bluuebunny/crossref_metadata_2025 huggingface dataset:
Sulphaemoglobin Formation in Fish: A Comparison Between the Haemoglobin Of the Sulphide-Sensitive Rainbow Trout (Oncorhynchus Mykiss) and of the Sulphide-Tolerant Common Carp (Cyprinus Carpio)
Authors: Völkel Susanne , Berenbrink Michael
Published: April 2021

A method for the quantitative determination of sulphaemoglobin (SHb) in a mixture of haemoglobin derivatives by spectral deconvolution is described. SHb formation was studied in haemolysates and in red blood cells of the sulphide-sensitive rainbow trout (Oncorhynchus mykiss) and of the sulphide-tolerant common carp (Cyprinus carpio). Addition of sulphide caused the formation of SHb in haemolysates of both animals. However, haemoglobin from common carp was much less sensitive to sulphide than was trout haemoglobin. The maximal obtainable SHb fraction was approximately 30 % in trout and 10 % in carp haemolysates. In both animals, the SHb fraction increased with increasing Hb and sulphide concentrations up to 100 μmol l−1 and 1 mmol l−1, respectively, and was favoured by a low pH. An increase of temperature between 5 and 25 °C strongly increased SHb formation in trout haemolysate. In contrast, temperature changes had almost no effect on SHb production in carp. Within trout red blood cells, approximately 7 % of total haemoglobin was converted to SHb during 60 min of incubation (with 2.5 mmol l−1 sulphide), inducing a 20 % loss of haemoglobin oxygen-saturation. In carp red blood cells incubated under identical conditions, SHb formation was minimal and haemoglobin oxygen-saturation was not affected.
Physical and Physiological Components Of The Graviresponses Of Wild-Type and Mutant Paramecium Tetraurelia
Authors: Nagel Ute , Machemer Hans
Published: April 2021

Wild-type and the morphological mutant kin 241 of Paramecium tetraurelia showed improved orientation away from the centre of gravity (negative gravitaxis) when accelerations were increased from 1 to 7 g. Gravitaxis was more pronounced in the mutant. A correlation between the efficiency of orientation and the applied g value suggests a physical basis for gravitaxis. Transiently enhanced rates of reversal of the swimming direction coincided with transiently enhanced gravitaxis because reversals occurred more often in downward swimmers than in upward swimmers. The results provide evidence of a physiological modulation of gravitaxis by means of the randomizing effect of depolarization-dependent swimming reversals. Gravity bimodally altered propulsion rates of wild-type P. tetraurelia so that sedimentation was partly antagonized in upward and downward swimmers (negative gravikinesis). In the mutant, only increases in propulsion were observed, although the orientation-dependent sensitivity of the gravikinetic response was the same as in the wild-type population. Observed swimming speed and sedimentation rates in the wild-type and mutant cells were linearly related to acceleration, allowing the determination of gravikinesis as a linear (and so far non-saturating) function of gravity.
The Electrical Properties of the Anterior Stomach of the Larval Mosquito (Aedes Aegypti)
Authors: Clark Thomas M. , Koch Alan , Moffett David F.
Published: April 2021

The electrical properties of the anterior stomach of the larval mosquito (Aedes aegypti) were determined. At late times after cannulation, the intraluminal space constant was 936 μm, which is almost as long as the isolated tissue itself. At this time, the resistance of the apical cell membranes dominates the transcellular resistance; it is approximately 14 times the resistance of the basal cell membrane. Two physiologically distinct epithelial cell types were identified. One type has a stable basal potential of approximately 65 mV and responds to 5-hydroxytryptamine with hyperpolarization. The second cell type initially shows a basal potential of 100 mV. However, this basal potential decays in the first few minutes in parallel with the decay of the transintestinal potential. This latter cell type does not respond to 5-hydroxytryptamine.
Directional Hearing of a Grasshopper in the Field
Authors: Gilbert Friederike , Elsner Norbert
Published: April 2021

An electrophysiological method for making long-term recordings from the tympanal nerve was developed in Chorthippus biguttulus (Gomphocerinae) to gain insight into the ecophysiological constraints of sound localization in acridid grasshoppers. Using this ‘biological microphone’, the directional dependence of auditory nerve activity was monitored both in the laboratory and in various natural habitats of this species. On gravel and in sparse vegetation, the overall patterns of directionality were found to be very similar to those in the free sound field in the laboratory, regardless of whether the animal was positioned horizontally or vertically. However, the differences between the ipsi- and contralateral sides were smaller in these habitats than in the laboratory. In dense vegetation, the directional patterns were greatly affected by the environment. Moreover, a minimum in nerve activity was not always reached on the contralateral side, as is typical for the free sound field situation. On the basis of these data, predictions can be made about the ability of the animals to determine the correct side of a sound source. In the free sound field of the laboratory, correct lateralizations are expected at all angles of sound incidence between 20 and 160 °, a prediction corresponding to the results of behavioural studies. In sparse vegetation, a similar accuracy can be anticipated, whereas on gravel and in dense vegetation directional hearing is expected to be severely degraded, especially if the animal is oriented horizontally. The predictions from our present electrophysiological investigations must now be confirmed by behavioural studies in the field.
Depression of Nuclear Transcription and Extension of mRNA Half-Life Under Anoxia in Artemia Franciscana Embryos
Authors: Breukelen Frank Van , Maier Ryan , Hand Steven C.
Published: April 2021

