nils-herrmann/clean_scirepeval huggingface dataset:
The turtle visual system mediates a complex spatiotemporal transformation of visual stimuli into cortical activity
Venue: Journal of Comparative Physiology A

The three-layered visual cortex of turtle is characterized by extensive intracortical axonal projections and receives non-retinotopic axonal projections from lateral geniculate nucleus. What spatiotemporal transformation of visual stimuli into cortical activity arises from such tangle of malleable cortical inputs and intracortical connections? To address this question, we obtained band-pass filtered extracellular recordings of neural activity in turtle dorsal cortex during visual stimulation of the retina. We discovered important spatial and temporal features of stimulus-modulated cortical local field potential (LFP) recordings. Spatial receptive fields span large areas of the visual field, have an intricate internal structure, and lack directional tuning. The receptive field structure varies across recording sites in a distant-dependent manner. Such composite spatial organization of stimulus-modulated cortical activity is accompanied by an equally multifaceted temporal organization. Cortical visual responses are delayed, persistent, and oscillatory. Further, prior cortical activity contributes globally to adaptation in turtle visual cortex. In conclusion, these results demonstrate convoluted spatiotemporal transformations of visual stimuli into stimulus-modulated cortical activity that, at present, largely evade computational frameworks.
On the role of brain aromatase in females: why are estrogens produced locally when they are available systemically?
Venue: Journal of Comparative Physiology A

The ovaries are often thought of as the main and only source of estrogens involved in the regulation of female behavior. However, aromatase, the key enzyme for estrogen synthesis, although it is more abundant in males, is expressed and active in the brain of females where it is regulated by similar mechanisms as in males. Early work had shown that estrogens produced in the ventromedial hypothalamus are involved in the regulation of female sexual behavior in musk shrews. However, the question of the role of central aromatase in general had not received much attention until recently. Here, I will review the emerging concept that central aromatization plays a role in the regulation of physiological and behavioral endpoints in females. The data support the notion that in females, brain aromatase is not simply a non-functional evolutionary vestige, and provide support for the importance of locally produced estrogens for brain function in females. These observations should also have an impact for clinical research.
Acute effects of sex steroids on visual processing in male goldfish
Venue: Journal of Comparative Physiology A

Elevations of sex steroids induced by social cues can rapidly modulate social behavior, but we know little about where they act within the nervous system to produce such effects. In male goldfish, testosterone (T) rapidly increases approach responses to the visual cues of females through its conversion to estradiol. Because aromatase is expressed in the retina, we tested if T can acutely influence retina responses to visual stimuli, and investigated the receptor mechanisms that may mediate such effects. Specifically, we measured FOS protein immunoreactivity to determine if T affects cellular responses to visual stimuli that include females, and used electrophysiology to investigate whether T can generally affect light sensitivity. We found that T acutely increased FOS responses to the simultaneous onset of light and the presence of female visual stimuli, both of which would normally be associated with early morning spawning, and increased electrophysiological responses to low intensity light pulses. Both effects were blocked by an estrogen receptor beta (ERβ) antagonist, indicating that T is likely being converted to estradiol (E2) and acting through an ERβ mediated mechanism to acutely modulate visual processing. Changes in sensory processing could subsequently influence approach behavior to increase reproductive success in competitive mating environments.
Responses of medullary lateral line units of the rudd, Scardinius erythrophthalmus, and the nase, Chondrostoma nasus, to vortex streets
Venue: Journal of Comparative Physiology A

