nils-herrmann/clean_scirepeval huggingface dataset:
Purification and characterization of a urea sensitive lactate dehydrogenase from skeletal muscle of the African clawed frog, Xenopus laevis
Venue: Journal of Comparative Physiology B

The African clawed frog, Xenopus laevis endures whole body dehydration which can increase its reliance on anaerobic glycolysis for energy production. This makes the regulation of the terminal enzyme of glycolysis, lactate dehydrogenase (LDH), crucial to stress survival. We investigated the enzymatic properties and posttranslational modification state of purified LDH from the skeletal muscle of control and dehydrated (30% total body water loss) X. laevis. LDH from the muscle of dehydrated frogs showed a 93% reduction in phosphorylation on threonine residues and an 80% reduction of protein nitrosylation. LDH from dehydrated muscle also showed a 74% lower Vmax in the pyruvate oxidizing direction and a 78% decrease in Vmax in the lactate reducing direction along with a 33% lower Km for pyruvate and a 40% higher Km for lactate. In the presence of higher levels of urea and molecular crowding by polyethylene glycol, used to mimic conditions in the cells of dehydrated animals, the Km values of control and dehydrated LDH demonstrated opposite responses. In the pyruvate oxidizing direction, control muscle LDH was unaffected by these additives, whereas the affinity for pyruvate dropped further for LDH from dehydrated muscle. The opposite effect was more pronounced in the lactate reducing direction as control LDH showed an increased affinity for lactate, whereas LDH from dehydrated animals showed a further reduction in affinity. The physiological consequences of dehydration-induced LDH regulation appear to poise the enzyme towards lactate production when urea levels are high and lactate catabolism when urea levels are low, perhaps helping to maintain glycolysis under dehydrating conditions whilst providing for the ability to recycle lactate upon rehydration.
Innate releasing mechanisms and fixed action patterns: basic ethological concepts as drivers for neuroethological studies on acoustic communication in Orthoptera
Venue: Journal of Comparative Physiology A

This review addresses the history of neuroethological studies on acoustic communication in insects. One objective is to reveal how basic ethological concepts developed in the 1930s, such as innate releasing mechanisms and fixed action patterns, have influenced the experimental and theoretical approaches to studying acoustic communication systems in Orthopteran insects. The idea of innateness of behaviors has directly fostered the search for central pattern generators that govern the stridulation patterns of crickets, katydids or grasshoppers. A central question pervading 50 years of research is how the essential match between signal features and receiver characteristics has evolved and is maintained during evolution. As in other disciplines, the tight interplay between technological developments and experimental and theoretical advances becomes evident throughout this review. While early neuroethological studies focused primarily on proximate questions such as the implementation of feature detectors or central pattern generators, later the interest shifted more towards ultimate questions. Orthoptera offer the advantage that both proximate and ultimate questions can be tackled in the same system. An important advance was the transition from laboratory studies under well-defined acoustic conditions to field studies that allowed to measure costs and benefits of acoustic signaling as well as constraints on song evolution.
Effects of acclimation temperature on the thermal tolerance, hypoxia tolerance and swimming performance of two endangered fish species in China
Venue: Journal of Comparative Physiology B