Transcriptional activity, as assessed by nuclear run-on assays, was constant during 10 h of normoxic development for embryos of the brine shrimp Artemia franciscana. Exposure of embryos to only 4 h of anoxia resulted in a 79.3±1 % decrease in levels of in-vivo-initiated transcripts, and transcription was depressed by 88.2±0.7 % compared with normoxic controls after 24 h of anoxia (means ± S.E.M., N=3). Initiation of transcription was fully restored after 1 h of normoxic recovery. Artificially lowering the intracellular pH of aerobic embryos to the value reflective of anoxia (pH 6.7) showed that acidification alone explained over half the transcriptional arrest. Initiation of transcription was not rescued by application of 80 % carbon monoxide under anoxia, which suggests that heme-based oxygen sensing is not involved in this global arrest.

When these transcriptional data are combined with the finding that mRNA levels are unchanged for at least 6 h of anoxia, it is clear that the half-life of mRNA is extended at least 8.5-fold compared with that in aerobic embryos. In contrast to the activation of compensatory mechanisms to cope with anoxia that occurs in mammalian cells, A. franciscana embryos enter a metabolically depressed state in which gene expression and mRNA turnover are cellular costs apparently not compatible with survival and in which extended tolerance supercedes the requirement for continued metabolic function.
The Ontogeny of Ultraviolet Sensitivity, Cone Disappearance and Regeneration in the Sockeye Salmon Oncorhynchus Nerka
Authors: Flamarique Iñigo Novales
Published: April 2021

This study examines the spectral sensitivity and cone topography of the sockeye salmon Oncorhynchus nerka throughout its life history with special emphasis on ultraviolet sensitivity. Electrophysiological recordings from the optic nerve show that ultraviolet sensitivity is greatly diminished at the smolt stage but reappears in adult fish weighing about 201 g. Concomitantly, light microscopy observations of the retina show that ultraviolet cones disappear from the dorsal and temporal retina at the smolt stage but reappear at the adult stage. These changes occur for sockeye salmon raised in fresh water or salt water after smoltification. In contrast to this ultraviolet cycle, the other cone mechanisms (short-, middle- and long-wavelength-sensitive) and the rod mechanism remain present throughout ontogeny. The natural appearance and disappearance of ultraviolet cones in salmonid retinas follows surges in blood thyroxine at critical developmental periods. Their presence coincides with times of prominent feeding on zooplankton and/or small fish that may be more visible under ultraviolet light. It is proposed that the primary function of ultraviolet cones in salmonids is to improve prey contrast.
The Ageing of the Low-Frequency Water Disturbances Caused by Swimming Goldfish and Its Possible Relevance to Prey Detection
Authors: Hanke Wolf , Brücker Christoph , Bleckmann Horst
Published: April 2021

Wakes caused by swimming goldfish (Carassius auratus) were measured with a particle image velocimetry system and analyzed using a cross-correlation technique. Particle velocities in a horizontal plane (size of measuring plane 24 cm×32 cm or 20 cm×27 cm) were determined, and the vorticity in the plane was derived from these data. The wake behind a swimming goldfish can show a clear vortex structure for at least 30 s. Particle velocities significantly higher than background noise could still be detected 3 min after a fish (body length 10 cm) had passed through the measuring plane. Within this time span, the lateral spread of fish-generated wakes could exceed 30 cm for a 10 cm fish and 20 cm for a 6 cm fish. Measurements in a man-made open-air pond showed that water velocities in a quasi-natural still water environment can be as small as 1 mm s−1. Background velocities did not exceed 3 mm s−1 as long as no moving animal was present in the measuring plane. The possible advantage for piscivorous predators of being able to detect and analyze fish-generated wakes is discussed.
Reaction to Disturbances of a Walking Leg During Stance
Authors: Bartling Christian , Schmitz Josef
Published: April 2021

The ground reaction forces exerted by the legs of freely walking stick insects, Carausius morosus, were recorded during normal and perturbed locomotion. The animals walked along a path into which a three-dimensional force transducer was integrated. The transducer registered all three components of the forces produced by a single leg when, by chance, it walked on the force platform. The stiffness of the walking surface was found to be a critical variable affecting the forces and the trajectories of leg movements during undisturbed walking. The forces produced by a leg were considerably smaller and the trajectories were closer to the body during walking on soft versus stiff surfaces. Perturbations during stance were generated by moving the platform in various directions within the horizontal plane and at two different rates.

