bluuebunny/crossref_metadata_2025 huggingface dataset:
Developmental changes in oxygen consumption regulation in larvae of the South African clawed frog Xenopus Laevis
Authors: Hastings Dulynn , Burggren Warren
Published: April 2021

Well-developed larval Xenopus laevis (NF stages 58–66) are oxygen regulators, at least during mild hypoxia. When and how they change from oxygen conformers (the presumed condition of the fertilized egg) to oxygen regulators is unknown. Also unknown is how anaerobic metabolic capabilities change during development, especially in response to acute hypoxia, and to what extent, if any, anaerobiosis is used to supplement aerobic metabolism. Consequently, we have investigated resting rates of oxygen consumption and concentrations of whole-body lactate (lactic acid) during development in normoxia and in response to acute hypoxia in Xenopus laevis. increased in an episodic, non-l inear fashion during development. Resting, normoxic increased about tenfold (to approximately 0.20 μmol g−1 h−1) between NF stages 1–39 and 40–44, and then another tenfold between NF stages 45–48 and 49–51 (to approximately 2.0 μmol g−1 h−1), remaining at about 2 μmol g−1 h−1 for the remainder of larval development. reached its highest level in newly metamorphosed frogs (nearly 4 μmol g−1 h−1), before decreasing to about 1.0 μmol g−1 h−1 in large adults. X. laevis embryos and larvae up to NF stage 54–57 were oxygen conformers when exposed to variable levels of acute hypoxia. The only exception was NF stage 45–48 (external gills present yet body mass still very small), which showed some capability of oxygen regulation. All larvae older than stage 54–57 and adults were oxygen regulators and had the lowest values of Pcrit (the oxygen partial pressure at which begins to decline). Whole-body lactate concentration in normoxia was about 1 μmol g−1 for all larval groups, rising to about 12 μmol g−1 in adults. Concentrations of lactic acid in NF stages 1–51 were unaffected by even severe ambient hypoxia. However, whole-body lactate levels in NF stages 52–66 increased in response to severe hypoxia, indicating that some anaerobic metabolism was being used to supplement diminishing aerobic metabolism. The largest increases in concentration of lactate occurred in late larvae and adults.
Immunolocalization of proton pumps (H+-ATPase) in pavement cells of rainbow trout gill
Authors: Sullivan Gary V. , Fryer James N. , Perry Steve F.
Published: April 2021

The expression of the V-type proton ATPase (H+-ATPase) was examined in the gill of the freshwater rainbow trout (Oncorhynchus mykiss) using immunocytochemistry in concert with laser scanning confocal or electron microscopy. A synthetic peptide consisting of the carboxy-terminal region of the 31 kDa subunit of the bovine renal H+-ATPase was used to generate an antiserum in rabbits, and its suitability for use in trout gill was confirmed by western blotting.

Gill epithelial cells demonstrated specific immunoreactivity, the intensity of which was increased markedly after 18 h of exposure to hypercapnia (1 % CO2 in air). The increased intensity of H+-ATPase immunoreactivity was associated with elevated branchial net acid excretion. In the hypercapnic fish, the specific immunoreactivity was associated with both the apical membrane and cytoplasm. Electron microscopy revealed that specific immunoreactivity was localized to the pavement cells and was particularly associated with the apical membrane and subapical cytoplasmic vesicles.

The increased H+-ATPase immunoreactivity in the epithelial cells of hypercapnic fish and the increased intensity of the immunoreactive bands in western blots from hypercapnic fish demonstrate an ‘up-regulation’ of this protein in response to respiratory acidosis. The results are discussed with reference to current models of acid–base and ion regulation in the gill of freshwater fish.
The Effect of Cycle Frequency on the Power Output of Rat Papillary Muscles in vitro
Authors: Layland Joanne , Young Iain S. , Altringham John D.
Published: April 2021

Papillary muscles were isolated from the right ventricles of rats and the length for maximum active force generation (Lmax) was determined isometrically. The work loop technique was used to derive the length for maximum work production (Lopt) at the cycle frequency, strain amplitude and stimulation phase shift found to be optimal for power output. Lopt was typically 7% shorter than Lmax and within the physiological length range (87.5%Lmax to Lmax). Net work and power output were measured during sinusoidal strain cycles around Lopt, over the cycle frequency range 1–9 Hz, strain amplitude and phase shift being optimised for work and power at each frequency. Experiments were performed at 37°C.

Distinct optima were found in both the work–frequency and the power–frequency relationships. The optimum cycle frequency for net work production was lower than the frequency for maximum power output. The mean maximum power output at 37°C was 8.62±0.50 W kg−1 (mean ± S.E.M., N=9) and was achieved at a cycle frequency of approximately 6 Hz, close to the estimated resting heart rate of 5.8 Hz for the rats used (mean mass 223±25 g). The cycle frequency, strain amplitude and stimulation phase shift found to be optimal for power output produced an in vitro contraction closely simulating the basal in vivo contraction.
Atmospheric Controls On Elephant Communication
Authors: Garstang Michael , Larom David , Raspet Richard , Lindeque Malan
Published: April 2021