Fish use their mechanosensory lateral line amongst others for the detection of vortices shed by an upstream object and/or for the detection of vortices caused by the tail fin movements of another fish. Thus, vortices are one type of hydrodynamic stimuli to which fish are exposed in their natural environment. We investigated the responses of medullary lateral line units of common rudd, Scardinius erythrophthalmus, and common nase, Chondrostoma nasus (Cyprinidae), to water flow (9.5–13.3 cm−1) that contained vortices (a Kármán vortex street) shed by an upstream cylinder (diameter 2 cm). The distance between the cylinder and the tip of the fish’s snout varied between 8 and 24 cm. 21 out of 42 units (S. erythrophthalmus), respectively, 9 out of 39 units (Chondrostoma nasus) responded to the vortices shed by the cylinder. Up to a cylinder distance of 24 cm, interburst intervals revealed the vortex shedding frequency, i.e., burst frequency was similar to or identical with the vortex shedding frequency.
Changes in thermoregulation and monoamine release in freely moving rats during cold exposure and inhibition of the ventromedial, dorsomedial, or posterior hypothalamus
Venue: Journal of Comparative Physiology B

The hypothalamus is critical for regulating thermogenesis, but the role of monoamines in specific hypothalamic subregions in thermogenesis is not thoroughly established. The purpose of this study was to confirm changes of body temperature (Tb) and thermoregulatory parameters upon inhibition of neural activity in hypothalamic subregions in freely moving rats. In addition, the pattern of monoamine release in these nuclei was measured during active thermoregulation using microdialysis. Tetrodotoxin (TTX) was perfused into the ventromedial hypothalamus (VMH), dorsomedial hypothalamus (DMH), or posterior hypothalamus (PH) at two different ambient temperatures (5 or 23 °C). Using telemetry, we continuously measured the Tb and the heart rate (HR) as an index of heat production as well as locomotor activity (Act). Tail skin temperature (Ttail) was also continuously measured as an index of heat loss. Although the perfusion of TTX into hypothalamic subregions had no effect on any of the measured thermoregulatory parameters at an ambient temperature of 23 °C, it induced significant Tb decrease under cold conditions only when perfused into the DMH and the PH. In contrast, the HR decreased only after perfusion of TTX into the PH during cold conditions, while the Ttail and Act remained unchanged. Serotonin (5-HT) in the DMH and dopamine (DA) metabolite 3,4-Dihydroxyphenylacetic acid in the PH, but not noradrenaline, increased significantly during exposure to cold temperatures. Our results indicate that the DMH and the PH, but not the VMH, are particularly involved in heat production under cold conditions. In addition, 5-HT in the DMH and DA in the PH may be involved in thermogenesis.
Venous pressures and cardiac filling in turtles during apnoea and intermittent ventilation
Venue: Journal of Comparative Physiology B

The amount of blood pumped by the heart (cardiac output) must be matched to the amount of blood returning to the heart (venous return), but the factors determining cardiac filling are sparsely understood in ectothermic vertebrates. Stroke volume is affected by heart rate along with central and peripheral venous pressures. In the present study, we investigated the heart rate dependency of cardiac filling in turtles, along with the changes in venous pressures that accompany ventilation. Experimental reductions in heart rate of anaesthetised turtles (Trachemys scripta) by the specific bradycardic agent zatebradine (2–3 mg kg−1) resulted in an elevation of stroke volume that compensated cardiac output. By contrast, in spontaneously ventilating turtles, stroke volume remained constant, even during the transitions from the pronounced bradycardia during breath-hold diving to the accelerated heart rate associated with spontaneous ventilation. Ventilation was associated with pronounced decreases in visceral, pericardial and central venous pressure, all of which became sub-ambient (especially during inspiration) and may provide a powerful ‘suctional’ element to cardiac filling. In addition, mean circulatory filling pressure, an index of vascular capacitance and the peripheral driving pressure for venous return, was increased by infusion of adrenaline (2.5 µg kg−1). Together these data demonstrate that changes in both central and peripheral venous pressures are key determinants of venous return that, in concert with direct regulation of the heart, contribute to the large scope for cardiac output in turtles.
Effects of water ionic composition on acid–base regulation in rainbow trout, during hypercarbia at rest and during sustained exercise
Venue: Journal of Comparative Physiology B