Perturbations were applied either immediately after leg contact or after a delay of 300 ms. The reactions to these disturbances were compatible with the hypothesis that the velocity of leg movement is under negative feedback control. This interpretation is also supported by comparison with simulations based upon other control schemes. We propose a model circuit that provides a combination of negative and positive feedback control mechanisms to resolve the apparent discrepancies between our results and those of previous studies.
Limits of human lung function at high altitude
Authors: Schoene Robert B.
Published: April 2021

This paper will review the function of the lung at high altitude in humans. As the first interface between the environment and the body, the lung serves a vital role in the transfer of oxygen from the air to the blood. I will describe the limits of response and adaptation of the lung to this hypoxic stress, both at rest and during exercise when oxygen and carbon dioxide flux from the tissues is greater. First, ventilation will be described in terms of the hypoxic stimulus that causes an increase in breathing (ventilatory drives) and the metabolic cost from the respiratory muscles incurred by this increase. Individuals at high altitude also have a substantial sense of dyspnea which, in and of itself, may limit exercise tolerance. The final function of the lung is to exchange oxygen and carbon dioxide, which it does at the alveolar–capillary interface. Here, important limitations are encountered because the driving pressure for oxygen from the air to the blood is lower and the more rapid transit time of blood across the pulmonary capillary allows less time for equilibration of oxygen with the blood. Both these phenomena lead to a limitation of diffusion of oxygen across the alveolar–capillary membrane and, thus, more accentuated hypoxemia. In spite of these restrictions, humans still do remarkably well in times of great stress from the hypoxic environment.
The home team advantage: reproduction in women indigenous to high altitude
Authors: Vitzthum V. J.
Published: April 2021

Although there is substantial evidence that environmental conditions disrupt reproductive function among newcomers to hypoxic settings, it is not certain that low oxygen pressure reduces fertility among those indigenous to high altitude. Even when fertility does appear to be relatively lower, numerous behavioral and sociocultural factors may be responsible. These are best examined within demographic frameworks that delineate a finite list of the proximate determinants of fertility. The findings presented here are based on several studies of indigenous Andean populations (Peruvian Quechua at 4000m, Bolivian Quechua at 3100m, Bolivian Aymara at 4000m). Data on ovarian function suggest that neither progesterone levels nor menstrual cycle length or regularity are significantly different from those of women at lower altitudes. Data on two behavioral factors that determine fertility levels, coital frequency and infant feeding practices, suggest that the former is not likely to be of significance in co-habitating couples, but that variation in breastfeeding patterns has probably made a substantial contribution to differences in fertility among at least some populations at high altitude.
Sensorimotor adaptations to microgravity in humans
Authors: Edgerton V. R. , McCall G. E. , Hodgson J. A. , Gotto J. , Goulet C. , Fleischmann K. , Roy R. R.
Published: April 2021

Motor function is altered by microgravity, but little detail is available as to what these changes are and how changes in the individual components of the sensorimotor system affect the control of movement. Further, there is little information on whether the changes in motor performance reflect immediate or chronic adaptations to changing gravitational environments. To determine the effects of microgravity on the neural control properties of selected motor pools, four male astronauts from the NASA STS-78 mission performed motor tasks requiring the maintenance of either ankle dorsiflexor or plantarflexor torque. Torques of 10 or 50% of a maximal voluntary contraction (MVC) were requested of the subjects during 10° peak-to-peak sinusoidal movements at 0.5Hz. When 10% MVC of the plantarflexors was requested, the actual torques generated in-flight were similar to pre-flight values. Post-flight torques were higher than pre- and in-flight torques. The actual torques when 50% MVC was requested were higher in- and post-flight than pre-flight. Soleus (Sol) electromyographic (EMG) amplitudes during plantarflexion were higher in-flight than pre- or post-flight for both the 10 and 50% MVC tasks. No differences in medial gastrocnemius (MG) EMG amplitudes were observed for either the 10 or 50% MVC tasks. The EMG amplitudes of the tibialis anterior (TA), an antagonist to plantarflexion, were higher in- and post-flight than pre-flight for the 50% MVC task. During the dorsiflexion tasks, the torques generated in both the 10 and 50% MVC tasks did not differ pre-, in- and post-flight. TA EMG amplitudes were significantly higher in- than pre-flight for both the 10 or 50% MVC tasks, and remained elevated post-flight for the 50% MVC test. Both the Sol and MG EMG amplitudes were significantly higher in-flight than either pre- or post-flight for both the 10 and 50% MVC tests. These data suggest that the most consistent response to space flight was an elevation in the level of contractions of agonists and antagonists when attempting to maintain constant torques at a given level of MVC. Also, the chronic levels of EMG activity in selected ankle flexor and extensor muscles during space flight and during routine activities on Earth were recorded. Compared with pre- and post-flight values, there was a marked increase in the total EMG activity of the TA and the Sol and no change in the MG EMG activity in-flight. These data indicate that space flight, as occurs on shuttle missions, is a model of elevated activation of both flexor and extensor muscles, probably reflecting the effects of programmed work schedules in flight rather than a direct effect of microgravity.
Quantifying Nutrient Production by the Microbial Symbionts in an Aphid
Authors: Douglas A. E. , Minto L. B. , Wilkinson T. L.
Published: April 2021