Atmospheric conditions conducive to long-range transmission of low-frequency sound as used by elephants are found to exist in the Etosha National Park in Namibia during the late dry season. Meteorological measurements show that strong temperature inversions form at the surface before sunset and decay with sunrise, often accompanied by calm wind conditions during the early evening. These observations are used in an acoustic model to determine the sensitivity of infrasound to the effects of (a) the strength, thickness and elevation of temperature inversions, and (b) the growth and decay of an inversion typical of dry, elevated African savannas. The results suggest that the range over which elephants communicate more than doubles at night. Optimum conditions occur 1–2 h after sunset on clear, relatively cold, calm nights. At these times, ranges of over 10 km are likely, with the greatest amplification occurring at the lowest frequency tested. This strong diurnal cycle in communication range may be reflected in longer-lasting changes in weather and may exert a significant influence on elephant behaviour on time scales from days to many years.
Perception of Ocean Wave Direction by Sea Turtles
Authors: Lohmann Kenneth J. , Swartz Andrew W. , Lohmann Catherine M. F.
Published: April 2021

At the beginning of their offshore migration, hatchling sea turtles enter the ocean at night and establish a course away from land by swimming directly into oceanic waves. How turtles can detect wave direction while swimming under water in darkness, however, has not been explained.

Objects in a water column beneath the surface of the ocean describe a circular movement as waves pass above. In principle, swimming turtles might, therefore, detect wave direction by monitoring the sequence of accelerations they experience under water. To determine whether loggerhead (Caretta caretta L.) and green turtle (Chelonia mydas L.) hatchlings can detect wave direction in this way, we constructed a wave motion simulator to reproduce in air the circular movements that occur beneath small ocean waves. Hatchlings suspended in air and subjected to movements that simulated waves approaching from their right sides attempted to turn right, whereas movements that simulated waves from the left elicited left-turning behavior. Movements simulating waves from directly in front of the turtles elicited little turning in either direction.

The results demonstrate that hatchling sea turtles can determine the propagation direction of ocean waves by monitoring the circular movements that occur as waves pass above. Although sea turtles are the first animals shown to be capable of detecting wave direction in this way, such an orientation mechanism may be widespread among other transoceanic migrants such as fish and cetaceans.
Different Neural Pathways Coordinate Drosophila Flight Initiations Evoked By Visual and Olfactory Stimuli
Authors: Trimarchi James R. , Schneiderman Anne M.
Published: April 2021

To determine the role played by the giant fiber interneurons (GFs) in coordinating the jumping stages of visually elicited and olfactory-induced flight initiation we have recorded extracellularly from the cervical connective nerve during flight initiation. A spike is recorded from the cervical connective upon brain stimulation that has the same threshold as does activation of the tergotrochanteral muscle (TTM) and dorsal longitudinal muscles (DLMs). A consistent time interval occurs between the spike and activation of the TTM. Thus, the spike probably results from activity in the GFs. The time intervals between the spike and activation of the TTM during GF stimulation and visually elicited flight initiation are similar. These results suggest that the GFs coordinate the activation of the TTM and DLMs during the jumping stage of visually elicited flight initiation.

A spike is also recorded from the cervical connective during olfactory-induced flight initiations, but its shape and the time interval between it and activation of the TTM is different from that observed during GF stimulation. Although some olfactory-induced flight initiations exhibit a pattern of muscle activation indistinguishable from that evoked by GF stimulation, our results indicate that, regardless of the pattern of muscle activation, olfactory-induced flight initiations are not coordinated by the GF circuit. The stereotypic sequence and timing of activation of TTM and DLMs characteristic of the GF pathway can, therefore, be evoked by neurons other than those constituting the GF pathway.
Cholesterol Levels Explain Inverse Compensation of Membrane Order in Brush Border But Not Homeoviscous Adaptation in Basolateral Membranes from the Intestinal Epithelia of Rainbow Trout
Authors: Crockett Elizabeth L. , Hazel Jeffrey R.
Published: April 2021

The role of cholesterol in the thermal adaptation of biological membranes is explored. Physical and chemical responses of membranes to acclimation temperature were evaluated using plasma membrane domains (basolateral and brush border) prepared from intestinal epithelia of 5- and 20 °C-acclimated rainbow trout (Oncorhynchus mykiss). Basolateral membranes (BLMs) exhibit perfect homeoviscous efficacy (indicated by fluorescence depolarization using 1,6-diphenyl-1,3,5-hexatriene), although cholesterol content does not change with acclimation temperature (molar ratios of cholesterol to phospholipid are 0.23± 0.01 from 5 °C-acclimated fish and 0.25±0.02 from 20°C-acclimated fish; mean ± S.E.M.). Reductions (greater than 30 %) in each of the two major saturated fatty acids (16:0 and 18:0), and a 42 % increase in the polyunsaturate 22:6 (n−3) are found in BLMs from fish acclimated to 5 °C compared with membranes from warm-acclimated animals, suggesting that the phospholipid acyl chain composition determines the physical properties of BLMs. In marked contrast, brush-border membranes (BBMs) display opposite trends. BBMs from 5 °C-acclimated fish are more ordered than BBMs from 20 °C-acclimated fish (inverse compensation). Cholesterol content expressed relative to protein or relative to total polar lipid (phospholipid plus glycolipid) is significantly higher in cold-than in warm-acclimated fish, and nearly so (P=0.15) relative to phospholipid (0.31±0.03 in 5 °C-acclimated animals and 0.25±0.02 in 20 °C-acclimated animals). Only minor changes in the acyl composition of BBMs are induced by temperature acclimation. These results suggest that bile, a constituent of the apical microenvironment, may impose unusual requirements for membrane order and/or stability in the brush border.
A Dorsal Light Reflex in a Squid
Authors: Preuss Thomas , Budelmann Bernd U.
Published: April 2021

