bluuebunny/crossref_metadata_2025 huggingface dataset:
Neural architecture of the electrosensory lateral line lobe: adaptations for coincidence detection, a sensory searchlight and frequency-dependent adaptive filtering
Authors: Berman Neil J. , Maler Leonard
Published: April 2021

The electrosensory lateral line lobe (ELL) of weakly electric fish is the only nucleus that receives direct input from peripheral electroreceptor afferents. This review summarises the neurotransmitters, receptors and second messengers identified in the intrinsic circuitry of the ELL and the extrinsic descending direct and indirect feedback pathways, as revealed by recent in vitro and in vivo studies. Several hypotheses of circuitry function are examined on this basis and on the basis of recent functional evidence: (1) fast primary afferent excitatory postsynaptic potentials (EPSPs) and fast granule cell 2 GABAA inhibitory postsynaptic potentials (IPSPs) suggest the involvement of basilar pyramidal cells in coincidence detection; (2) voltage-dependent EPSPs and IPSPs, dendritic spike bursts and frequency-dependent synaptic facilitation support a sensory searchlight role for the direct feedback pathway; and (3) the contributions of distal and proximal inhibition, anti-Hebbian plasticity and beam versus isolated fiber activity patterns are discussed with reference to an adaptive spatio-temporal filtering role for the indirect descending pathway.
Encoding and processing of sensory information in neuronal spike trains
Authors: Gabbiani F. , Metzner W.
Published: April 2021

Recently, a statistical signal-processing technique has allowed the information carried by single spike trains of sensory neurons on time-varying stimuli to be characterized quantitatively in a variety of preparations. In weakly electric fish, its application to first-order sensory neurons encoding electric field amplitude (P-receptor afferents) showed that they convey accurate information on temporal modulations in a behaviorally relevant frequency range (<80 Hz). At the next stage of the electrosensory pathway (the electrosensory lateral line lobe, ELL), the information sampled by first-order neurons is used to extract upstrokes and downstrokes in the amplitude modulation waveform. By using signal-detection techniques, we determined that these temporal features are explicitly represented by short spike bursts of second-order neurons (ELL pyramidal cells). Our results suggest that the biophysical mechanism underlying this computation is of dendritic origin. We also investigated the accuracy with which upstrokes and downstrokes are encoded across two of the three somatotopic body maps of the ELL (centromedial and lateral). Pyramidal cells of the centromedial map, in particular I-cells, encode up- and downstrokes more reliably than those of the lateral map. This result correlates well with the significance of these temporal features for a particular behavior (the jamming avoidance response) as assessed by lesion experiments of the centromedial map.
Molecular Biology of the Apteronotus NMDA Receptor NR1 Subunit
Authors: Dunn Robert J. , Bottai Daniele , Maler Leonard
Published: April 2021

The complete sequences and expression patterns of the NR1 (aptNR1) subunit of the N-methyl-D-aspartate (NMDA) receptor and its alternative splice isoforms have been determined for the weakly electric fish Apteronotus leptorhynchus. The deduced amino acid sequence of aptNR1 is approximately 88 % identical to the NR1 sequences of other vertebrate. Two of the three alternative splice cassettes previously described for mammalian NR1s, N1 and C1, are present in aptNR1, but the third cassette, C2, is not found. In addition, two teleost-specific splice cassettes occur on the N-terminal side of the C1 sequence. The cellular patterns of aptNR1 expression, including the patterns of N1 and C1 splicing, have been mapped using the in situ hybridization technique. High levels of aptNR1 mRNA were detected throughout the central nervous system including most neurons of the electrosensory system, with the highest levels in electrosensory lateral line lobe pyramidal cells. Expression of the N1 splice isoform was higher in more caudal regions of the brain, and expression of the C1 splice isoform was higher in more rostral regions. The N1 splice isoform was present in almost all NR1-positive cells, in contrast to the C1 splice isoform which was restricted to a subset of NR1-positive cells. These results demonstrate that the NR1 subunit of the NMDA receptor is evolutionarily conserved across species and that regulation of alternative RNA splicing modulates the properties of NR1 in different neurons of the central nervous system of A. leptorhynchus.
Synaptic plasticity in the mormyrid electrosensory lobe
Authors: Bell Curtis C. , Han Victor Z. , Sugawara Yoshiko , Grant Kirsty
Published: April 2021

The mormyrid electrosensory lateral line lobe (ELL) is one of several different sensory structures in fish that behave as adaptive sensory processors. These structures generate negative images of predictable features in the sensory inflow which are added to the actual inflow to minimize the effects of predictable sensory features. The negative images are generated through a process of association between centrally originating predictive signals and sensory inputs from the periphery. In vitro studies in the mormyrid ELL show that pairing of parallel fiber input with Na+ spikes in postsynaptic cells results in synaptic depression at the parallel fiber synapses. The synaptic plasticity observed at the cellular level and the associative process of generating negative images of predicted sensory input at the systems level share a number of properties. Both are rapidly established, anti-Hebbian, reversible, input-specific and tightly restricted in time. These common properties argue strongly that associative depression at the parallel fiber synapse contributes to the adaptive generation of negative images in the mormyrid ELL.
Signals and noise in the elasmobranch electrosensory system
Authors: Montgomery J. C. , Bodznick D.
Published: April 2021

