bluuebunny/crossref_metadata_2025 huggingface dataset:
Leptocephalus energetics: metabolism and excretion
Authors: Bishop R. E. , Torres J. J.
Published: April 2021

Leptocephali are the unusual transparent larvae that are typical of eels, bonefish, tarpon and ladyfish. Unlike the larvae of all other fishes, leptocephali may remain in the plankton as larvae for several months before metamorphosing into the juvenile form. During their planktonic phase, leptocephali accumulate energy reserves in the form of glycosaminoglycans, which are then expended to fuel metamorphosis. The leptocephalus developmental strategy is thus fundamentally different from that exhibited in all other fishes in two respects: it is far longer in duration and energy reserves are accumulated.

It was anticipated that the unusual character of leptocephalus development would be reflected in the energy budget of the larva. This study describes the allocation of energy to metabolism and excretion, two important elements of the energy budget. Metabolic rates were measured directly in four species of leptocephali, Paraconger caudilimbatus, Ariosoma balearicum, Gymnothorax saxicola and Ophichthus gomesii, using sealed-jar respirometry at sea. Direct measurements of metabolic rates were corroborated by measuring activities of lactate dehydrogenase and citrate synthase, two key enzymes of intermediary metabolism, in addition to that of Na+/K+-ATPase, a ubiquitous ion pump important in osmotic regulation. Excretion rates were determined by subsampling the sea water used in the respiratory incubations. The entire premetamorphic size range for each species was used in all assays.

Mass-specific oxygen consumption rate, excretion rate and all enzyme activities (y) declined precipitously with increasing mass (M) according to the equation y=aMb, where a is a species-specific constant and −1.74<b<−0.44. In leptocephali, the highly negative slope of the familiar allometric equation describing the relationship between mass-specific metabolic rate and mass, normally between −0.33 and 0, showed that a massive decline in metabolic rate occurs with increasing size. The result suggests that the proportion of actively metabolizing tissue also declines with size, being replaced in large measure by the metabolically inert energy depot, the glycosaminoglycans. Leptocephali can thus grow to a large size with minimal metabolic penalty, which is an unusual and successful developmental strategy.
Artificial Selection For Increased Wheel-Running Activity In House Mice Results In Decreased Body Mass At Maturity
Authors: Swallow John G. , Koteja Pawel , Carter Patrick A. , Garland Theodore
Published: April 2021

To test the hypothesis that body size and activity levels are negatively genetically correlated, we conducted an artificial selection experiment for increased voluntary wheel-running activity in house mice (Mus domesticus). Here, we compare body masses of mice from control and selected lines after 14 generations of selection. In both groups, beginning at weaning and then for 8 weeks, we housed half of the individuals with access to running wheels that were free to rotate and the other half with wheels that were locked to prevent rotation. Mice from selected lines were more active than controls at weaning (21 days) and across the experiment (total revolutions during last week: females 2.5-fold higher, males 2.1-fold higher). At weaning, mice from selected and control lines did not differ significantly in body mass. At 79 days of age, mice from selected lines weighed 13.6 % less than mice from control lines, whereas mice with access to free wheels weighed 4.5 % less than ‘sedentary’ individuals; both effects were statistically significant and additive. Within the free-wheel-access group, individual variation in body mass of males was negatively correlated with amount of wheel-running during the last week (P<0.01); for females, the relationship was also negative but not statistically significant (P>0.40). The narrow-sense genetic correlation between wheel-running and body mass after 8 weeks of wheel access was estimated to be −0.50. A negative genetic correlation could account for the negative relationship between voluntary wheel-running and body mass that has been reported across 13 species of muroid rodents.
Regulation of swimming in the Culex pipiens (Diptera, Culicidae) pupa: kinematics and locomotory trajectories
Authors: Brackenbury John
Published: April 2021

High-speed videography was used to investigate swimming kinematics and locomotory trajectories during escape responses in the pupa of Culex pipiens (Diptera, Culicidae). The pupa can perform straight-line motion despite undergoing backward and forward somersaults through 400 ° at a rate of 20 s−1. For linear motion to occur, the effective stroke of the abdomen must be delivered during the part of each cycle when the body is facing forwards, allowing passive rotation to carry the body round to the correct position for the start of the next half-stroke. On–off motion of the abdomen is regulated by a click mechanism based on stressed integumentary plates which buckle at strategic points in the cycle. The importance of self-inertia as a component in positional regulation was demonstrated by increasing the kinematic viscosity of the medium: this retarded rotation and resulted in somersaulting on the spot. Whereas normally the pupa invariably directs its swimming downwards, reversal of the usual light gradient produced upward paths as well. It is concluded that straight-line motion is generated automatically by the locomotory machine without any need for sensory feedback about body orientation during each cycle, but that swimming direction can be influenced by sensory cues such as light.
Ca2+ uptake in the sarcoplasmic reticulum from the systemic heart of octopod cephalopods
Authors: Altimiras Jordi , Hove-Madsen Leif , Gesser Hans
Published: April 2021

