nils-herrmann/clean_scirepeval huggingface dataset:
Capacity for intracellular pH compensation during hypercapnia in white sturgeon primary liver cells
Venue: Journal of Comparative Physiology B

Fish, exposed to elevated water CO2, experience a rapid elevation in blood CO2 (hypercapnia), resulting in acidification of both intra- and extra-cellular compartments. White sturgeon, Acipenser transmontanus, are exceptionally CO2 tolerant and can regulate tissue intracellular pH (pHi) in the presence of a pronounced hypercapnic acidosis (preferential pHi regulation). In this study, pHi regulatory capacity of sturgeon liver cells in primary culture was examined to assess the suitability of employing this in vitro system to understand in vivo CO2 tolerance in sturgeon. Using the pH-sensitive fluoroprobe BCECF, real-time changes in resting pHi and rates of pHi recovery were investigated during exposure to hypercapnia (3 and 6% CO2) in the absence and presence of additional acid loads induced by (20 mM) ammonium prepulse. During short-term (10 min) exposure to hypercapnia (3 and 6% CO2), sturgeon cells were acidified and no pHi compensation was observed. However, when exposure to 6% CO2 was extended to over 19 h, the CO2-induced intracellular acidosis was partially compensated by a pHi increase of over 0.2 pH unit despite the sustained extracellular acidosis, indicative of a capacity for preferential pHi regulation in vitro. Since this capacity in sturgeon liver is present both in vivo and in vitro, the transmembrane transporters involved may be the same. Therefore, cell culture may be a suitable tool to identify the transporters (i.e., the cellular mechanisms underlying in vivo CO2 tolerance) in white sturgeon and possibly in other hypercapnia-tolerant species.
Tests of the contribution of acclimation to geographic variation in water loss rates of the West Indian lizard Anolis cristatellus
Venue: Journal of Comparative Physiology B

Phenotypic plasticity can contribute to the process of adaptive radiation by facilitating population persistence in novel environments. West Indian Anolis lizards provide a classic example of an adaptive radiation, in which divergence has occurred along two primary ecological axes: structural microhabitat and climate. Adaptive plasticity in limb morphology is hypothesized to have facilitated divergence along the structural niche axis in Anolis, but very little work has explored plasticity in physiological traits. Here, we experimentally ask whether Puerto Rican Anolis cristatellus from mesic and xeric habitats differ in desiccation rates, and whether these lizards exhibit an acclimation response to changes in relative humidity. We first present microclimatic data collected at lizard perch sites that demonstrate that abiotic conditions experienced by lizards differ between mesic and xeric habitat types. In Experiment 1, we measured desiccation rates of lizards from both habitats maintained under identical laboratory conditions. This experiment demonstrated that desiccation rates differ between populations; xeric lizards lose water more slowly than mesic lizards. In Experiment 2, lizards from each habitat were either maintained under the conditions of Experiment 1, or under extremely low relative humidity. Desiccation rates did not differ between lizards from the same habitat maintained under different treatments and xeric lizards maintained lower desiccation rates than mesic lizards within each treatment. Our results demonstrate that A. cristatellus does not exhibit an acclimation response to abrupt changes of hydric conditions, and suggest that tropical Anolis lizards might be unable to exhibit physiological plasticity in desiccation rates in response to varying climatic conditions.
Cardiorespiratory responses to hypoxia in the African catfish, Clarias gariepinus (Burchell 1822), an air-breathing fish
Venue: Journal of Comparative Physiology B