Analyzing signal and noise for any sensory system requires an appreciation of the biological and physical milieu of the animal. Behavioral studies show that elasmobranchs use their electrosensory systems extensively for prey detection, but also for mate recognition and possibly for navigation. These biologically important signals are detected against a background of self-generated bioelectric fields. Noise-suppression mechanisms can be recognized at a number of different levels: behavior, receptor anatomy and physiology, and at the early stages of sensory processing. The peripheral filters and receptor characteristics provide a detector with permissive temporal properties but restrictive spatial characteristics. Biologically important signals probably cover the range from direct current to 10 Hz, whereas the bandwidth of the receptors is more like 0.1–10 Hz. This degree of alternating current coupling overcomes significant noise problems while still allowing the animal to detect external direct current signals by its own movement. Self-generated bioelectric fields modulated by breathing movement have similar temporal characteristics to important external signals and produce very strong modulation of electrosensory afferents. This sensory reafference is essentially similar, or common-mode, across all afferent fibers. The principal electrosensory neurons (ascending efferent neurons; AENs) of the dorsal octavolateralis nucleus show a greatly reduced response to common-mode signals. This suppression is mediated by the balanced excitatory and inhibitory components of their spatial receptive fields. The receptive field characteristics of AENs determine the information extracted from external stimuli for further central processing.
Neural circuitry for communication and jamming avoidance in gymnotiform electric fish
Authors: Metzner Walter
Published: April 2021

Over the past decade, research on the neural basis of communication and jamming avoidance in gymnotiform electric fish has concentrated on comparative studies of the premotor control of these behaviors, on the sensory processing of communication signals and on their control through the endocrine system, and tackled the question of the degree to which these behaviors share neural elements in the sensory–motor command chain by which they are controlled. From this wealth of investigations, we learned, first, how several segregated premotor pathways controlling a single central pattern generator, the medullary pacemaker nucleus, can provide a large repertoire of behaviorally relevant motor patterns. The results suggest that even small evolutionary modifications in the premotor circuitry can yield extensive changes in the behavioral output. Second, we have gained some insight into the concerted action of the brainstem, the diencephalon and the long-neglected forebrain in sensory processing and premotor control of communication behavior. Finally, these studies shed some light on the behavioral significance of multiple sensory brain maps in the electrosensory lateral line lobe that long have been a mystery. From these latter findings, it is tempting to interpret the information processing in the electrosensory system as a first step in the evolution towards the ‘distributed hierarchical’ organization commonly realized in sensory systems of higher vertebrates.
Resolving competing theories for control of the jamming avoidance response: the role of amplitude modulations in electric organ discharge decelerations
Authors: Takizawa Yumi , Rose Gary J. , Kawasaki Masashi
Published: April 2021

The algorithm for the control of the jamming avoidance response (JAR) of Eigenmannia has been the subject of debate for over two decades. Two competing theories have been proposed to explain how fish determine the correct direction to shift their pacemaker frequency during jamming. One theory emphasizes the role of time-asymmetric beat envelopes, while the other emphasizes the role of amplitude- and phase-difference computations that arise from the differences in spatial geometry of the electric fields of neighboring fish. In repeating earlier experiments, we found that the decision to raise or lower the pacemaker frequency reliably above or below its resting level depends on the latter process, and that frequency deceleration responses to amplitude modulation appear to be sufficient to explain previous experimental results on which the former theory is based. Specifically, fish of the genus Eigenmannia show differential deceleration responses to asymmetric beat envelopes. The deceleration responses do not require phase modulation and show a sensitivity for amplitude modulation depth and selectivity for amplitude modulation rate comparable with that of JARs that are elicited when amplitude- and phase-difference information is available.
Neural command of electromotor output in mormyrids
Authors: Grant Kirsty , Emde Gerhard Von Der , Sena Leonel Gomez , Mohr Claudia
Published: April 2021

The electric discharge of mormyrid fish has an irregular pattern controlled by the electromotor command nucleus in the medulla. Anatomical studies suggest that much of the descending information integrated by the command nucleus comes from the diencephalic precommand nucleus. But field potentials related to the motor command occur later in the precommand nucleus than in the command nucleus, suggesting that they are a corollary rather than a cause of electromotor command initiation. Recorded extracellularly, certain precommand nucleus units fire spontaneously between electromotor commands but pause briefly following each command; others units fire a burst of spikes only during the post-command pause. The firing frequency of the former is correlated with the duration of the interval between successive electromotor commands when the fish is discharging at more than approximately 5 Hz. The post-command pause in spontaneous firing is due to corollary-discharge-mediated feedback inhibition, probably generated by the activity of the bursting units that fire only during this period. Precommand nucleus neurons are activated by electrosensory input, and stimulation of the precommand nucleus modulates the endogenous pattern of electromotor command. We propose that the irregular rhythm of the motor command depends largely on the integration of descending information of various origins, conveyed via the precommand nucleus to the command nucleus, and that this process is regulated by corollary discharge feedback inhibition to the precommand nucleus.
Communication signals and sound production mechanisms of mormyrid electric fish
Authors: Crawford John D. , Huang Xiaofeng
Published: April 2021

The African weakly electric fishes Pollimyrus isidori and Pollimyrus adspersus (Mormyridae) produce elaborate acoustic displays during social communication in addition to their electric organ discharges (EODs). In this paper, we provide new data on the EODs of these sound-producing mormyrids and on the mechanisms they use to generate species-typical sounds.