A dorsal light reflex is described in the squid Lolliguncula brevis. When illuminated from the side in visually homogeneous surroundings, a free-swimming squid rolls the dorsal side of its head and trunk 10–20 ° towards the light. With the trunk restricted in a holder, the squid rolls its head 4–5 ° towards the light; this reaction increases by about 50 % when the statocysts are bilaterally removed and increases further when the neck receptor organ is also destroyed. The results indicate a multi-modal interaction of visual, statocyst and proprioceptive inputs during postural control.
Synthesis of Stress Protein 70 (Hsp70) in Rainbow Trout (Oncorhynchus Mykiss) Red Blood Cells
Authors: Currie Suzanne , Tufts Bruce L.
Published: April 2021

Unlike enucleated mammalian red blood cells (rbcs), the nucleated rbcs of lower vertebrates are capable of protein synthesis and may, therefore, serve as a valuable model to investigate the adaptive significance of stress protein synthesis in cells. This study examined the synthesis of stress protein 70 (Hsp70) in rbcs of the temperature-sensitive rainbow trout Oncorhynchus mykiss in response to heat shock and anoxia. Through western blot analysis, we have demonstrated that rainbow trout rbcs synthesize Hsp70 both constitutively and in response to an increase in temperature. Radioisotopic labelling experiments indicated that the temperature at which Hsp70 synthesis was induced in fish acclimated to 10 °C was between 20 and 25 °C. Actinomycin D blocked de novo Hsp70 synthesis, implying that synthesis of Hsp70 is regulated at the level of transcription in rainbow trout rbcs. Since trout rbcs rely heavily on aerobic metabolism, but may also experience very low oxygen levels within the circulation, we also examined the relative importance of (1) anoxia as a stimulus for Hsp70 synthesis and (2) oxygen as a requirement for protein synthesis under control and heat-shock conditions. We found that trout rbcs were capable of protein synthesis during 2 h of anoxia, but did not increase Hsp70 synthesis. Moreover, rbcs subjected to combined anoxia and heat shock exhibited increases in Hsp70 synthesis that were similar in magnitude to those in cells exposed to heat shock alone. The latter results suggest that rainbow trout rbcs are (1) able to synthesize non-stress proteins during anoxia, (2) capable of tolerating periods of reduced oxygen availability without increased synthesis of stress proteins and (3) able to maintain the integrity of their heat-shock response even during periods of anoxia.
Species-Specific Action And Distribution Of Tachykinin-Related Peptides In The Foregut Of The Cockroaches Leucophaea Maderae And Periplaneta Americana
Authors: Nässel Dick R. , Eckert Manfred , Muren J. Eric , Penzlin Heinz
Published: April 2021

Nine tachykinin-related peptides (TRPs) have been isolated from the brain and intestine of the cockroach Leucophaea maderae. In the present investigation, two of the nine TRPs, LemTRP 1 and 5, were tested for their ability to stimulate contractions in the foregut of the cockroaches L. maderae and Periplaneta americana in vitro. The two LemTRPs and the related locust peptide locustatachykinin I (LomTK I) induced contractions in the foregut of P. americana in a dose-dependent manner, but had no myostimulatory action in L. maderae. A half-maximal response for the LemTRPs and LomTK I was obtained at 5×10−9 mol l−1. In both species, the neuropeptide proctolin stimulated foregut contractions. Using an antiserum to LomTK I, we demonstrated that in both species there are LomTK-like-immunoreactive (LomTK-LI) cell bodies and fibers within the ganglia and nerves of the stomatogastric nervous system. However, correlated with the species-specific action of the TRPs, we found efferent LomTK-LI nerve fibers supplying muscle fibers in the foregut of P. americana, but not in L. maderae. In both cockroach species, there is a rich supply of proctolin-immunoreactive fibers to the foregut muscle. Some of the LomTK-LI fibers supplying the P. americana foregut muscle contain co-localized proctolin immunoreactivity. These fibers appear to be derived from a large cell body in the frontal ganglion which also displayed co-localized immunoreactivities. Since TRP-containing neurons are restricted to the nerves and ganglia of the stomatogastric nervous system both in P. americana and L. maderae, TRPs may be involved in the control of foregut movements in both species, but in P. americana the control may be more complex with the additional peripherally projecting LomTK-LI neurons.
Arousal Shifts in Quiescent Locusts
Authors: Schuppe H. , Burrows M.
Published: April 2021

Locusts are usually quiescent at night, but this state can be interrupted by spontaneous periods of motor activity, or arousals, that can also be induced by exposure to light stimuli. To investigate whether repeated arousing stimulation has any lasting effect on behaviour, locusts were confronted at night with a series of 1 s light stimuli. Groups of three stimuli at intervals of 60 s were repeated 11 times at 10 min intervals during the first experimental night, and three stimuli at intervals of 90 s were repeated at 15 min intervals during the next night. Arousals and the effects of stimulation were monitored as changes in the spike activity of muscles in the basal part (the scapus) of the right antenna. In the early part of the night preceding the presentation of the light stimuli, neither 60 s nor 90 s periods were present as significant peaks in spontaneous changes in spike activity. The initial stimulus of a series evoked an arousal response that habituated on repetition of the stimulus. The end of the series of stimuli was followed by changes in spike activity that tended to have the same periodicity as the preceding stimuli. Furthermore, a single light stimulus at the end of the night evoked changes in spike activity that again tended to have the same periodicity as the preceding entraining stimuli. Repeated stimulation may therefore establish a memory trace for the period of stimulation that can be recalled either spontaneously or by the application of an appropriate external stimulus.
Neither Respiration Nor Cytochrome c Oxidase Affects Mitochondrial Morphology in Saccharomyces Cerevisiae
Authors: Church Cynthia , Poyton Robert O.
Published: April 2021