Aquatic hypercarbia (elevated environmental CO2) results in a blood acidosis in fish, which is compensated by the exchange of Na+ and/or Cl− for its acid/base counterpart (H+, HCO3−) across the gill epithelium. To date, no studies exist on how a single species, capable of inhabiting both fresh and saltwater, responds to hypercarbia, at rest or during sustained exercise. Rainbow trout was acclimated to soft water (in mmol l− 1: Na+, 0.08; Cl−, 0.05; pH 6.7–6.8), hard water (in mmol l− 1: Na+, 2.4; Cl−, 0.2; pH 7.9–8.0), or 85% saltwater (28 ppt) (in mmol l− 1: Na+, 410; Cl−, 476; pH 7.8–8.0). Acid–base relevant blood parameters were measured during a 1 kPa CO2 hypercarbia exposure, both at rest and during sustained exercise (~ 60% Ucrit). After 48 h of hypercarbia, resting hard-, and saltwater trout fully restored blood pH, whereas soft-water-acclimated trout was only 60.6 ± 10.5% recovered. In all fish, recovery was associated with an increase in plasma [HCO3−] and an equimolar reduction in plasma [Cl−]. Following 8 h of hypercarbia during sustained exercise, saltwater fish fully restored blood pH, while soft- and hard water fish were 42 ± 18.1 and 64 ± 6.8% recovered, respectively. Results provide intra-specific support demonstrating that saltwater acclimated fish acid–base compensate faster than freshwater fish during hypercarbia. Furthermore, data indicate that recovery during hypercarbia in trout is more rapid during exercise than rest. This not only demonstrates an important link between ambient water ion levels and ability to recover from acid–base disturbances, but also it presents novel data, suggesting that exercise may enhance acid–base regulation.
Songbird chemical signals reflect uropygial gland androgen sensitivity and predict aggression: implications for the role of the periphery in chemosignaling
Venue: Journal of Comparative Physiology A

Chemical signals can provide useful information to potential mates and rivals. The production mechanisms of these signals are poorly understood in birds, despite emerging evidence that volatile compounds from preen oil may serve as chemosignals. Steroid hormones, including testosterone (T), may influence the production of these signals, yet variation in circulating T only partly accounts for this variation. We hypothesized that odor is a T-mediated signal of an individual’s phenotype, regulated in part by androgen sensitivity in the uropygial gland. We quantified natural variation in chemosignals, T, uropygial gland androgen sensitivity, and aggressive behavior in dark-eyed juncos (Junco hyemalis). The interaction between circulating T and androgen receptor transcript abundance significantly correlated with volatile concentrations in male, but not female, preen oil. In both sexes, odorant variables correlated with aggressive response to an intruder. Our results suggest that preen oil volatiles could function as signals of aggressive intent, and, at least in males, may be regulated by local androgen receptor signaling in the uropygial gland. Because these behavioral and chemical traits have been linked with reproductive success, local regulation of androgen sensitivity in the periphery has the potential to be a target of selection in the evolution of avian olfactory signaling.
Androgen receptors and muscle: a key mechanism underlying life history trade-offs
Venue: Journal of Comparative Physiology A

Sexual dimorphism in skeletal muscle is prominent in mammals, with males typically having larger and stronger muscles than females. Furthermore, neuromuscular systems with sexual functions are remarkably sexually dimorphic in a wide variety of vertebrates. Endocrine mechanisms are of central importance for sexual differentiation of these traits, and anabolic actions of gonadal testosterone have been intensively studied. Here we review the relationship between androgen receptor (AR) and sexual differentiation of neuromuscular systems. We focus our review on the hypotheses that sexual dimorphism and androgen responsiveness of neuromuscular systems is a function of the amount of AR expressed by muscle and that AR in muscle is a key mechanism on which evolution acts to shape individual and species differences in reproductive behavior.
Genes linked to species diversity in a sexually dimorphic communication signal in electric fish
Venue: Journal of Comparative Physiology A

