bluuebunny/crossref_metadata_2025 huggingface dataset:
Bimodal breathing in jumping spiders: morphometric partitioning of the lungs and tracheae inSalticus scenicus(Arachnida, Araneae, Salticidae)
Authors: Schmitz Anke , Perry Steven F.
Published: April 2021

In jumping spiders, both the book lungs and the tracheal system are well-developed. The tracheal system consists of four thick primary tracheae that branch into small secondary tracheae, some of them ending in the opisthosoma and others entering the prosoma. We used stereological morphometric methods to investigate the morphological diffusing capacity of the lungs and of the walls of the secondary tracheae (‘lateral diffusing capacity’) of two groups of Salticus scenicus with mean body masses of 2.69 mg (group A) and 5.28 mg (group B). The thickness of the gas-exchange epithelium of the lungs was 0.164 μm (group A) and 0.186 μm (group B) for the total diffusion barrier. The secondary tracheae were divided arbitrarily into seven classes according to their inner diameter (1–7 μm). The diffusion barriers of the tracheal walls tend to be thinnest (0.17 and 0.18 μm) for the smallest tracheae, the walls of the other tracheal classes having approximately the same thickness of diffusion barrier (0.24–0.32 μm).

The calculated oxygen-diffusing capacity (DO2) for the lungs was 16.4 μl min–1 g–1 kPa–1 for group A and 12 μl min–1 g–1 kPa–1 for group B; the DO2 of the walls of all secondary tracheae was 5.91 μl min–1 g–1 kPa–1 for group A animals and 6.63 μl min–1 g–1 kPa–1 for group B animals.

Our results are consistent with the hypothesis that the tracheal system plays an important role in gas exchange in jumping spiders. Resting and low-activity oxygen consumption rates can be met by the lungs or the tracheae alone, while high oxygen demands can be met only if both respiratory systems are working together. Tracheae entering the prosoma have only 4–10 % of the total tracheal diffusing capacity, thus providing sufficient oxygen for the nervous system but not being able to prevent muscle fatigue. The similar thickness of the walls of all tracheal classes is consistent with the hypothesis that the secondary tube tracheae function as ‘tracheal lungs’, supplying the haemolymph and organs by lateral diffusion.
Growth and metabolism of larval zebrafish: effects of swim training
Authors: Bagatto B. , Pelster B. , Burggren W. W.
Published: April 2021

Larval zebrafish (Danio rerio) of three different age classes (‘yolk-sac’ larvae, 96 h; ‘swim-up’ larvae, 9 days old; and ‘free-swimming’ larvae, 21 days old) were trained for 2, 6 and 11 days, respectively, to swim at 0 body lengths per second (BL s–1), 2 BL s–1 and 5 BL s–1. Survival was significantly diminished in larvae trained at 5 BL s–1 compared to controls (0 BL s–1). Although training produced no significant differences in mass and length, the youngest larvae absorbed their yolk at a faster rate during training. Routine oxygen consumption (ṀO2r) and mass-specific routine oxygen consumption (ṀO2r,m) were not significantly affected by chronic training in the yolk-sac larvae and swim-up larvae. However, trained free-swimming larvae had a significantly higher ṀO2r (after 11 days of training) and ṀO2r,m (after 8 and 11 days of training) compared to control larvae. Trained free-swimming larvae consumed significantly less oxygen during swimming compared to control larvae, as measured by closed-system respirometry. Trained yolk-sac larvae exposed to increasing hypoxia levels were more effective O2 regulators. Additionally, training enhanced survival during exposure to extreme hypoxia in all age groups. Thus, physiological acclimation to chronic swimming occurs in the earliest stages of life in the zebrafish.
Control of heart rate during thermoregulation in the heliothermic lizard Pogona barbata: importance of cholinergic and adrenergic mechanisms
Authors: Seebacher F. , Franklin C. E.
Published: April 2021

During thermoregulation in the bearded dragon Pogona barbata, heart rate when heating is significantly faster than when cooling at any given body temperature (heart rate hysteresis), resulting in faster rates of heating than cooling. However, the mechanisms that control heart rate during heating and cooling are unknown. The aim of this study was to test the hypothesis that changes in cholinergic and adrenergic tone on the heart are responsible for the heart rate hysteresis during heating and cooling in P. barbata. Heating and cooling trials were conducted before and after the administration of atropine, a muscarinic antagonist, and sotalol, a β-adrenergic antagonist. Cholinergic and β-adrenergic blockade did not abolish the heart rate hysteresis, as the heart rate during heating was significantly faster than during cooling in all cases. Adrenergic tone was extremely high (92.3 %) at the commencement of heating, and decreased to 30.7 % at the end of the cooling period. Moreover, in four lizards there was an instantaneous drop in heart rate (up to 15 beats min–1) as the heat source was switched off, and this drop in heart rate coincided with either a drop in β-adrenergic tone or an increase in cholinergic tone. Rates of heating were significantly faster during the cholinergic blockade, and least with a combined cholinergic and β-adrenergic blockade. The results showed that cholinergic and β-adrenergic systems are not the only control mechanisms acting on the heart during heating and cooling, but they do have a significant effect on heart rate and on rates of heating and cooling.
Defensive Responses of Larval Manduca Sexta and Their Sensitization by Noxious Stimuli In the Laboratory and Field
Authors: Walters Edgar T. , Illich Paul A. , Weeks Janis C. , Lewin Matthew R.
Published: April 2021