Previous studies have reported that mitochondrial morphology and volume in yeast cells are linked to cellular respiratory capacity. These studies revealed that mitochondrial morphology in glucose-repressed or anaerobically grown cells, which lack or have reduced levels of respiration, is different from that in fully respiring cells. Although both oxygen deprivation and glucose repression decrease the levels of respiratory chain proteins, they decrease the expression of many non-mitochondrial proteins as well, making it difficult to determine whether it is a defect in respiration or something else that effects mitochondrial morphology. To determine whether mitochondrial morphology is dependent on respiration per se, we used a strain with a null mutation in PET100, a nuclear gene that is specifically required for the assembly of cytochrome c oxidase. Although this strain lacks respiration, the mitochondrial morphology and volumes are both comparable to those found in its respiration-proficient parent. These findings indicate that respiration is not involved in the establishment or maintenance of yeast mitochondrial morphology, and that the previously observed effects of oxygen availability and glucose repression on mitochondrial morphology are not exerted through the respiratory chain. By applying the principle of symmorphosis to these findings, we conclude that the shape and size of the mitochondrial reticulum found in respiring yeast cells is maintained for reasons other than respiration.
The Concentration-Dependence of Crf-Like Diuretic Peptide: Mechanisms of Action
Authors: Clark Thomas M. , Hayes Timothy K. , Holman G. M. , Beyenbach Klaus W.
Published: April 2021

The mechanism of action of synthetic CCRF-DP, the corticotropin-releasing factor (CRF)-related diuretic peptide of the salt marsh mosquito Culex salinarius, was investigated in isolated Malpighian tubules of the yellow fever mosquito Aedes aegypti. A low concentration of CCRF-DP (10−9 mol l−1) caused a small but insignificant increase in transepithelial secretion of NaCl and fluid, but significantly reduced transepithelial voltage and resistance without a change in short-circuit current, pointing to the stimulation of passive Cl− transport through the paracellular pathway as the principal mechanism of a mild diuresis. Significant changes in voltage and resistance but not in short-circuit current were duplicated by the ionophore A23187 (0.4 μmol l−1), suggesting Ca2+ as a second messenger at 10−9 mol l−1 CCRF-DP. A high concentration of CCRF-DP (10−7 mol l−1) significantly increased transepithelial secretion of NaCl and fluid and significantly increased short-circuit current, pointing to the stimulation of active Na+ transport through the transcellular pathway as the mechanism of a strong diuresis. This effect was mimicked by dibutyryl-cAMP, suggesting cAMP as a second messenger at 10−7 mol l−1 CCRF-DP. Dibutyryl-cGMP had no effects. These results suggest dose-dependent, receptor-mediated effects of CCRF-DP that target discrete transport pathways via discrete second messengers: low concentrations of CCRF-DP cause a mild diuresis, apparently via Ca2+-mediated effects on paracellular Cl− transport, and high concentrations cause a strong diuresis via cAMP-mediated effects on active transcellular Na+ transport in addition to the effects on the paracellular pathway.
Confocal Laser Scanning and Electron Microscopical Studies on Osmoregulatory Epithelia in the Branchial Cavity of the Lobster Homarus Gammarus
Authors: Haond C. , Flik G. , Charmantier G.
Published: April 2021

The adult lobster Homarus gammarus is a weak hyper-regulator at low salinity. The objective of this study was to locate the ion-transporting tissues in the branchial chamber of this species, using electron microscopy and confocal laser scanning microscopy with a fluorescent vital stain for mitochondria, DASPMI, which is widely used to locate mitochondria-rich cells in ion-transporting epithelia of fish. A thick mitochondria-rich epithelium is present on the inner side of the branchiostegite and over the entire surface of the epipodites. Ultrastructural observations confirm that this tissue has features typical of an ion-transporting epithelium. When the lobster is transferred to low salinity, these epithelia undergo marked ultrastructural changes, such as an increase in thickness related to the development of basolateral infoldings, the appearance of numerous vesicles and an increase in height of the apical microvilli. In the gills, the branchial filaments are lined by a thin and poorly differentiated epithelium, containing numerous mitochondria; no significant ultrastructural changes were observed in the gills of animals acclimated to low salinity. In summary, in H. gammarus, no evidence of osmoregulatory structures was found in the gills. Differentiated ion-transporting epithelia are present in the branchial cavity, on the inner side of the branchiostegite and on the epipodites; these organs are probably involved in osmoregulation.
Long-Term Adaptation of Ca2+-Dependent Behaviour in Paramecium Tetraurelia
Authors: Preston Robin R. , Hammond Jocelyn A.
Published: April 2021

