in the rate at which the fore-, mid- and hindgut emptied. Therefore a change in the rate of decline in negative feedback from gut stretch receptors does not underlie the alteration in interfeed interval. 4. 40% of the difference in blood osmolality between p- and P-fed insects was attributable to changes in the blood concentration of free amino acids. Of the 16 free amino acids found, 11 occurred in significantly higher concentrations in the blood of P-fed insects. 5. There was no significant difference in the polypeptide and protein content of the blood of insects fed the p- or P-diet. 6. Increasing either blood osmolality or free amino acid concentration by injection delayed the next meal:injections that increased both had the greatest effect. 7. A mechanism is discussed whereby both blood osmolality and the concentration of various free amino acids regulate the time between meals, and thus compensatory feeding in response to changes in dietary protein.

A Comparative Study of the Flight Mechanism of Diptera

Abstract: 1. 1. The mechanism of dipteran flight has been investigated in a comparative study involving thorax manipulation, analysis of high-speed films and direct observation of tethered flies under stroboscopic illumination. 2. 2. The click action observed in CCl4-anaesthetized Calliphora was found to be due to an interaction between the radial stop and the pleural wing process at the top of the upstroke. The movements occurring during unanaesthetized tethered flight were quite different as these structures were vertically separated except towards the bottom of the downstroke (Miyan & Ewing, 1985 a,b ). 3. 3. Results of observations on tethered insect flight and on morphology did not give full support to either the click mechanism (Boettiger & Furshpan, 1952) or the model of Miyan & Ewing. 4. 4. A novel model for the wingbeat is proposed. Distortion of the thorax brought about by the flight muscles results in upward and outward movement of the lateral scutum during the downstroke and inward and downward movement during the upstroke. In more advanced flies flexion lines result in a differentiated scutellar lever and parascutal shelf. Distortion is thereby limited largely to the posterior scutum. The parascutal shelf moves as a part of the scutal distortion, not as an independent element in the articulation, and the system is not bistable. 5. 5. The automatic changes in angle of attack are caused by inertial and aerodynamic forces acting around the torsional axis of the wing during the beat, which twist the compliant wing base.

Branchial and Antennal Gland Na+/K+- Dependent ATPase and Carbonic Anhydrase Activity During Salinity Acclimation of the Euryhaline Crayfish Pacifastacus Leniusculus

Abstract: Haemolymph and urine electrolyte status and branchial and antennal gland activities of Na+/K+-ATPase and carbonic anhydrase (CA) were determined in the crayfish Padfastacus leniusculus after 3 weeks acclimation in fresh water (FW) and 350 and 750mosmolkg−1 sea water (SW). In FW the crayfish maintained haemolymph osmolality around 370 mosmol kg−1 due to hyperionic regulation of the major electrolytes. Involved in this are ion uptake mechanisms situated on the gills, and mechanisms of ion reabsorption from the primary urinary filtrate in the antennal gland (AG). Both of these processes are associated with high activities of Na+/K+- ATPase and CA. The two enzymes are uniformly distributed on gill sets 2–7, unlike the situation in euryhaline marine species. Additionally, activity levels of both enzymes are extremely high in the AG and can be correlated with the ability to produce a hypo-osmotic urine. In comparison, enzyme activity is negligible in marine species which produce isosmotic urine. Crayfish continued to hyperosmoregulate in 350 mosmolkg−1 SW. High levels of Na+/K+-ATPase confirmed the presence of a component active in the uptake of major electrolytes in the gills and also in the AG, where ion reabsorption persisted. In 750 mosmolkg−1 SW crayfish became isosmotic. Since ATPase is regulated chiefly by deactivation/activation of pre-existing enzyme, overall activity was mostly unchanged. CA activity was significantly reduced in both 350 and 750 mosmol kg−1 SW and correlated with the transition from osmoregulation to osmoconformity, suggesting that it is regulated primarily by deinduction/induction of new enzyme. The difference in the mechanism of regulation exhibited by these two enzymes is believed to relate to their subcellular distribution.