Sensitization of defensive responses following noxious stimulation occurs in diverse species, but no demonstration of nociceptive sensitization in insects has been reported. A set of defensive behavior patterns in larval Manduca sexta is described and shown to undergo sensitization following noxious mechanical stimulation. The striking response is a rapid bending that accurately propels the head towards sharply poking or pinching stimuli applied to most abdominal segments. The strike is accompanied by opening of the mandibles and, sometimes, regurgitation. The strike may function to dislodge small attackers and startle larger predators. When the same stimuli are applied to anterior segments, the head is pulled away in a withdrawal response. Noxious stimuli to anterior or posterior segments can evoke a transient withdrawal (cocking) that precedes a strike towards the source of stimulation and may function to maximize the velocity of the strike. More intense noxious stimuli evoke faster, larger strikes and may also elicit thrashing, which consists of large, cyclic, side-to-side movements that are not directed at any target. These are sometimes also associated with low-amplitude quivering cycles. Striking and thrashing sequences elicited by obvious wounding are sometimes followed by grooming-like behavior. Very young larvae also show locomotor responses to noxious stimuli. Observations in the field of attacks on M. sexta larvae by Cardinalis cardinalis, an avian predator, suggest that thrashing decreases the success of a bird in biting a larva. In the laboratory, noxious stimulation was found to produce two forms of sensitization. Repeated pinching of prolegs produces incremental sensitization, with later pinches evoking more strikes than the first pinch. Brisk pinching or poking of prolegs also produces conventional sensitization, in which weak test stimuli delivered to another site evoke more strikes following noxious stimulation. The degree and duration of sensitization increase with more intense noxious stimulation. The most intense stimulus sequences were found to enhance strike frequency for approximately 60 min. Nociceptive sensitization generalizes to sites distant from sites of noxious stimulation, suggesting that it involves a general, but transient, arousal of defensive responses.

Movies available on-line:

http://www.biologists.com/JEB/movies/jeb3271.html
Physiological and Molecular Characterization of Urea Transport by the Gills of the Lake Magadi Tilapia (Alcolapia Grahami)
Authors: Walsh Patrick J. , Grosell Martin , Goss Greg G. , Bergman Harold L. , Bergman Annie N. , Wilson Paul , Laurent Pierre , Alper Seth L. , Smith Craig P. , Kamunde Collins , Wood Chris M.
Published: April 2021

The Lake Magadi tilapia (Alcolapia grahami) is an unusual fish, excreting all its nitrogenous waste as urea because of its highly alkaline and buffered aquatic habitat. Here, using both physiological and molecular studies, we describe the mechanism of branchial urea excretion in this species. In vivo, repeated short-interval sampling revealed that urea excretion is continuous. The computed urea permeability of A. grahami gill is 4.74×10−5±0.38×10−5 cm s−1 (mean ± S.E.M., N=11), some 10 times higher than passive permeability through a lipid bilayer and some five times higher than that of even the most urea-permeable teleosts studied to date (e.g. the gulf toadfish). Transport of urea was bidirectional, as demonstrated by experiments in which external [urea] was elevated. Furthermore, urea transport was inhibited by classic inhibitors of mammalian and piscine urea transporters in the order thiourea>N-methylurea>acetamide. A 1700 base pair cDNA for a putative Magadi tilapia urea transporter (mtUT) was cloned, sequenced and found to display high homology with urea transporters from mammals, amphibians and other fishes. When cRNA transcribed from mtUT cDNA was injected into Xenopus laevis oocytes, phloretin-inhibitable urea uptake was enhanced 3.4-fold relative to water-injected controls. Northern analysis of gill, red blood cells, liver, muscle and brain using a portion of mtUT as a probe revealed that gill is the only tissue in which mtUT RNA is expressed. Magadi tilapia gill pavement cells exhibited a trafficking of dense-cored vesicles between the well-developed Golgi cisternae and the apical membrane. The absence of this trafficking and the poor development of the Golgi system in a non-ureotelic relative (Oreochromis niloticus) suggest that vesicle trafficking could be related to urea excretion in Alcolapia grahami. Taken together, the above findings suggest that the gills of this alkaline-lake-adapted species excrete urea constitutively via the specific facilitated urea transporter mtUT.
Low Metabolic Rate in Scorpions: Implications for Population Biomass and Cannibalism
Authors: Lighton John R. B. , Brownell Philip H. , Joos Barbara , Turner Robbin J.
Published: April 2021