Although it is known that the EODs are usually species-specific and sexually dimorphic, the EODs of closely related sound-producing mormyrids have not previously been compared. The data presented demonstrate that there is a clear sexual dimorphism in the EOD waveform of P. isidori. Females have a multi-phasic EOD that is more complex than the male’s biphasic EOD. In this respect, P. isidori is similar to its more thoroughly studied congener P. adspersus, which has a sexually dimorphic EOD. The new data also reveal that the EODs of these two species are distinct, thus showing for the first time that species-specificity in EODs is characteristic of these fishes, which also generate species-specific courtship sounds.

The sound-generating mechanism is based on a drumming muscle coupled to the swimbladder. Transverse sections through decalcified male and female P. adspersus revealed a muscle that envelops the caudal pole of the swimbladder and that is composed of dorso-ventrally oriented fibers. The muscle is five times larger in males (14.5±4.4 μl, mean ± S.D.) than in females (3.2±1.8 μl). The fibers are also of significantly larger diameter in males than in females. Males generate courtship sounds and females do not.

The function of the swimbladder muscle was tested using behavioral experiments. Male P. adspersus normally produce acoustic courtship displays when presented with female-like electrical stimuli. However, local anesthesia of the swimbladder muscle muted males. In control trials, males continued to produce sounds after injection of either lidocaine in the trunk muscles or saline in the swimbladder muscles.
Blowfly flight and optic flow : I. Thorax kinematics and flight dynamics
Authors: Schilstra C. , Van Hateren J. H.
Published: April 2021

The motion of the thorax of the blowfly Calliphora vicina was measured during cruising flight inside a cage measuring 40 cm×40 cm×40 cm. Sensor coils mounted on the thorax picked up externally generated magnetic fields and yielded measurements of the position and orientation of the thorax with a resolution of 1 ms, 0.3 ° and 1 mm. Flight velocities inside the cage were up to 1.2 m s−1, and accelerations were up to 1 g (≈10m s−2) vertically and 2 g horizontally. During flight, blowflies performed a series of short (approximately 20–30 ms) saccade-like turns at a rate of approximately 10 s−1. The saccades consisted of a succession of rotations around all axes, occurring in a fixed order. First, a roll was started. Second, the rolled thorax pitched (pulling the nose up) and yawed, resulting in a turn relative to the outside world. Finally, the thorax rolled back to a level position. Saccades had yaw amplitudes of up to 90 °, but 90 % were smaller than 50 °. Maximum angular velocities were 2000 ° s−1, and maximum accelerations were 105 ° s−2. The latter correspond to torques consistent with the maximal force (2×10−3 N) that can be generated by the flight motor as inferred from the maximal linear acceleration. Furthermore, the sequence of energy investment in consecutive rotations around different axes appears to be optimized during a saccade.
Blowfly flight and optic flow: II. Head movements during flight
Authors: Hateren J. H. Van , Schilstra C.
Published: April 2021

The position and orientation of the thorax and head of flying blowflies (Calliphora vicina) were measured using small sensor coils mounted on the thorax and head. During flight, roll movements of the thorax are compensated by counter rolls of the head relative to the thorax. The yaw turns of the thorax (thorax saccades) are accompanied by faster saccades of the head, starting later and finishing earlier than the thorax saccades. Blowfly flight can be divided into two sets of episodes: ‘during saccades’, when high angular velocities of up to a few thousand degrees per second are reached by both the thorax and head, and ‘between saccades’, when the orientation of the thorax and, in particular, the head is well stabilized. Between saccades, the angular velocities of the head are approximately half those of the thorax and lie mostly in the range 0–100 ° s−1 for any rotation (yaw, pitch and roll). These velocities are low enough to limit the visual blur attributable to rotation. It is argued that the split into periods during which either rotational optic flow (‘during saccades’) or translatory optic flow (‘between saccades’) dominates is helpful for processing optic flow when signals and neurons are noisy.
Time course of salinity adaptation in a strongly euryhaline estuarine teleost, Fundulus heteroclitus: a multivariable approach
Authors: Marshall W. S. , Emberley T. R. , Singer T. D. , Bryson S. E. , McCormick S. D.
Published: April 2021

