bluuebunny/crossref_metadata_2025 huggingface dataset:
Field estimates of body drag coefficient on the basis of dives in passerine birds
Authors: Hedenström Anders , Liechti Felix
Published: April 2021

During forward flight, a bird’s body generates drag that tends to decelerate its speed. By flapping its wings, or by converting potential energy into work if gliding, the bird produces both lift and thrust to balance the pull of gravity and drag. In flight mechanics, a dimensionless number, the body drag coefficient (CD,par), describes the magnitude of the drag caused by the body. The drag coefficient depends on the shape (or streamlining), the surface texture of the body and the Reynolds number. It is an important variable when using flight mechanical models to estimate the potential migratory flight range and characteristic flight speeds of birds. Previous wind tunnel measurements on dead, frozen bird bodies indicated that CD,par is 0.4 for small birds, while large birds should have lower values of approximately 0.2. More recent studies of a few birds flying in a wind tunnel suggested that previous values probably overestimated CD,par.

We measured maximum dive speeds of passerine birds during the spring migration across the western Mediterranean. When the birds reach their top speed, the pull of gravity should balance the drag of the body (and wings), giving us an opportunity to estimate CD,par. Our results indicate that CD,par decreases with increasing Reynolds number within the range 0.17–0.77, with a mean CD,par of 0.37 for small passerines. A somewhat lower mean value could not be excluded because diving birds may control their speed below the theoretical maximum. Our measurements therefore support the notion that 0.4 (the ‘old’ default value) is a realistic value of CD,par for small passerines.
Maximum cold-induced food consumption in mice selected for high locomotor activity: implications for the evolution of endotherm energy budgets
Authors: Koteja Paweł , Swallow John G. , Carter Patrick A. , Garland Theodore
Published: April 2021

We studied house mice (Mus domesticus) that had been artificially selected for high activity to test the hypothesis that a high capacity for energy assimilation in cold-exposed endotherms could evolve as a correlated response to selection for increased locomotor activity. After 10 generations of selection for increased voluntary wheel-running, mice from four selected lines ran 75 % more wheel revolutions per day than did mice from four random-bred, control lines. The maximum cold-induced rates of food consumption (Cmax; mean 10.6 g day−1 ) and energy assimilation (Amax; mean 141 kJ day−1 ) were not significantly higher in the selected than in the control mice. However, in cold-exposure trials, mice from the selected lines maintained body mass better than did mice from the control lines. Cmax and Amax were positively correlated with the amount of wheel-running activity measured before cold-exposure and also with the rates of food consumption measured when the mice had access to running wheels. In females at least, the correlation was significant not only among individuals but also among adjusted means of the replicate lines, which suggests the presence of a positive genetic correlation between the traits. Thus, despite the lack of a significant difference between the selected and control lines in maximum rate of food consumption, the remaining results conform to the hypothesis that a selection for increased locomotor activity could be a factor behind the evolution of the ability to sustain activity and maintain energy balance during prolonged cold-exposure, as occurred during the evolution of mammalian and avian endothermy.
Regional effects of voluntary exercise on cell size and contraction-frequency responses in rat cardiac myocytes
Authors: Natali A. J. , Turner D. L. , Harrison S. M. , White E.
Published: April 2021

A model of voluntary exercise, in which rats are given free access to a running wheel over a 14-week period, led to left ventricular hypertrophy. To test whether the hypertrophic response to exercise was uniformly distributed across the ventricular wall, single ventricular myocytes were isolated from the sub-epicardium (EPI) and sub-endocardium (ENDO) of exercised rats and from sedentary rats for comparison. Cellular hypertrophy (approximately 20 % greater cell volume) was seen in ENDO cells from exercised animals, but no significant changes were observed in EPI cells when compared with sedentary controls. This regional effect of exercise may be a response to transmural changes in ventricular wall stress and/or strain.

Cell contraction was measured as cell shortening in ENDO and EPI cells at stimulation frequencies between 1 and 9 Hz at 37 °C. Exercise training had no effect on cell shortening. Positive and negative contraction–frequency relationships (CFRs) were found in both EPI and ENDO cells between 1 and 5 Hz; at higher frequencies (5–9 Hz), all myocytes displayed a negative CFR. The CFR of a myocyte was, therefore, independent of regional origin and unaffected by exercise. These results suggest that, in vivo, the rat heart displays a negative CFR. We conclude that increased cell size may be a more important adaptive response to exercise than a modification of excitation– contraction coupling.
Effects of season on kidney morphology in house sparrows
Authors: Casotti Giovanni
Published: April 2021