Prolonged exposure to KCl has long been recognized to modify swimming behaviour in Paramecium tetraurelia, a phenomenon known as ‘adaptation’. In this study, we have investigated behavioural adaptation systematically. A 24 h exposure to 30 mmol l−1 KCl deprived cells of the ability to respond behaviourally to two established chemoeffectors. We also explored the effects of 30 mmol l−1 KCl on the duration of backward swimming induced by Ba2+ and Mg2+. A brief (60 min) exposure prevented cells from swimming backwards in response to either cation, but recovery was rapid (<60 min) following a return to control medium. Prolonged (48 h) exposure caused a more persistent loss of response to Ba2+, so that several hours was now required for recovery. Surprisingly, responses to Mg2+ reappeared during 6–8 h in KCl, with backward swimming durations increasing to more than 300 % of control values after 26 h. Thus, we can distinguish two phases to adaptation. The short-term phase is characterized by an inability to respond behaviourally to most stimuli and might be adequately explained in terms of Ca2+ channel inactivation and K+-induced shifts in membrane potential. The long-term phase is characterized by enhanced responses to Mg2+ (and also to Na+), suggesting that a more extensive reprogramming of membrane excitability may occur during chronic K+-induced depolarization.
Digging in Sand Crabs: Coordination of Joints in Individual Legs
Authors: Faulkes Zen , Paul Dorothy H.
Published: April 2021

Sand crabs use their multi-jointed legs to dig into sand. Combined movement and electromyogram (EMG) analyses showed that the pattern of intra-leg coordination in the legs of two sand crabs of different families (Blepharipoda occidentalis and Emerita analoga) is similar in legs 2 and 3, but very different in leg 4. For example, the sequence of proximal joint movements in legs 2 and 3 is elevation, retraction, depression and protraction (similar to backward walking in most decapods), but the sequence of proximal joint movements in leg 4 is elevation, protraction, retraction and depression (similar to forward walking). The synergies are the same during leg movements in sea water and in sand, suggesting that the same motor programme is used in both situations. At the transition from sea water into sand, however, both the frequency and amplitude of the EMG potentials increase, and the phasing of the motor output to leg 2 (and presumably leg 3) changes from proportional (both power and return strokes co-vary with period) to return stroke constant (power strokes co-vary much more with period than do return strokes). The motor output to leg 4 remains intermediate between proportional and return stroke constant in sea water and in sand. On the basis of the segmental specialisation of the motor patterns for the legs, we hypothesize that sand crab digging may be an evolutionary mosaic of disparate ancestral locomotor behaviours.
Burrow Ventilation in the Tube-Dwelling Shrimp Callianassa Subterranea (Decapoda: Thalassinidea):I. Morphology and Motion of the Pleopods, Uropods and Telson
Authors: Stamhuis Eize J. , Videler John J.
Published: April 2021

The morphology of the pleopods, uropods and telson of the tube-dwelling shrimp Callianassa subterranea have been studied using dissection microscopy and scanning electron microscopy. The kinematics of these appendages were examined by motion analysis of macro-video recordings of ventilating shrimps in transparent artificial burrows. The pleopods show the usual crustacean biramous anatomy, but all segments are rostro-caudally flattened. The protopodite bears a triangular medially oriented endopodite and a scoop-shaped exopodite. The contralateral endopodites are linked by the appendix interna, ensuring a perfect phase relationship between contralateral pleopods. The outer rims of the exopodites are fringed with long fern-leaf-like plumose setae bearing flattened setules. These setae have very mobile joints and can be turned caudally. The slits between contralateral endopodites have rims of leaf-like setae as well. Setae of the same leaf-like type fringe the uropods, but these are non-motile. The telson has a narrow fringe of leaf-like setae, locally interrupted by long mechanoreceptory setae.

A shrimp, wandering through the burrow or resting, holds its pleopods against the abdomen with the exopodites and their setal fringes retracted medially. The uropods are folded medially as well, probably to reduce the shrimp’s drag. During ventilation, the uropods are extended against the tube wall, leaving only a small opening for flow ventral from the telson, and the pleopods beat at a frequency of approximately 1 Hz (0.9±0.2 Hz). Fourier analysis of pleopod kinematics showed that the motion pattern of the first flow-generating pleopod pair (PP1) consisted mainly of the first harmonic (75 %) and to a lesser extent of the third harmonic (20 %), resulting in almost perfect sinusoidal motion. The motion patterns of PP2 and PP3 could be modelled by assigning pure sinusoids with a 120 ° phase shift and a rostro-caudal ranking to the three pairs of pleopods.
Burrow Ventilation in the Tube-Dwelling Shrimp Callianassa Subterranea (Decapoda: Thalassinidea):II. The Flow in the Vicinity of the Shrimp and the Energetic Advantages of a Laminar Non-Pulsating Ventilation Current
Authors: Stamhuis Eize J. , Videler John J.
Published: April 2021

The ventilation flow in the vicinity of the pleopod-pumping thalassinid shrimp Callianassa subterranea in an artificial transparent burrow has been mapped using particle image velocimetry. The flow in the tube in front of the shrimp was unidirectional, laminar and steady, with a parabolic cross-sectional velocity profile. The mean flow velocity was 2.0±0.1 mm s−1. The flow passed the thorax of the shrimp along the lateral and ventral sides. Ventral to the abdomen, the flow was dominated by the metachronally oscillating pleopods. The water around a pleopod is accelerated caudally and ventrally during the power stroke, and decelerated to a much lesser extent during the recovery stroke owing to a reduction in pleopod area. On average, the flow ventral to the abdomen converged towards the small opening underneath the telson, simultaneously increasing in velocity. A jet with a core velocity of 18–20 mm s−1 entered the area behind the shrimp from underneath the telson. This caused a separation zone with backflow caudal to the telson. Owing to the high rates of shear, the jet diverged and re-adjusted to a parabolic cross-sectional profile within 1–2 body lengths behind the shrimp, showing no traces of pulsation. The metachronal pleopod movements in combination with the increase in flow velocity at the constriction in the tube caused by the uropods and the telson probably prevented pulsation. The energetic consequences of pulsating and steady flows in combination with several tube configurations were evaluated. The results suggested that, by constricting the tube and keeping the flow steady, C. subterranea saves on ventilation costs by a factor of up to six compared with oscillatory flow in a tube without the tail-fan constriction.
Evidence for Membrane-Bound Carbonic Anhydrase in the Air Bladder of bowfin (Amia Calva), a Primitive air-Breathing Fish
Authors: Gervais Matthieu R. , Tufts Bruce L.
Published: April 2021

