nils-herrmann/clean_scirepeval huggingface dataset:
Effects of biotic and abiotic factors on the oxygen content of green sea turtle nests during embryogenesis
Venue: Journal of Comparative Physiology B

Several biotic and abiotic factors can influence nest oxygen content during embryogenesis. Several of these factors were determined during each developmental stage of green sea turtle embryos on Wan-an Island, Penghu Archipelago, Taiwan. We examined oxygen content in 7 nests in 2007 and 11 in 2008. Oxygen in the adjacent sand, total and viable clutch sizes, air, sand and nest temperatures, and sand characters of each nest were also determined. Oxygen content was lower in late stages than in the early and middle stages. It was also lower in the middle layer than in the upper and bottom layers. Nest temperature showed opposite trends, reaching its maximum value in late stages of development. Nest oxygen content was influenced by fraction of viable eggs, total clutch sizes, sand temperatures, maximum nest temperature and maximum change in the nest temperature during incubation. Clutch size during embryogenesis was the most influential factor overall. However, the major influential factors were different for different developmental stages. In the first half of the incubation, the development rate was low, and the change in the nest oxygen content was influenced mainly by the clutch size. During the second half, the rapid embryonic development rate became the dominant factor, and hatchling activities caused even greater oxygen consumption during the last stage of development.
Mitochondrial physiology of diapausing and developing embryos of the annual killifish Austrofundulus limnaeus: implications for extreme anoxia tolerance
Venue: Journal of Comparative Physiology B

Diapausing embryos of the annual killifish Austrofundulus limnaeus have the highest reported anoxia tolerance of any vertebrate and previous studies indicate modified mitochondrial physiology likely supports anoxic metabolism. Functional mitochondria isolated from diapausing and developing embryos of the annual killifish exhibited VO2, respiratory control ratios (RCR), and P:O ratios consistent with those obtained from other ectothermic vertebrate species. Reduced oxygen consumption associated with dormancy in whole animal respiration rates are correlated with maximal respiration rates of mitochondria isolated from diapausing versus developing embryos. P:O ratios for developing embryos were similar to those obtained from adult liver, but were diminished in mitochondria from diapausing embryos suggesting decreased oxidative efficiency. Proton leak in adult liver corresponded with that of developing embryos but was elevated in mitochondria isolated from diapausing embryos. In metabolically suppressed diapause II embryos, over 95% of the mitochondrial oxygen consumption is accounted for by proton leak across the inner mitochondrial membrane. Decreased activity of mitochondrial respiratory chain complexes correlates with diminished oxidative capacity of isolated mitochondria, especially during diapause. Respiratory complexes exhibited suppressed activity in mitochondria with the ATP synthase exhibiting the greatest inhibition during diapause II. Mitochondria isolated from diapause II embryos are not poised to produce ATP, but rather to shuttle carbon and electrons through the Kreb’s cycle while minimizing the generation of a proton motive force. This particular mitochondrial physiology is likely a mechanism to avoid production of reactive oxygen species during large-scale changes in flux through oxidative phosphorylation pathways associated with metabolic transitions into and out of dormancy and anoxia.
Foraging grass-cutting ants (Atta vollenweideri) maintain stability by balancing their loads with controlled head movements
Venue: Journal of Comparative Physiology A

Grass-cutting ants (Atta vollenweideri) carry leaf fragments several times heavier and longer than the workers themselves over considerable distances back to their nest. Workers transport fragments in an upright, slightly backwards-tilted position. To investigate how they maintain stability and control the carried fragment’s position, we measured head and fragment positions from video recordings. Load-transporting ants often fell over, demonstrating the biomechanical difficulty of this behavior. Long fragments were carried at a significantly steeper angle than short fragments of the same mass. Workers did not hold fragments differently between the mandibles, but performed controlled up and down head movements at the neck joint. By attaching additional mass at the fragment’s tip to load-carrying ants, we demonstrated that they are able to adjust the fragment angle. When we forced ants to transport loads across inclines, workers walking uphill carried fragments at a significantly steeper angle, and downhill at a shallower angle than ants walking horizontally. However, we observed similar head movements in unladen workers, indicating a generalized reaction to slopes that may have other functions in addition to maintaining stability. Our results underline the importance of proximate, biomechanical factors for the understanding of the foraging process in leaf-cutting ants.
Neural mechanisms of target ranging in FM bats: physiological evidence from bats and frogs
Venue: Journal of Comparative Physiology A