The Tuned Singing Burrow of Mole Crickets

Abstract: During burrow digging by the mole cricket Scapteriscus acletus Rehn and Hubbard, the burrow is enlarged and shaped in a series of digging cycles, each lasting 1–2min, and song chirps are produced after every cycle. The song becomes up to 18 dB louder and acoustically purer during burrow building. The shape of the song pulse envelope changes so that its average power density becomes greater and its build-up and decay become more gradual. The forewings show a single resonance of the harp (Cu 1 cell) regions at 2.5-3.0 kHz: the normal song carrier frequency is 2.5-2.7kHz. Removal of the outer parts of the forewings does not affect the radiated sound power. The singing burrow has an exponential horn opening at the soil surface and an internal bulb. The calculated cut-off frequency of the horn is 1–34 kHz and that of the first resonance is 2.5-2.7 kHz. The volume of the bulb is close to that required to tune the throat: obliteration of the burrow bulb causes a substantial decrease in the radiated sound pressure levels before singing ceases. The horn mouth acts as a finite sound source, with large acoustic reactance. The acoustics of the burrow were measured with a small doublet source inserted at the position at which the cricket sings. At this position, the burrow resonates at 2.75-3 kHz, with a quality factor (Q), measured both by the - 3 dB bandwidth and by the build-up and decay of tone bursts, of 2.5-2.7. The sound pressure produced by the doublet source is up to 24 dB louder when it is in the burrow than when it is in free air. Further in or out from the insect9s singing position, the effective gain of the burrow is reduced and other resonances and anti-resonances are observed. Obliteration of the burrow bulb reduces the effective gain of the burrow by 6–10 dB and the burrow ceases to resonate at 2.75 kHz. It is proposed that the tuned burrow acts as a resistive load on the vibrating harps, so allowing good coupling between the small wings and the surrounding medium while allowing a pure carrier frequency to be radiated.

Mechanisms of function of neural grafts in the adult mammalian brain.

Abstract: Evidence for the survival, growth and function of grafted neural tissues in the adult mammalian brain is reviewed. In addition to considering the viability of grafts in the different model systems that have been investigated, consideration is given to alternative mechanisms by which the grafts might exert a functional influence over the host brain and the host animal9s behaviour: (a) acute influence over spontaneous recovery of function, (b) chronic but diffuse secretion of neurochemicals into the host neuropile, (c) tonic reinnervation of the host brain, (d) bridging grafts, and (e) reciprocal reinnervation and full incorporation of graft tissue into host circuitry. It is concluded that no one mechanism is primary, but that different levels of reorganization can take place in different graft paradigms and neural systems.

Compensation of Progressive Hypercapnia in Channel Catfish and Blue Crabs

Abstract: Channel catfish ( Ictalurus punctatus Rafinesque) were progressively acclimated to CO2 partial pressures of 7.5, 15, 30, 45 and 58 mmHg (1, 2, 4, 6 and 8% CO2 in air) and blue crabs ( Callinectes sapidus Rathbun) to 15, 30 and 45 mmHg, with 24 h at each partial pressure. Measurements of both conventional acid-base parameters (pH, PCO2. total CO2) and ‘strong’ ion concentrations (Na+, K+, Mg2+, Ca2+ and Cl−) were made at various times during each treatment. Intracellular [Na+], [K+] and [Cl−] were determined for red and white muscle in control and hypercapnic (8%) catfish. Extracellular [HCO3−] and strong ion difference (SID) both rose during hypercapnic compensation, with correlation coefficients ( r ) of 0.97 ( P <0.01) for catfish and 0.41 (NS) for blue crabs. Since [HCO3−] is calculated from two rapid measurements, and SID from four separate procedures, the former appears to be the measurement of choice. The results also dispel the notion of a 30 mequiv1−1 upper limit to bicarbonate compensation: [HCO3−] values over 50mequiv1−1 were achieved in both animals, and %pH regulation remained around 70% at the highest PCO2 Due to superior intracellular buffering, the large change in extracellular SID did not lead to a measurable change in the concentrations of the major intracellular ions. The primary gill filaments of hypercapnic catfish showed a 30% increase in numbers and a 75% increase in area of apical crypts of chloride cells. The chloride cell ‘patches’ in crab gills increased in staining density after hypercapnia but did not enlarge. Note: Present address: Department of Biology, Dalhousie University, Halifax, NS, Canada B3H4JI.