The symbiotic bacteria Buchnera sp. provide aphids with essential amino acids, nutrients in short supply in the aphid diet of plant phloem sap. The contribution of Buchnera-derived amino acids to net protein growth of the aphid Aphis fabae was quantified from the protein growth of aphids reared on chemically defined diets lacking individual amino acids. The amino acid production rates varied among the nine essential amino acids over the range 8–156 pmol μg−1 protein day−1 (for tryptophan and leucine, respectively), equivalent to 0.02–0.33 fmol Buchnera−1 day−1. In a complementary metabolic analysis, the aphids incorporated radioactivity from dietary [14C]glutamic acid into the essential amino acids isoleucine, lysine and threonine. Incorporation into isoleucine was significantly elevated by the omission of dietary isoleucine, indicating that dietary supply may affect the biosynthetic rates of certain amino acids by Buchnera. Aphids experimentally deprived of Buchnera did not synthesize essential amino acids from dietary glutamic acid. The mortality of aposymbionts was high over 7 days on the phenylalanine-free diet, and their assimilation of dietary leucine was depressed on the complete diet, suggesting that both the absence of bacteria-derived amino acids and the low rates of assimilation of certain dietary amino acids may contribute to the poor growth of these insects.
Hepatic Phosphoenolpyruvate Carboxykinase Gene Expression is not Repressed by Dietary Carbohydrates in Rainbow Trout (Oncorhynchus Mykiss)
Authors: Panserat S. , Plagnes-Juan E. , Bréque J. , Kaushik S.
Published: April 2021

Phosphoenolpyruvate carboxykinase (PEPCK) is a rate-limiting enzyme in hepatic gluconeogenesis and therefore plays a central role in glucose homeostasis. The aim of this study was to analyse the nutritional regulation of PEPCK gene expression in rainbow trout (Oncorhynchus mykiss), which are known to use dietary carbohydrates poorly. A full-length hepatic PEPCK cDNA (2637 base pairs with one open reading frame putatively encoding a 635-residue protein) was cloned and found to be highly homologous to mammalian PEPCKs. The presence of a putative peptide signal specific to a mitochondrial-type PEPCK in the deduced amino acid sequence suggests that this PEPCK gene codes for a mitochondrial form. In gluconeogenic tissues such as liver, kidney and intestine, this PEPCK gene was expressed at high levels and, in the liver we found no regulation of PEPCK gene expression by dietary carbohydrates. These results suggest that the first step of the hepatic gluconeogenic pathway in rainbow trout is functional and highly active irrespective of the dietary carbohydrate supply.
Maturation of muscle properties and its hormonal control in an adult insect
Authors: Rose Uwe , Ferber Michael , Hustert Reinhold
Published: April 2021

The oviposition of female locusts requires longitudinal muscles to tolerate remarkable lengthening. Whether this ability together with concomitant properties develops during maturation or is present throughout life was investigated. The properties of the locust abdominal muscles involved in oviposition behaviour were investigated with respect to their maturation, segment- and gender-specificity and regulation by juvenile hormone (JH). Muscles from the sixth abdominal segment (an oviposition segment) of mature females (>18 days old) were able to tolerate large extensions (>8 mm). At this length, muscles were still able to generate considerable neurally evoked twitch tension. In contrast, muscle fibres from females less than 5 days old did not tolerate extension of more than 4 mm. At this length, tension generation was negligible. The maximum tension generated at different stimulus frequencies was significantly higher in muscles of females more than 18 days old than in females less than 5 days old. Furthermore, the cross-sectional area of muscle fibres increased significantly during reproductive development. Current-clamp recordings from denervated muscle fibres of females more than 18 days old revealed their ability to generate overshooting action potentials. The potentials were tetrodotoxin (TTX)-insensitive (0.5 μmol l–1 TTX), but were blocked by Cd2+ (50 μmol l–1) or nifedipine (50 μmol l–1), which suggests the involvement of L-type Ca2+ channels. Action potentials recorded from females less than 5 days old differed considerably in amplitude and shape from those recorded from females more than 18 days old, suggesting their maturation during the first 2 weeks of adult life. Inactivation of the corpora allata (CA) by precocene inhibited the maturation of these muscle properties, whereas injection of JH into precocene-treated females reversed this effect. Homologous muscles from the third abdominal segment (a non-oviposition segment, M169) and muscles from males (M214) revealed no comparable changes, although some minor changes occurred during reproductive development. The results suggest a gender- and segment-specific maturation of muscle properties that is related to reproductive behaviour and controlled by JH.
The mechanical power output of the pectoralis muscle of blue-breasted quail (Coturnix chinensis): thein vivolength cycle and its implications for muscle performance
Authors: Askew Graham N. , Marsh Richard L.
Published: April 2021

Sonomicrometry and electromyographic (EMG) recordings were made for the pectoralis muscle of blue-breasted quail (Coturnix chinensis) during take-off and horizontal flight. In both modes of flight, the pectoralis strain trajectory was asymmetrical, with 70 % of the total cycle time spent shortening. EMG activity was found to start just before mid-upstroke and continued into the downstroke. The wingbeat frequency was 23 Hz, and the total strain was 23 % of the mean resting length.

Bundles of fibres were dissected from the pectoralis and subjected in vitro to the in vivo length and activity patterns, whilst measuring force. The net power output was only 80 W kg–1 because of a large artefact in the force record during lengthening. For more realistic estimates of the pectoralis power output, we ignored the power absorbed by the muscle bundles during lengthening. The net power output during shortening averaged over the entire cycle was approximately 350 W kg–1, and in several preparations over 400 W kg–1. Sawtooth cycles were also examined for comparison with the simulation cycles, which were identical in all respects apart from the velocity profile. The power output during these cycles was found to be 14 % lower than during the in vivo strain trajectory. This difference was due to a higher velocity of stretch, which resulted in greater activation and higher power output throughout the later part of shortening, and the increase in shortening velocity towards the end of shortening, which facilitated deactivation.