We have measured Ca2+ uptake in crude homogenates of heart tissue, as well as cell shortening and ionic currents in isolated myocytes exposed to caffeine, to characterize Ca2+ uptake in the sarcoplasmic reticulum (SR) of the systemic heart of octopus. The maximal rate of SR Ca2+ uptake in crude homogenates of octopus heart was 43±4 (mean ± S.E.M., N=7), compared with 28±2 nmol min−1 mg−1 protein (N=4) in homogenates of rat heart. The Ca2+-dependency of SR Ca2+ uptake was similar for the two species, with a Ca2+ activity at half-maximal uptake rate (pCa50) of 6.04±0.02 for octopus and 6.02±0.05 for rat. Exposure of isolated myocytes to 10 mmol l−1 caffeine resulted in cell shortening to 53±2 % of the resting cell length and an inward trans-sarcolemmal ionic current. The charge carried by this current was 3.28±0.70 pC pF−1 (mean ± S.E.M., N=5) corresponding to extrusion of 34.0±0.7 amol Ca2+ pF−1 from the cell by Na+/Ca2+ exchange. This is approximately 50 times more than the Ca2+ carried by the Ca2+ current elicited by a 200 ms depolarization from —80 to 0 mV and corresponds to an increase in the total intracellular [Ca2+] of 404±86 μmol l−1 non-mitochondrial volume due to Ca2+ release from the SR. Thus, we find that at 20 °C in the SR both Ca2+ content and Ca2+ uptake rate in the systemic heart of octopus are comparable with or larger than the corresponding values obtained in the rat heart. These results support the argument that the SR may play an important role in the regulation of contraction in the systemic heart of cephalopods.
Ultrastructural and protein analysis of surfactant in the Australian lungfish Neoceratodus forsteri: evidence for conservation of composition for 300 million years
Authors: Power J. H. T. , Doyle I. R. , Davidson K. , Nicholas T. E.
Published: April 2021

The Australian lungfish Neoceratodus forsteri is the most primitive member of the lungfish family, with a surfactant lipid composition similar to the actinopterygiian fishes, which evolved 400 million years ago. We have analysed the proteins associated with surfactant isolated from lung lavage of this species, and used electron microscopy and immunohistochemistry to examine the surfactant structures and the subcellular localisation of these proteins. The epithelial lining of the gas-exchange region of the lungfish lung consists of one basic cell type, which has characteristics of both mammalian alveolar type I and type II cells and may be the common ancestor of both. It has long cytoplasmic plates containing microvilli, large osmiophilic bodies resembling mammalian lamellar bodies and a cytoplasm rich in metabolic organelles. Extracellular structures reminiscent of mammalian surfactant forms, but not including tubular myelin, were observed in the airspaces. Immunochemical analysis of the lungfish surfactant and lung tissue, using antibodies to human SP-A and SP-B, showed a similar staining pattern to human surfactant, indicating that SP-A- and SP-B-like proteins are present. Immunohistochemistry revealed that both SP-A and SP-B reactivity was present in the secretory cell osmiophilic bodies. In conclusion, our results suggest that, despite the great diversity in present day lung structures, a common cellular mechanism may have evolved to overcome fundamental problems associated with air-breathing.
Work-dependent deactivation of a crustacean muscle
Authors: Josephson Robert K. , Stokes Darrell R.
Published: April 2021

Active shortening of respiratory muscle L2B from the crab Carcinus maenas results in contractile deactivation, seen as (1) a decline of force during the course of isovelocity shortening, (2) a reduction in the rate of force redevelopment following shortening, (3) a depression of the level of isometric force reached following shortening, and (4) an accelerated relaxation at the end of stimulation. The degree of deactivation increases with increasing distance of shortening, decreases with increasing shortening velocity, and is approximately linearly related to the work done during shortening. Deactivation lasts many seconds if stimulation is maintained, but is largely although not completely removed if the stimulation is temporarily interrupted so that the force drops towards the resting level. Deactivation for a given distance and velocity of shortening increases with increasing muscle length above the optimum length for force production. Stimulating muscle L2B at suboptimal frequencies gives tetanic contractions that are fully fused but of less than maximal amplitude. The depression of force following shortening, relative to the force during an isometric contraction, is independent of the stimulus frequency used to activate the muscle, indicating that deactivation is not a function of the background level of stimulus-controlled muscle activation upon which it occurs. Deactivation reduces the work required to restretch a muscle after it has shortened, but it also lowers the force and therefore the work done during shortening. The net effect of deactivation on work output over a full shortening/lengthening cycle is unknown.
The bioenergetics of embryonic diapause in an annual killifish, Austrofundulus limnaeus
Authors: Podrabsky Jason E. , Hand Steven C.
Published: April 2021