Echolocating bats assess target range by the delay in echo relative to the emitted sonar pulse. Earlier studies in FM bats showed that a population of neurons in auditory centers above the inferior colliculus (IC) is tuned to echo delay, with different neurons tuned to different echo delays. A building block for delay-tuned responses is paradoxical latency shift (PLS), featuring longer response latencies to more intense sounds. PLS is first created in the IC, where neurons exhibit unit-specific quantum increase in response latency with increasing sound level. Other IC neurons display oscillatory discharges whose period is unit-specific and level tolerant, indicating that this is attributable to cell’s intrinsic properties. High-threshold inhibition of oscillatory discharge produces PLS, indicating that oscillatory discharge is a building block for PLS. To investigate the cellular basis of oscillatory discharges, we performed whole-cell patch-clamp recordings from IC neurons in leopard frogs (which also exhibit oscillatory discharges and PLS). These recordings show that IC neurons are heterogeneous displaying diverse biophysical phenotypes; each phenotype (and cell) has its own membrane time constant, input resistance, and strengths of Ih, Ikir, Ikv—these intrinsic properties give rise to cell-specific resonance which can be observed through current and afferent stimulations.
Scaling with body mass of mitochondrial respiration from the white muscle of three phylogenetically, morphologically and behaviorally disparate teleost fishes
Venue: Journal of Comparative Physiology B

White muscle (WM) fibers in many fishes often increase in size from <50 μm in juveniles to >250 μm in adults. This leads to increases in intracellular diffusion distances that may impact the scaling with body mass of muscle metabolism. We have previously found similar negative scaling of aerobic capacity (mitochondrial volume density, Vmt) and the rate of an aerobic process (post-contractile phosphocreatine recovery) in fish WM. In the present study, we examined the scaling with body mass of oxygen consumption rates of isolated mitochondria (VO2mt) from WM in three species from different families that vary in morphology and behavior: an active, pelagic species (bluefish, Pomatomus saltatrix), a relatively inactive demersal species (black sea bass, Centropristis striata), and a sedentary, benthic species (southern flounder, Paralichthys lethostigma). In contrast to our prior studies, the measurement of respiration in isolated mitochondria is not influenced by the diffusion of oxygen or metabolites. Vmt was measured in WM and in high-density isolates used for VO2mt measurements. WM Vmt was significantly higher in the bluefish than in the other two species and VO2mt was independent of body mass when expressed per milligram protein or per milliliter mitochondria. The size-independence of VO2mt indicates that differences in WM aerobic function result from variation in Vmt and not to changes in VO2mt. This is consistent with our prior work that indicated that while diffusion constraints influence mitochondrial distribution, the negative scaling of aerobic processes like post-contractile PCr recovery can largely be attributed to the body size dependence of Vmt.
Temperature sensitivity of cardiac mitochondria in intertidal and subtidal triplefin fishes
Venue: Journal of Comparative Physiology B

The heart is acutely sensitive to temperature in aquatic ectotherms and appears to fail before any other organ as the thermal maximum is reached, although the exact cause of this failure remains unknown. The heart is highly aerobic and therefore dependent on mitochondrial oxidative phosphorylation (OXPHOS) to meet energy requirements, but the role of cardiac mitochondria in limiting heart function at high temperatures remains unclear. We used permeabilised ventricle fibres to explore heart mitochondrial function in situ in three closely related species of small New Zealand triplefin fishes in response to temperature. We compared this to measures of whole animal respiration rates and critical oxygen tensions in these fishes. Bellapiscis medius, an intertidal species, had the greatest tolerance to hypoxia at higher temperatures and had more efficient OXPHOS at 30°C than the two subtidal species Forsterygion varium and F. malcolmi. B. medius also displayed the highest cytochrome c oxidase flux, which may in part explain how B. medius tolerates higher temperatures and hypoxia. Triplefin heart mitochondria exhibit decreased coupling to phosphorylation with increasing temperature. This most likely impairs ATP supply to the heart at elevated temperatures, potentially contributing to heart failure at ecologically relevant temperatures.
Maximum rates of sustained metabolic rate in cold-exposed Djungarian hamsters (Phodopus sungorus): the second wind
Venue: Journal of Comparative Physiology B