Freshwater-adapted killifish (Fundulus heteroclitus) were transferred directly from soft fresh water to full-strength sea water for periods of 1 h, 3 h, 8 h and 1, 2, 7, 14 and 30 days. Controls were transferred to fresh water for 24 h. Measured variables included: blood [Na+], osmolality, glucose and cortisol levels, basal and stimulated rates of ion transport and permeability of in vitro opercular epithelium, gill Na+/K+-ATPase and citrate synthase activity and chloride cell ultrastructure. These data were compared with previously published killifish cystic fibrosis transmembrane conductance regulator (kfCFTR) expression in the gills measured over a similar time course. Plasma cortisol levels peaked at 1 h, coincident with a rise in plasma [Na+]. At 8 h after transfer to sea water, a time at which previous work has shown kfCFTR expression to be elevated, blood osmolality and [Na+] were high, and cortisol levels and opercular membrane short-circuit current (Isc; a measure of Cl− secretion rate) were low. The 24 h group, which showed the highest level of kfCFTR expression, had the highest plasma [Na+] and osmolality, elevated plasma cortisol levels, significantly lower opercular membrane resistance, an increased opercular membrane ion secretion rate and collapsed tubule inclusions in mitochondria-rich cells, but no change in gill Na+/K+-ATPase and citrate synthase activity or plasma glucose levels. Apparently, killifish have a rapid (<1 h) cortisol response to salinity coupled to subsequent (8–48 h) expression of kfCFTR anion channel proteins in existing mitochondria-rich cells that convert transport from ion uptake to ion secretion.
Developmental patterns of heart rate in altricial avian embryos and hatchlings
Authors: Pearson James T. , Noma Yasuhiro , Tazawa Hiroshi
Published: April 2021

The aims of this study were to determine the patterns of development of heart rate (fH) in altricial avian embryos and hatchlings, and then to examine how fH is regulated to meet metabolic requirements in altricial embryos. Embryonic mean heart rate in 12 altricial species (Passeriformes and Psittaciformes) increased during pre-pipping incubation in all species except the cockatiel (Nymphicus hollandicus), in which tended to decrease prior to pipping. The rate of increase in fH tripled during the pipping phase in all species, and was significantly higher during the pipping period and in hatchlings than during pre-pipping development. The O2 pulse (O2 consumed per cardiac beat) of altricial embryos increased in direct proportion to embryo mass (loge /loge base), although was often low prior to pipping, implying that stroke volume increases in the second half of incubation. We conclude that fH contributes more than other factors towards supplying the metabolic demands of the embryo during the middle of incubation and the final pipping phase, but less during the intervening period of late incubation.
Salivary glands of the sand fly Phlebotomus papatasi contain pharmacologically active amounts of adenosine and 5′-AMP
Authors: Ribeiro José M. C. , Katz Oren , Pannell Lewis K. , Waitumbi John , Warburg Alon
Published: April 2021

Salivary gland homogenates of the sand fly Phlebotomus papatasi contain large amounts of adenosine and 5′-AMP, of the order of 1 nmol per pair of glands, as demonstrated by liquid chromatography, ultraviolet spectrometry, mass spectrometry and bioassays. These purines, 75–80 % of which are secreted from the glands following a blood meal, have vasodilatory and anti-platelet activities and probably help the fly to obtain a blood meal. Salivary 5′-AMP is also responsible for the previously reported protein phosphatase inhibitor in the salivary glands of P. papatasi, which is shown to be artifactual in nature as a result of allosteric modification by AMP of the phosphatase substrate used (phosphorylase a).
Influence of odour plume structure on upwind flight of mosquitoes towards hosts
Authors: Geier Martin , Bosch Oliver Jörg , Boeckh Jürgen
Published: April 2021

Both the concentration and the fine-scale plume structure of host odours influence the upwind flight of female mosquitoes Aedes aegypti (L.) (Diptera: Culicidae) in a wind tunnel. The attractive effects of carbon dioxide, human skin odour and L-(+)-lactic acid were tested in homogeneous, turbulent and filamentous odour plumes. With carbon dioxide, the percentage of upwind-flying mosquitoes increased with the increasing fluctuations in concentration that occur in turbulent and filamentous plumes. In homogeneous plumes, an initial activation effect was observed, but sustained upwind flights were less frequent than in the other plumes. The opposite was found with plumes of human skin odour: the highest number of mosquitoes flew upwind in the homogeneous plume, whereas in turbulent or filamentous plumes their numbers were significantly lower. Regardless of plume type, the percentage of upwind-flying mosquitoes increased with increasing concentrations of carbon dioxide and of skin odour. With L-(+)-lactic acid, the dose–response characteristics were not consistent, and the relative effects of different plume types upon upwind flights differed within different ranges of concentration. Even maximum reactions to this compound were modest compared with those to carbon dioxide or to skin odour. Our findings demonstrate (1) that mosquitoes are able to orient upwind under continuous odour stimulation and (2) that upwind flight is dependent upon plume structure in different ways for different host odour components.
Arterial blood gas levels and cardiovascular function during varying environmental conditions in a mudskipper, Periophthalmodon schlosseri
Authors: Ishimatsu Atsushi , Aguilar Nancy M. , Ogawa Kougi , Hishida Yasuhiro , Takeda Tatsusuke , Oikawa Shin , Kanda Takeshi , Huat Khoo Khay
Published: April 2021

Changes in blood gas levels, blood pressure and heart rate were studied in chronically cannulated mudskippers, Periophthalmodon schlosseri, subjected to air exposure (6 h), aquatic hypoxia with access to air (water <0.9 kPa, 6 h) and forced submersion in normoxic water (12 h) at 30 °C.

Air exposure did not affect either blood O2 and had little effect on blood CO2 levels, but blood pH increased slightly, but significantly. Blood ammonia concentration was elevated sixfold during air exposure. Aquatic hypoxia caused no significant changes in blood gas levels. When the fish was forcibly submerged, blood O2 saturation decreased rapidly to approximately 30 %. Blood and total CO2 also decreased, but blood pH was unaffected by forcible submersion.