Temperature is one of the most important environmental factors affecting the physiological activities and, thus, the fitness of fish, and physiological studies can help predict the effects of climate change on fish species in the field. The aim of this study was to investigate the effect of acclimation temperature on the thermal tolerance, hypoxia tolerance and swimming ability of two endangered fish species in the upper reach of the Yangtze River, namely, the Chinese sucker (Myxocyprinus asiaticus) and rock carp (Procypris rabaudi). The fish were acclimated at either 15 °C or 25 °C for a 3-week period. Then, thermal tolerance as indicated by the critical thermal maximum (CTmax) and critical thermal minimum (CTmin), hypoxia tolerance as indicated by the aquatic surface respiration (ASR50) and loss of equilibrium (LOE50), swimming performance as indicated by the critical swimming speed (Ucrit), aerobic capacity as indicated by the maximum metabolic rate and aerobic scope were measured. As expected, the thermal indicators of both species increased with temperature, and their values at both acclimation temperatures were similar to those of fish living in the Yangtze River. However, both species showed poor hypoxia tolerance compared to most fish species in the Yangtze River, according to previous studies. In particular, Chinese sucker acclimated at a low temperature exhibited an unusually strong decrease in hypoxia tolerance with decreasing temperature (fish usually showed high hypoxia tolerance due to decreased oxygen demand and high environmental oxygen tension at low temperature). Furthermore, Chinese sucker exhibited poorer swimming performance than rock carp (which is also a relatively poor swimmer among the fish species in the Yangtze River) when maintained at a high temperature due to low swimming efficiency, possibly as a consequence of its deep body shape. The difference in Ucrit was magnified at low temperature due to the more profound decrease in metabolic scope in Chinese sucker than in rock carp (55% vs 20%), but Chinese sucker showed a higher resting metabolic rate than rock carp at a low temperature, which is difficult to explain. This result suggested that low hypoxia tolerance and poor swimming performance due to the low cardiorespiratory capacity and (or) non-streamlined body shape of both fish species, especially Chinese sucker, reared at low temperature might be two of the reasons why they are not well adjusted to the change in their natural habitat and have thus declined in recent decades. The underlying physiological and biochemical mechanisms involved in the unusual adjustment of the physiological function of Chinese sucker and its ecological relevance must be investigated further. The present study provides a good example of a physiological investigation yielding very interesting and useful data for species conservation in a changing world.
Effects of autonomic denervations on the rhythms in axial length and choroidal thickness in chicks
Venue: Journal of Comparative Physiology A

In chicks, axial length and choroidal thickness undergo circadian oscillations. The choroid is innervated by both branches of the autonomic nervous system, but their contribution(s) to these rhythms is unknown. We used two combination lesions to test this. For parasympathectomy, nerve VII was sectioned presynaptic to the pterygopalatine ganglia, and the ciliary post-ganglionics were cut (double lesion; n = 8). Triple lesions excised the sympathetic superior cervical ganglion as well (n = 8). Sham surgery was done in controls (n = 7). 8–14 days later, axial dimensions were measured with ultrasonography at 4-h intervals over 24 h. Rhythm parameters were assessed using a “best fit” function, and growth rates measured. Both types of lesions resulted in ultradian (> 1 cycle/24 h) rhythms in choroidal thickness and axial length, and increased vitreous chamber growth (Exp-fellow: double: 69 µm; triple: 104 µm; p < 0.05). For double lesions, the frequency was 1.5 cycles/day for both rhythms; for triples the choroidal rhythm was 1.5 cycles/day, and the axial was 3 cycles/day. For double lesions, the amplitudes of both rhythms were larger than those of sham surgery controls (axial: 107 vs 54 µm; choroid: 124 vs 29 µm, p < 0.05). These findings provide evidence for the involvement of abnormal ocular rhythms in the growth stimulation underlying myopia development.
Physiological effects of dissolved oxygen are stage-specific in incubating Atlantic salmon (Salmo salar)
Venue: Journal of Comparative Physiology B