The muscle was found to operate at a mean length shorter than the plateau of the length/force relationship, which resulted in the isometric stress measured at the mean resting length being lower than is typically reported for striated muscle.
The mechanical power output of the flight muscles of blue-breasted quail (Coturnix chinensis) during take-off
Authors: Askew Graham N. , Marsh Richard L. , Ellington Charles P.
Published: April 2021

Blue-breasted quail (Coturnix chinensis) were filmed during take-off flights. By tracking the position of the centre of mass of the bird in three dimensions, we were able to calculate the power required to increase the potential and kinetic energy. In addition, high-speed video recordings of the position of the wings over the course of the wing stroke, and morphological measurements, allowed us to calculate the aerodynamic and inertial power requirements. The total power output required from the pectoralis muscle was, on average, 390 W kg–1, which was similar to the highest measurements made on bundles of muscle fibres in vitro (433 W kg–1), although for one individual a power output of 530 W kg–1 was calculated. The majority of the power was required to increase the potential energy of the body. The power output of these muscles is the highest yet found for any muscle in repetitive contractions.

We also calculated the power requirements during take-off flights in four other species in the family Phasianidae. Power output was found to be independent of body mass in this family. However, the precise scaling of burst power output within this group must await a better assessment of whether similar levels of performance were measured across the group. We extended our analysis to one species of hawk, several species of hummingbird and two species of bee. Remarkably, we concluded that, over a broad range of body size (0.0002–5 kg) and contractile frequency (5–186 Hz), the myofibrillar power output of flight muscles during short maximal bursts is very high (360–460 W kg–1) and shows very little scaling with body mass. The approximate constancy of power output means that the work output varies inversely with wingbeat frequency and reaches values of approximately 30–60 J kg–1 in the largest species.
Functional implications of supercontracting muscle in the chameleon tongue retractors
Authors: Herrel Anthony , Meyers Jay J. , Aerts Peter , Nishikawa Kiisa C.
Published: April 2021

Chameleons capture prey items using a ballistic tongue projection mechanism that is unique among lizards. During prey capture, the tongue can be projected up to two full body lengths and may extend up to 600 % of its resting length. Being ambush predators, chameleons eat infrequently and take relatively large prey. The extreme tongue elongation (sixfold) and the need to be able to retract fairly heavy prey at any given distance from the mouth are likely to place constraints on the tongue retractor muscles. The data examined here show that in vivo retractor force production is almost constant for a wide range of projection distances. An examination of muscle physiology and of the ultrastructure of the tongue retractor muscle shows that this is the result (i) of active hyoid retraction, (ii) of large muscle filament overlap at maximal tongue extension and (iii) of the supercontractile properties of the tongue retractor muscles. We suggest that the chameleon tongue retractor muscles may have evolved supercontractile properties to enable a substantial force to be produced over a wide range of tongue projection distances. This enables chameleons successfully to retract even large prey from a variety of distances in their complex three-dimensional habitat.
Aerobic respiratory costs of swimming in the negatively buoyant brief squidLolliguncula brevis
Authors: Bartol Ian K. , Mann Roger , Patterson Mark R.
Published: April 2021

Because of the inherent inefficiency of jet propulsion, squid are considered to be at a competitive disadvantage compared with fishes, which generally depend on forms of undulatory/oscillatory locomotion. Some squid, such as the brief squid Lolliguncula brevis, swim at low speeds in shallow-water complex environments, relying heavily on fin activity. Consequently, their swimming costs may be lower than those of the faster, more pelagic squid studied previously and competitive with those of ecologically relevant fishes. To examine aerobic respiratory swimming costs, O2 consumption rates were measured for L. brevis of various sizes (2–9 cm dorsal mantle length, DML) swimming over a range of speeds (3–30 cm s–1) in swim tunnel respirometers, while their behavior was videotaped. Using kinematic data from swimming squid and force data from models, power curves were also generated. Many squid demonstrated partial (J-shaped) or full (U-shaped) parabolic patterns of O2 consumption rate as a function of swimming speed, with O2 consumption minima at 0.5–1.5 DML s–1. Power curves derived from hydrodynamic data plotted as a function of swimming speed were also parabolic, with power minima at 1.2–1.7 DML s–1. The parabolic relationship between O2 consumption rate/power and speed, which is also found in aerial flyers such as birds, bats and insects but rarely in aquatic swimmers because of the difficulties associated with low-speed respirometry, is the result of the high cost of generating lift and maintaining stability at low speeds and overcoming drag at high speeds. L. brevis has a lower rate of O2 consumption than the squid Illex illecebrosus and Loligo opalescens studied in swim tunnel respirometers and is energetically competitive (especially at O2 consumption minima) with fishes, such as striped bass, mullet and flounder. Therefore, the results of this study indicate that, like aerial flyers, some negatively buoyant nekton have parabolic patterns of O2 consumption rate/power as a function of speed and that certain shallow-water squid using considerable fin activity have swimming costs that are competitive with those of ecologically relevant fishes.
Effects of hypoxia on egg capsule conductance inAmbystoma(Class Amphibia, Order Caudata)
Authors: Mills Nathan E. , Barnhart M. Christopher , Semlitsch R. D.
Published: April 2021