The African catfish, Clarias gariepinus, possesses a pair of suprabranchial chambers located in the dorsal-posterior part of the branchial cavity having extensions from the upper parts of the second and fourth gill arches, forming the arborescent organs. This structure is an air-breathing organ (ABO) and allows aerial breathing (AB). We evaluated its cardiorespiratory responses to aquatic hypoxia. To determine the mode of air-breathing (obligate or accessory), fish had the respiratory frequency (fR) monitored and were subjected to normoxic water (PwO2 = 140 mmHg) without becoming hyperactive for 30 h. During this period, all fish survived without displaying evidences of hyperactivity and maintained unchanged fR, confirming that this species is a facultative air-breather. Its aquatic O2 uptake ($$ \dot{V}{\text{O}}_{2} $$) was maintained constant down to a critical PO2 (PcO2) of 60 mmHg, below which $$ \dot{V}{\text{O}}_{2} $$ declined linearly with further reductions of inspired O2 tension (PiO2). Just above the PcO2 the ventilatory tidal volume (VT) increased significantly along with gill ventilation ($$ \dot{V}_{\text{G}} $$), while fR changed little. Consequently, the water convection requirement $$ \left( {\dot{V}_{\text{G}} /\dot{V}{\text{O}}_{2} } \right) $$ increased steeply. This threshold applied to a cardiac response that included reflex bradycardia. AB was initiated at PiO2 = 140 mmHg (normoxia) and air-breathing episodes increased linearly with more severe hypoxia, being significantly higher at PiO2 tensions below the PcO2. Air-breathing episodes were accompanied by bradycardia pre air-breath, to tachycardia post air-breath.
Seasonality of glycogen phosphorylase activity in crucian carp (Carassius carassius L.)
Venue: Journal of Comparative Physiology B

Seasonal changes in the activity of glycogen phosphorylase (GP), a rate-limiting enzyme of glycogen degradation, were examined in an anoxia-tolerant fish species, the crucian carp (Carassius carassius L.). In muscle and brain, the activity of GP remained constant throughout the year when tested at 25°C. In contrast, the activities of liver and heart GP displayed striking increases in summer. When seasonal temperature changes are taken into account, the activity of GP during the anoxic mid-winter is only 4–6% of its summer time activity in the muscle, heart and liver, and 13% in brain. In winter-acclimatized fish, experimental anoxia (1–6 weeks) caused sustained depression of the GP activity in heart and gills. In liver and muscle, a transient depression of GP activity occurred during the first week of anoxia but later GP activity recovered back to the normoxic level. GP of the brain was completely resistant to anoxia. In all studied tissues, the constitutive activity of GP is more than sufficient to degrade glycogen deposits during winter anoxia without anoxia-induced activation of GP. The seemingly paradoxical summer-time increase in the activity of liver and heart GP could be related to active life-style of the summer-acclimatized fish (growth, reproduction), the increased demand of energy and molecular precursors of anabolic metabolism being satisfied by preferential degradation of glycogen. The high glycogen content of winter-acclimatized crucian carp is not associated with the elevated GP activity or anoxic activation of GP.
AMP-activated protein kinase plays a role in initiating metabolic rate suppression in goldfish hepatocytes
Venue: Journal of Comparative Physiology B

In the present study, we test the hypothesis that AMP-activated protein kinase (AMPK) initiates metabolic rate suppression in isolated goldfish hepatocytes. To accomplish this, we attempted to pharmacologically activate AMPK in goldfish hepatocytes with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and the thienopyridone, A769662, to examine the effects of AMPK activation on eukaryotic elongation factor-2 (eEF2), protein synthesis, and cellular oxygen consumption rate ($$ \dot{M}_{{{\text{O}}_ }} $$). Goldfish hepatocytes treated with 1 mM AICAR under normoxic conditions (>200 μM O2) showed a modest but significant 1.1-fold increase in AMPK phosphorylation, a 7.5-fold increase in AMPK activity, a 1.4-fold increase in eEF2 phosphorylation, and a 24% decrease in $$ \dot{M}_{{{\text{O}}_ }} $$. At physiologically relevant [O2] (<40 μM O2), the addition of 1 mM AICAR resulted in only a 13% decrease in cellular $$ \dot{M}_{{{\text{O}}_ }} $$ with no change in sensitivity to [O2] as assessed by estimates of cellular P50 and P90 values. The addition of compound C, a general protein kinase inhibitor, after AICAR incubation did not reverse the effects of AICAR on $$ \dot{M}_{{{\text{O}}_ }} $$ in normoxia. Treatment of hepatocytes with ≤200 μM A769662 did not affect AMPK activity, AMPK phosphorylation, eEF2 phosphorylation, or cellular $$ \dot{M}_{{{\text{O}}_ }} $$. These data suggest that A769662 is not an activator of AMPK in goldfish hepatocytes. Although our study provides support for the hypothesis that AMPK plays a role in initiating metabolic rate suppression in goldfish hepatocytes, this support must be viewed cautiously because of the known off-target effects of the pharmacological agents used.
Signal variation and its morphological correlates in Paramormyrops kingsleyae provide insight into the evolution of electrogenic signal diversity in mormyrid electric fish
Venue: Journal of Comparative Physiology A