The purpose of this study was to examine the subcellular distribution and isoenzyme characteristics of carbonic anhydrase from the gills and respiratory air bladder of bowfin Amia calva, a primitive air-breathing fish. Separation of subcellular fractions by differential centrifugation revealed that the vast majority of carbonic anhydrase from the gills of bowfin originated from the cytoplasmic fraction. Washing of the gill microsomal pellet also indicated that the carbonic anhydrase originally associated with this pellet was largely due to contamination from the cytoplasmic fraction. Experiments with a carbonic anhydrase inhibitor, sulphanilamide, and the plasma carbonic anhydrase inhibitor from this species confirmed that the bowfin gill probably contains only one carbonic anhydrase isoenzyme which had properties resembling those of CA II. In contrast to the situation in the gills, a relatively large percentage (27 %) of the total air bladder carbonic anhydrase was associated with the microsomal fraction. Washing of the air bladder microsomal pellet removed little of the carbonic anhydrase activity, indicating that most of the carbonic anhydrase in the microsomal fraction was associated with the membranes. Like the mammalian pulmonary CA IV isoenzyme, microsomal carbonic anhydrase from the bowfin air bladder was less sensitive to the bowfin plasma carbonic anhydrase inhibitor, sodium dodecylsulphate (SDS) and sulphanilamide than was cytoplasmic carbonic anhydrase from the air bladder. Microsomal carbonic anhydrase from the bowfin air bladder also resembled CA IV in that it appears to be anchored to the membrane via a phosphatidylinositol–glycan linkage which could be cleaved by phosphatidylinositol-specific phospholipase C. Taken together, these results suggest that a membrane-bound carbonic anhydrase isoenzyme resembling mammalian CA IV in terms of inhibition characteristics and membrane attachment is present in the air-breathing organ of one of the most primitive air-breathing vertebrates.
Relationships Between Blood Pressure and Heart Rate in the Saltwater Crocodile Crocodylus Porosus
Authors: Altimiras Jordi , Franklin Craig E. , Axelsson Michael
Published: April 2021

The cardiac limb of the baroreflex loop was studied in the saltwater crocodile Crocodylus porosus. The classical pharmacological methodology using phenylephrine and sodium nitroprusside was used to trigger blood pressure changes, and the resulting alterations in heart rate were analysed quantitatively using a logistic function. Interindividual differences in resting heart rates and blood pressures were observed, but all seven animals displayed clear baroreflex responses. Atropine and sotalol greatly attenuated the response. A maximal baroreflex gain of 7.2 beats min−1 kPa−1 was found at a mean aortic pressure of 6.1 kPa, indicating the active role of the baroreflex in a wide pressure range encompassing hypotensive and hypertensive states. At the lowest mean aortic pressures (5.0 kPa), the synergistic role of the pulmonary-to-systemic shunt in buffering the blood pressure drop also contributes to blood pressure regulation.

Pulse pressure showed a better correlation with heart rate and also a higher gain than mean aortic, systolic or diastolic pressures, and this is taken as an indicator of the existence of a differential control element working simultaneously with a linear proportional element.
Enhancement of Insect Antifreeze Protein Activity by Solutes of Low Molecular Mass
Authors: Li Ning , Andorfer Cathy A. , Duman John G.
Published: April 2021

Antifreeze proteins (AFPs) lower the non-equilibrium freezing point of water (in the presence of ice) below the melting point, thereby producing a difference between the freezing and melting points that has been termed thermal hysteresis. In general, the magnitude of the thermal hysteresis depends upon the specific activity and concentration of the AFP. This study describes several low-molecular-mass solutes that enhance the thermal hysteresis activity of an AFP from overwintering larvae of the beetle Dendroides canadensis. The most active of these is citrate, which increases the thermal hysteresis nearly sixfold from 1.2 °C in its absence to 6.8 °C. Solutes which increase activity approximately fourfold are succinate, malate, aspartate, glutamate and ammonium sulfate. Glycerol, sorbitol, alanine and ammonium bicarbonate increased thermal hysteresis approximately threefold. Interestingly, 0.5 mol l−1 sodium sulfate eliminated activity. Solute concentrations between 0.25 and 1 mol l−1 were generally required to elicit optimal thermal hysteresis activity. Glycerol is the only one of these enhancing solutes that is known to be present at these concentrations in overwintering D. canadensis, and therefore the physiological significance of most of these enhancers is unknown. The mechanism(s) of this enhancement is also unknown.