Djungarian hamsters (Phodopus sungorus) tolerate short-term exposure to ambient temperatures (Tas) down to −70°C, but surprisingly, previously appeared to reach maximum sustainable metabolic rate (SusMR) when kept at Tas as high as ≥−2°C. We hypothesized that SusMR in Djungarian hamsters may be affected by the degree of prior cold acclimation and temporal patterns of Ta changes experienced by the animals, as average Ta declines. After cold-acclimation at +5°C for 6 weeks, hamsters reached rates of SusMR that were 35% higher than previously determined and were able to maintain positive energy balances down to Ta −9°C. SusMR was unaffected, however, by whether mean cold load was constant or caused by Tas cycling between +3°C and as low as −25°C, at hourly intervals. At mean Tas between +3 and −3°C hamsters significantly reduced body mass and energy expenditure, but were able to maintain stable body mass at lower Tas (−5 to −9°C). These results indicate that prior cold-acclimation profoundly affects SusMR in hamsters and that body mass regulation may play an integral part in maintaining positive energy balance during cold exposure. Because the degree of instantaneous cold load had no effect on SusMR, we hypothesize that limits to energy turnover in Djungarian hamsters are not determined by the capacity to withstand extreme temperatures (i.e., peripheral limits) but are due to central limitation of energy intake.
Auditory sensitivity and ecological relevance: the functional audiogram as modelled by the bat detecting moth ear
Venue: Journal of Comparative Physiology A

Auditory sensitivity has often been measured by identifying neural threshold in real-time (online) which can introduce bias in the audiograms that are produced. We tested this by recording auditory nerve activity of the notodontid moth Nadata gibbosa elicited by bat-like ultrasound and analysing the response offline. We compared this audiogram with a published online audiogram showing that the bias introduced can result in a difference in the audiogram shape. In the second part of our study we compared offline audiograms using spike number as threshold with others that used spike period and stimulus/spike latency, variables that have been suggested as providing behaviourally functional criteria. These comparisons reveal that functional audiograms are more flatly tuned than simple spike audiograms. The shapes of behavioural audiograms are discussed in the context of the selection pressure that maintains their shape, bat predation. Finally, we make predictions on the distance from bats at which notodontid moths use negative phonotaxis or the acoustic startle response.
Regularly firing neurons in the inferior colliculus have a weak interaural intensity difference sensitivity
Venue: Journal of Comparative Physiology A

The spike discharge regularity may be important in the processing of information in the auditory pathway. It has already been shown that many cells in the central nucleus of the inferior colliculus fire regularly in response to monaural stimulation by the best frequency tones. The aim of this study was to find how the regularity of units was affected by adding ipsilateral tone, and how interaural intensity difference sensitivity is related to regularity. Single unit recordings were performed from 66 units in the inferior colliculus of the anaesthetized guinea pig in response to the best frequency tone. Regularity of firing was measured by calculating the coefficient of variation as a function of time of a unit’s response. There was a positive correlation between coefficient of variation and interaural intensity difference sensitivity, indicating that highly regular units had very weak and irregular units had strong interaural intensity difference sensitivity responses. Three effects of binaural interaction on the sustained regularity were observed: constant coefficient of variation despite change in rate (66% of the units), negative (20%) and positive (13%) rate–CV relationships. A negative rate-coefficient of variation relationship was the dominant pattern of binaural interaction on the onset regularity.
Comparison of properties of cortical echo delay-tuning in the short-tailed fruit bat and the mustached bat
Venue: Journal of Comparative Physiology A