Scorpions are abundant in arid areas, where their population biomass may exceed that of vertebrates. Since scorpions are predators of small arthropods and feed infrequently across multi-year lifespans, a parsimonious explanation for their observed, anomalously high biomass may be a depressed metabolic rate (MR). We tested the hypothesis that scorpion MR is significantly depressed compared with that of other arthropods, and we also measured the temperature-dependence of the MR of scorpions to quantify the interaction between large seasonal variations in desert temperatures and MR and, thus, long-term metabolic expenditure. Scorpion MR increased markedly with temperature (mean Q10=2.97) with considerable inter-individual variation. At 25 °C, the MRs of scorpions from two genera were less than 24 % of those of typical terrestrial arthropods (spiders, mites, solpugids and insects) of the same mass. It is likely, therefore, that the low MR of scorpions contributes to their high biomass in arid areas. The combination of high biomass and high production efficiency associated with low MR may also favor a density-dependent ‘transgenerational energy storage’ strategy, whereby juveniles are harvested by cannibalistic adults that may be closely related to their juvenile prey.
The Production of Elevated Flight Force Compromises Manoeuvrability in the Fruit Fly Drosophila Melanogaster
Authors: Lehmann Fritz-Olaf , Dickinson Michael H.
Published: April 2021

In this study, we have investigated how enhanced total flight force production compromises steering performance in tethered flying fruit flies, Drosophila melanogaster. The animals were flown in a closed-loop virtual-reality flight arena in which they modulated total flight force production in response to vertically oscillating visual patterns. By simultaneously measuring stroke amplitude and stroke frequency, we recorded the ability of each fly to modulate its wing kinematics at different levels of aerodynamic force production. At a flight force that exactly compensates body weight, the temporal deviations with which fruit flies vary their stroke amplitude and frequency are approximately 2.7 ° and 4.8 Hz of their mean value, respectively. This variance in wing kinematics decreases with increasing flight force production, and at maximum force production fruit flies are restricted to a unique combination of stroke amplitude, stroke frequency and mean force coefficient. This collapse in the kinematic envelope during peak force production could greatly attenuate the manoeuvrability and stability of animals in free flight.
Diurnal and Seasonal Variations in the Duration and Depth of the Longest Dives in Southern Elephant Seals (Mirounga Leonina): Possible Physiological and Behavioural Constraints
Authors: Bennett K. A. , Mcconnell B. J. , Fedak M. A.
Published: April 2021

This study seeks to understand how the physiological constraints of diving may change on a daily and seasonal basis. Dive data were obtained from southern elephant seals (Mirounga leonina) from South Georgia using satellite relay data loggers. We analysed the longest (95th percentile) dive durations as proxies for physiological dive limits. A strong, significant relationship existed between the duration of these dives and the time of day and week of year in which they were performed. The depth of the deepest dives also showed a significant, but far less consistent, relationship with local time of day and season. Changes in the duration of the longest dives occurred irrespective of their depth. Dives were longest in the morning (04:00–12:00 h) and shortest in the evening (16:00–00:00 h). The size of the fluctuation varied among animals from 4.0 to 20.0 min. The daily pattern in dive depth was phase-shifted in relation to the diurnal rhythm in dive duration. Dives were deeper at midday and shallower around midnight. Greater daily changes in duration occurred in seals feeding in the open ocean than in those foraging on the continental shelf. The seasonal peak in the duration of the longest dives coincided with austral midwinter. The size of the increase in dive duration from autumn/spring to winter ranged from 11.5 to 30.0 min. Changes in depth of the longest dives were not consistently associated with particular times of year. The substantial diurnal and seasonal fluctuations in maximum dive duration may be a result of changes in the physiological capacity to remain submerged, in addition to temporal changes in the ecological constraints on dive behaviour. We speculate about the role of melatonin as a hormonal mediator of diving capability.
In Situ Analysis of pH Gradients in Mosquito Larvae Using Non-Invasive, Self-Referencing, pH-Sensitive Microelectrodes
Authors: Boudko Dmitri Y. , Moroz Leonid L. , Linser Paul J. , Trimarchi James R. , Smith Peter J. S. , Harvey William R.
Published: April 2021

The alkaline environment, pH approximately 11, in the anterior midgut lumen of mosquito larvae is essential for normal nutrition and development. The mechanism of alkalization is, however, unknown. Although evidence from immunohistochemistry, electron microscopy and electrophysiology suggests that a V-ATPase is present in the basal membranes of the epithelial cells, its physiological role in the alkalization process has not been demonstrated. To investigate a possible role of the V-ATPase in lumen alkalization, pH gradients emanating from the hemolymph side of the midgut in semi-intact mosquito larvae were measured using non-invasive, self-referencing, ion-selective microelectrodes (SERIS). Large H+ concentration gradients, with highest concentrations close to the basal membrane (outward [H+ ] gradients), were found in the anterior midgut, whereas much smaller gradients, with concentrations lowest close to this membrane (inward [H+ ] gradients), were found in the gastric caeca and posterior midgut. Similar region-specific pH gradients, with consistent anterior-to-posterior profiles, were observed in individuals of two Aedes species, Aedes aegypti from semi-tropical Florida and Aedes canadensis from north-temperate Massachusetts. The gradients remained in a steady state for up to 6 h, the maximum duration of the recordings.