Sexually dimorphic behaviors are often regulated by androgens and estrogens. Steroid receptors and metabolism are control points for evolutionary changes in sexual dimorphism. Electric communication signals of South American knifefishes are a model for understanding the evolution and physiology of sexually dimorphic behavior. These signals are regulated by gonadal steroids and controlled by a simple neural circuit. Sexual dimorphism of the signals varies across species. We used transcriptomics to examine mechanisms for sex differences in electric organ discharges (EODs) of two closely related species, Apteronotus leptorhynchus and Apteronotus albifrons, with reversed sexual dimorphism in their EODs. The pacemaker nucleus (Pn), which controls EOD frequency (EODf), expressed transcripts for steroid receptors and metabolizing enzymes, including androgen receptors, estrogen receptors, aromatase, and 5α-reductase. The Pn expressed mRNA for ion channels likely to regulate the high-frequency activity of Pn neurons and for neuromodulator and neurotransmitter receptors that may regulate EOD modulations used in aggression and courtship. Expression of several ion channel genes, including those for Kir3.1 inward-rectifying potassium channels and sodium channel β1 subunits, was sex-biased or correlated with EODf in ways consistent with EODf sex differences. Our findings provide a basis for future studies to characterize neurogenomic mechanisms by which sex differences evolve.
Ethanol metabolism varies with hypoxia tolerance in ten cyprinid species
Venue: Journal of Comparative Physiology B

During periods of severe hypoxia or anoxia, Carassius spp. are known for their ability to produce ethanol as their anaerobic end product, which diffuses into the environment thereby reducing the osmotic and acidotic load associated with “anaerobic” glycolysis. However, the relationship between alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) activities, key ethanol metabolizing enzymes, and hypoxia tolerance among Carassius spp. and their closely related non-ethanol-producing cyprinids remains unclear. To address this, we quantified the activity levels of key anaerobic enzymes in liver and muscle in species of cyprinids over 48 h of severe hypoxia exposure (0.7 kPa). As predicted, muscle ADH activity was highest in the two most hypoxia-tolerant species (Carassius spp.), with very low levels present in the other species examined. However, liver ADH activities showed an inverse relationship with hypoxia tolerance, with the most hypoxia-tolerant fish having the lowest ADH activity. There was no correlation between hypoxia tolerance and ALDH and LDH activities in muscle or liver. All species produced lactate, reaching their highest levels after 8 h, but returning to near-baseline levels by 48 h of sustained exposure to hypoxia, suggesting lactate oxidation or depressed ATP demand. Liver glycogen content was not affected by 48 h hypoxia exposure in the most hypoxia-tolerant species, whereas the least tolerant species consumed the majority of the liver glycogen stores, which is probably due to the greater relative hypoxia exposure experienced by these species. Our findings that liver ADH activities were inversely related to hypoxia tolerance suggests that in all but Carassius spp., the ethanol metabolizing pathways in cyprinids is largely similar to that observed in other vertebrates and plays a role in the detoxification of ethanol. Furthermore, conservation of glycogen stores may be the result of metabolic-depressing pathways in the more tolerant species, regardless of the ability to produce ethanol, or adaptations that improve oxygen uptake to reduce metabolic demands due to hypoxia.
Evolution of the androgen-induced male phenotype
Venue: Journal of Comparative Physiology A

The masculine reproductive phenotype varies significantly across vertebrates. As a result, biologists have long recognized that many of the mechanisms that support these phenotypes—particularly the androgenic system—is evolutionarily labile, and thus susceptible to the effects of selection for different traits. However, exactly how androgenic signaling systems vary in a way which results in dramatically different functional outputs, remain largely unclear. We explore this topic here by outlining four key—but non-mutually exclusive—hypotheses that propose how the mechanisms of androgenic signaling might change over time to potentiate the emergence of phenotypical variation in masculine behavior and physiology. We anchor this framework in a review of our own studies of a tropical bird called the golden-collared manakin (Manacus vitellinus), which has evolved an exaggerated acrobatic courtship display that is heavily androgen-dependent. The result is an example of how the cellular basis of androgenic action can be modified to support a unique reproductive repertoire. We end this review by highlighting a broad pathway forward to further pursue the intricate ways by which the mechanisms of hormone action evolve to support processes of adaptation and animal design.
Frequency sensitivity in Northern saw-whet owls (Aegolius acadicus)
Venue: Journal of Comparative Physiology A