Seasonal variability in kidney morphology of the house sparrow Passer domesticus was examined using light microscopy. Sparrows were captured from the wild in winter, spring, summer and autumn. The kidneys were perfused with half-strength Karnovsky’s fixative and processed for light microscopy by embedding in either paraffin wax or JB4 acrylic resin. Absolute volumes of the kidneys, their components (cortex, medulla and blood vessels), components of the nephron (renal corpuscles, proximal tubules, loops of Henle, distal tubules and collecting ducts) and the capillaries surrounding the nephron were quantified using stereology. Tissue processed in paraffin wax had a mean shrinkage of 17.7 % compared with 10.1 % in JB4 resin. Absolute volumes of the kidneys and nephrons were compared statistically between tissue processing methods and among seasons. Absolute volumes of the structures within the kidneys were not significantly different between treatments or among seasons. Within the nephron, the only measured variables to show significant differences were the absolute volumes of the distal tubules and cortical collecting ducts between tissue processing treatments. Thus, kidney morphology was relatively unaffected by changes in season. In addition, the results show that embedding tissue using acrylic resin causes less shrinkage, and it should therefore be the preferred embedding medium for quantitative morphologists.
Strike feeding behavior in the muskellunge, Esox masquinongy: contributions of the lateral line and visual sensory systems
Authors: New John G. , Fewkes Lisa Alborg , Khan Asma N.
Published: April 2021

The muskellunge, Esox masquinongy, is a predatory esocid fish with well-developed visual and lateral line systems. The purpose of this study was to determine the relative roles of these two sensory modalities in organizing the strike behavior of the animal. Subadult muskellunge were videotaped in a test arena while feeding on fathead minnows (Pimephales promelas). Animals were tested under five conditions: (i) control animals in which the visual and lateral line systems were intact; (ii) animals with lateral line afference suppressed by immersion for 12–24 h in 0.1 mmol l−1 CoCl2; (iii) animals blinded by bilateral optic nerve transection; (iv) animals that had been unilaterally blinded; and (v) animals in which the lateral line system had been unilaterally denervated.

The feeding behavior of the muskellunge consists of two phases: a slow stalk of the prey with minimal body movement followed by an explosive C-or S-start lunge at the prey. Quantitative comparisons of animals in the five test groups indicate that, although vision is used in the initial acquisition of the prey, both vision and the lateral line system play important roles in determining the initiation of the rapid strike. The lateral line system may play a critical role in the final capture of the prey at the end of the strike. In addition, lateral-line-suppressed muskellunge strongly alter their approaches to more distant prey. Bilaterally blinded muskellunge do not stalk their prey, but will lunge only at prey that are at close range. Unilaterally blinded or denervated muskellunge also alter their detection of and approach to prey, attending to a wider region of the intact sensory hemisphere.

Our data suggest not only that the visual and lateral line systems play complementary roles in the feeding behavior sequence but also that each system plays a more or less dominant role during consecutive phases of the behavior.
Opposing actions of nitric oxide on synaptic inputs of identified interneurones in the central nervous system of the crayfish
Authors: Aonuma Hitoshi , Newland Philip L.
Published: April 2021

Little is known of the action of nitric oxide (NO) at the synaptic level on identified interneurones in local circuits that process mechanosensory signals. Here, we examine the action of NO in the terminal abdominal ganglion of the crayfish Pacifastacus leniusculus, where it has modulatory effects on the synaptic inputs of 17 identified ascending interneurones mediated by electrical stimulation of a sensory nerve. To analyse the role of NO in the processing of sensory signals, we bath-applied the NO donor SNAP, the NO scavenger PTIO, the nitric oxide synthase (NOS) inhibitor L-NAME, the NOS substrate L-arginine, a cyclic GMP (cGMP) analogue, 8-Br-cGMP, and the soluble guanylate cyclase (sGC) inhibitor ODQ. The effects of these chemicals on the synaptic inputs of the interneurones could be divided into two distinct classes. The NO donor SNAP enhanced the inputs to one class of interneurone (class 1) and depressed those to another (class 2). Neither the inactive isomer NAP nor degassed SNAP had any effect on the inputs to these same classes of interneurone. The NO scavenger PTIO caused the opposite effects to those of the NO donor SNAP, indicating that endogenous NO may have an action in local circuits. Preventing the synthesis of NO using L-NAME had the opposite effect to that of SNAP on each response class of interneurone. Increasing the synthesis of endogenous NO by applying L-arginine led to effects on both response classes of interneurone similar to those of SNAP. Taken together, these results suggested that NO was the active component in mediating the changes in amplitude of the excitatory postsynaptic potentials. Finally, the effects of 8-Br-cGMP were similar to those of the NO donor, indicating the possible involvement of a NO-sensitive guanylate cyclase. This was confirmed by preventing the synthesis of cGMP by sGC using ODQ, which caused the opposite effects to those of 8-Br-cGMP on the two response classes of interneurone. The results indicate that a NO–cGMP signal transduction pathway, in which NO regulates transmitter release from mechanosensory afferents onto intersegmental ascending interneurones, is probably present in the local circuits of the crayfish.
A study of helical and planar waves on sea urchin sperm flagella, with a theory of how they are generated
Authors: Woolley D. M. , Vernon G. G.
Published: April 2021