Temperature affects the diffusion of small molecules through cytosol of fish muscle

Abstract: Undiluted cytosolic extracts were prepared from fast glycolytic muscle tissue of white perch (Morone americanus). Diffusion coefficients (D) through the cytosol preparations were estimated in vitro for a series of selected low molecular weight compounds using an experimental diffusion chamber. Determinations were made at 5 degrees and 25 degrees C to assess thermal sensitivity of the process. Non-metabolizable analogues of naturally occurring compounds were employed to avoid chemical alteration of solutes by the catalytically competent preparations during diffusion experiments. Kinematic viscosity of cytosolic extracts, which is a major determinant of diffusive resistance, increases from 2.94 +/- 0.06 to 5.35 +/- 0.02 X 10(-2) cm2 s-1 between temperatures of 25 degrees and 5 degrees C (Q10 = 1.35 +/- 0.01). The diffusion coefficients (D) of D-lactic acid are 2.26 +/- 0.84 and 0.79 +/- 0.15 X 10(-6) cm2s-1 at 25 degrees and 5 degrees C, respectively (Q10 = 1.84 +/- 0.36). The D values of 2-deoxyglucose are 2.87 +/- 1.01 and 1.22 +/- 0.36 X 10(-6) cm2s-1 at 25 degrees and 5 degrees C (Q10 = 1.75 +/- 0.54). The D values of Ca2+ are 2.47 +/- 0.28 and 1.09 +/- 0.36 X 10(-6) cm2s-1 at 25 degrees and 5 degrees C (Q10 = 2.04 +/- 0.36). The D values for the ATP analogue, AMP-PNP, are 0.87 +/- 0.33 and 0.81 +/- 0.15 X 10(-6) cm2s-1 at 25 degrees and 5 degrees C (Q10 = 0.98 +/- 0.12). AMP-PNP is the only compound tested which did not show significant thermal sensitivity of diffusion. Recently reported changes in muscle cell ultrastructure induced by temperature acclimation of fishes may serve to counteract the effect of temperature change on diffusion of key small molecules through the aqueous cytoplasm, thus maintaining flux rates between cellular compartments. These mechanisms may be of considerable import in achieving relative temperature independence of cellular function that is characteristic of many eurythermal aquatic animals.

Gliding Birds: The Effect of Variable Wing Span

Abstract: SUMMARY 1. The equilibrium gliding performance of a bird is described by the relationship between sinking speed (VB) and air speed (V). When V3 is plotted against V, the points fall in a 'performance area' because the wing span is changed during gliding. 2. The lowest V, for each V in the performance area defines a 'maximum performance curve'. This curve can be predicted by a mathematical model that changes the wing span, area and profile drag coefficient (Crj,rr) of a hypothetical bird to minimize drag. The model can be evaluated for a particular species given (a) a linear function relating wing area to wing span, and (b) a 'polar curve' that relates C Dp r and the lift coefficient (CL) of the wings. 3. For rigid wings, a single polar curve relates C Dp r to CL values at a given Reynolds number. The position and shape of the polar curve depend on the aerofoil section of the wing and the Reynolds number. In contrast, the adjustable wings of a laggar falcon (Falco jugger) and a black vulture (Coragyps atratus) gliding in a wind tunnel have CL, and CD pr values that fall in a 'polar area' rather than on a curve. The minimum values of CD pr at each CL bound the polar area and define a polar curve that is suitable for evaluating the model. 4. Although the falcon and the vulture have wings that are markedly different in appearance, the data for either bird are enclosed by the same polar area, and fitted by the same polar curve for minimum Co,pr at each CL value. This curve is a composite of the polar curves for rigid wings with aerofoils similar to those found in avian wings. These observations suggest that the polar curves of other gliding birds may be similar to that of the falcon and the vulture. 5. Other polar curves are defined by CL and CD pr values for the falcon and the vulture gliding at a constant speed but at different glide angles. Each speed has a different polar curve; but for a given speed, the same polar curve fits the data for either bird. 6. The falcon and the vulture gliding in the wind tunnel at a given speed were found to increase their drag by decreasing their wing span. This change increases induced drag and probably increases CD pr for the inner parts of the wing because of an unusual property of bird-like aerofoil sections: wings with such sections have minimum values of C Dp r at CL values near 1, while conventional wings have minimum values of CotPr at CL values near 0.