The AFP used in this study (DAFP-4) is nearly identical to previously described D. canadensis AFPs. The mature protein consists of 71 amino acid residues arranged in six 12-or 13-mer repeats with a consensus sequence consisting of Cys-Thr-X3-Ser-X5-X6-Cys-X8-X9-Ala-X11-Thr-X13, where X3 and X11 tend to be charged residues, X5 tends to be Thr or Ser, X6 to be Asn or Asp, X9 to be Asn or Lys and X13 to be Ala in the 13-mers. DAFP-4 is shorter by one repeat than previously described D. canadensis AFPs.
Effects of Wheat Germ Agglutinin and Colchicine on Microtubules of the Mitochondria-Rich Cells and Ca2+ Uptake in Tilapia (Oreochromis Mossambicus) Larvae
Authors: Tsai Jong-Chang , Hwang Pung-Pung
Published: April 2021

The organization of the microtubules and actin filaments in the gills of tilapia (Oreochromis mossambicus) larvae was revealed by confocal microscopy. The fluorescence intensity of the microtubules in the gills was increased by adding wheat germ agglutinin (WGA, 40 ng ml−1) to the ambient water for 30 min, but the staining pattern of the actin filaments was not changed. The fluorescence intensity of the microtubules in the gills was decreased by treatment with the microtubule-disrupting reagent colchicine at 0.2 mmol l−1 for 4 h. WGA treatment concurrently raised Ca2+ influx rates, and the increase was particularly large when the larvae were kept in water with extremely low Ca2+ levels ([Ca2+]=0.002 mmol l−1). Colchicine treatment, in contrast, reduced the Ca2+ influx rate. These results indicate that the microtubule network in tilapia gills, particularly in mitochondria-rich cells, could play a critical role in the uptake of Ca2+ in tilapia larvae.
The Rhodopsin Gene of the Cuttlefish Sepia Officinalis: Sequence and Spectral Tuning
Authors: Bellingham James , Morris Alex G. , Hunt David M.
Published: April 2021

The cephalopod molluscs are a group of invertebrates that occupy a wide range of oceanic photic environments. They are an ideal group of animals, therefore, in which to study the evolution of rhodopsin. The cDNA sequence of the rhodopsin gene of the cuttlefish Sepia officinalis (L.) (Sub-class Coleoidea, Order Sepiida) is presented, together with an analysis of the structure of the gene. A proline-rich C terminus is present; this structure is characteristic of cephalopod rhodopsins. In common with all invertebrate opsins studied so far, the equivalent site to the counterion in vertebrate opsins is occupied by an aromatic amino acid. An intron is present that splits codon 107, in contrast to the intronless rhodopsin gene in two species of myopsid squid. A spectral tuning model involving substitutions at only three amino acid sites is proposed for the spectral shifts between the rhodopsins of Sepia officinalis, three species of squid and Paroctopus defleini.
Biosynthetic Activity of Corpora Allata, Growth of Sex Accessory Glands and Mating in the Male Moth Agrotis Ipsilon (Hufnagel)
Authors: Duportets Line , Dufour Marie-Cécile , Couillaud Franck , Gadenne Christophe
Published: April 2021

The involvement of both juvenile hormone acid (JHA) and the sex accessory glands (SAGs) in the reproduction of the male moth Agrotis ipsilon was studied as a function of age and mating status. Total protein content analysis followed by gel electrophoresis of the SAGs, radiochemical assay for JHA biosynthesis and surgical and behavioural experiments were performed. Both the protein content of the SAGs and the biosynthetic activity of the corpora allata (CA) increased with age. Allatectomy and JHA/JH treatments showed that the protein content of the SAGs is linked with the activity of the CA. The protein content of the glands, but not the rate of JHA biosynthesis, decreased just after mating, and both increased sharply 24 h later. Injection of fluvastatin, an inhibitor of JH biosynthesis, in males immediately after mating prevented the increase in JHA synthesis and lowered the total protein content of the SAGs. Moreover, fluvastatin disrupted normal spermatophore transfer during the next mating of the injected males. Our results show that JHA controls the reproduction of A. ipsilon males by its separate actions on the sex accessory glands and on sexual behaviour.
Are there Distinct Subcellular Populations of Mitochondria in Rainbow Trout Red Muscle?
Authors: Battersby Brendan J. , Moyes Christopher D.
Published: April 2021

Ultrastructural analysis typically shows vertebrate striated muscles to possess mitochondria residing primarily in two locations. One population is interlaced throughout the myofibrils and another occurs directly beneath the cell membrane. The two populations of mitochondria can be separated and studied in vitro. Subsarcolemmal mitochondria (SSmt) are released by mechanical shearing of the tissue, whereas protease treatment is required to release the intermyofibrillar population (IMFmt). These methods were applied to rainbow trout (Oncorhynchus mykiss) red muscle to investigate the possible existence of distinct populations in this tissue. The two populations were very similar in mitochondrial DNA content (mtDNA mg−1 mitochondrial protein) and enzymatically (activities of carnitine palmitoyl transferase, β-hydroxyacyl CoA dehydrogenase, complex I, citrate synthase, cytochrome c oxidase expressed per milligram of mitochondrial protein). Respiration rates were the same for pyruvate and succinate, but IMFmt oxidized palmitoyl carnitine 26 % faster than SSmt (P<0.05). Apart from these minor differences in fatty acyl carnitine oxidation rates, no differences in biochemical or genetic properties were detected between populations. The lack of distinct subcellular populations in fish, in contrast to the situation in mammalian striated muscle, probably relates to the high mitochondrial volume density in fish red muscle.
Photoreception in the planktonic larvae of two species of pullosquilla, a lysiosquilloid stomatopod crustacean
Authors: Jutte Pamela A. , Cronin Thomas W. , Caldwell Roy L.
Published: April 2021