When the spermatozoon of Echinus esculentus swims in sea water containing methyl cellulose (viscosity 1.5–4 Pa s), its flagellum may generate either a helical or a planar waveform, each type being stable. The helical wave, which is dextral, is complicated by the concurrent passage of miniature waves along it. These miniature waves have a pulsatile origin in the neck region of the spermatozoon. Our videotape analysis indicates that there are two pulses of mechanical activity for each true cycle of the helical wave. (The true helical frequency was obtained from the apparent wave frequency and the roll frequency of the sperm head, the latter being detectable in some sperm when lit stroboscopically.) The planar wave has a meander shape. During the propagation of planar waves, the sliding displacements are adjustable in either direction; moribund flagella can undergo unrestricted sliding. The planar waves are, in fact, exactly planar only at interfaces. Otherwise, there tend to be torsions in the interbend segments between planar bends. Mechanical stimulation of the flagellum can cause a sudden transition from the helical to the planar waveform. To account for the two modes of beating, we advance the hypothesis that circumferential linkages yield beyond a threshold strain. Whether this yield point is exceeded, we suggest, depends upon the balance between the active shear force and the external viscosity (among other factors). We propose that a subthreshold force originates in one array and then triggers the other dynein arrays circumferentially, but unidirectionally, around the base of the flagellum; whereas a suprathreshold force provokes bi-directional circumferential triggering. These may be the two patterns of activation that result in helical and planar waveforms, respectively. The transition from helical to planar bending may result from an increment in the force produced by the dynein motors. The pulsatile origin of the helical wave resembles behaviour described previously for spermatozoa of Ciona intestinalis and of the quail Coturnix coturnix.
Consequences of transient fluid forces for compliant benthic organisms
Authors: Gaylord Brian , Hale Benjamin B. , Denny Mark W.
Published: April 2021

The diversity of form among benthic marine plants and animals on rocky coasts is remarkable. Stiff and strong organisms grow alongside others that are compliant and flimsy. Given the severity of wave action on many shores and thus the potential for the imposition of large hydrodynamic forces, this immediately raises the question of how, from this overall spectrum of designs, flexible and weak organisms survive. A number of explanations have been proposed, most emphasizing one or more of several possible advantages of deformability. Here, we explore quantitatively two of the more common of these explanations: (i) that strength can be traded against extensibility in allowing stretchy organisms to withstand transient wave forces, and (ii) that greater compliance (and thus longer organism response times) allows universally for the amelioration of brief loads. We find that, although these explanations contain kernels of validity and are accurate for a subset of conditions, they are not as general as has often been assumed.
Seasonal hypothermia in a large migrating bird: saving energy for fat deposition?
Authors: Butler P. J. , Woakes A. J.
Published: April 2021

We have tested the hypothesis that a large (2 kg) migratory bird, such as the barnacle goose Branta leucopsis, becomes hypothermic before its autumn migration, when food is not scarce, but when it is necessary to conserve and/or store energy in the form of fat. Abdominal temperature (Tab) was measured in wild geese using an implanted data logger. Commencing a few days before and continuing until approximately 20 days after the start of their autumn migration, mean daily Tab fell progressively by 4.4 °C. Thus, it is suggested that, rather than increasing the rate of pre-migratory fattening, the energy saved as a result of this hypothermia reduces the rate at which fat is used and thus enables its more rapid replacement following and, possibly during, migration. The energy saved may also be used for the replacement of non-fat tissues such as the locomotory muscles and gastro-intestinal tract. These observations are the first of their kind from birds in their natural environment and, together with other data, demonstrate that hypothermia in endotherms is not necessarily related to extremely low environmental temperature, to shortage of food or to the resting phase of the daily cycle. The data also highlight the relationship between hypothermia and fat deposition over extended periods in relatively large, endothermic animals and may have some relevance to obesity in humans.
Scale effects on the attachment pads and friction forces in syrphid flies (Diptera, Syrphidae)
Authors: Gorb Stanislav , Gorb Elena , Kastner Victoria
Published: April 2021

To test the role of constructional and dimensional factors in the generation of friction force by systems of setose attachment pads, six species of syrphid fly (Platycheirus angustatus, Sphaerophoria scripta, Episyrphus balteatus, Eristalis tenax, Myathropa florea and Volucella pellucens) were studied using light and scanning electron microscopy. Flies were selected according to their various body mass and attachment pad dimensions. Such variables as pad area, setal density, the area of a single setal tip and body mass were individually measured. A centrifugal force tester, equipped with a fibre-optic sensor, was used to measure the friction forces of the pads on a smooth horizontal surface made of polyvinylchloride. Friction force, which is the resistance force of the insect mass against the sum of centrifugal and tangential forces, was greater in heavier insects such as Er. tenax, M. florea and V. pellucens. Although lighter species generated lower frictional forces, the acceleration required to detach an insect was greater in smaller species. The area of attachment pads, setal tip area and setal density differed significantly in the species studied, and the dependence of these variables on body mass was significant.