Air exposure did not affect blood pressure or heart rate. Aquatic hypoxia did not affect blood pressure but transiently increased heart rate. In contrast, forced submersion significantly depressed heart rate throughout the period of submersion, while blood pressure decreased only transiently. Upon emersion, the heart rate immediately increased to above the control level when the fish took its first air breath.

Key words: mudskipper, Periophthalmodon schlosseri, blood gas, cardiac function, hypoxia, air exposure.
A high-resolution in vitro bioassay to identify neurons containing red pigment concentrating hormone
Authors: Alvarado-Álvarez Ramón , Becerra Elizabeth , García Ubaldo
Published: April 2021

The release of red pigment concentrating hormone (RPCH) by single peptidergic neurons of the crayfish X organ/sinus gland system (XO-SG) was demonstrated using a novel in vitro bioassay in which XO neurons were co-cultured with tegumentary erythrophores. Local retraction of the pigmentary matrix within filipodia from erythrophores plated next to presumptive RPCH-containing neurons suggest spontaneous hormone release. Topical application of synthetic RPCH onto long filipodia also produced a local response. The time course of pigmentary matrix aggregation depended on the dose of synthetic RPCH. The effect of peptide on the cultured target cells was blocked by a polyclonal antiserum against RPCH. In co-culture conditions, the time course of pigmentary matrix aggregation was accelerated when presumptive RPCH-containing neurons were depolarized by intracellular current injection or by voltage-clamping to activate the Ca2+ current. The aggregation response evoked by these maneuvers was similar to that obtained with synthetic RPCH at a concentration of 1 fmol l−1. The immune serum was also used to identify a subset of 3–7 immunoreactive neurons localized in the external rim of the XO close to the medulla interna. Under culture conditions, this subset of neurons corresponded to the cells that induced the erythrophore response.
Echolocation behaviour and prey-capture success in foraging bats: laboratory and field experiments on Myotis daubentonii
Authors: Britton Adam R. C. , Jones Gareth
Published: April 2021

During prey-capture attempts, many echolocating bats emit a ‘terminal buzz’, when pulse repetition rate is increased and pulse duration and interpulse interval are shortened. The buzz is followed by a silent interval (the post-buzz pause). We investigated whether variation in the structure of the terminal buzz, and the calls and silent periods following it, may provide information about whether the capture attempt was successful and about the size of prey detected – detail that is valuable in studies of habitat use and energetics. We studied the trawling bat Myotis daubentonii. The time between the first call of the approach phase and the end of the terminal phase was not related to prey size in the laboratory. The last portion of the terminal buzz (buzz II) was shortened or omitted during aborted capture attempts. Both in the laboratory and in the field, the mean interpulse interval immediately after the terminal buzz (post-buzz interpulse interval) was longer in successful captures than in unsuccessful attempts. In the laboratory, the post-buzz pause was longer after successful captures than for unsuccessful attempts, and the minimum frequency of the first search-phase call emitted after the buzz (Fmin) was higher than that of the last such call prior to the buzz. These effects were not apparent in field data. Both in the laboratory (85 %) and in the field (74 %), significant discrimination between successful and unsuccessful capture attempts was possible when the duration of the post-buzz pause, post-buzz interpulse interval and Fmin were entered into a discriminant analysis. Thus, variation in the echolocation calls of bats during prey-capture attempts can reveal substantial information about capture success and prey size.
Transduction of mechanical energy into sound energy in the cicada Cyclochila australasiae
Authors: Bennet-Clark H. C. , Daws A. G.
Published: April 2021

The anatomy of the paired tymbal muscles of Cyclochila australasiae was described. Force–distance relationships of the sound-producing in–out cycle of tymbal movement were measured. The largest forces were measured when the push occurred at the apodeme pit on the tymbal plate at angles similar to the angles of internal pull of the tymbal muscle. Initially, inward movement was opposed by the elasticity of the tymbal, which stored energy. At a mean force of 0.38 N after a mean inward strain of 368 μm, the tymbal ribs buckled, the mean energy release being 45.1 μJ. The energy release occurred over 2–10 ms in three or four sound-producing steps as successive tymbal ribs buckled inwards. After the ribs had buckled, the force decreased to a mean value of 0.17 N. The force returned to zero during the outward movement, during which the tymbal ribs buckled outwards. The mean energy dissipated in the outward movement was 32.8 μJ. During contraction, the tymbal muscle produced mean values for the peak active force of 0.31 N over 295 μm, which gave mean values for the area of the work loops of 47.0 μJ.