Bafilomycin A1 (10−5, 10−7 mol l−1 ) on the hemolymph side greatly diminished the [H+ ] gradients in the anterior midgut but had no effect on the gradients in the gastric caecum and posterior midgut. These physiological data are consistent with the previous findings noted above. Together, they support the hypothesis that a basal, electrogenic H+ V-ATPase energizes luminal alkalization in the anterior midgut of larval mosquitoes.
Ultrasound Avoidance Behaviour in the Bushcricket Tettigonia Viridissima (Orthoptera: Tettigoniidae)
Authors: Schulze Wolfram , Schul Johannes
Published: April 2021

The responses of female Tettigonia viridissima to simulated bat echolocation calls were examined during tethered flight. The insects responded with three distinct behaviours, which occurred at graded stimulus intensities. At low intensities (threshold 54 dB SPL), T. viridissima responded by steering away from the sound source (negative phonotaxis). At intensities approximately 10 dB higher, beating of the hindwing was interrupted, although the insect remained in the flight posture. A diving response (cessation of the wingbeat, closure of the forewings and alignment of the legs against the body) occurred with a threshold of 76 dB SPL. Considering these thresholds, we estimate that the diving response occurs at approximately the sound amplitude at which many aerial-hawking bats first receive echoes from the insect. The other behaviours probably occur before the bat detects the insect and should therefore be interpreted as early avoidance behaviours.

The repertoire of startle responses in T. viridissima, with directional and non-directional components, is similar to those of crickets and moths, but quite different from those described for another bushcricket (Neoconocephalus ensiger), which shows only a non-directional response. This supports the conclusion that bat-evasive behaviours are not conserved within the Tettigoniidae, but instead are shaped by the ecological constraints of the insects.
Resting Metabolic Rate and Morphology in Mice (Mus Musculus) Selected for High and Low Food Intake
Authors: Selman Colin , Lumsden Suzanne , Bünger Lutz , Hill William G. , Speakman John R.
Published: April 2021

We investigated the relationship between resting metabolic rate (RMR) and various morphological parameters in non-breeding mice, selected for high and low food intake corrected for body mass. RMR was measured at 30 °C, and mice were subsequently killed and dissected into 19 body components. High-food-intake mice had significantly greater body masses and a significantly elevated RMR compared with the low-intake mice. Data pooled across strains indicated that body mass, sex and strain together explained over 56 % of the observed variation in RMR. The effects of strain and sex on RMR and tissue morphology were removed, and three separate statistical analyses to investigate the relationship between RMR and organ morphology were performed: (i) employing individual regression analysis with each tissue component as a separate predictor against RMR; (ii) individual regression analysis with residual organ mass against residual RMR (i.e. with strain, sex and body mass effects removed); and (iii) pooling of some organ masses into functional groupings to reduce the number of predictors. Liver mass was the most significant morphological trait linked to differences in RMR. Small intestine length was significantly greater in the high-intake line; however, no difference was observed between strains in the dry mass of this organ, and there was no evidence to associate variability in the mass of the alimentary tract with variability in RMR. The effects of strain on RMR independent of the effect on body mass were consistent with the anticipated effect from the strain differences in the size of the liver.
Modulation of Haemocyanin Oxygen Affinity: Properties and Physiological Implications in a Changing World
Authors: Bridges C. R.
Published: April 2021

Crustacean haemocyanin oxygen affinity may be modified through changes in concentration of various inorganic and organic allosteric modulators. These may act in both positive and negative directions, increasing or decreasing haemocyanin oxygen affinity, and assist both in oxygen loading at the gills and oxygen release in the tissues. Inorganic ions, except for Mg2+, do not normally influence cooperativity or the Bohr effect, whereas most of the organic modulators decrease cooperativity without affecting the Bohr coefficient. Several new findings on the influence of sulphide and thiosulphate are reviewed together with evidence for unidentified factors that decrease haemocyanin oxygen affinity. The physiological implications of all these findings are discussed in the context of maintaining a flexible response to a changing environment.
Growth Factors, Heat-Shock Proteins and Regeneration in Echinoderms
Authors: Patruno M. , Thorndyke M. C. , Carnevali M. D. Candia , Bonasoro F. , Beesley P. W.
Published: April 2021

The study of regeneration in armed echinoderm species, including crinoids, ophiuroids and asteroids, is attracting increasing attention. Recent interest has focused on the presence and potential role of growth factors, including members of the nerve growth factor (NGF) and transforming growth factor-beta (TGF-β) families, in the regenerative process and their possible relationship to the normal developmental (ontogenetic) regulatory cascade. In addition, the expression patterns of the heat-shock family of stress proteins (Hsps) during regeneration are also important. Their role forms part of a normal stress response to the trauma of autotomy in combination with a putative function in tissue remodelling and associated protein turnover during regeneration. The temporal dynamics of the stress response may also be strongly indicative of environmentally adaptive pressures operating on these systems.
The Morphology of Autotomy Structures in the Sea Cucumber Eupentacta Quinquesemita Before and During Evisceration
Authors: Byrne Maria
Published: April 2021

Evisceration in the dendrochirotid sea cucumber Eupentacta quinquesemita is a whole-body response involving a predictable series of events including muscle contraction and failure of three autotomy structures: (i) the introvert, the dexterous anterior extensible portion of the body wall, (ii) the tendon linking the pharyngeal retractor muscle to the longitudinal body wall muscle and (iii) the intestine–cloacal junction. The autotomy structures are histologically complex, consisting of muscle, nervous and connective tissue. Autotomy resulted from complete loss in the tensility of the connective tissue ground substance. Separation of the autotomy structures was facilitated by muscle contraction. The cell and tissue changes involved with autotomy were documented by microscopic examination of autotomising tissue. Change in the autotomy structures appears to initiate from the peritoneal side with delamination of the peritoneum followed by a wave of disruption as the connective tissue is infiltrated by coelomic fluid. Evisceration and autotomy in E. quinquesemita are neurally controlled, so particular attention was paid to the fate of neuronal elements.