The frictional properties of the material of the setal tips were not dependent on the dimensions of the fly species. Similar results were obtained for the frictional properties of the pulvillus as a whole. Thus, the properties of the secretion and the mechanical properties of the material of the setal tips are approximately constant among the species studied. It is concluded that differences in friction force must be related mainly to variations in the real contact area generated by the pad on the smooth surface. The real contact area can be estimated as the summed area of the broadened setal tips of the pad in contact with the surface. The real contact area depends on such morphological variables as setal density and the area of a single setal tip. Although individual variables vary among flies with different dimensions, they usually compensate such that smaller setal tip area is partially compensated for by higher setal density.
Ultrastructural design of anuran muscles used for call production in relation to the thermal environment of a species
Authors: Ressel Stephen J.
Published: April 2021

I examined the aerobic trunk muscles, which are used for call production, of male frogs from species that breed in different thermal environments to test the hypothesis that cold-adapted frogs should have fewer capillaries per unit mitochondrial volume in oxidative muscles than warm-adapted frogs because of reduced mitochondrial function at low temperatures. The species of interest were the cold-temperate Pseudacris crucifer and the warm-tropical Hyla microcephala in the family Hylidae, and the cold-temperate Rana sylvatica and the warm-temperate Rana clamitans in the family Ranidae. Trunk-muscle mitochondrial volume, VV(mt,f), was proportionally higher in species with higher mean calling rates (number of notes per hour), irrespective of the familial affinity of a species and the thermal environment in which it vocalized. Trunk-muscle capillary length density, JV(c,f), was significantly lower in P. crucifer than in H. microcephala because of significantly higher mean fiber area, a− (f). Conversely, trunk-muscle JV(c,f) was similar in the two ranid species. Using total capillary length, J(c), and total mitochondrial volume, V(mt,m), as a measure of maximal oxygen supply and demand, respectively, in trunk muscles, J(c)-to-V(mt,m) ratios were significantly lower in cold-adapted P. crucifer (4.3 km cm−3 ) and R. sylvatica (4.8 km cm−3 ) than in warm-adapted H. microcephala (7.1 km cm−3 ) and R. clamitans (6.4 km cm−3 ). In contrast, J(c)-to-V(mt,m) ratios in the more anaerobic gastrocnemius muscle of these species was not related to the thermal environment of a species, which may reflect capillaries conforming to microcirculatory functions, e.g. lactate removal, that take precedence over oxygen delivery. Mitochondrial cristae surface area, SV(im,mt), in P. crucifer trunk and gastrocnemius muscles (37.7±1.6 and 35.9±1.5 m2 cm−3 respectively) was, on average, similar to mammalian values, suggesting equivalent structural capacities of muscle mitochondria in these two taxa. Taken together, the present data suggest that trunk-muscle respiratory design may reflect a capillary supply commensurate with maximal levels of oxygen delivery set by mitochondria operating at different environmental temperatures. P. crucifer and H. microcephala trunk muscles were also characterized by a high lipid content, which contrasted with a near absence of trunk-muscle lipids in R. sylvatica and R. clamitans. The extraordinarily high lipid content of P. crucifer trunk muscles (26 % of muscle volume) may serve as an auxiliary oxygen pathway to mitochondria and thus compensate in part for this tissue’s reduced capillary/fiber interface. The effect of potentially high depletion rates of trunk-muscle lipid stores on metabolic rates of male frogs while calling is discussed.
Flexibility in flight behaviour of barn swallows (Hirundo rustica) and house martins (Delichon urbica) tested in a wind tunnel
Authors: Bruderer Lukas , Liechti Felix , Bilo Dietrich
Published: April 2021

The flight behaviour of barn swallows (Hirundo rustica) and house martins (Delichon urbica) was tested in a wind tunnel at 15 combinations of flight angles and speeds. In contrast to that of most other small passerines, the intermittent flight of hirundines rarely consists of regular patterns of flapping and rest phases. To vary mechanical power output, both species used intermittent flight, controlling the number of single, pulse-like wingbeats per unit time. House martins in descent tended to concentrate their wingbeats into bursts and performed true gliding flight during rest phases. Barn swallows mainly performed partial bounds during brief interruptions of upstrokes, which they progressively prolonged with decreasing flight angle. Thus, identification of distinct flapping phases to calculate wingbeat frequencies was not feasible. Instead, an effective wingbeat frequency for flight intervals of 20 s, including partial bounds, was introduced. The effective wingbeat frequencies of house martins (N=3) ranged from 2 to 10.5 s−1, those of barn swallows (N=4) from 2.5 to 8.5 s−1. In both hirundine species, effective wingbeat frequency was found to decrease almost linearly with decreasing flight angle. With changes in air speed, wingbeat frequency varied according to a U-shaped curve, suggesting a minimum power speed of roughly 9 m s−1. The duration of the down- and upstrokes varied systematically depending on flight angle and air speed.
Could osmotaxis explain the ability of blue petrels to return to their burrows at night?
Authors: Bonadonna Francesco , Spaggiari Jérôme , Weimerskirch Henri
Published: April 2021

Like many other species of petrel, blue petrel (Halobaena caerulea) are able to return to their nest burrows at night in complete darkness. Since petrels have a well-developed olfactory system, we carried out an experiment to test whether blue petrels use olfaction to localise their nest burrows. Incubating birds were injected intranasally with a zinc sulphate solution, which reversibly impairs the sensitivity of the olfactory mucosa; control birds were treated with physiological saline solution. None of the anosmic birds returned to their burrows, whereas all the birds treated with saline solution did. Our results suggest that olfactory cues are necessary for blue petrels to find their burrows.
High-frequency initial pulses do not affect efficiency in rat fast skeletal muscle
Authors: Abbate F. , De Ruiter C. J. , De Haan A.
Published: April 2021