The annual killifish Austrofundulus limnaeus inhabits ephemeral ponds that dry out on a seasonal basis, thereby killing the adult and juvenile forms. Populations persist because diapausing embryos become embedded in the pond sediments. The rate of oxygen consumption of diapause II embryos is depressed by up to 90 % compared with that of developing embryos, and a parallel reduction is observed in heart rate. Developmental arrest was identified by cessation of somite proliferation and blockage of the ontogenetic increase in DNA content. Surprisingly, the arrest of metabolism and development is temporally offset as embryos reach diapause II; metabolic rate begins to decline 12 days prior to arrest of development. Release of embryos from diapause II is facilitated by increasing the light phase of the photoperiod. The rate of oxygen consumption of diapause III embryos is 84 % lower than the value preceding diapause III. The total energy flow of diapause II embryos apparently includes a contribution from anaerobic processes on the basis of calorimetric/respirometric ratios that are above the oxycaloric equivalent. Accumulations of lactate and ethanol at the expense of glycogen reserves are small or undetectable and do not account for the excess heat signal. Diapause II embryos maintain high [ATP]/[ADP] ratios and adenylate energy charge during diapause, consistent with a simultaneous depression of energy use and demand. Levels of AMP increase during early development and diapause II despite the highly charged adenylate pool. High values for [AMP]/[ATP] ratios in diapause II embryos are correlated with decreased rates of oxygen consumption and heat dissipation, which suggests a role for AMP in the depression of metabolism during early development and diapause II.
Ovipositing butterflies use a red receptor to see green
Authors: Kelber Almut
Published: April 2021

Swallowtail butterflies of the species Papilio aegeus oviposit on the leaves of Rutaceae plants in Australia. They possess receptor types with sensitivity peaks around 390 nm (violet receptor) and 610 nm (red receptor), in addition to the receptor types common in insects with sensitivity peaks at 360 nm (ultraviolet receptor), 440 nm (blue receptor) and 540 nm (green receptor). Multiple-and dual-choice experiments show that females of P. aegeus prefer to oviposit on substrata that look green to humans. A class of simple models is developed to describe this choice behaviour in terms of linear interactions between the different spectral types of photoreceptors. The green receptor has a positive influence, whereas the blue (and possibly the ultraviolet and violet) receptor and the red receptor have negative influences on the choice behaviour. Colour choice for oviposition is thus guided by a single chromatic mechanism. Caterpillars of P. aegeus grow faster on young leaves which, according to the model, should be preferred by females for oviposition. The importance of the red receptor for the discrimination between different green leaves is discussed in ecological and comparative contexts. Finally, in an evolutionary perspective, the possibility is discussed that colour vision systems like those of honeybees might have evolved as a combination of two or more such chromatic mechanisms.
Measurement of oxygen partial pressure, its control during hypoxia and hyperoxia, and its effect upon light emission in a bioluminescent elaterid larva
Authors: Timmins Graham S. , Penatti Carlos A. A. , Bechara Etelvino J. H. , Swartz Harold M.
Published: April 2021

This study investigates the respiratory physiology of bioluminescent larvae of Pyrearinus termitilluminans in relation to their tolerance to hypoxia and hyperoxia and to the supply of oxygen for bioluminescence. The partial pressure of oxygen was measured within the bioluminescent prothorax by in vivo electron paramagnetic resonance (EPR) oximetry following acclimation of larvae to hypoxic, normoxic and hyperoxic (normobaric) atmospheres and during periods of bioluminescence (during normoxia). The in the prothorax during exposure to an external of 15.2, 160 and 760 mmHg was 10.3±2.6, 134±0.9 and 725±73 mmHg respectively (mean ± S.D., N=5; 1 mmHg=0.1333 kPa). Oxygen supply to the larvae via gas exchange through the spiracles, measured by determining the rate of water loss, was also studied in the above atmospheres and was found not to be dependent upon . The data indicated that there is little to no active control of extracellular tissue within the prothorax of these larvae. The reduction in prothorax observed during either attack-response-provoked bioluminescence or sustained feeding-related bioluminescence in a normoxic atmosphere was variable, but fell within the range 10–25 mmHg. The effect of hypoxic atmospheres on bioluminescence was measured to estimate the intracellular within the photocytes of the prothorax. Above a threshold value of 50–80 mmHg, bioluminescence was unaffected by . Below this threshold, an approximately linear relationship between and bioluminescence was observed. Taken together with the extracellular measurements, this suggests that control of within the photocyte may occur. This work establishes that EPR oximetry is a valuable technique for long-term measurement of tissue in insects and can provide valuable insights into their respiratory physiology. It also raises questions regarding the hypothesis that bioluminescence can have a significant antioxidative effect by reduction of prothorax through oxygen consumption.
Fate of dietary sucrose and neosynthesis of amino acids in the pea aphid, Acyrthosiphon pisum, reared on different diets
Authors: Febvay G. , Rahbé Y. , Rynkiewicz M. , Guillaud J. , Bonnot G.
Published: April 2021