Oxygen availability is highly variable during salmonid incubation in natural redds and also in aquaculture incubation systems. Hypoxia generally decreases growth and aerobic metabolism prior to hatching, in parallel with eliciting physiological modifications that enhance oxygen delivery. However, it is less-well known whether developmental hyperoxia can drive the opposite effect. Moreover, there is insufficient understanding of stage-specific developmental windows during which ambient oxygen availability may be of greater or lesser impact to incubating embryos. Here, we tested the effects of hypoxia (50% dissolved oxygen: DO, % air saturation) and hyperoxia (150% DO) on the growth, routine aerobic metabolism ($$\dot {M}{{\text{O}}_{{\text{2rout}}}}$$M˙O2rout) and hypoxia tolerance (O2crit) of Atlantic salmon (Salmo salar) during seven developmental windows throughout incubation. Embryos exposed to hyperoxia (150% DO) did not differ from the normoxic group in growth, $$\dot {M}{{\text{O}}_{{\text{2rout}}}}$$M˙O2rout or O2crit at any developmental window. In contrast, embryos exposed to hypoxia grew slower and had a lower $$\dot {M}{{\text{O}}_{{\text{2rout}}}}$$M˙O2rout, but had higher hypoxia tolerance (lower O2crit) than normoxic and hyperoxic counterparts. Interestingly, these differences were only apparent when the embryos were measured prior to hatching. Larvae (alevins) incubated in hypoxia following hatching grew similarly to normoxia-incubated alevins. Our results provide evidence that Atlantic salmon embryos are most sensitive to hypoxia prior to hatching, probably due to increasing (absolute) oxygen requirements concurrent with restricted oxygen diffusion through the egg. Moreover, the similarities between normoxia- and hyperoxia-incubated salmon demonstrate that embryos are not oxygen-limited under normoxic conditions.
Effects of thyroid hormones and cold acclimation on the energy metabolism of the striped hamster (Cricetulus barabensis)
Venue: Journal of Comparative Physiology B

To examine the effects of low ambient temperature and thyroid hormones on the energy metabolism of the striped hamster (Cricetulus barabensis), adult male striped hamsters were kept at 30 °C, or acclimated to 5 °C, for 4 weeks. During this time, hamsters were treated with a synthetic thyroxine, levothyroxine sodium (LTS), the antithyroid drug methimazole, or saline solution (control). Hamster’s food intake, basal metabolic rate (BMR), non-shivering thermogenesis (NST), thyroid hormones, body fat content, mitochondrial state-4 respiration, cytochrome c oxidase, and uncoupling protein 1 (UCP1) gene expression in brown adipose tissue (BAT), were measured. Both acclimation to 5 °C and LTS increased serum levels of triiodothyronine, which was associated with increased food and energy intake and BMR. Interestingly, although acclimation to 5 °C also increased NST and UCP1 gene expression in BAT, and decreased body fat content, these changes were not induced by LTS treatment. Finally, exposure to 5 °C reduced the effects of LTS on energy intake and expenditure in specific metabolic markers and organs. Together, these data illustrate that ambient temperature and thyroid hormones can have both independent, and interactive, effects on the metabolic changes in striped hamsters induced by cold acclimation.
Jittered echo-delay resolution in bottlenose dolphins (Tursiops truncatus)
Venue: Journal of Comparative Physiology A

Psychophysical methods similar to those employed with bats were used to examine jittered echo-delay resolution in bottlenose dolphins (Tursiops truncatus). Two dolphins were trained to produce echolocation clicks and report a change from electronic echoes with a fixed delay of ~ 12.6 ms (~ 9.4 m simulated range) to echoes with delays that alternated (jittered) between successive emitted signals. Jitter delays varied from 0 to 50 µs. Jittered echo-delay thresholds were between 1 and 2 µs—the lowest achievable (non-zero) values with the hardware configuration. Error functions matched the click autocorrelation function near zero jitter delay, and were well within the envelope of the autocorrelation function; however, measured jitter delay thresholds were larger than predictions for a coherent or semicoherent receiver at comparable signal-to-noise ratios. When one of the two alternating jittered echoes was inverted in polarity, both dolphins reliably discriminated echoes at all jittered echo delays, including 0 µs (i.e., only jittering in polarity, not delay). Finally, both dolphins used unusual patterns of click emissions, where groups of echolocation clicks were interspersed with silent gaps. Further tests with sub-microsecond jitter values and various echo signal-to-noise ratios would be necessary for proper direct comparison with jitter detection values obtained for bats.
Acute hypoxia/reoxygenation affects muscle mitochondrial respiration and redox state as well as swimming endurance in zebrafish
Venue: Journal of Comparative Physiology B