This study investigated the effects of high-frequency initial pulses on the efficiency (=total work output/high-energy phosphate consumption) of rat fast skeletal muscle. In situ rat medial gastrocnemius muscles performed 15 repeated shortening contractions (2 s−1 ; velocity 50 mm s−1 ) with occluded blood flow while activated with triplets of 400 Hz followed by 60 Hz trains (T400;60) or with constant-frequency trains of either 60 or 91 Hz. All stimulation patterns consisted of six pulses. After the last contraction, the muscles were quickly freeze-clamped and analysed for metabolite levels. The calculated efficiencies were 20.4±3.0 mJ μmol−1 P (N=7), 19.4±1.8 mJ μmol−1 P (N=8) and 19.6±2.5 mJ μmol−1 P (N=7; means ± S.D.) for T400;60, 60 and 91 Hz stimulation respectively (P>0.05). It is concluded that, although high-frequency initial pulses can enhance muscle performance, the efficiency of rat fast skeletal muscle did not differ from that for submaximal constant-frequency stimulation patterns.
Regulation of Na+ transport across leech skin by peptide hormones and neurotransmitters
Authors: Milde Helga , Weber Wolf-Michael , Salzet Michel , Clauss Wolfgang
Published: April 2021

An increase in intracellular cyclic AMP concentration stimulates transepithelial Na+ transport across the skin of the leech Hirudo medicinalis, but it is unclear how cytosolic cyclic AMP levels are elevated in vivo. In search of this external stimulus, we performed Ussing chamber experiments to test several peptide hormones and neurotransmitters for their effect on Na+ transport across leech dorsal integument. Although all the peptide hormones under investigation significantly affected ion transport across leech integument, none of them mimicked the effect of an experimental rise in intracellular cyclic AMP level. The invertebrate peptides conopressin and angiotensin II amide inhibited short-circuit-current-(Isc) and amiloride-sensitive Na+ transport (Iamil), although to slightly different degrees. The vertebrate peptide hormones 8-arginine-vasopressin and 8-lysine-vasopressin both produced an inhibition of Iamil comparable with that caused by angiotensin II amide. However, 8-lysine-vasopressin reduced Isc, whereas 8-arginine-vasopressin induced a moderate increase in Isc. The neurotransmitter dopamine, which occurs in the leech central nervous system in relatively large amounts, and its precursor L-dopamine both induced large decreases in Isc and Iamil. However, the reactions evoked by the catecholamines showed no pronounced similarity to the effects of intracellular cyclic AMP. Two other neurotransmitters known to occur in leeches, serotonin (5-hydroxytryptamine) and γ-n-aminobutyric acid (GABA), had no influence on transepithelial ion transport in leech skin.
Hydrodynamic Drag of Diving Birds: Effects Of Body Size, Body Shape And Feathers At Steady Speeds
Authors: Lovvorn James R. , Liggins Geoffrey A. , Borstad Matthias H. , Calisal Sander M. , Mikkelsen Jon
Published: April 2021

For birds diving to depths where pressure has mostly reduced the buoyancy of air spaces, hydrodynamic drag is the main mechanical cost of steady swimming. Drag is strongly affected by body size and shape, so such differences among species should affect energy costs. Because flow around the body is complicated by the roughness and vibration of feathers, feathers must be considered in evaluating the effects of size and shape on drag. We investigated the effects of size, shape and feathers on the drag of avian divers ranging from wing-propelled auklets weighing 75 g to foot-propelled eiders weighing up to 2060 g. Laser scanning of body surfaces yielded digitized shapes that were averaged over several specimens per species and then used by a milling machine to cut foam models. These models were fitted with casts of the bill area, and their drag was compared with that of frozen specimens. Because of the roughness and vibration of the feathers, the drag of the frozen birds was 2–6 times that of the models. Plots of drag coefficient (CD) versus Reynolds number (Re) differed between the model and the frozen birds, with the pattern of difference varying with body shape. Thus, the drag of cast models or similar featherless shapes can differ both quantitatively and qualitatively from that of real birds. On the basis of a new towing method with no posts or stings that alter flow or angles of attack, the dimensionless CD/Re curves differed among a size gradient of five auklet species (75–100 g) with similar shapes. Thus, extrapolation of CD/Re curves among related species must be performed with caution. At lower speeds, the CD at a given Re was generally higher for long-necked birds that swim with their neck extended (cormorants, grebes, some ducks) than for birds that swim with their head retracted (penguins, alcids), but this trend was reversed at high speeds. Because swimming birds actually travel at a range of instantaneous speeds during oscillatory strokes, species variations in drag at different speeds must be considered in the context of accelerational stroking.
The Influence of Stimulus and Background Colour on Signal Visibility in the Lizard Anolis Cristatellus
Authors: Fleishman Leo J. , Persons Matthew
Published: April 2021