The fate of sucrose, the major nutrient of an aphid’s natural food, was explored by radiolabeling in the pea aphid Acyrthosiphon pisum. To investigate the influence of nitrogen quality of food on amino acid neosynthesis, pea aphids were reared on two artificial diets differing in their amino acid composition. The first (diet A) had an equilibrated amino acid balance, similar to that derived from analysis of aphid carcass, and the other (diet B) had an unbalanced amino acid composition similar to that of legume phloem sap. Aphids grown on either diet expired the same quantity of sucrose carbon as CO2, amounting to 25–30 % of the ingested sucrose catabolized in oxidation pathways. On diet A, the aphids excreted through honeydew about twice as much sucrose carbon as on diet B (amounting to 12.6 % of the ingested sucrose for diet A and 8.4 % for diet B), while amounts of sucrose carbons incorporated into exuviae were almost identical (1.9 % of the ingested sucrose on diet A and 2.7 % on diet B). There was also no difference in the amounts of sucrose carbon incorporated into the aphid tissues, which represented close to 50 % of the ingested sucrose. Sucrose carbons in the aphid tissues were mainly incorporated into lipids and the quantities involved were the same in aphids reared on either diet. On diet B, we observed neosynthesis of all protein amino acids from sucrose carbons and, for the first time in an aphid, we directly demonstrated the synthesis of the essential amino acids leucine, valine and phenylalanine. Amino acid neosynthesis from sucrose was significantly higher on diet B (11.5 % of ingested sucrose carbons) than on diet A (5.4 %). On diet A, neosynthesis of most of the amino acids was significantly diminished, and synthesis of two of them (histidine and arginine) was completely suppressed. The origin of amino acids egested through honeydew was determined from the specific activity of the free amino acid pool in the aphid. Aphids are able to adjust to variation in dietary amino acids by independent egestion of each amino acid. While more than 80 % of excreted nitrogen was from food amino acids, different amino acids were excreted in honeydew of aphids reared on the two diets. The conversion yields of dietary sucrose into aphid amino acids determined in this study were combined with those obtained previously by studying the fate of amino acids in pea aphids reared on diet A. The origin of all the amino acid carbons in aphid tissues was thus computed, and the metabolic abilities of aphid are discussed from an adaptive point of view, with respect to their symbiotic status.
Nitrogen excretion and expression of urea cycle enzymes in the atlantic cod (Gadus morhua L.): a comparison of early life stages with adults
Authors: Chadwick Terry D. , Wright Patricia A.
Published: April 2021

For many years, the urea cycle was considered to be relatively unimportant in the life history of most teleost fishes. In previous studies, we were surprised to find that newly hatched freshwater rainbow trout embryos had relatively high activities of the key urea cycle enzyme, carbamoyl phosphate synthetase III (CPSase III), and other enzymes in the pathway, whereas adult trout had much lower or non-detectable activities. The present study tested the hypothesis that urea cycle enzyme expression is unique to early stages of rainbow trout. In marine Atlantic cod (Gadus morhua) embryos, CPSase III, ornithine transcarbamoylase (OTCase), glutamine synthetase (GSase) and arginase activities were all expressed prior to hatching. Urea excretion was detected shortly after fertilization and rates were high relative to those of ammonia excretion (50–100 % of total nitrogen excreted as urea nitrogen; total=ammonia+urea). Urea concentration was relatively constant in embryos, but ammonia concentration increased by about fourfold during embryogenesis. Two populations of cod embryos were studied (from Newfoundland and New Brunswick), and significant differences in enzyme activities and excretion rates were detected between the two populations. In adult cod, CPSase III was not detectable in liver, white muscle, intestine and kidney tissues, but OTCase, GSase and arginase were present. Adult cod excreted about 17 % of nitrogenous waste as urea. Taken together, these data indicate that early urea cycle enzyme expression is not unique to rainbow trout but is also a feature of Atlantic cod development, and possibly other teleosts. The relatively high urea excretion rates underline the importance of urea as the primary nitrogen excretory product in Atlantic cod during early embryogenesis.
Contractile properties of atrial and ventricular myocardium of the heart of rainbow trout Oncorhynchus mykiss: effects of thermal acclimation
Authors: Aho Eija , Vornanen Matti
Published: April 2021