Rapid fluctuations of the oxygen content of both natural and anthropogenic origin are relatively common in freshwater environments. Fish adaptation to these conditions implies tolerance of both low levels of oxygen availability and reoxygenation. Hypoxia tolerance in fish has been widely studied, but the involvement of mitochondria in the response of fish to rapid hypoxia/reoxygenation stress is less known. Zebrafish, a floodplain species, is likely facing significant changes in dissolved oxygen in its natural environment and displays a moderate ability to tolerate hypoxia. In the present study, we report the effects of an acute hypoxia/reoxygenation stress (H/R) protocol on mitochondrial functionality (respiration, complex activities, rate of H2O2 release) and redox state (level of HPs and protein oxidation) of muscle tissue. In parallel, the animal metabolic performance (routine metabolism, nitrogen excretion and swimming performance) was measured. Additionally, the recovery from H/R was tested 20 h after treatment. A significant stimulation by H/R of muscle mitochondrial respiration and H2O2 release was observed, which was only in part counteracted by stimulation of the antioxidant system, resulting in an increased level of lipid peroxides and protein carbonyls. In parallel, H/R increased the animal oxygen consumption and urea excretion rate and reduced routine activity. A significant strong reduction of endurance at 80% Ucrit was also observed. Most of the altered parameter did not recover 20 h after reoxygenation. These data indicate a significant alteration of zebrafish muscle mitochondrial state after acute H/R, associated with changes in tissue redox state and locomotor performance.
Preparing to migrate: expression of androgen signaling molecules and insulin-like growth factor-1 in skeletal muscles of Gambel’s white-crowned sparrows
Venue: Journal of Comparative Physiology A

Migratory birds, including Gambel’s white-crowned sparrows (Zonotrichia leucophrys gambelii), exhibit profound modifications of skeletal muscles prior to migration, notably hypertrophy of the pectoralis muscle required for powered flight. Muscle growth may be influenced by anabolic effects of androgens; however, prior to spring departure, circulating androgens are low in sparrows. A seasonal increase in local androgen signaling may occur within muscle to promote remodeling. We measured morphological parameters, plasma and tissue levels of testosterone, as well as mRNA expression levels of androgen receptor, 5α-reductase (converts testosterone to 5α-dihydrotestosterone), and the androgen-dependent myotrophic factor insulin-like growth factor-1. We studied the pectoralis muscle as well as the gastrocnemius (leg) muscle of male sparrows across three stages on the wintering grounds: winter (February), pre-nuptial molt (March), and pre-departure (April). Testosterone levels were low, but detectable, in plasma and muscles at all three stages. Androgen receptor mRNA and 5α-reductase Type 1 mRNA increased at pre-departure, but did so in both muscles. Notably, mRNA levels of insulin-like growth factor-1, an androgen-dependent gene critical for muscle remodeling, increased at pre-departure in the pectoralis but decreased in the gastrocnemius. Taken together, these data suggest a site-specific molecular basis for muscle remodeling that may serve to enable long-distance flight.
The impact of age and egg-laying cycle on female grasshoppers’ preference functions for acoustic signals
Venue: Journal of Comparative Physiology A

Female responsiveness and the shape of preference functions for male signal traits are important determinants for male mating success. We observed the responsiveness and the selectivity of virgin grasshopper females (Chorthippus biguttulus L.) for different features of males’ acoustic signals throughout their life span to detect possible influences of age on the females’ preference functions. In particular, we explored the hypothesis that the females may become less selective with increasing age and, therefore, would start to accept songs that are normally rejected. Such an age effect could relieve the selection pressure on male signal traits. In the majority of animals tested, the general responsiveness decreased with age although a few individuals exhibited an opposite trend. Contrary to the above expectation, there was no indication of a loss of selectivity in older females or an increased acceptance of normally unattractive song models. The timing within the oviposition cycle had a strong effect on responsiveness: near oviposition the general responsiveness increased and with it also the half width of the preference functions. However, highly unattractive song models remained unattractive also near oviposition.
Mechanisms of Ca2+ uptake in freshwater and seawater-acclimated killifish, Fundulus heteroclitus, and their response to acute salinity transfer
Venue: Journal of Comparative Physiology B