Neurosecretory-like processes containing large dense vesicles and axons were present in the connective tissue layers of the autotomy structures in association with extracellular matrix, muscles and neurons. These neuronal elements remained largely intact during autotomy and did not appear to be a source of factors that effect connective tissue change. They may, however, be involved in muscle activity. Holothuroid autotomy structures are completely or partially bathed in coelomic fluid, so there is potential for hormonal or neurosecretory activity using the coelomic fluid as a conduit. Connective tissue change during evisceration appears to be effected or mediated by an evisceration factor present in coelomic fluid that has a direct transmitter-like or neurosecretory-like mode of operation. The final outcome, expulsion of the viscera, is likely to result from a suite of factors that interact in a manner yet to be determined.
The Enteric Nervous System of Echinoderms: Unexpected Complexity Revealed by Neurochemical Analysis
Authors: García-Arrarás José E. , Rojas-Soto Michelle , Jiménez Luis B. , Díaz-Miranda Lucy
Published: April 2021

Echinoderms are one of the most important groups of metazoans from the point of view of evolution, ecology and abundance. Nevertheless, their nervous system has been little studied. Particularly unexplored have been the components of the nervous system that lie outside the ectoneural and hyponeural divisions of the main nerve ring and radial nerve cords. We have gathered information on the nervous components of the digestive tract of echinoderms and demonstrate an unexpected level of complexity in terms of neurons, nerve plexi, their location and neurochemistry. The nervous elements within the digestive system consist of a distinct component of the echinoderm nervous system, termed the enteric nervous system. However, the association between the enteric nervous system and the ectoneural and hyponeural components of the nervous system is not well established. Our findings also emphasize the importance of the large lacunae in the neurobiology of echinoderms, a feature that should be addressed in future studies.
Is the Resting Rate of Oxygen Consumption of Locomotor Muscles in Crustaceans Limited by the Low Blood Oxygenation Strategy?
Authors: Forgue Jean , Legeay Alexia , Massabuau J.-C.
Published: April 2021

Numerous water-breathers exhibit a gas-exchange regulation strategy that maintains O2 partial pressure, , in the arterial blood within the range 1–3 kPa at rest during the daytime. In a night-active crustacean, we examined whether this could limit the rate of O2 consumption of locomotor muscles and/or the whole body as part of a coordinated response to energy conservation. In the crayfish Astacus leptodactylus, we compared the in vitro relationship between the of locomotor muscles as a function of the extracellular and and in vivo circadian changes in blood gas tensions at various values of water . In vitro, the of locomotor muscle, either at rest or when stimulated with CCCP, was O2-dependent up to an extracellular of 8–10 kPa. In vivo, the existence of a night-time increase in arterial of up to 4 kPa at water values of 20 and 40 kPa was demonstrated, but an experimental increase in arterial during the day did not lead to any rise in whole-body . This suggested that the low blood in normoxia has no global limiting effect on daytime whole-body . The participation of blood O2 status in shaping the circadian behaviour of crayfish is discussed.
Ecophysiological Adaptation to salinity throughout a Life Cycle: A Review in Homarid Lobsters
Authors: Charmantier Guy , Haond Christophe , Lignot Jean-H. , Charmantier-Daures Mireille
Published: April 2021

Adaptations to salinity are reviewed throughout development in both species of the genus Homarus. Some populations of homarid lobsters are known to inhabit coastal and estuarine areas where salinity fluctuates. Salinity tolerance varies during development, with 50 % lethal salinities (LS50) ranging from approximately 15–17 ‰ in larvae to approximately 12 ‰ in postlarvae and 10 ‰ in adults. Larval and adult lobsters can avoid low-salinity areas using behavioural strategies.

When exposed to low salinity, the capacity to osmoregulate varies with development. Embryos are osmoconformers and are osmotically protected by the egg membranes. Larvae are also osmoconformers, and the pattern of osmoregulation changes at metamorphosis to hyper-regulation, which is retained throughout the later stages up to the adult stage. Exposure to low salinity increases the activity of Na+/K+-ATPase in postlarvae and later stages. The level of osmoregulation evaluated through the osmoregulatory capacity (the difference between haemolymph and medium osmolalities) is negatively affected by low temperature (2 °C). The variations in haemolymph osmolality resulting from osmoconforming or partial osmoregulation are compensated by intracellular iso-osmotic regulation. Neuroendocrine control of osmoregulation appears in postlarvae and seems to involve the crustacean hyperglycaemic hormone. In adult lobsters, the gills appear to have a respiratory function only, and extracellular osmoregulation is effected by the epipodites, with the addition of the branchiostegites at low salinity. These organs are present at hatching. Transmission electron microscopy and immunolocalization of Na+/K+-ATPase reveal that the epipodites become functional in larvae and that the branchiostegites become functional in postlarvae. An integrated series of events links the appearance of osmoregulatory tissues, the increase in Na+/K+-ATPase activity, the occurrence in postlarvae of hyper-regulation at low salinity and the increase in salinity tolerance. Further ecological and physiological studies are proposed for a better understanding of the adaptive significance of the ontogeny of osmoregulation in lobsters.
Environmentally Mediated Carbonic Anhydrase Induction in the Gills of Euryhaline Crustaceans
Authors: Henry Raymond P.
Published: April 2021