We describe patterns of geographic variation in electric signal waveforms among populations of the mormyrid electric fish species Paramormyrops kingsleyae. This analysis includes study of electric organs and electric organ discharge (EOD) signals from 553 specimens collected from 12 localities in Gabon, West-Central Africa from 1998 to 2009. We measured time, slope, and voltage values from nine defined EOD “landmarks” and determined peak spectral frequencies from each waveform; these data were subjected to principal components analysis. The majority of variation in EODs is explained by two factors: the first related to EOD duration, the second related to the magnitude of the weak head-negative pre-potential, P0. Both factors varied clinally across Gabon. EODs are shorter in eastern Gabon and longer in western Gabon. Peak P0 is slightly larger in northern Gabon and smaller in southern Gabon. P0 in the EOD is due to the presence of penetrating-stalked (Pa) electrocytes in the electric organ while absence is due to the presence of non-penetrating stalked electrocytes (NPp). Across Gabon, the majority of P. kingsleyae populations surveyed have only individuals with P0-present EODs and Pa electrocytes. We discovered two geographically distinct populations, isolated from others by barriers to migration, where all individuals have P0-absent EODs with NPp electrocytes. At two sites along a boundary between P0-absent and P0-present populations, P0-absent and P0-present individuals were found in sympatry; specimens collected there had electric organs of intermediate morphology. This pattern of geographic variation in EODs is considered in the context of current phylogenetic work. Multiple independent paedomorphic losses of penetrating stalked electrocytes have occurred within five Paramormyrops species and seven genera of mormyrids. We suggest that this key anatomical feature in EOD signal evolution may be under a simple mechanism of genetic control, and may be easily influenced by selection or drift throughout the evolutionary history of mormyrids.
Two-dimensional receptive fields of midbrain lateral line units in the goldfish, Carassius auratus
Venue: Journal of Comparative Physiology A

We determined the receptive fields of midbrain lateral line units in goldfish, Carassius auratus, with a 50 Hz vibrating sphere placed at various azimuths and elevations alongside the fish and studied how responses were affected by different directions of sphere vibration. The receptive fields of toral lateral line units, in contrast to those of primary afferent nerve fibers, did not represent the pressure gradient pattern generated by a vibrating sphere. Thus, unlike primary afferents, single toral lateral line units did not code for source location in their spatial discharge patterns. The two-dimensional receptive fields were round, horizontally or vertically stretched, or complex. While some toral lateral line units were sensitive to the direction of sphere vibration others were not.
Octopamine and serotonin have opposite effects on antipredator behavior in the orb-weaving spider, Larinioides cornutus
Venue: Journal of Comparative Physiology A

In this study, we experimentally elevated levels of octopamine and serotonin in an orb-weaving spider, and observed the effects on the antipredator behavior thanatosis (death feigning), activity level, and running speed. We found that octopamine significantly shortened the duration of thanatosis, and its effect wore off over 24 h. We also found that serotonin significantly lengthened thanatosis, but in this case, the effect persisted for over 24 h. Neither octopamine nor serotonin affected the general activity or running speed of the spiders. To our knowledge, this is the first study to directly explore the role of biogenic amines on a specific antipredator behavior in spiders. Given that spiders must be both aggressive toward prey, yet wary of predators, we believe that this system will be an outstanding model to explore connections between behavioral ecology and neurochemistry.
Responses of brainstem lateral line units to different stimulus source locations and vibration directions
Venue: Journal of Comparative Physiology A