Aquatic amphibian eggs frequently encounter hypoxic conditions that have the potential to limit oxygen uptake and thereby slow embryonic development and hatching. Oxygen limitation might be avoided if egg capsule surface area and oxygen conductance increased in response to hypoxia. We investigated this possibility in two salamander species, Ambystoma annulatum and Ambystoma talpoideum. The effective surface area of egg capsules increased in response to hypoxia, which increased the conductance for oxygen and enhanced oxygen transport. The ability of amphibian eggs to adjust their conductance in response to oxygen availability may increase survival in hypoxic environments.
Chemolithoheterotrophy in a metazoan tissue: thiosulfate production matches ATP demand in ciliated mussel gills
Authors: Doeller Jeannette E. , Grieshaber Manfred K. , Kraus David W.
Published: April 2021

The ribbed mussel Geukensia demissa inhabits sulfide-rich coastal sediments with a distribution that suggests a preference for exposure to sulfide. Although sulfide is a respiratory poison, it is also a potent reductant. Geukensia demissa gill mitochondria can use sulfide as a respiratory substrate for ATP production, and the gills of this species exhibit sulfide-supported oxygen consumption that matches the energy demand of ciliary beating. Here, we demonstrate (i) that the major product of G. demissa gill sulfide oxidation is thiosulfate and (ii) that the rate of sulfide oxidation also matches the cellular energy demand, resulting in a ratio near unity of oxygen consumed to sulfide oxidized at both low and high ciliary beat frequencies. A value for this ratio of unity is consistent with electrons from sulfide oxidation entering the mitochondrial electron transport chain. In the gills of the blue mussel Mytilus edulis from sulfide-free conditions, this ratio is 3–5 times higher, indicating an uncoupling of oxygen consumption from sulfide oxidation. Whereas M. edulis gills exhibit anaerobic metabolism during sulfide exposure, G. demissa gills do not, indicating a difference in sulfide tolerance between the two mussel species.
Respiratory water loss in free-flying pigeons
Authors: Michaeli Gilead , Pinshow Berry
Published: April 2021

We assessed respiratory and cutaneous water loss in trained tippler pigeons (Columba livia) both at rest and in free flight. In resting pigeons, exhaled air temperature Tex increased with ambient air temperature Ta (Tex=16.3+0.705Ta) between 15°C and 30°C, while tidal volume VT (VT=4.7±1.0 ml, mean ± s.d. at standard temperature and pressure dry) and breathing frequency fR (fR=0.46±0.06 breaths s–1) were independent of Ta. Respiratory water loss, RWL, was constant over the range of Ta (RWL=1.2±0.4 mg g–1 h–1) used. In flying pigeons, Tex increased with Ta (Tex=25.8+0.34Ta), while fR was independent of Ta (fR=5.6±1.4 breaths s–1) between 8.8°C and 27°C. Breathing frequency varied intermittently between 2 and 8 breaths s–1 during flight and was not always synchronized with wing-beat frequency. RWL was independent of air temperature (RWL=9.2±2.9 mg g–1 h–1), but decreased with increasing inspired air water vapor density (ρin) (RWL=12.5–0.362ρin), whereas cutaneous water loss, CWL, increased with air temperature (CWL=10.122+0.898Ta), but was independent of ρin. RWL was 25.7–32.2 %, while CWL was 67.8–74.3 % of the total evaporative water loss. The data indicate that pigeons have more efficient countercurrent heat exchange in their anterior respiratory passages when at rest than in flight, allowing them to recover more water at rest at lower air temperatures. When evaporative water loss increases in flight, especially at high Ta, the major component is cutaneous rather than respiratory, possibly brought about by reducing the skin water vapor diffusion resistance. Because of the tight restrictions imposed by gas exchange in flight, the amount of water potentially lost through respiration is limited.
Suppression of aggression in rainbow trout (Oncorhynchus mykiss) by dietaryl-tryptophan
Authors: Winberg Svante , Øverli Øyvind , Lepage Olivier
Published: April 2021

Juvenile rainbow trout Oncorhynchus mykiss were isolated in individual compartments in observation aquaria and allowed to acclimate for 1 week, during which they were fed commercial trout feed. Thereafter, the fish were tested for aggressive behaviour using a resident/intruder test. Following this first resident/intruder test, the feed was exchanged for an experimental wet feed supplemented with 0.15 % or 1.5 % l-tryptophan (by wet mass). Controls received the same feed but without l-tryptophan supplementation. The fish were fed to satiety daily, and their individual feed intake was recorded. Aggressive behaviour was quantified again after 3 and 7 days of l-tryptophan feeding using the resident/intruder test. Feeding the fish l-tryptophan-supplemented feed for 3 days had no effect on aggressive behaviour, whereas feeding the fish l-tryptophan-supplemented feed for 7 days significantly suppressed aggressive behaviour in the fish, an effect seen at both levels of l-tryptophan supplementation. Fish fed l-tryptophan-supplemented feed showed elevated plasma and brain levels of l-tryptophan. The amino acid l-tryptophan is the precursor of serotonin, and supplementary dietary l-tryptophan was found to elevate levels of 5-hydroxyindoleacetic acid (5-HIAA) and the 5-HIAA/serotonin concentration ratio in the brain. Neither feed intake nor plasma cortisol level was significantly affected by dietary l-tryptophan. Central serotonin is believed to have an inhibitory effect on aggressive behaviour, and it is suggested that the suppressive effect of dietary l-tryptophan on aggressive behaviour is mediated by an elevation of brain serotonergic activity.
Effects of the sap of the common oleander Nerium indicum (Apocyanaceae) on male fertility and spermatogenesis in the oriental tobacco budworm Helicoverpa assulta (Lepidoptera, Noctuidae)
Authors: Jeong Seong Eun , Lee Yun , Hwang Jeong Hee , Knipple Douglas C.
Published: April 2021