Anoline lizards communicate with visual displays in which they open and close a colourful throat fan called the dewlap. We used a visual fixation reflex as an assay to test the effects of stimulus versus background chromatic and brightness contrast on the probability of detecting a moving coloured (i.e. dewlap-like) stimulus in Anolis cristatellus. The probability of stimulus detection depended on two additive visual-system channels, one responding to brightness contrast and one responding to chromatic contrast, independent of brightness. The brightness channel was influenced only by wavelengths longer than 450 nm and probably received input only from middle- and/or long-wavelength photoreceptors. The chromatic contrast channel appeared to receive input from three, or possibly four, different classes of cone in the anoline retina, including one with peak sensitivity in the ultraviolet. We developed a multi-linear regression equation that described most of the results of this study to a reasonable degree of accuracy. In the future, this equation could be used to predict the relative visibility of different-coloured stimuli in different habitat light conditions, which should be very useful for testing hypotheses that attempt to relate habitat light conditions and visual-system response to the evolution of signal design.
The Guidance of Desert Ants by Extended Landmarks
Authors: Collett T. S. , Collett M. , Wehner R.
Published: April 2021

Desert ants (Cataglyphis fortis) were trained to follow a fixed route around a barrier to a feeder. Their homeward trajectories were recorded on a test field containing a similar barrier, oriented either as in training or rotated through 22 or 45 °. Under one set of experimental conditions, the homeward trajectories rotated with the orientation of the barrier, implying that the visual features of this extended landmark can determine the route independently of compass cues: the barrier provided a ‘visual scene’ that controlled the trajectories of the ants. Under other conditions, the trajectories after rotation were a compromise between the habitual compass direction and the direction with respect to the rotated barrier.

Trajectories were determined primarily by the visual scene when ants were allowed to return close to the nest before being caught and tested. The compromise trajectories were observed when ants were taken from the feeder. It seems that ants exhibit at least two separate learnt responses to the barrier: (i) a habitual compass direction triggered by the sight of the barrier and (ii) a visual scene direction that is compass-independent. We suggest that the weighting accorded to these different learnt responses changes with the state of the path integration system.
Changes in the Thoracic Temperature of Honeybees While Receiving Nectar From Foragers Collecting at Different Reward Rates
Authors: Farina Walter M. , Wainselboim Alejandro J.
Published: April 2021

Mouth-to-mouth food exchange in eusocial insects (trophallaxis) contributes to the organization of complex social activities. In the case of honeybees, foragers returning from a nectar source transfer the food collected to receiver colony-mates through oral contact. Previous studies have shown that the speed of nectar transfer within each contact (unloading rate) increases when foragers return from feeding sites with higher profitability, i.e. with more concentrated sugar solutions or higher solution flow rates. However, there is no evidence that the nectar unloading rate is actually evaluated by hive-mates during food exchange. To investigate this, trophallaxis between donor bees returning from a feeder with different flow rates of sucrose solution (range 1.0–8.2 μl min−1 of 50 % w/w sucrose solution) and receiver hive-mates was studied by combining behavioural and infrared thermal analysis.

The results show that when foraging bees returned from a feeder delivering a higher flow rate they initiated unloading at higher thoracic temperatures and transferred the solution at higher speed. During these food exchanges, the thoraces of receiver bees warmed up faster in proportion to increasing forager temperature and unloading rate. Therefore, whatever the variable actually evaluated by receivers (mostly nectar processors, i.e. bees that handle nectar in the hive) during trophallaxis (unloading rate and/or donor thoracic temperature), they raised their activity level in proportion to that of the foragers. In this way, receiver bees will intensify their nectar processing when nectar foragers return from more profitable sites.
Seasonal Change in the Capacity for Supercooling By Neonatal Painted Turtles
Authors: Packard Gary C. , Packard Mary J. , Mcdaniel Leonard L.
Published: April 2021

Hatchlings of the North American painted turtle (Chrysemys picta) typically spend their first winter of life inside the shallow, subterranean nest where they completed incubation the preceding summer. This facet of their natural history commonly causes neonates in northerly populations to be exposed in mid-winter to ice and cold, which many animals survive by remaining unfrozen and supercooled. We measured the limit of supercooling in samples of turtles taken shortly after hatching and in other samples after 2 months of acclimation (or acclimatization) to a reduced temperature in the laboratory or field. Animals initially had only a limited capacity for supercooling, but they acquired an ability to undergo deeper supercooling during the course of acclimation. The gut of most turtles was packed with particles of soil and eggshell shortly after hatching, but not after acclimation. Thus, the relatively high limit of supercooling for turtles in the days immediately after hatching may have resulted from the ingestion of soil (and associated nucleating agents) by the animals as they were freeing themselves from their eggshell, whereas the relatively low limit of supercooling attained by acclimated turtles may have resulted from their purging their gut of its contents. Parallels may, therefore, exist between the natural-history strategy expressed by hatchling painted turtles and that expressed by numerous terrestrial arthropods that withstand the cold of winter by sustaining a state of supercooling.
Behavioral recovery from spinal cord injury following delayed application of polyethylene glycol
Authors: Borgens Richard B. , Shi Riyi , Bohnert Debra
Published: April 2021