Optical microscopy, electron microscopy and microspectrophotometry were used to characterize pigments in the eyes of planktonic larvae of two species of the lysiosquilloid stomatopod Pullosquilla, P. litoralis and P. thomassini, which live sympatrically in French Polynesia. In contrast to the adult retina, which contains a diverse assortment of visual pigments in the main rhabdoms, the principal photoreceptors throughout the larval eyes of both species were found to contain a single rhodopsin with an absorption maximum (λmax) close to 446 nm. The expression of this visual pigment may survive metamorphosis, since several adult rhodopsins occur at a similar spectral position. The retinas of these planktonic larvae also contain a novel yellow photostable pigment, which is arrayed in a regular pattern at the distal margin of the larval retina. The absorption spectrum of this pigment is well matched to the larval rhodopsin, suggesting that it acts to screen the rhabdoms from stray light. By replacing opaque, black screening pigment, the transparent yellow pigment may act together with a blue iridescent layer in the larval retina to reduce the visual contrast of the larval eye against downwelling and sidewelling light, while simultaneously acting as a retinal screen.
Functional geometry of ciliated tentacular arrays in active suspension feeders
Authors: Grünbaum Daniel , Eyre David , Fogelson Aaron
Published: April 2021

Parallel tentacular structures with lateral cilia that produce suspension-feeding and respiratory flows occur repeatedly in many diverse taxonomic groups. We use a computational hydrodynamic model of flow through ciliated tentacles to simulate flow rates through ciliated tentacle arrays. We examine the functional relationship of one performance measure, flow rate per unit length of array, to geometrical variables, such as cilia length, cilia tip speed and the gap between adjacent tentacles, and to hydrodynamic operating conditions, such as adverse pressure drops across the array. We present a scaling and interpolation scheme to estimate flow rates for a wide range of geometries that span many taxa. Our estimates of flow rate can be coupled with the hydrodynamic characteristics of biological piping systems to understand design trade-offs between components of these systems. As a case study, we apply the model to the blue mussel Mytilus edulis by investigating the effect on performance of changes in the gap between neighboring tentacles. Our model suggests that the observed gaps between tentacles in M. edulis reflect flow-maximizing geometries. Even relatively weak adverse pressure drops have strong effects on flow-maximizing geometries and flow rates. One consequence is that an intermediate range of pressure drops may be unfavorable, suggesting that animals may specialize into high-pressure and low-pressure piping systems associated with differences in organism size and with their strategy for eliminating depleted water.
Air transmissivity of feathers
Authors: Müller Werner , Patone Giannino
Published: April 2021

The flight feathers and their coverts of a European kestrel Falco tinnunculus have been tested for their air transmissivity. The transmissivity was measured in both directions, i.e. from ventral to dorsal and vice versa; the mean difference between the two directions was less than 10 %. However, the transmissivity of the inner versus outer vanes of the remiges and coverts differed significantly, with the outer vanes being more transmissive than the inner vanes. A functional interpretation of the different transmissivities of the inner and outer vanes is given, and we propose that its significance lies in the formation of a smooth, continuous wing surface. The individual feathers are pushed firmly towards one another as a result of the different transmissivities, which cause a pressure gradient to build up from the less-transmissive inner vane towards the overlying, more-transmissive outer vane of the adjacent feather. In another test series, the transmissivity of the flight and covert feathers of 27 species was measured; the differences found between species were small.
Underwater punting by an intertidal crab: a novel gait revealed by the kinematics of pedestrian locomotion in air versus water
Authors: Martinez Marlene M. , Full R. J. , Koehl M. A. R.
Published: April 2021

As an animal moves from air to water, its effective weight is substantially reduced by buoyancy while the fluid-dynamic forces (e.g. lift and drag) are increased 800-fold. The changes in the magnitude of these forces are likely to have substantial consequences for locomotion as well as for resistance to being overturned. We began our investigation of aquatic pedestrian locomotion by quantifying the kinematics of crabs at slow speeds where buoyant forces are more important relative to fluid-dynamic forces. At these slow speeds, we used reduced-gravity models of terrestrial locomotion to predict trends in the kinematics of aquatic pedestrian locomotion. Using these models, we expected animals in water to use running gaits even at slow speeds. We hypothesized that aquatic pedestrians would (1) use lower duty factors and longer periods with no ground contact, (2) demonstrate more variable kinematics and (3) adopt wider stances for increased horizontal stability against fluid-dynamic forces than animals moving at the same speed on land. We tested these predictions by measuring the three-dimensional kinematics of intertidal rock crabs (Grapsus tenuicrustatus) locomoting through water and air at the same velocity (9 cm s−1) over a flat substratum. As predicted from reduced-gravity models of running, crabs moving under water showed decreased leg contact times and duty factors relative to locomotion on land. In water, the legs cycled intermittently, fewer legs were in contact with the substratum and leg kinematics were much more variable than on land. The width of the crab’s stance was 19 % greater in water than in air, thereby increasing stability against overturning by hydrodynamic forces. Rather than an alternating tetrapod or metachronal wave gait, crabs in water used a novel gait we termed ‘underwater punting’, characterized by alternating phases of generating thrust against the substratum and gliding through the water.