We investigated the effects of sap of the common oleander Nerium indicum (Apocyanaceae) on male fertility and spermatogenesis in the oriental tobacco budworm Helicoverpa assulta. We found that continuous feeding of oleander sap during the larval period significantly affects fertility in males but not in females. This effect was also induced by direct injection of oleander sap into the hemocoel of 2-day-old pupae. Histological analyses of developing testes following oleander injection revealed a developmental delay and progressively more severe morphological abnormalities in the later stages of development. The effects of oleander sap on spermatogenesis in H. assulta were associated with greatly reduced levels of the two major polyamines, spermidine and spermine, in testis compared with saline-injected controls. In contrast, levels of putrescine, which is a precursor of both spermidine and spermine, and the activities of the enzymes ornithine decarboxylase and arginine decarboxylase, which are involved in the biosynthesis of putrescine, were initially elevated following oleander injection, but subsequently failed to undergo the induction that normally occurs during late pupal development. The effects of oleander sap on spermidine and spermine levels could be the result of direct inhibition by chemical constituents of the oleander sap of one of the enzymes used in common in the conversions of putrescine to spermidine and spermidine to spermine; alternatively, these effects on polyamine metabolism could be secondary to the disruption of a more fundamental process in the developmental program guiding spermatogenesis in H. assulta.
Diving development in nursing harbour seal pups
Authors: Jørgensen Christian , Lydersen Christian , Brix Ole , Kovacs Kit M.
Published: April 2021

This study investigated physiological and behavioural aspects of diving development in pups of the harbour seal Phoca vitulina. Behavioural data (4280 h, 6027 dives) from time/depth recorders (N=13) deployed on pups aged 0–19 days are presented concomitantly with physiological measurements (N=8, sampled both early and late in the nursing period) of blood oxygen stores and body composition. Pups grew from 12.6±1.8 kg (mean age 2 days, total body fat 16±4 %) to 22.2±2.5 kg (mean age 16 days, total body fat 35±5 %; means ± s.d.) over the duration of the experiment. Pups less than 5 days of age had an elevated haematocrit and reduced plasma volume compared with older pups. Although plasma volume and blood volume increased, mass-specific blood oxygen stores (total haemoglobin) fell during the study period. Simultaneously, the following behavioural indicators of diving ability increased: the proportion of time spent in the water, dive depth, dive duration, bottom time and maximum daily swimming velocity. In addition, the proportion of dives that were identified by cluster analyses as being U-shaped increased significantly with age. On the basis of the measured blood oxygen stores, less than 1 % of the recorded dives exceeded the calculated aerobic dive limit. Thus, development in blood oxygen stores or rates of oxygen consumption did not seem to restrain the rate of neonatal dive development in harbour seals. It appears that behavioural modifications (experience and learning) may be the primary rate-limiting factors for ontogeny of diving skills in neonates of this species.
Altered dietary nutrient intake maintains metabolic homeostasis in parasitized larvae of the insect Manduca sexta L.
Authors: Thompson S. N. , Redak R. A. , Wang L.-W.
Published: April 2021

Manduca sexta larvae exhibited altered food selection over a 2- or 3-day feeding period when parasitized by Cotesia congregata, and offered a choice of two chemically defined diets, one containing casein without sucrose and a second with sucrose but no casein. While normal larvae consumed the diets in a ratio of approximately 2:1 protein:carbohydrate (w/w), parasitized insects consumed a ratio of approximately 1:1. The altered nutrient ratio consumed by parasitized insects was principally due to a decrease in consumption of the protein diet, and was only partially explained by their lower growth. Conditioning larvae for 1 day to either one of the choice diets had little effect on subsequent dietary intake over a 2-day feeding period. Conditioned larvae, regardless of parasitism, initially fed on the opposite diet immediately after conditioning. Although this suggests that the altered nutrient intake displayed by parasitized insects was not due to any failure in their capacity for dietary selection, these results do not definitively demonstrate an altered nutrient intake target by parasitized larvae. Rather, parasitism may compromise dietary selection, resulting in random feeding. When parasitized larvae were maintained on several isocaloric diets with a varying ratio of casein and sucrose, those larvae feeding on the diet with a ratio of 1:1 of these nutrients supported the largest parasite population. Previous investigation of larvae maintained on a single artificial diet established that parasitized insects display an aberrant induction of gluconeogenesis, so that haemolymph trehalose is maintained at a level equivalent to that of normal insects. In contrast, the present results demonstrated that parasitized larvae offered a choice of diets, and feeding at the altered nutrient ratio above, maintain haemolymph sugar but have the same level of gluconeogenesis as normal larvae given the same dietary choice. These investigations suggest that altered food selection by parasitized M. sexta larvae maintains metabolic homeostasis and, moreover, may be adaptive for C. congregata, potentially maximizing the number of parasites developing in a single host larva.
Evidence for facilitated lactate uptake in lizard skeletal muscle
Authors: Donovan E. R. , Gleeson T. T.
Published: April 2021