We recorded responses of lateral line units in the medial octavolateralis nucleus in the brainstem of goldfish, Carassius auratus, to a 50 Hz vibrating sphere and studied how responses were affected by placing the sphere at various locations alongside the fish and by different directions of vibration. In most units (88%), stimulation with the sphere from one or more spatial locations caused an increase and/or decrease in discharge rate. In few units (10%), discharge rate was increased by stimulation from one location and decreased by stimulation from an adjacent location in space. In a minority of the units (2%), changing sphere location did not affect discharge rates but caused a change in phase coupling. Units sensitive to a distinct sphere vibration direction were not found. The data also show that the responses of most brainstem units differ from those of primary afferent nerve fibers. Whereas primary afferents represent the pressure gradient pattern generated by the sphere and thus encode location and vibration direction of a vibrating sphere, most brainstem units do not. This information may be represented in the brainstem by a population code or in higher centers of the ascending lateral line pathway.
Ecology and neuroethology of bat echolocation: a tribute to Gerhard Neuweiler
Venue: Journal of Comparative Physiology A

Gerhard Neuweiler was born on 18 May 1935 in a small village in the black forest in south-western Germany. From 1955 to 1962, he studied biology, chemistry, biochemistry and physics at the universities of Tübingen and Munich. For his doctoral dissertation, he investigated the anatomy and physiology of the visual system, and especially the eye, in the Indian flying fox (Pteropus giganteus). He also developed an interest in the behavior of these large nonecholocating bats. This work was supervised by Franz Möhres, head of the Tübingen animal physiology department at the time. In 1962, Gerhard Neuweiler was awarded the doctoral degree (Dr. rer. nat.) with distinction (summa cum laude). After his PhD, Gerhard Neuweiler moved to India for 2 years to study behavior and social interactions of flying foxes in the wild. For this time, he was a fellow of the government of India and of the German Academic Exchange Service. Gerhard Neuweiler used these Indian years to get deeply familiar with the fauna and flora, but also the art, the religion and the people of his guest country. Throughout his scientific career, he kept research contacts with India and Sri Lanka and returned many times. In 1986, Neuweiler was awarded an honorary professorship at the Department of Animal Behaviour and Neurobiology at Madurai University. Later, he was nominated Honorary Fellow of the Indian Academy of Sciences Bangalore and Distinguished Fellow of Jawaharlal Nehru Centre for Advanced Scientific Research in Bangalore. It was also in India that Neuweiler and Indian colleagues performed an early comparative study on bat audition, published in the present journal (Neuweiler et al. 1984). This might have marked the onset of Neuweiler’s interest in the adaptation of bat echolocation systems to ecology; a topic on which he later published several influential review papers (Neuweiler 1989, 1990). And it was again in India and Sri Lanka where he gained important insights into echolocation behavior of free-ranging bats in the field (Habersetzer et al. 1984; Neuweiler et al. 1987). But first back to Germany. Gerhard Neuweiler returned from Madurai to Tübingen in 1964. He continued at the Department of Animal Physiology, first as an assistant professor (‘‘Wissenschaftlicher Assistent’’, 1964–1970) and after his habilitation, in 1970, as an associate professor This special issue of the Journal of Comparative Physiology is dedicated to the memory of the late Professor Dr. Gerhard Neuweiler and his legacy in bat echolocation research. Professor Neuweiler died on 15 August 2008 in Munich.
Click-based echolocation in bats: not so primitive after all
Venue: Journal of Comparative Physiology A

Echolocating bats of the genus Rousettus produce click sonar signals, using their tongue (lingual echolocation). These signals are often considered rudimentary and are believed to enable only crude performance. However, the main argument supporting this belief, namely the click’s reported long duration, was recently shown to be an artifact. In fact, the sonar clicks of Rousettus bats are extremely short, ~50–100 μs, similar to dolphin vocalizations. Here, we present a comparison between the sonar systems of the ‘model species’ of laryngeal echolocation, the big brown bat (Eptesicus fuscus), and that of lingual echolocation, the Egyptian fruit bat (Rousettus aegyptiacus). We show experimentally that in tasks, such as accurate landing or detection of medium-sized objects, click-based echolocation enables performance similar to laryngeal echolocators. Further, we describe a sophisticated behavioral strategy for biosonar beam steering in clicking bats. Finally, theoretical analyses of the signal design—focusing on their autocorrelations and wideband ambiguity functions—predict that in some aspects, such as target ranging and Doppler-tolerance, click-based echolocation might outperform laryngeal echolocation. Therefore, we suggest that click-based echolocation in bats should be regarded as a viable echolocation strategy, which is in fact similar to the biosonar used by most echolocating animals, including whales and dolphins.
Melatonin in octopus (Octopus vulgaris): tissue distribution, daily changes and relation with serotonin and its acid metabolite
Venue: Journal of Comparative Physiology A