Atrial and ventricular myocardium perform different tasks in the pumping work of the vertebrate heart, which are reflected in their contractile properties. Although atrial contraction is assumed to have an important role in the function of fish heart, the contractile properties of atrial and ventricular myocardium have not been directly compared in any fish species. The objective of this study was to clarify any contractile differences in the heart of teleost fish and, in particular, to elucidate the contribution of myofibrillar ATPase and intracellular Ca2+ stores to the characteristics of atrial and ventricular contraction. Experiments were conducted on thermally acclimated rainbow trout Oncorhynchus mykiss to determine whether the effects of temperature adaptation are the same in atrial and ventricular tissue. It was shown that the rate of isometric contraction is much faster in atrial than in ventricular tissue of the fish heart and that acclimation to cold increases the rate of contraction in both cardiac compartments. The rapid contraction kinetics of the atrial tissue were associated with higher myofibrillar ATPase activity and faster Ca2+ uptake rate of the sarcoplasmic reticulum (SR) compared with ventricular tissue. Similarly, the faster kinetics of contraction following cold acclimation could be attributed to enhancement of the myofibrillar and/or SR function. The atrio-ventricular and temperature-induced differences were also expressed in the recovery of force from inactivation, i.e. in the mechanical restitution. The refractory period and the rate constant of force restitution were shorter in atrial than in ventricular muscle tissue. Similar differences also existed between the tissues of cold-acclimated (CA, 4 °C) and warm-acclimated (WA, 17 °C) fish. The fast recovery of force from inactivation in the heart of the CA trout was, at least in part, due to more active SR. Furthermore, it was shown that the force of atrial contraction in the CA trout is sensitive to ryanodine (10 μmol l−1), a Ca2+-release channel blocker of SR, at physiological body temperature (4 °C) and at a physiological pacing rate (0.6 Hz). This finding indicates that the Ca2+ stores of SR contribute to activation of cardiac contraction in the fish heart, and that the SR of fish heart is able to retain its Ca2+ load at low body temperatures, i.e. the Ca2+ release channels of SR are not leaky in the cold. The present data show that in the atrial tissue of CA trout, the SR directly contributes to the cytosolic Ca2+ and that in the atrium and ventricle of CA trout, the SR significantly accelerates the recovery of contractility from inactivation. The fast recovery from inactivation allows relatively high heart rates and therefore adequate cardiac outputs at low environmental temperatures for the cold-active rainbow trout.
Effects of exogenous 17β-estradiol on the reproductive physiology and reproductive performance of european starlings (Sturnus vulgaris)
Authors: Christians Julian K. , Williams Tony D.
Published: April 2021

Egg mass shows large intraspecific variation in birds and yet the mechanisms underlying this variation remain unknown. We hypothesized that estradiol would play a central role in determining egg mass, since this hormone stimulates the production of yolk precursors (vitellogenin and very-low density lipoprotein, VLDL) by the liver, and of albumen by the oviduct. We gave European starlings (Sturnus vulgaris) silastic implants containing estradiol prior to egg formation, which we predicted would increase egg mass. As expected, exogenous estradiol stimulated a marked (49 %) increase in plasma vitellogenin levels at the beginning of laying. At clutch completion, plasma VLDL levels and oviduct mass were also elevated in estradiol-treated females compared with controls. However, estradiol had no effect on fresh egg mass or clutch size. Estradiol treatment actually decreased the mass of yolk protein and lipid, perhaps by decreasing the rate of uptake of yolk precursors at the ovary. The failure of estradiol to increase egg mass indicates that this phenotype may be regulated at higher levels of organization (e.g. negative feedback, uptake of yolk precursors) than those studied in this experiment. Despite elevating yolk precursor levels, treatment with estradiol had no effect on the mass of the liver or endogenous stores of protein and lipid at clutch completion.
Development of an acoustic telemetry tag for monitoring electromyograms in free-swimming fish
Authors: Dewar Heidi , Deffenbaugh Max , Thurmond Gary , Lashkari Khosrow , Block Barbara A.
Published: April 2021

We report the development of an acoustic telemetry tag used to monitor electromyograms (EMGs) remotely from free-swimming marine fish. The device described amplifies and filters the EMG and then converts the electrical waveform into a frequency-modulated acoustic signal that is transmitted through water. The signal is then received, demodulated and recorded by the receiving system. The EMG tag described has been tested on a range of species, including toadfish Opsanus tau, spiny dogfish Squalus acanthias, yellowfin tuna Thunnus albacares and eastern Pacific bonito Sarda chiliensis, in different tank environments. In certain tanks the fidelity with which the system replicates the EMG is sufficient to quantify accurately the onset, offset, duration, the integrated area under the absolute value of the signal and the number of signal zero crossings. This EMG tag will expand the scope of questions that can be addressed about the behavior and physiology of free-swimming fish.
Laboratory selection for the comparative physiologist
Authors: Gibbs Allen G.
Published: April 2021

An increasingly popular experimental approach in comparative physiology is to study the evolution of physiological traits in the laboratory, using microbial, invertebrate and vertebrate models. Because selective conditions are well-defined, selected populations can be replicated and unselected control populations are available for direct comparison, strong conclusions regarding the adaptive value of an evolved response can be drawn. These studies have shown that physiological systems evolve rapidly in the laboratory, but not always as one would expect from comparative studies of different species. Laboratory environments are often not as simple as one thinks, so that the evolution of behavioral differences or selection acting on different life stages can lead to unanticipated results. In some cases, unexpected responses to laboratory selection may suggest new insights into physiological mechanisms, which might not be available using other experimental approaches. I outline here recent results (including success stories and caveats for the unwary investigator) and potential directions for selection experiments in comparative physiology.
Mosquito hearing: sound-induced antennal vibrations in male and female Aedes aegypti
Authors: Göpfert Martin C. , Briegel Hans , Robert Daniel
Published: April 2021