The enzyme carbonic anhydrase appears to be a central molecular component in the suite of physiological and biochemical adaptations to low salinity found in euryhaline crustaceans. It is present in high activities in the organs responsible for osmotic and ionic regulation, the gills, and more specifically, the individual gills that are specialized for active ion uptake from dilute sea water. Within those gills carbonic anhydrase is distributed among different subcellular pools, the cytoplasm, mitochondria and microsomes. The cytoplasmic pool represents the largest subcellular fraction of carbonic anhydrase activity, and it is this fraction that undergoes a tenfold induction during acclimation to low salinity. Carbonic anhydrase activity is present in excess of that needed to support the general ion-transport processes, and so it is doubtful that carbonic anhydrase activity itself is a point of short-term regulation in response to salinity changes. Rather, upregulation of carbonic anhydrase appears to be a result of selective gene expression, representing a permanent response to long-term adaptation to low salinity. The exact signal that initiates the induction of carbonic anhydrase, and the pathway through which that signal is transduced to the activation of the carbonic anhydrase gene, are unknown, but two promising avenues of research exist. First, induction of carbonic anhydrase is immediately preceded by hemodilution and subsequent cell swelling, a potential initiating event in the process. Second, recent work indicates that expression of carbonic anhydrase is under the control of a repressor substance, located in the eyestalk, whose effect is removed upon exposure to low salinity.
Daily variations in crustacean hyperglycaemic hormone and serotonin immunoreactivity during the development of crayfish
Authors: Escamilla-Chimal Elsa G. , Van Herp François , Fanjul-Moles María-Luisa
Published: April 2021

The present study investigated changes in crustacean hyperglycaemic hormone (CHH) and serotonin (5-hydroxytryptamine, 5-HT) immunoreactivity in the retina and the X-organ/sinus gland complex (XO-SG) of the crayfish Procambarus clarkii at two developmental stages, post-embryonic stage two (PO2) and the juvenile stage, at three different times of day, under a photoperiod cycle of 12 h:12 h L:D, using qualitative and quantitative immunohistochemical methods. In the retina, CHH immunoreactivity is located in the tapetal cells, while 5-HT immunoreactivity is found in the retinular cells. In the XO-SG, CHH-immunoreactivity is localized to the CHH-producing cell perikarya and in their axons and endings in the sinus gland, while 5-HT immunoreactivity is restricted to axon endings branching into the perikarya of the CHH-producing cells. A stereological analysis demonstrates that the PO2 and juvenile stages show significant differences in the amount of the immunoreactive CHH and 5-HT material at the three selected time points, indicating daily and related changes in the levels of CHH and 5-HT in the XO-SG and the retina. Our findings therefore support the idea that daily rhythms in the secretory activity of the XO-SG complex affect the circadian sensitivity of the eye. Furthermore, the differences found between the PO2 and juvenile stages suggest that both CHH and 5-HT are key factors in the development of the circadian rhythm of retinal sensitivity.
Reproductive behaviour in the male cricket Gryllus bimaculatus DeGeer. II. Neural control of the genitalia
Authors: Kumashiro Mikihiko , Sakai Masaki
Published: April 2021

To understand the neural mechanisms of reproductive behaviour in the male cricket, we identified motor neurones innervating the muscles in each genital organ by backfilling with cobalt/nickel and recording their extracellular spike activity from nerve bundles of the terminal abdominal ganglion during tethered copulation and spermatophore formation. During tethered copulation, at least two motor neurones innervating two ipsilateral muscles were activated during projection of the guiding rod of the phallic dorsal pouch. Only one motor neurone, innervating four ipsilateral muscles of the dorsal pouch, was responsible for spermatophore extrusion by deforming the dorsal pouch. For spermatophore transfer, three motor neurones, singly innervating three epiphallus muscles, played a major role in opening passages for haemolymph to enter the ventral lobes and median pouch by bending the epiphallus. Two ventral lobe and 3–5 median pouch motor neurones seemed to play a role in expanding or folding the two membranous structures by relaxing or contracting their muscle fibres. After spermatophore transfer, most of the genital motor neurones exhibited a rhythmic burst of action potentials causing movement of the phallic complex coupled with strong abdominal contractions. For spermatophore formation, the genital motor neurones began to accelerate their rhythmic bursts approximately 30 s prior to subgenital plate opening and then changed their activity to tonic bursting or silence. The results have allowed us to describe the timing of the onset and termination of genital muscle contraction more precisely than before, to examine the neural mechanisms of copulatory motor control and to speculate on the neural organization of the reproductive centre for spermatophore extrusion and protrusion.
Spatio-temporal gait characteristics of level and vertical locomotion in a ground-dwelling and a climbing gecko
Authors: Zaaf A. , Van Damme R. , Herrel A. , Aerts P.
Published: April 2021