Information regarding melatonin production in molluscs is very limited. In this study the presence and daily fluctuations of melatonin levels were investigated in hemolymph, retina and nervous system-related structures in the cephalopod Octopus vulgaris. Adult animals were maintained in captivity under natural photoperiod and killed at different times in a regular daily cycle. Levels of melatonin, serotonin (5-HT) and its acid metabolite (5-hydroxyindole acetic acid, 5-HIAA) in the hemolymph, retina, optic lobe, and cerebral ganglion were assayed by HPLC. Melatonin content fluctuated rhythmically in the retina and hemolymph, peaking at night. In the retina, but not in the other neural tissues, the rhythm was opposite to that of 5-HT, which displayed basal levels at night. Also, 5-HIAA levels in the retina were higher during the night, supporting that rhythmic melatonin production could be linked to diurnal changes in 5-HT degradation. The high levels of melatonin found in the retina point to it as the major source of melatonin in octopus; in addition, a large variation of melatonin content was found in the optic lobe with maximal values at night. All these data suggest that melatonin might play a role in the transduction of the light–dark cycle information for adjustment of rhythmic physiological events in cephalopods.
Effects of environmental oxygen on development and respiration of Australian lungfish (Neoceratodus forsteri) embryos
Venue: Journal of Comparative Physiology B

The effects of oxygen partial pressure ($$ P_{{{\text{O}}_{2} }} $$) on development and respiration were investigated in the eggs of the Australian lungfish, Neoceratodus forsteri. At 20°C, embryonic survival and development was optimal at 15 and 20.9 kPa. Development was slowed at 5 and 10 kPa and embryos did not survive 2 kPa. At lower $$ P_{{{\text{O}}_{2} }} $$, the rate of oxygen consumption also decreased. Embryos responded to hypoxia by hatching at an earlier age and stage of development, and hatching wet and dry gut-free masses were reduced. The role of oxygen conductance ($$ G_{{{\text{O}}_{2} }} $$) in gas exchange was also examined under selected environmental $$ P_{{{\text{O}}_{2} }} $$ and temperatures. The breakdown of the vitelline membrane changed capsule geometry, allowed water to be absorbed into the perivitelline space and increased capsule $$ G_{{{\text{O}}_{2} }} $$. This occurred at embryonic stage 32 under all treatments and was largely independent of both $$ P_{{{\text{O}}_{2} }} $$ and temperature (15, 20 and 25°C), demonstrating that capsule $$ G_{{{\text{O}}_{2} }} $$ cannot adaptively respond to altered environmental conditions. The membrane breakdown increased capsule diffusive $$ G_{{{\text{O}}_{2} }} $$ and stabilised perivitelline $$ P_{{{\text{O}}_{2} }} $$, but reduced the convective $$ G_{{{\text{O}}_{2} }} $$ of the perivitelline fluid, as the large perivitelline volume and inadequate convective current resulted in a $$ P_{{{\text{O}}_{2} }} $$ gradient within the egg prior to hatch.
Temporal fluctuations of the geomagnetic field affect pigeons’ entire homing flight
Venue: Journal of Comparative Physiology A

Tracks of pigeons, recorded with the help of GPS-receivers from two sites 30 km north and south of the Frankfurt loft, were analyzed in view of an influence of irregular fluctuations of the geomagnetic field. The data obtained were correlated with indices characterizing different aspects of these fluctuations. We found the best correlations with the index quantifying the average amplitude of the magnetic disturbance, and with an index that quantifies the average variability of the magnetic field on the day of release: stronger and more variable fluctuations lead to a counter-clockwise shift of the mean headings during the initial phase at the release site and the following departure phase, but not during the final homing phase leading to the loft. The steadiness of flight was not affected during the initial phase; however, during the later parts of the homing flight, stronger fluctuations, as well as higher variability in the magnetic field led to a marked decrease in steadiness. This continuing effect of magnetic fluctuations indicates that magnetic factors not only affect the beginning, but remain an integral part of the pigeons’ navigational processes during the entire homing flight.