Male mosquitoes are attracted by the flight sounds of conspecific females. In males only, the antennal flagellum bears a large number of long hairs and is therefore said to be plumose. As early as 1855, it was proposed that this remarkable antennal anatomy served as a sound-receiving structure. In the present study, the sound-induced vibrations of the antennal flagellum in male and female Aedes aegypti were compared, and the functional significance of the flagellar hairs for audition was examined. In both males and females, the antennae are resonantly tuned mechanical systems that move as simple forced damped harmonic oscillators when acoustically stimulated. The best frequency of the female antenna is around 230 Hz; that of the male is around 380 Hz, which corresponds approximately to the fundamental frequency of female flight sounds. The antennal hairs of males are resonantly tuned to frequencies between approximately 2600 and 3100 Hz and are therefore stiffly coupled to, and move together with, the flagellar shaft when stimulated at biologically relevant frequencies around 380 Hz. Because of this stiff coupling, forces acting on the hairs can be transmitted to the shaft and thus to the auditory sensory organ at the base of the flagellum, a process that is proposed to improve acoustic sensitivity. Indeed, the mechanical sensitivity of the male antenna not only exceeds the sensitivity of the female antenna but also those of all other arthropod movement receivers studied so far.
Locomotion on the water surface: hydrodynamic constraints on rowing velocity require a gait change
Authors: Suter Robert B. , Wildman Horatio
Published: April 2021

Fishing spiders, Dolomedes triton (Araneae, Pisauridae), propel themselves across the water surface using two gaits: they row with four legs at sustained velocities below 0.2 m s−1 and they gallop with six legs at sustained velocities above 0.3m s−1. Because, during rowing, most of the horizontal thrust is provided by the drag of the leg and its associated dimple as both move across the water surface, the integrity of the dimple is crucial. We used a balance, incorporating a biaxial clinometer as the transducer, to measure the horizontal thrust forces on a leg segment subjected to water moving past it in non-turbulent flow. Changes in the horizontal forces reflected changes in the status of the dimple and showed that a stable dimple could exist only under conditions that combined low flow velocity, shallow leg-segment depth and a long perimeter of the interface between the leg segment and the water. Once the dimple disintegrated, leaving the leg segment submerged, less drag was generated. Therefore, the disintegration of the dimple imposes a limit on the efficacy of rowing with four legs. The limited degrees of freedom in the leg joints (the patellar joints move freely in the vertical plane but allow only limited flexion in other planes) impose a further constraint on rowing by restricting the maximum leg-tip velocity (to approximately 33 % of that attained by the same legs during galloping). This confines leg-tip velocities to a range at which maintenance of the dimple is particularly important.

The weight of the spider also imposes constraints on the efficacy of rowing: because the drag encountered by the leg-cum-dimple is proportional to the depth of the dimple and because dimple depth is proportional to the supported weight, only spiders with a mass exceeding 0.48 g can have access to the full range of hydrodynamically possible dimple depths during rowing. Finally, the maximum velocity attainable during rowing is constrained by the substantial drag experienced by the spider during the glide interval between power strokes, drag that is negligible for a galloping spider because, for most of each inter-stroke interval, the spider is airborne.

We conclude that both hydrodynamic and anatomical constraints confine rowing spiders to sustained velocities lower than 0.3 m s−1, and that galloping allows spiders to move considerably faster because galloping is free of these constraints.
Effect of High Altitude and In Vivo Adenosine/β-Adrenergic Receptor Blockade on ATP and 2,3Bpg Concentrations in Red Blood Cells of Avian Embryos
Authors: Dragon Stefanie , Carey Cynthia , Martin Kathy , Baumann Rosemarie
Published: April 2021

In chick embryos, developmental changes of the blood oxygen tension control hemoglobin (Hb) oxygen affinity via modulation of ATP and 2,3BPG concentrations in red blood cells. Hypoxia, which is a normal developmental condition for late chick embryos, causes a decrease of the red cell ATP concentration (and increase of red cell oxygen affinity) as well as activation of 2,3BPG synthesis via cyclic AMP-dependent signaling. Adenosine and catecholamines have been implicated as signaling substances in these red cell responses. To assess the extent to which adenosine and catecholamines are involved in vivo in the control of red cell ATP/2,3BPG concentrations, day 13 chick embryos were treated for 24 h with adenosine A2 and/or β-adrenergic receptor blockers and red cell ATP and 2,3BPG levels were determined. The data suggest that adaptive effects later in development in chick embryos induced by adenosine and catecholamines are vital. We have also tested whether avian embryos of the free-living, high-altitude, native white-tailed ptarmigan (Lagopus leucurus) alter their organic phosphate pattern in red cells in response to incubation at different altitudes. Embryos incubated at 3600–4100 m decrease their red cell ATP concentration much more rapidly than embryos of the same clutch incubated at 1600 m. From these data it can be inferred that the oxygen affinity of high altitude embryos will be adjusted to the altitude at which the eggs are incubated.
Experience-dependent modification of ultrasound auditory processing in a cricket escape response
Authors: Engel Jeff E. , Hoy Ronald R.
Published: April 2021

The ultrasound acoustic startle response (ASR) of crickets (Teleogryllus oceanicus) is a defense against echolocating bats. The ASR to a test pulse can be habituated by a train of ultrasound prepulses. We found that this conditioning paradigm modified both the gain and the lateral direction of the startle response. Habituation reduced the slope of the intensity/response relationship but did not alter stimulus threshold, so habituation extended the dynamic range of the ASR to higher stimulus intensities. Prepulses from the side (90 ° or 270 ° azimuth) had a priming effect upon the lateral direction of the ASR, increasing the likelihood that test pulses from the front (between −22 ° and +22 °) would evoke responses towards the same side as prepulse-induced responses. The plasticity revealed by these experiments could alter the efficacy of the ASR as an escape response and might indicate experience-dependent modification of auditory perception.