Topical application of the hydrophilic polymer polyethylene glycol (PEG) to isolated adult guinea pig spinal cord injuries has been shown to lead to the recovery of both the anatomical integrity of the tissue and the conduction of nerve impulses through the lesion. Furthermore, a brief (2 min) application of the fusogen (Mr 1800, 50 % w/v aqueous solution) to the exposed spinal cord injury in vivo can also cause rapid recovery of nerve impulse conduction through the lesion in association with functional recovery. Behavioral recovery was demonstrated using a long-tract, spinal-cord-dependent behavior in rodents known as the cutaneus trunci muscle (CTM) reflex. This reflex is observed as a contraction of the skin of the back in response to tactile stimulation. Here, we confirm and extend these preliminary observations. A severe compression/contusion injury to the exposed thoracic spinal cord of the guinea pig was performed between thoracic vertebrae 10 and 11. Approximately 7 h later, a topical application of PEG was made to the injury (dura removed) for 2 min in 15 experimental animals, and levels of recovery were compared with those of 13 vehicle-treated control animals. In PEG-treated animals, 93 % recovered variable levels of CTM functioning and all recovered some level of conduction through the lesion, as measured by evoked potential techniques. The recovered reflex was relatively normal compared with the quantitative characteristics of the reflex prior to injury with respect to the direction, distance and velocity of skin contraction. Only 23 % of the control population showed any spontaneous CTM recovery (P=0.0003) and none recovered conduction through the lesion during the 1 month period of observation (P=0.0001). These results suggest that repair of nerve membranes by polymeric sealing can provide a novel means for the rapid restoration of function following spinal cord injury.
Three-dimensional morphometry of spinal cord injury following polyethylene glycol treatment
Authors: Duerstock Bradley S. , Borgens Richard B.
Published: April 2021

We are developing a novel means of restoring function after severe acute spinal cord injury. This involves a brief application of polyethylene glycol (PEG) to the site of injury. In the companion paper, we have shown that a delayed application of PEG can produce strikingly significant physiological and behavioral recovery in 90–100 % of spinal-cord-injured guinea pigs. In the present paper, we used three-dimensional computer reconstructions of PEG-treated and sham-treated spinal cords to determine whether the pathological character of a 1-month-old injury is ameliorated by application of PEG. Using a novel isocontouring algorithm, we show that immediate PEG treatment and treatment delayed by up to 7 h post-injury statistically increased the volume of intact spinal parenchyma and reduced the amount of cystic cavitation. Furthermore, in PEG-treated animals, the lesion was more focal and less diffuse throughout the damaged segment of the spinal cord, so that control cords showed a significantly extended lesion surface area. This three-dimensional computer evaluation showed that the functional recovery produced by topical application of a hydrophilic polymer is accompanied by a reduction in spinal cord damage.
Amino acid modulation of in vivo intestinal zinc absorption in freshwater rainbow trout
Authors: Glover Chris N. , Hogstrand Christer
Published: April 2021

The composition of the intestinal lumen is likely to have considerable influence upon the absorption, and consequently the nutrition and/or toxicity, of ingested zinc in aquatic environments, where zinc is both a nutrient and a toxicant of importance. The effects of amino acids upon intestinal zinc uptake in freshwater rainbow trout (Oncorhynchus mykiss) were studied using an in vivo perfusion technique. The presence of histidine, cysteine and taurine had distinct modifying actions upon quantitative and qualitative zinc absorption, compared to perfusion of zinc alone. Alterations in zinc transport were not correlated with changes in levels of free zinc ion. The chemical nature of the zinc–amino acid chelate, rather than the chelation itself, appeared to have the most important influence upon zinc absorption. l-histidine, despite a strong zinc-chelating effect, maintained quantitative zinc uptake at control (zinc alone) levels. This effect correlated with the formation of Zn(His)2 species. d-histidine at a luminal concentration of 100 mmol l–1 significantly enhanced subepithelial zinc accumulation, but reduced the fraction of zinc that was retained and absorbed by the fish. The possibility of a Zn(His)2-mediated pathway for intestinal uptake is discussed. l-cysteine specifically stimulated the accumulation of zinc post-intestinally, an effect attributed to enhanced zinc accumulation in the blood. Taurine increased subepithelial zinc accumulation, but decreased the passage of zinc to post-intestinal compartments. Amino acids are proposed to have important roles in modifying intestinal zinc uptake with potential implications for environmental toxicity as well as aquaculture.
Circadian rhythm of acidification in insect vas deferens regulated by rhythmic expression of vacuolar H+-ATPase
Authors: Bebas Piotr , Cymborowski Bronislaw , Giebultowicz Jadwiga M.
Published: April 2021