Target-distance computation by cortical neurons sensitive to echo delay is an essential characteristic of the auditory system of insectivorous bats. To assess if functional requirements such as detection of small insects versus larger stationary surfaces of plants are reflected in cortical properties, we compare delay-tuned neurons in a frugivorous (C. perspicillata, CP) and an insectivorous (P. parnellii, PP) bat species that belong to related families within the superfamily of Noctilionoidea. The bandwidth and shape of delay-tuning curves and the range of characteristic delays are similar in both species and hence are not related to different echolocation strategies. Most units respond at 2–6 ms echo delay with most sensitive thresholds of 20–30 dB SPL. In CP, units tuned to delays >12 ms are slightly more abundant and are more sensitive than in PP. All delay-tuned neurons in CP reliably respond to single pure-tone stimuli, whereas such responses are only observed in 49% of delay-tuned units in PP. The cortical representation of echo delay (chronotopy) covers a larger area in CP but is less precise than described in PP. Since chronotopy is absent in certain other insectivorous bat species, it is open if these differences in topography are related to echolocation behaviour.
Sounds of shallow water fishes pitch within the quiet window of the habitat ambient noise
Venue: Journal of Comparative Physiology A

The habitat ambient noise may exert an important selective pressure on frequencies used in acoustic communication by animals. A previous study demonstrated the presence of a match between the low-frequency quiet region of the stream ambient noise (termed ‘quiet window’) and the main frequencies used for sound production and hearing by two stream gobies (Padogobius bonelli, Gobius nigricans). The present study examines the spectral features of ambient noise in very shallow freshwater, brackish and marine habitats and correlates them to the range of dominant frequencies of sounds used by nine species of Mediterranean gobies reproducing in these environments. Ambient noise spectra of these habitats featured a low-frequency quiet window centered at 100 Hz (stream, sandy/rocky sea shore), or at 200 Hz (spring, brackish lagoon). The analysis of the ambient noise/sound spectrum relationships showed the sound frequencies matched the frequency band of the quiet window in the ambient noise typical of their own habitat. Analogous ambient noise/sound frequency relationships were observed in other shallow-water teleosts living in similar underwater environments. Conclusions may be relevant to the understanding of evolution of fish acoustic communication and hearing.
Caterpillar crawling over irregular terrain: anticipation and local sensing
Venue: Journal of Comparative Physiology A

Animal locomotion is produced by co-coordinated patterns of motor activity that are generally organized by central pattern generators and modified by sensory feedback. Animals with remote sensing can anticipate obstacles and make adjustments in their gait to accommodate them. It is largely unknown how animals that rely on touch might use such information to adjust their gait. One possibility is immediate (reflexive) change in motor activity. Elongated animals, however, might modulate movements by passing information from anterior to posterior segments. Using the caterpillar Manduca sexta we examined the movements of the most anterior abdominal prolegs as they approached an obstacle. The first pair of prolegs anticipated the obstacle by lifting more quickly in the earliest part of the swing phase: the caterpillar had information about the obstacle at proleg lift-off. Sometimes the prolegs corrected their trajectory mid-step. Removal of sensory hairs on the stepping leg did not affect the early anticipatory movements, but did change the distance at which the mid-step corrections occurred. We conclude that anterior sensory information can be passed backwards and used to modulate an ongoing crawl. The local sensory hairs on each body segment can then fine-tune movements of the prolegs as they approach an obstacle.
Jumping kinematics in the wandering spider Cupienniussalei
Venue: Journal of Comparative Physiology A

Spiders use hemolymph pressure to extend their legs. This mechanism should be challenged when required to rapidly generate forces during jumping, particularly in large spiders. However, effective use of leg muscles could facilitate rapid jumping. To quantify the contributions of different legs and leg joints, we investigated jumping kinematics by high-speed video recording. We observed two different types of jumps following a disturbance: prepared and unprepared jumps. In unprepared jumps, the animals could jump in any direction away from the disturbance. The remarkable directional flexibility was achieved by flexing the legs on the leading side and extending them on the trailing side. This behaviour is only possible for approximately radial-symmetric leg postures, where each leg can fulfil similar functions. In prepared jumps, the spiders showed characteristic leg positioning and the jumps were directed anteriorly. Immediately after a preliminary countermovement in which the centre of mass was moved backwards and downwards, the jump was executed by extending first the fourth and then the second leg pair. This sequence provided effective acceleration to the centre of mass. At least in the fourth legs, the hydraulic and the muscular mechanism seem to interact to generate ground reaction forces.
Winter body temperature patterns in free-ranging Cape ground squirrel, Xerus inauris: no evidence for torpor
Venue: Journal of Comparative Physiology B