We also examined stimulus control of habituation by prepulse intensity or direction. Only suprathreshold prepulses induced habituation. Prepulses from one side habituated the responses to test pulses from either the ipsilateral or contralateral side, but habituation was strongest for the prepulse-ipsilateral side. We suggest that habituation of the ASR occurs in the brain, after the point in the pathway where the threshold is mediated, and that directional priming results from a second process of plasticity distinct from that underlying habituation. These inferences bring us a step closer to identifying the neural substrates of plasticity in the ASR pathway.
Modelling the locomotor energetics of extinct hominids
Authors: Kramer Patricia Ann
Published: April 2021

Bipedality is the defining characteristic of Hominidae and, as such, an understanding of the adaptive significance and functional implications of bipedality is imperative to any study of human evolution. Hominid bipedality is, presumably, a solution to some problem for the early hominids, one that has much to do with energy expenditure. Until recently, however, little attention could be focused on the quantifiable energetic aspects of bipedality as a unique locomotor form within Primates because of the inability to measure empirically the energy expenditure of non-modern hominids. A recently published method provides a way of circumventing the empirical measurement dilemma by calculating energy expenditure directly from anatomical variables and movement profiles. Although the origins of bipedality remain clouded, two discernible forms of locomotor anatomy are present in the hominid fossil record: the australopithecine and modern configurations. The australopithecine form is best represented by AL 288-1, a partial skeleton of Australopithecus afarensis, and is characterized as having short legs and a wide pelvis. The modern form is represented by modern humans and has long legs and a narrow pelvis. Human walking is optimized to take advantage of the changing levels of potential and kinetic energy that occur as the body and limbs move through the stride cycle. Although this optimization minimizes energy expenditure, some energy is required to maintain motion. I quantify this energy by developing a dynamic model that uses kinematic equations to determine energy expenditure.

By representing both configurations with such a model, I can compare their rates of energy expenditure. I find that the australopithecine configuration uses less energy than that of a modern human. Despite arguments presented in the anthropological literature, the shortness of the legs of AL 288-1 provides no evidence that she was burdened with a compromised or transitional locomotor anatomy. Instead, she may well have been an effective biped at walking speeds, not despite her short legs, but rather because of them.
Physiological responses of king penguins during simulated diving to 136 m depth
Authors: Ponganis P. J. , Kooyman G. L. , Van Dam R. , LeMaho Y.
Published: April 2021

To evaluate blood N2 uptake and the role of the respiratory volume (air sacs/lungs) as a N2 and O2 reservoir in deep-diving penguins, diving respiratory volume (VDR), heart rate (fH), venous , blood volume (Vb) and hemoglobin (Hb) concentration were measured in king penguins (Aptenodytes patagonicus) during forced submersions and compressions equivalent to depths up to 136 m. VDR was 69±18 ml kg−1 (mean ± S.D.) in 62 submersions ranging from 4.4 atmospheres absolute (ATA; 1 ATA=101 kPa) (34 m) to 14.6 ATA (136 m). Submersion fH averaged 30±7 beats min−1 (N=18), approximately 20 % of pre- and post-submersion values. Venous values during and after submersions as deep as 11.2 ATA (102 m) were all less than 2.8 atmospheres N2 (283 kPa) above ambient pressure, a previously measured threshold for symptomatic bubble formation. Mean Vb was 83±8 ml kg−1 (N=6); [Hb] was 17.6±0.7 g dl−1 (N=7). On a mass-specific basis, mean VDR, and therefore total available N2, is 41 % of that in shallow-diving penguin species. Total body O2 stores, calculated from measured VDR, Vb, [Hb], muscle mass and myoglobin concentration, are 45 ml kg−1, with 23 % in the respiratory system. This small respiratory fraction in comparison with that in shallow-diving penguins suggests a lesser reliance on the respiratory oxygen store for extended breath-holding and also a reduced uptake of nitrogen at depth.
Directional acoustic radiation in the strut display of male sage grouse Centrocercus urophasianus
Authors: Dantzker Marc S. , Deane Grant B. , Bradbury Jack W.
Published: April 2021