To understand more fully lactate metabolism in reptilian muscle, lactate uptake in lizard skeletal muscle was measured and its similarities to the monocarboxylate transport system found in mammals were examined. At 2 min, uptake rates of 15 mmol l–1 lactate into red iliofibularis (rIF) were 2.4- and 2.2-fold greater than white iliofibularis (wIF) and mouse soleus, respectively. α-Cyano-4-hydroxycinnamate (15 mmol l–1) caused little inhibition of uptake in wIF but caused a 42–54 % reduction in the uptake rate of lactate into rIF, suggesting that much of the lactate uptake by rIF is via protein-mediated transport. N-ethymaleimide (ETH) (10 mmol l–1) also caused a reduction in the rate of uptake, but measurements of adenylate and phosphocreatine concentrations show that ETH had serious effects on rIF and wIF and may not be appropriate for transport inhibition studies in reptiles. The higher net uptake rate by rIF than by wIF agrees with the fact that rIF shows much higher rates of lactate utilization and incorporation into glycogen than wIF. This study also suggests that lactate uptake by reptilian muscle is similar to that by mammalian muscle and that, evolutionarily, this transport system may be relatively conserved even in animals with very different patterns of lactate metabolism.
Complete suppression of protein synthesis during anoxia with no post-anoxia protein synthesis debt in the red-eared slider turtleTrachemys scripta elegans
Authors: Fraser Keiron P. P. , Houlihan Dominic F. , Lutz Peter L. , Leone-Kabler Sandra , Manuel Liscia , Brechin James G.
Published: April 2021

Two previous studies of the effects of anoxia on protein synthesis in anoxia-tolerant turtles (Trachemys scripta elegans, Chrysemys picta bellii) have generated opposing results. Using the flooding-dose method, we measured the rate of protein synthesis following injection and incorporation of a large dose of radiolabelled phenylalanine to resolve the question of whether anoxia results in a downregulation of protein synthesis. After 1 h of anoxia, levels of protein-incorporated radiolabel indicated that protein synthesis rates in the intestine, heart, liver, brain, muscle and lungs were not significantly different from those of normoxic controls. However, from 1 to 6 h of anoxia, quantities of protein-incorporated radiolabel did not increase, suggesting that protein synthesis had ceased or had decreased below a measurable level. There was also no significant post-anoxia increase in protein synthesis rates above normoxic control levels during 3 h of recovery from anoxia. RNA-to-protein ratios did not change significantly in any tissue except the heart, in which RNA levels decreased below normoxic control levels after 6 h of anoxia. Except in the heart, downregulation of protein synthesis during anoxia does not appear to be mediated by changes in tissue RNA concentration.
Cells in Regenerating Deer Antler Cartilage Provide a Microenvironment That Supports Osteoclast Differentiation
Authors: Faucheux C. , Nesbitt S. A. , Horton M. A. , Price J. S.
Published: April 2021

Deer antlers are a rare example of mammalian epimorphic regeneration. Each year, the antlers re-grow by a modified endochondral ossification process that involves extensive remodelling of cartilage by osteoclasts. This study identified regenerating antler cartilage as a site of osteoclastogenesis in vivo. An in vitro model was then developed to study antler osteoclast differentiation. Cultured as a high-density micromass, cells from non-mineralised cartilage supported the differentiation of large numbers of osteoclast-like multinucleated cells (MNCs) in the absence of factors normally required for osteoclastogenesis. After 48 h of culture, tartrate-resistant acid phosphatase (TRAP)-positive mononuclear cells (osteoclast precursors) were visible, and by day 14 a large number of TRAP-positive MNCs had formed (783±200 per well, mean ± S.E.M., N=4). Reverse transcriptase/ polymerase chain reaction (RT-PCR) showed that receptor activator of NFκB ligand (RANKL) and macrophage colony stimulating factor (M-CSF) mRNAs were expressed in micromass cultures. Antler MNCs have the phenotype of osteoclasts from mammalian bone; they expressed TRAP, vitronectin and calcitonin receptors and, when cultured on dentine, formed F-actin rings and large resorption pits. When cultured on glass, antler MNCs appeared to digest the matrix of the micromass and endocytose type I collagen. Matrix metalloproteinase-9 (MMP-9) may play a role in the resorption of this non-mineralised matrix since it is highly expressed in 100 % of MNCs. In contrast, cathepsin K, another enzyme expressed in osteoclasts from bone, is only highly expressed in resorbing MNCs cultured on dentine. This study identifies the deer antler as a valuable model that can be used to study the differentiation and function of osteoclasts in adult regenerating mineralised tissues.