Excitatory Actions of Antho-RFamide, An Anthozoan Neuropeptide, on Muscles and Conducting Systems in the Sea Anemone Calliactis Parasitica

Abstract: SUMMARY In the sea anemone Calliactis parasitica endodermal application of the anthozoan neuropeptide Antho-RFamide (

Turning flight of bats.

Abstract: The turning flight of six microchiropteran bat species is described. The bats' abilities to turn tightly were determined by their abilities to fly slowly and to generate high lateral accelerations. Rhinolophus ferrumequinum developed high lateral accelerations by flapping its banked wings while flying at very low speed. Plecotus auritus turned at relatively low speed and at low lateral acceleration. The other species were all moving fast as they turned and generated lateral accelerations either by developing high bank angles or by flapping their wings with low bank angles. There was a significant correlation between wing loading and turning curvature, indicating that low wing loadings improve manoeuvrability.

The efficiency of sound production in two cricket species, gryllotalpa australis and teleogryllus commodus (orthoptera: grylloidea)

Abstract: 1. Males of Gryllotalpa australis (Erichson) (Gryllotalpidae) and Teleogryllus commodus (Walter) (Gryllidae) produced their calling songs while confined in respirometers. 2.G. australis males used oxygen during calling at a mean rate of 4.637 ml O2 h−1, equivalent to 27.65 mW of metabolic energy, which was 13 times higher than the resting metabolic rate. T. commodus males used oxygen during calling at a rate of 0.728 ml O2 h−1, equivalent to 4.34 mW, which was four times the resting metabolic rate. 3. The sound field during calling by males represents a sound power output of 0.27 mW for G. australis and l.51 × l0.3 mW for T. commodus. 4. The efficiency of sound production was 1.05% for males of G. australis and 0.05% for males of T. commodus. Comparison with other insect species suggests that none is more than a few percent efficient in sound production.

The actions of FMRFamide-like peptides on visceral and somatic muscles of the snail Helix aspersa.

Abstract: Phe-Met-Arg-Phe-NH2 (FMRFamide) and pyroGlu-Asp-Pro-Phe-Leu-Arg-Phe-NH2 (pQDPFLRFamide) occur in the ganglia and tissues of the snail, Helix aspersa. This report describes the effects of these two neuropeptides on five visceral organs or somatic muscles isolated from the snail (Table 1). The epiphallus, as well as the rest of the male reproductive tract, was contracted by both FMRFamide and pQDPFLRFamide, and the threshold was usually below 5 X 10(-9) mol l-1 (Fig. 1). Both peptides also reduced the resting tone of the crop and decreased the force and frequency of its rhythmic activity; FMRFamide is about 10 times more potent (Fig. 4). In contrast, pQDPFLRFamide was about 100 times more potent than FMRFamide as a cardioexcitatory agent (Fig. 5). The actions of the peptides on the pharyngeal and tentacle retractor muscles were markedly different: FMRFamide primarily contracted these muscles; and pQDPFLRFamide usually had no effect alone, but relaxed or diminished contractions induced by FMRFamide and acetylcholine (ACh) (Figs 6, 8, 9). Other analogues of FMRFamide were tested, but none was as effective a relaxing agent as pQDPFLRFamide. The effects of FMRFamide and pQDPFLRFamide on all of the preparations could be distinguished from those produced by ACh and 5-hydroxytryptamine (5-HT); thus the actions of the neuropeptides were not mediated by cholinergic or serotonergic neurones. The stimulation of the musculature in the male reproductive tract and the inhibition of motility of the digestive system by FMRFamide and pQDPFLRFamide implicate these peptides in the control of reproductive behaviour. The effectiveness of pQDPFLRFamide in relaxing the retractor muscles and as a cardioexcitatory agent led to the hypothesis that this heptapeptide and FMRFamide, acting at distinct receptors, cooperate to regulate the excitability and contractility of the snail's musculature between the extremes of aestivation and active locomotion.