The effects of incline (vertical versus horizontal) on spatio-temporal gait characteristics (stride and step length, frequency, duty factor, degree of sprawling) were measured over a range of speeds in a ground-dwelling (Eublepharis macularius) and a climbing (Gekko gecko) species of gecko. Surprisingly, the climbing species also performs very well when moving on the horizontal substratum. In the present experiments, climbing speeds ranged from 0.6 to 1.2 m s−1, whereas speeds for level locomotion were between 0.6 and 1.8 m s−1. In contrast, the vertical climbing capacities of the ground-dweller are limited (speeds below 0.1 m s−1versus level speeds between 0.2 and 1.1 m s−1 ). In general, we demonstrate that very little adjustment in gait characteristics is made by either species when they are forced to move on their non-habitual substratum. Moreover, gait characteristics differ little between the species despite the clear differences in ecological niche. Higher level or climbing speeds are realized mainly (or exclusively in the case of level locomotion in G. gecko) by increasing stride frequency. Stride lengths and duty factors vary with speed in the ground-dweller, but not in the climbing species. Step length and the degree of sprawling are speed-independent (except for hind-limb sprawling in G. gecko on the level). It is argued that this common strategy suits climbing (fixed spatial variables, no floating phases) rather than level locomotion.
Evidence for a form of adrenergic response to stress in the mollusc Crassostrea gigas
Authors: Lacoste A. , Malham S. K. , Cueff A. , Jalabert F. , Gélébart F. , Poulet S. A.
Published: April 2021

Catecholamines and pro-opiomelanocortin (POMC)-derived peptides, some of the central regulators of the stress-response systems of vertebrates, are also present in invertebrates. However, studies are needed to determine how these hormones participate in the organisation of neuroendocrine stress-response axes in invertebrates. Our present work provides evidence for the presence of an adrenergic stress-response system in the oyster Crassostrea gigas. Noradrenaline and dopamine are released into the circulation in response to stress. Storage and release of these hormones take place in neurosecretory cells presenting morphological and biochemical similarities with vertebrate chromaffin cells. Both in vivo and in vitro experiments showed that applications of the neurotransmitters acetylcholine or carbachol caused no significant release of noradrenaline or dopamine. Moreover, the nicotinic antagonists hexamethonium and α-bungarotoxin and the muscarinic antagonist atropine caused no significant inhibition of catecholamine release in stressed oysters. Adrenocorticotropic hormone (ACTH) induced a significant release of noradrenaline, but the release of dopamine in response to ACTH was not significant. These results suggest that, unlike that of vertebrates, the adrenergic stress-response system of oysters is not under the control of acetylcholine and that other factors, such as the neuropeptide ACTH, might control this system.
Defensive inking in Aplysia spp: multiple episodes of ink secretion and the adaptive use of a limited chemical resource
Authors: Nolen Thomas G. , Johnson P. M.
Published: April 2021

The seahare Aplysia spp. extracts many of its defensive chemicals from its red seaweed diet, including its purple ink, which is an effective deterrent against predators such as anemones and crabs. It is believed that the inking behavior is a high-threshold, all-or-none fixed act that nearly completely depletes the seahare of its ink supply. If a seahare depletes its gland of ink, it must seek out a source of red seaweed and then feed for at least 2 days to replenish its ink supply. This suggests that the animal would not be able to deploy ink more than once in rapid succession in response to successive attacks from one or more predators.

However, we found that Aplysia spp. can secrete ink in response to three or more successive stimulations with (i) anemone tentacles, (ii) a mechanical stimulus, consisting of grabbing and lifting the animal from the substratum, or (iii) a noxious electric shock. A spectro-photometric measure of ink secretion showed that only approximately 48 % of the gland’s releasable ink reserves are deployed initially. Thus, deployment of this defensive chemical is not strictly all-or-nothing, although the trigger mechanism is. Moreover, the animal tends to secrete a relatively fixed proportion (30–50 %) of its available ink reserves even after its gland has been depleted to approximately half its initial content. Since an animal need only use a proportion of its ink reserves to deter an attacker effectively, the inking behavior is adaptive in its economical use of a limited resource.
Tympanic membrane oscillations and auditory receptor activity in the stridulating cricket Gryllus bimaculatus
Authors: Poulet J. F. A. , Hedwig B.
Published: April 2021

The ears of stridulating crickets are exposed to loud self-generated sounds that might desensitise the auditory system and reduce its responsiveness to environmental sounds. We examined whether crickets prevent self-induced auditory desensitisation, and measured the responsiveness of the peripheral auditory system of the cricket (acoustic spiracle, tympanic membrane and tympanic nerve) during pharmacologically induced sonorous (two-winged) and silent (one-winged) stridulation.

The acoustic spiracles remained open during stridulation, so the self-generated auditory signal had full access to both the external side and the internal side of the tympanic membrane. When the spiracles shut in resting crickets, the responsiveness of the tympanic membrane to acoustic stimuli varied according to the phase of ventilation and was minimal during expiration. The tympanic membrane oscillated in phase with the self-generated sounds during sonorous chirps and did not oscillate during silent chirps. In both sonorously and silently singing crickets, the responses of the tympanic membrane to acoustic stimuli were identical during the chirps and the chirp intervals.