The calling song of C. australasiae had a mean pulse rate of 234 Hz (117 Hz for each side of the insect). The peak power to mean power ratio for the songs was 8.51:1 (+9.30 dB). Measurements of the sound field around tethered insects and of the peak power to mean power ratio of the songs gave values for the mean power of the song of 3.15–7 mW; these correspond to an energy per song pulse of 13.5–30 μJ. Previously reported mean values are 3.15 mW for protest song and 5.1 mW for calling song. The efficiency of transduction of mechanical energy into sound energy is between 18 and 46 %
Lipid accumulation in the ovaries of a marine shrimp Penaeus semisulcatus (de haan)
Authors: Ravid T. , Tietz A. , Khayat M. , Boehm E. , Michelis R. , Lubzens E.
Published: April 2021

By the end of oocyte development, the ovaries of Penaeus semisulcatus have accumulated almost equal amounts (approximately 16 mg lipid g−1 protein) of phospholipids and triacylglycerols. The phospholipids consist mainly of phosphatidylcholine (75–80 %) and phosphatidylethanolamine (20–25 %). Approximately 30 % of the total fatty acid content of both phospholipids and triacylglycerols is made up of polyunsaturated fatty acids. In fractions obtained by centrifugation of ovarian homogenates, most of the increase in levels of ovarian lipids during ovarian maturation was associated with an increase in triacylglycerol levels in the floating fat fraction and of phospholipids in the infranatant fraction. The presence of polyunsaturated fatty acids in the ovaries indicates the occurrence of lipid transport to the ovary during oocyte maturation. The gradual decrease in the relative abundance of polyunsaturated fatty acids as the ovaries matured supports previously published results suggesting intra-ovarian synthesis of saturated and mono-unsaturated fatty acids.

Most of the lipids found in the female haemolymph (64.8 %) were recovered in the high-density lipoprotein fraction after density ultracentrifugation. The haemocyanin fraction recovered from this stage of fractionation contained substantial amounts of lipid (16.8 %) that could be removed by further sequential centrifugation at a higher NaBr density, leaving less than 0.9 % of the total haemolymph lipids associated with this fraction. While 16.2 % of the lipids were recovered from the very high-density lipoprotein fractions, these lipoproteins carried only 64–89 μg lipid mg−1 protein compared with 538.9 μg lipid mg−1 protein in the high-density lipoprotein fraction, indicating that the high-density lipoproteins are more likely to be the main transporters of lipids to the ovary. However, the contribution of very high-density lipoproteins to lipid transport cannot be ruled out at this stage.

In this study, we present two models for lipid transport to the ovary based on the abundance of phospholipids and triacylglycerols in the haemolymph and on the amounts of polyunsaturated fatty acids accumulated within the ovary during vitellogenesis.
Learning walks and landmark guidance in wood ants (Formica rufa)
Authors: Nicholson D. J. , Judd S. P. D. , Cartwright B. A. , Collett T. S.
Published: April 2021

We have examined a behaviour pattern in wood ants which in some respects resembles and in other respects differs from the learning flights of bees and wasps. Wood ants returning to their nest from a newly discovered food source turn back and look at landmarks near to the feeder, but the feeder itself does not attract sustained fixations. The frequency of landmark inspections is highest when the ant is close to the feeder and falls as the ant moves away. In common with learning flights, inspections of landmarks on departure become less frequent as ants become familiar with their surroundings and reappear after a long interval without foraging. A principal difference between the learning flights of wasps and bees and this putative learning behaviour in ants is the emphasis that ants place on landmark fixation. Ants and honeybees move differently when searching for a goal within an array of transformed landmarks. We have explored, using computer simulation, whether this difference can be explained by the prominence ants give to the matching of landmarks viewed in the frontal visual field.
No evidence for olfactory blocking in honeybee classical conditioning
Authors: Gerber Bertram , Ullrich Juliane
Published: April 2021

We use binary odorant compounds to investigate ‘blocking’ in honeybees which learn to associate an odorant (A–D) with a sucrose reward as the reinforcer (+). ‘Blocking’ means that learning about a stimulus B is reduced when trained in compound with a stimulus A that has previously been trained alone. Thus, reinforcement of B in these circumstances is not sufficient to induce learning. Such blocking is a frequently observed phenomenon in vertebrate learning and has also recently been reported in honeybee olfactory learning. To explain blocking, current models of conditioning include cognition-like concepts of attention or expectation which, consequently, seem also to apply to honeybees. Here, we first reproduce a blocking-like effect in an experimental design taken from the literature. We identify two confounding variables in that design and experimentally demonstrate their potential to support a blocking-like effect. After eliminating these confounding variables using a series of different training procedures, the blocking-like effect disappeared. Thus, convincing evidence for blocking in honeybee classical conditioning is at present lacking. This casts doubt on the applicability of cognition-like concepts to honeybees.
Tympanal hearing in the sarcophagid parasitoid fly Emblemasoma sp.: the biomechanics of directional hearing
Authors: Robert D. , Miles R. N. , Hoy R. R.
Published: April 2021

In Diptera, tympanal hearing has evolved at least twice in flies that belong to two different families, the tachinids and the sarcophagids. Common to these flies is their parasitoid reproductive strategy, both relying on the acoustic detection and localization of their hosts, singing insects, by means of tympanal hearing organs. In the present study, the external anatomy of the unusual hearing organs of the sarcophagid fly Emblemasoma sp. is described. The sarcophagid ears bear numerous anatomical similarities with those of ormiine tachinids: they are located on the ventral prosternum and possess a pair of scolopidial mechanoreceptive sense organs. A striking difference, however, resides in the lack of a well-defined presternum in the sarcophagid tympanal system. Instead, a deep longitudinal fold, the tympanal fold, spans both hemilateral tympanal membranes across the midline of the animal. Measured using laser Doppler vibrometry, the tympanal mechanical response in the sound field reveals asymmetrical deflection shapes that differ from those of tachinids. Lacking a central fulcrum, the sarcophagid tympanal complex presents different vibrational modes that also result in interaural coupling. The evolutionarily convergent, yet distinct, solutions used by these two small auditory systems to extract directional cues from the sound field and the role of tympanal coupling in this process are discussed.
Ixodid ticks avoid contact with liquid water
Authors: Kröber T. , Guerin P. M.
Published: April 2021