We present evidence that the acoustic component of the strut display of male sage grouse Centrocercus urophasianus is highly directional and that the nature of this directionality is unique among measured vertebrates. Where vertebrate acoustic signals have been found to be directional, they are most intense anteriorly and are bilaterally symmetrical. Our results show that sage grouse acoustic radiation (beam) patterns are often asymmetric about the birds’ anterior–posterior axis. The beam pattern of the ‘whistle’ note is actually strikingly bilobate with a deep null directly in front of the displaying bird. While the sage grouse display serves to attract potential mates, male sage grouse rarely face females head on when they call. The results of this study suggest that males may reach females with a high-intensity signal despite their preference for an oblique display posture relative to those females. We characterized these patterns using a novel technique that allowed us to map acoustic radiation patterns of unrestrained animals calling in the wild. Using an eight-microphone array, our technique integrates acoustic localization with synchronous pressure-field measurements while controlling for small-scale environmental variation in sound propagation.
Evolutionary and acclimation-induced variation in the heat-shock responses of congeneric marine snails (genus Tegula) from different thermal habitats: implications for limits of thermotolerance and biogeography
Authors: Tomanek Lars , Somero George N.
Published: April 2021

Heat stress sufficient to cause cellular damage triggers the heat-shock response, the enhanced expression of a group of molecular chaperones called heat-shock proteins (hsps). We compared the heat-shock responses of four species of marine snails of the genus Tegula that occupy thermal niches differing in absolute temperature and range of temperature. We examined the effects of short-term heat stress and thermal acclimation on the synthesis of hsps of size classes 90, 77, 70 and 38 kDa by measuring incorporation of 35S-labeled methionine and cysteine into newly synthesized proteins in gill tissue. Temperatures at which enhanced synthesis of hsps first occurred (Ton), temperatures of maximal induction of hsp synthesis (Tpeak) and temperatures at which hsp synthesis was heat-inactivated (Toff) were lowest in two low-intertidal to subtidal species from the temperate zone, T. brunnea and T. montereyi, intermediate in a mid-to low-intertidal species of the temperate zone, T. funebralis, and highest in a subtropical intertidal species from the Gulf of California, T. rugosa. Synthesis of hsps and other classes of protein by T. brunnea and T. montereyi was heat-inactivated at temperatures commonly encountered by T. funebralis during low tides on warm days. In turn, protein synthesis by T. funebralis was blocked at the upper temperatures of the habitat of T. rugosa. Acclimation of snails to 13 °C, 18 °C and 23 °C shifted Ton and Tpeak for certain hsps, but did not affect Toff. The heat-shock responses of field-acclimatized snails were generally reduced in comparison with those of laboratory-acclimated snails. Overall, despite the occurrence of acclimatory plasticity in their heat-shock responses, genetically fixed differences in Ton, Tpeak and Toff appear to exist that reflect the separate evolutionary histories of these species and may play important roles in setting their thermal tolerance limits and, thereby, their biogeographic distribution patterns.
Inhibiting ventilatory evaporation produces an adaptive increase in cutaneous evaporation in mourning doves Zenaida macroura
Authors: Hoffman Ty C. M. , Walsberg Glenn E.
Published: April 2021

We tested the hypothesis that birds can rapidly change the conductance of water vapor at the skin surface in response to a changing need for evaporative heat loss. Mourning doves (Zenaida macroura) were placed in a two-compartment chamber separating the head from the rest of the body. The rate of cutaneous evaporation was measured in response to dry ventilatory inflow at three ambient temperatures and in response to vapor-saturated ventilatory inflow at two ambient temperatures. At 35 °C, cutaneous evaporation increased by 72 % when evaporative water loss from the mouth was prevented, but no increase was observed at 45 °C. For both dry and vapor-saturated treatments, cutaneous evaporation increased significantly with increased ambient temperature. Changes in skin temperature made only a minor contribution to any observed increase in cutaneous evaporation. This indicates that Z. macroura can effect rapid adjustment of evaporative conductance at the skin in response to acute change in thermoregulatory demand.
Sources of magnetic sensory input to identified neurons active during crawling in the marine mollusc Tritonia diomedea
Authors: Popescu I. R. , Willows A. O. D.
Published: April 2021

Although the nudibranch mollusc Tritonia diomedea orients to the geomagnetic field, the anatomical site and the mechanism of the geomagnetic transducer are not known. Previous work on semi-intact preparations of Tritonia diomedea in which the brain is intact and nerve connections to the periphery are maintained showed that identifiable pedal ganglion neurons Pd5 fired an increased number of action potentials when the horizontal component of the ambient magnetic field was rotated. This response disappeared when all nerves emerging from the brain were cut, suggesting a peripheral locus for the geomagnetic transducer.

In the present work, we recorded intracellularly from Pd5 in preparations in which all peripheral nerves were cut except those containing the axons of neurons Pd5 (pedal nerves 2 and 3). These uncut, mixed, sensory-motor trunks innervate the locomotory epithelium of the foot upon which the animal crawls. In this further-reduced preparation, Pd5 again responded to magnetic field rotations with action potentials. To determine the direction of this action potential transmission in response to magnetic field rotations, we analyzed extracellular recordings from nerves containing the Pd5 axons and found that action potentials elicited in Pd5 by magnetic stimuli originate centrally and are transmitted peripherally.

In addition, we have explored the behavioral function of Pd5 neurons by simultaneously recording intracellular electrical activity and crawling rate of the semi-intact animal. A significant correlation was found between crawling rate and Pd5 action potential rate. We also found that action potentials in dorsal swim interneurons depolarized both Pd5 and the established locomotion motoneuron Pd21.