Recent studies have demonstrated that the peripheral tissues of vertebrates and invertebrates contain circadian clocks; however, little is known about their functions and the rhythmic outputs that they generate. To understand clock-controlled rhythms at the cellular level, we investigated a circadian clock located in the reproductive system of a male moth (the cotton leaf worm Spodoptera littoralis) that is essential for the production of fertile spermatozoa. Previous work has demonstrated that spermatozoa are released from the testes in a daily rhythm and are periodically stored in the upper vas deferens (UVD). In this paper, we demonstrate a circadian rhythm in pH in the lumen of the UVD, with acidification occurring during accumulation of spermatozoa in the lumen. The daily rhythm in pH correlates with a rhythmic increase in the expression of a proton pump, the vacuolar H+-ATPase (V-ATPase), in the apical portion of the UVD epithelium. Rhythms in pH and V-ATPase persist in light/dark cycles and constant darkness, but are abolished in constant light, a condition that disrupts clock function and renders spermatozoa infertile. Treatment with colchicine impairs the migration of V-ATPase-positive vesicles to the apical cell membrane and abates the acidification of the UVD lumen. Bafilomycin, a selective inhibitor of V-ATPase activity, also prevents the decline in luminal pH. We conclude that the circadian clock generates a rhythm of luminal acidification by regulating the levels and subcellular distribution of V-ATPase in the UVD epithelium. Our data provide the first evidence for circadian control of V-ATPase, the fundamental enzyme that provides the driving force for numerous secondary transport processes. They also demonstrate how circadian rhythms displayed by individual cells contribute to the synchrony of physiological processes at the organ level.
Nitrogen metabolism and excretion in the mangrove killifish Rivulus marmoratus I. The influence of environmental salinity and external ammonia
Authors: Frick N. T. , Wright P. A.
Published: April 2021

At a field site in Belize, mangrove killifish Rivulus marmoratus inhabit hypersaline waters (up to 48 ‰) containing approximately 1 mmol l–1 ammonia. We tested the hypotheses that R. marmoratus modify their nitrogen metabolism and excretion (i) by accumulating free amino acids (FAAs) and urea in the tissues during hyperosmotic stress and (ii) by shifting to ureotelism and accumulating FAAs during hyperammonia stress. Urea excretion (JUrea) (but not ammonia excretion, JAmm) displayed a diurnal pattern, with significantly less (75 %) urea excreted at night than during the day in both laboratory-reared clones and wild-caught killifish. When fish were exposed to hypersaline conditions (45 ‰ sea water), JUrea was significantly reduced and tissue urea and FAA levels were elevated compared with those of control fish (15 ‰ sea water). When R. marmoratus were exposed to 0, 1, 2, 5 and 10 mmol l–1 NH4Cl (pH 8) for 48 h, no differences were found in JUrea. Remarkably, prolonged exposure (10 days) to 5 mmol l–1 NH4Cl (pH 8) did not result in an elevation of tissue ammonia levels. In addition, tissue urea and total FAA levels did not differ between control and ammonia-exposed fish after ⩾4 days. We propose that the euryhaline R. marmoratus retain urea and FAAs within their tissues in response to extreme osmotic stress. In contrast to many ammonia-tolerant fishes, R. marmoratus do not shift to ureotelism during prolonged hyperammonia stress, nor do they convert nitrogenous wastes into FAAs. The data suggest that killifish continue to eliminate ammonia despite an unfavourable blood-to-water gradient, thereby avoiding accumulation of ammonia.
Nitrogen metabolism and excretion in the mangrove killifishRivulus marmoratusII. Significant ammonia volatilization in a teleost during air-exposure
Authors: Frick N. T. , Wright P. A.
Published: April 2021

The mangrove killifish Rivulus marmoratus can tolerate prolonged periods of air-exposure (>1 month). During these periods of emersion, we hypothesized that R. marmoratus would convert potentially toxic ammonia into urea and free amino acids (FAAs). In air-exposed fish, both ammonia (JAmm) and urea (JUrea) excretion continued at approximately 57 % and 39 %, respectively, of submerged rates. Remarkably, approximately 42 % of the total ammonia excreted during air-exposure was through NH3 volatilization. Ammonia did not accumulate in whole-body tissues of air-exposed fish, but levels of both urea and some FAAs (primarily alanine and glutamine) were up to twofold higher after 10 days. The activities of the ornithine–urea cycle enzymes carbamoyl phosphate synthetase III and ornithine transcarbamylase increased (by approximately 30 % and 36 %, respectively) in whole-body tissues of air-exposed fish, while levels of arginase remained unchanged. The activities of enzymes involved in amino acid and oxidative metabolism were not significantly different between control and air-exposed fish. Partitioning of the anterior and posterior ends of immersed fish revealed that just over half (57 %) of the total nitrogen (ammonia+urea) was excreted through the anterior end of the fish, presumably via the branchial tissues, while emersed fish increased excretion via the posterior end (kidney+skin). R. marmoratus do not undergo a shift towards ureotelism during air-exposure. Rather, we propose that R. marmoratus are able to survive on land for extended periods without significant ammonia accumulation because they continuously release ammonia, partially by NH3 volatilization.
The mechanics of wave-swept algae
Authors: Denny Mark , Gaylord Brian
Published: April 2021

Wave-swept marine algae must contend with the hydrodynamic forces imposed by extreme water velocities. Nonetheless, they seldom have a shape that appears streamlined and they are constructed of weak, compliant materials. How do they survive? The answer is complex, but a coherent story is beginning to emerge. The combined effect of frond shape and material properties ensures that algae are flexible. In small individuals, flexibility allows the plant to reorient and reconfigure in flow, thereby assuming a streamlined shape and reducing the applied hydrodynamic force. In large individuals, flexibility allows fronds to `go with the flow', a strategy that can at times allow the plant to avoid hydrodynamic forces but may at other times impose inertial loads. Our understanding of algal mechanics is such that we can begin to predict the survivorship of algae as a function of size, spatial distribution and wave climate.