Larvae of the cattle tick Boophilus microplus and all life stages of the European sheep tick Ixodes ricinus avoid walking on a wet membrane surface surrounding a dry patch. Of 170 reactions made at a border with liquid water by 22 B. microplus larvae, 40 % consisted of immediate turns to the opposite side to bring all the legs back onto a dry patch, 41 % were walks along the border, during which the ticks maintained contact with both the dry and wet zones, and 19 % were returns to the dry patch after a short excursion onto the wet surround. Since contact with one front leg tip was sufficient to cause return reactions from the wet surface in most of the border contacts, the water receptor(s) that enable ticks to perceive the wet surface are probably located in terminal pore sensilla on the first-leg tarsi. Observations on the return reactions of ticks with different groups of chemosensilla masked confirmed this. Ticks have an ambiguous relationship with water: they appear to avoid direct contact with it, but they need a high humidity to compensate for any deficit in body water.
Functional complementation of the malvolio mutation in the taste pathway of Drosophila melanogaster by the human natural resistance-associated macrophage protein 1 (Nramp-1)
Authors: D’Souza Jasmine , Cheah Peh Yean , Gros P. , Chia W. , Rodrigues V.
Published: April 2021

The malvolio (mvl) gene of Drosophila melanogaster encodes a protein with a high degree of homology to natural resistance-associated macrophage proteins (Nramps). This family of integral membrane proteins, many of which appear to function as cation transporters, is remarkably conserved in several phylogenetically distinct species. In Drosophila melanogaster, the protein Mvl is expressed in macrophages and in differentiated neurons; loss-of-function mutations lead to defects in gustatory behaviour. The human Nramp-1 protein was expressed in Drosophila melanogaster using the hsp70 promoter. Overexpression in normal animals does not lead to any alterations in their behaviour or physiology. In mutants, however, ubiquitous expression of human Nramp-1 can totally rescue the taste defect. This finding that Nramp-1 can complement the taste defect in mvl mutants provides a potent means of exploiting behavioural genetics to dissect the function of Nramp-1 and to identify other molecules involved with this transport system.
The photoreceptors and visual pigments in the retina of a boid snake, the ball python (Python regius)
Authors: Sillman A. J. , Carver J. K. , Loew E. R.
Published: April 2021

The photoreceptors and visual pigments of Python regius were studied using microspectrophotometry and scanning electron microscopy. The retina contains rods and cones, with rods constituting at least 90 % of the photoreceptor population. The rods are of a single type with long, narrow outer segments and are tightly packed. The wavelength of maximum absorbance (λmax) of the visual pigment in the rods is in the region of 494 nm. Two distinct types of cone are present. The most common cone, with a stout but stubby outer segment, contains a visual pigment with λmax at approximately 551 nm. A relatively rare cone, with a long, slender outer segment, contains an ultraviolet-sensitive visual pigment with λmax at approximately 360 nm. All the visual pigments have chromophores based on vitamin A1. The results are discussed in relation to the behavior of P. regius.
Voltage-activated whole-cell K+ currents in lamina cells of the desert locust Schistocerca gregaria
Authors: Benkenstein Christian , Schmidt Manfred , Gewecke Michael
Published: April 2021

Voltage-dependent outward currents were studied in freshly dissociated somata of locust lamina cells. These currents were recorded in 142 somata using the whole-cell patch-clamp technique. By measuring the reversal potential at altered external [K+] and by replacing internal K+ with Cs+, we determined that the outward currents were carried by K+. The outward currents consist of a transient A-type K+ current (KA) and a delayed-rectifier-like K+ current (KD). Amongst the cells studied, we observed two distinct groups of cells. The most obvious difference between the two groups is that in group I cells the total outward current is dominated by KA (KA/KD=12.5), whereas in group II cells KA makes a smaller contribution (KA/KD=2.1). Furthermore, in cells of group I, the KA current shows a steeper voltage-dependence of activation, where VG50 is −29.9 mV and s is 11.9 (N=22), and inactivation, where VI50 is −84.5 mV and s is −6.3 (N=18), compared with the KA current in cells of group II: VG50=−7.9 mV; s=26.6 (N=36) and VI50=−68.4 mV; s=−7.5 (N=21) (VG50 is the voltage at which the whole-cell conductance G is half-maximally activated, VI50 is the voltage of half-maximal inactivation and s is the slope of the voltage-dependence). The transient KA current in group I cells decayed mono-exponentially. The decay of the KA current in group II cells was fitted with a double-exponential curve and was significantly faster than in group I cells. In contrast to the large differences in KA currents, the KD currents appeared to be quite similar in the two groups of cells.
Chemolithoheterotrophy in a metazoan tissue: sulfide supports cellular work in ciliated mussel gills
Authors: Doeller Jeannette E. , Gaschen Brian K. , Parrino Vincent , Kraus David W.
Published: April 2021