The body temperature (Tb) of Cape ground squirrels (Xerus inauris, Sciuridae) living in their natural environment during winter has not yet been investigated. In this study we measured abdominal Tb of eight free-ranging Cape ground squirrels over 27 consecutive days during the austral winter. Mean daily Tb was relatively stable at 37.0 ± 0.2°C (range 33.4 to 40.2°C) despite a marked variation in globe temperature (Tg) (range −7 to 37°C). Lactating females (n = 2) consistently had a significantly higher mean Tb (0.7°C) than non-lactating females (n = 3) and males. There was a pronounced nychthemeral rhythm with a mean active phase Tb of 38.1 ± 0.1°C and a mean inactive phase Tb of 36.3 ± 0.3°C for non-lactating individuals. Mean daily amplitude of Tb rhythm was 3.8 ± 0.2°C. Tb during the active phase closely followed Tg and mean active phase Tb was significantly correlated with mean active phase Tg (r2 = 0.3–0.9; P < 0.01). There was no evidence for daily torpor or pronounced hypothermia during the inactive phase, and mean minimum inactive phase Tb was 35.7 ± 0.3°C for non-lactating individuals. Several alternatives (including nocturnal huddling, an aseasonal breeding pattern and abundant winter food resources) as to why Cape ground squirrels do not employ nocturnal hypothermia are discussed.
Detecting substrate engagement: responses of tarsal campaniform sensilla in cockroaches
Venue: Journal of Comparative Physiology A

Sensory signals of contact and engagement with the substrate are important in the control and adaptation of posture and locomotion. We characterized responses of campaniform sensilla, receptors that encode forces as cuticular strains, in the tarsi (feet) of cockroaches using neurophysiological techniques and digital imaging. A campaniform sensillum on the fourth tarsal segment was readily identified by its large action potential in nerve recordings. The receptor discharged to contractions of the retractor unguis muscle, which engages the pretarsus (claws and arolium) with the substrate. We mimicked the effects of muscle contractions by applying displacements to the retractor apodeme (tendon). Sensillum firing did not occur to unopposed movements, but followed engagement of the claws with an object. Vector analysis of forces suggested that resisted muscle contractions produce counterforces that axially compress the tarsal segments. Close joint packing of tarsal segments was clearly observed following claw engagement. Physiological experiments showed that the sensillum responded vigorously to axial forces applied directly to the distal tarsus. Discharges of tarsal campaniform sensilla could effectively signal active substrate engagement when the pretarsal claws and arolium are used to grip the substrate in climbing, traversing irregular terrains or walking on inverted surfaces.
A computational fluid dynamics model of viscous coupling of hairs
Venue: Journal of Comparative Physiology A

Arrays of arthropod filiform hairs form highly sensitive mechanoreceptor systems capable of detecting minute air disturbances, and it is unclear to what extent individual hairs interact with one another within sensor arrays. We present a computational fluid dynamics model for one or more hairs, coupled to a rigid-body dynamics model, for simulating both biological (e.g., a cricket cercal hair) and artificial MEMS-based systems. The model is used to investigate hair–hair interaction between pairs of hairs and quantify the extent of so-called viscous coupling. The results show that the extent to which hairs are coupled depends on the mounting properties of the hairs and the frequency at which they are driven. In particular, it is shown that for equal length hairs, viscous coupling is suppressed when they are driven near the natural frequency of the undamped system and the damping coefficient at the base is small. Further, for certain configurations, the motion of a hair can be enhanced by the presence of nearby hairs. The usefulness of the model in designing artificial systems is discussed.