Northern saw-whet owls (Aegolius acadicus) are known for their unique asymmetrical ear structure and ability to localize prey acoustically, yet few attempts have been made to explore the auditory capabilities of this species. In this study, we evoked auditory brainstem responses (ABRs) with tonebursts to assess three main hypotheses regarding the evolution of auditory sensitivity: sender-receiver matching, ecological constraints, and phylogenetic/morphological constraints. We found that ABR amplitude increased with increasing stimulus level, which is consistent with results in other avian species. ABR amplitudes, latencies, and thresholds indicate that the hearing range of Northern saw-whet owls extends from 0.7 to 8.6 kHz, with an extended frequency range of best sensitivity between 1.6 and 7.1 kHz. Sensitivity fell off rapidly above and below these frequencies. The average audiogram was structurally similar to those found in other species of owls, suggesting that phylogeny or morphology may be constraining the frequency range of auditory sensitivity. However, ABR thresholds were 10–25 dB lower than those of Eastern screech-owls (Megascops asio), with thresholds below 0 dB SPL in some individuals. The lowest thresholds were at frequencies not found in the vocalizations of Northern saw-whet owls, suggesting ecological constraints rather than conspecific vocalizations are driving absolute sensitivity.
Insight into the neuroendocrine basis of signal evolution: a case study in foot-flagging frogs
Venue: Journal of Comparative Physiology A

A hallmark of sexual selection is the evolution of elaborate male sexual signals. Yet, how the physiology of an animal changes to support a new or modified signal is a question that has remained largely unanswered. Androgens are important in regulating male reproductive behavior, therefore, selection for particular signals may drive the evolution of increased androgenic sensitivity in the neuro-motor systems underlying their production. Studies of the neuroendocrine mechanisms of anuran sexual signaling provide evidence to support this idea. Here, we highlight two such cases: first, a large body of work in Xenopus frogs demonstrates that sexually dimorphic androgen receptor (AR) expression in the laryngeal nerves and muscles underlies sexually dimorphic vocal behavior, and second, our own work showing that the recent evolution of a hind limb signal (known as the “foot flag”) in Staurois parvus is accompanied by a dramatic increase in androgenic sensitivity of the thigh muscles that control limb movement. Together, these examples illustrate that the evolutionary modification or gain of a sexual signal is linked with a novel pattern of AR expression in the tissues that support it. We suggest that such co-evolution of AR expression and sex-specific or species-specific signaling behavior exists across vertebrates.
Thermal windows and metabolic performance curves in a developing Antarctic fish
Venue: Journal of Comparative Physiology B

For ectotherms, temperature modifies the rate of physiological function across a temperature tolerance window depending on thermal history, ontogeny, and evolutionary history. Some adult Antarctic fishes, with comparatively narrow thermal windows, exhibit thermal plasticity in standard metabolic rate; however, little is known about the shape or breadth of thermal performance curves of earlier life stages of Antarctic fishes. We tested the effects of acute warming (− 1 to 8 °C) and temperature acclimation (2 weeks at − 1, 2, 4 °C) on survival and standard metabolic rate in early embryos of the dragonfish Gymnodraco acuticeps from McMurdo Sound, Ross Island, Antarctica. Contrary to predictions, embryos acclimated to warmer temperatures did not experience greater mortality and nearly all embryos survived acute warming to 8 °C. Metabolic performance curve height and shape were both significantly altered after 2 weeks of development at − 1 °C, with further increase in curve height, but not alteration of shape, with warm temperature acclimation. Overall metabolic rate temperature sensitivity (Q10) from − 1 to 8 °C varied from 2.6 to 3.6, with the greatest thermal sensitivity exhibited by embryos at earlier developmental stages. Interclutch variation in metabolic rates, mass, and development of simultaneously collected embryos was also documented. Taken together, metabolic performance curves provide insight into the costs of early development under warming temperatures, with the potential for thermal sensitivity to be modified by dragonfish phenology and magnitude of seasonal changes in temperature.