Hydrogen sulfide, a common constituent of marine intertidal sediments, is both a potent toxin of aerobic cellular respiration and an electron-rich molecule used by some prokaryotic organisms as a source of energy. In ciliated gills from Geukensia demissa, a marine mussel from sulfide-rich sediments, sulfide oxidation supports cellular work. Evidence for this comes from measurements of ciliary beat frequency (fCB) as a measure of ATP turnover rate, the rate of gill oxygen consumption as a measure of ATP production rate, and mitochondrial cytochrome redox state as an indicator of the path of electron flow. Results from experiments performed in the presence and absence of the mitochondrial complex III inhibitor antimycin A to limit endogenous carbon substrate oxidation showed that exposure to sulfide stimulated oxygen consumption and ciliary beating, with cytochrome c being the dominant redu ced species. These results, along with the resultant ratio, are qualitatively and quantitatively consistent with the hypothesis that electrons from sulfide oxidation support mitochondrial ATP production. We propose that Geukensia demissa gills use sulfide as a respiratory substrate when given the choice and thus function metabolically as facultative chemolithoheterotrophs. Similar conclusions could not be drawn for the ciliated gills from Mytilus edulis, a marine mussel from aerated habitats, or for the ciliated lungs from the phylogenetically distinct leopard frog Rana pipiens.
Haemoglobin H+ equilibria in lamprey (Lampetra fluviatilis) and hagfish (Myxine glutinosa)
Authors: Jensen Frank B.
Published: April 2021

Agnathans, comprising lamprey and hagfish species, have been reported to be practically devoid of HCO3−/Cl− exchange across the red blood cell membrane. This suggests that the capacity of their haemoglobin (Hb) to remove H+ is essential for obtaining a high CO2-carrying capacity in the blood. Hydrogen ion titrations were performed on oxygenated and deoxygenated composite Hbs from river lamprey and from Atlantic hagfish at 15 °C and an ionic strength of 0.1 (0.1 mol l−1 KCl). Lamprey Hb was characterised by very low buffer values when the degree of oxygenation was constant, whereas the fixed-acid Haldane effect was large (uptake of approximately 0.9 H+ per monomer upon deoxygenation). Hagfish Hb, in contrast, had large buffer values and a moderate fixed-acid Haldane effect. In deoxygenated Hb, the low buffer values in lamprey correlated with the presence of only 1–1.5 titratable ‘neutral’ groups (normally histidines and α-amino groups) per monomer, whereas there were 4–5 titratable ‘neutral’ groups per monomer in hagfish. The large differences in Hb/H+ equilibria between the two species reflect the early evolutionary divergence between lampreys and hagfish. With respect to CO2 transport, the special Hb/H+ equilibria and the high red blood cell pH in lamprey ensure a high concentration of free HCO3− inside the red cells in venous blood, which compensates for the absence of a shift of HCO3− to the plasma. The Hb/H+ equilibria in hagfish are less effective in ensuring a high CO2-carrying capacity given the virtual absence of a red blood cell HCO3−/Cl− exchange, and other adaptations may be involved.
Flight performance during hunting excursions in Eleonora’s falcon Falco eleonorae
Authors: Hedenström Anders , Rosén Mikael , Åkesson Susanne , Spina Fernando
Published: April 2021

Among birds, falcons are high-performance flyers, in many cases adapted for aerial hunting and hence suitable targets for investigating limits to flight performance. Using an optical range finder, we measured flight tracks of Eleonora’s falcon (Falco eleonorae), a species breeding in the Mediterranean region and specialised for hunting autumn passage bird migrants, when commuting between their nesting colony and offshore hunting areas (straight transportation flight) and when searching for prey (transecting and searching flight). Airspeed during searching flight was significantly slower than during straight transportation and transecting flight, but there was no significant difference in airspeed between the latter two flight modes. Straight transportation flight was significantly faster than predicted minimum power speed. Also, during straight transportation flight, the falcons responded to head- and tailwinds by increasing their airspeed when flying into the wind. However, they did not show any significant airspeed adjustments with respect to the angle between the track and the heading, as would be expected in birds trying to maintain a constant track direction. Mean sustainable climb rate (during ≥:240 s) was 1.4±0.31 m s−1 (mean ± S.D., N=13), which is rather a high rate for a bird the size of an Eleonora’s falcon. The climb rate was used to calculate maximum load-carrying capacity and maximum sustained horizontal flapping flight speed. The mean wingbeat frequency during powered climbing flight was 4.68 Hz, which was used to estimate the mass-specific muscle work.

When falcons were leaving the colony for offshore hunting, they gained altitude by slope-soaring when there was an onshore wind. We formulated a simple criterion for the required gliding-flight rate of climb during an initial slope-soaring episode when minimizing the energy cost of reaching a certain altitude far out over the sea (which is where the prey is to be found). This climb rate was 0.36 m s−1, and our observations indicated that the falcons experienced climb rates above this value when soaring in slope-lift.