Bursts of activity were recorded in the tympanic nerve during sonorous chirps; however, activity was minor during silent chirps. In sonorously and in silently singing crickets, the summed nerve response to acoustic stimuli in the chirp intervals was the same as in resting crickets. The response to stimuli presented during the syllable intervals of sonorous chirps was slightly reduced compared with the response in the chirp intervals as a consequence of receptor habituation. In silently singing crickets, acoustic stimuli elicited the same summed nerve response during chirps and chirp intervals. These data indicate that in the cricket no specific mechanism acts to reduce the responsiveness of the peripheral auditory pathway during stridulation.
Mechanisms of frequency-specific responses of ω neuron 1 in crickets (Teleogryllus oceanicus): a polysynaptic pathway for song?
Authors: Faulkes Zen , Pollack Gerald S.
Published: April 2021

In crickets (Teleogryllus oceanicus), the auditory interneuron omega neuron 1 (ON1) responds to sounds over a wide range of frequencies but is most sensitive to the frequency of conspecific songs (4.5 kHz). Response latency is longest for this same frequency. We investigate the mechanisms that might account for the longer latency of ON1 to cricket-like sounds. Intracellular recordings revealed no evidence for appropriately timed postsynaptic inhibition of ON1 that might increase its latency, nor was latency affected by picrotoxin. The onset of excitatory postsynaptic potentials (EPSPs) was delayed for 4.5 kHz stimuli compared with ultrasound stimuli, pointing to a presynaptic locus for the latency difference. When ON1 is stimulated with high frequencies, discrete, apparently unitary EPSPs can be recorded in its dendrite, and these are latency-locked to spikes recorded simultaneously in the auditory nerve. This suggests that input to ON1 from high-frequency-tuned auditory receptor neurons is monosynaptic. In agreement with this, brief ultrasound stimuli evoke a single, short-latency EPSP in ON1. In contrast, the EPSP evoked by a brief 4.5 kHz stimulus consists of an early component, similar in latency to that evoked by ultrasound and possibly evoked by ultrasound-tuned receptors, and a later, dominant component. We interpret the early peak as arising from a monosynaptic afferent pathway and the late peak from a polysynaptic afferent pathway. Multiple-peak EPSPs, with timing similar to those evoked by sound stimuli, were also evoked by electrical stimulation of the auditory nerve.
Prey detection in selective plankton feeding by the paddlefish: is the electric sense sufficient?
Authors: Wilkens Lon A. , Wettring Barbara , Wagner Eva , Wojtenek Winfried , Russell David
Published: April 2021

The long rostrum of the paddlefish Polyodon spathula supports an extensive array of ampullary electroreceptors and has been proposed to function as an antenna for detecting planktonic prey. Evidence in support of this hypothesis is presented in experiments that preclude the use of other sensory mechanisms for plankton detection. Paddlefish swimming in a recirculating observation chamber are shown to feed normally in the dark when prey-related chemical and hydrodynamic sensory cues are masked or attenuated. Specifically, we demonstrate that the spatial distribution of plankton captured by paddlefish is little changed when the plankton are individually encapsulated in agarose, when a high background concentration of plankton extract is added to the chamber, when the nares are plugged and under turbulent water flow conditions. Paddlefish also discriminate between encapsulated plankton and ‘empty’ agarose particles of the same size. Although capture distributions differed somewhat under certain conditions, the general pattern and effectiveness of prey capture were not disrupted by these procedures. These results support the conclusion that paddlefish, as zooplanktivores, rely on their passive electric sense for prey detection.
Count and spark? The echo response of the weakly electric fish Gnathonemus petersii to series of pulses
Authors: Schuster Stefan
Published: April 2021

Weakly electric fish of the pulse type electrolocate objects in the dark by emitting discrete electric organ discharges (EODs) separated by intervals of silence. Two neighbouring pulse-type fish often reduce the risk of discharging simultaneously by means of an ‘echo response’: one fish will respond to a neighbour’s EOD with a discharge of its own following at a fixed short latency so that its EOD will occur long before the next EOD of its neighbour. Although working elegantly for two partners, this simple strategy should fail in larger groups because two fish could discharge in response to the same EOD of a third fish. Here, I show that the mormyrid fish Gnathonemus petersii could use a simple mechanism to reduce this problem. Individuals were stimulated with two closely spaced pulses, the second following so as to coincide with an echo given in response to the first. All the fish examined were able to respond more to the second pulse so that most of their echoes did not collide with the second pulse. An analysis was made of how echoing more to the second pulse depends on (i) the delay at which the stimulus followed the last spontaneous EOD, (ii) the spontaneous firing rate, (iii) the intensity of the stimulus, (iv) the number of stimulus pulses, (v) the interval between stimulus pulses, and (vi) the level of previous stimulation with double pulses. The results suggest that echoing more in response to the second pulse is probably because the first pulse causes an after-effect whose inferred properties would be compatible with the properties of the mormyromast afferences thought to be involved in the echo response.