Killifish (Fundulus heteroclitus) has been extensively used as a model for ion regulation by euryhaline fishes. Na+ and Cl− dynamics have been well studied in killifish, but few studies have addressed that of Ca2+. Therefore, this study aimed to characterize Ca2+ fluxes in freshwater (FW) and seawater (SW)-acclimated killifish, their response to salinity transfer, and to elucidate the mechanisms of Ca2+ influx in FW and SW. SW killifish displayed a significantly higher Ca2+ influx rate than that of FW fish, while Ca2+ efflux rates were comparable in both salinities. Ca2+ influx was saturable in FW (Km = 78 ± 19 µmol/L; Jmax = 53 ± 3 nmol/g/h) and influx by SW killifish was linear up to 7 mmol/L Ca2+. In SW-acclimated fish, 36% of Ca2+ influx was attributed to “intestinal Ca2+ intake”, likely caused by drinking, whereas intestinal Ca2+ intake in FW contributed to < 2% of total. Throughout the study, results suggested that “cation competition” in SW modulates Ca2+ influx. Therefore, we hypothesized that SW-acclimated fish actually have a higher affinity Ca2+ influx system than FW-acclimated fish but that it is competitively inhibited by competing SW cations. In agreement with this cation competition hypothesis, we demonstrated for the first time that “extra-intestinal” Ca2+ influx was inhibited by Mg2+ in both FW and SW-acclimated killifish. Following acute salinity transfer, extra-intestinal Ca2+ influx was rapidly regulated within 12–24 h, similar to Na+ and Cl−. Ca2+ influx in FW was inhibited by La3+, an epithelial Ca2+ channel blocker, whereas La3+ had no significant effect in SW.
Ecoimmunology in degus: interplay among diet, immune response, and oxidative stress
Venue: Journal of Comparative Physiology B

The relationships between immunity, oxidative stress, and diet have not often been studied together. Despite this, it has been shown that dietary proteins can have effects on the functioning of the immune system and the oxidative status of animals. Here we evaluated the effects of dietary proteins on the response to an antigen and oxidative status of Octodon degus (Rodentia). We acclimated adult individuals to high-protein and low-protein diets and evaluated several aspects of the acute phase response and variables associated with oxidative status. After the immune challenge, animals acclimated to the high-protein diet had more inflammatory proteins and body mass losses than the group acclimated to a low-protein diet. Overall, the immune challenge increased the production of inflammatory proteins, total antioxidant capacity, lipid peroxidation, and duration of rest periods. In contrast, we did not find an interaction between diet and the challenge with the antigen. Overall, our results do not reveal an enhanced response to an antigen nor effects on the oxidative status of degus individuals subjected to a high-protein diet.
Thermal physiology of a range-restricted desert lark
Venue: Journal of Comparative Physiology B

Much recent work on avian physiological adaptation to desert environments has focused on larks (Passeriformes: Alaudidae). We tested the prediction that the threatened red lark (Calendulauda burra), a species restricted to very arid parts of South Africa and which is not known to drink, exhibits highly efficient evaporative cooling and makes pronounced use of facultative hyperthermia when exposed to high air temperatures (Ta). We also predicted that C. burra possesses similarly low basal metabolic rate (BMR) and total evaporative water loss (EWL) at moderate Ta as reported for species from the deserts of the Middle East. Rest-phase thermoregulation in C. burra was characterized by an unusually low lower critical limit of thermoneutrality at Ta = ~ 21 °C and a BMR of 0.317 ± 0.047 W, the lowest BMR relative to allometrically-expected values yet reported in any lark. During the diurnal active phase, red larks were able to tolerate Ta up to 50 °C, with the onset of panting occurring at Ta = 38 °C. Maximum EWL was 1.475 ± 0.107 g h− 1 at Ta = 50 °C, equivalent to 620% of minimum EWL at thermoneutrality. The maximum ratio of evaporative heat dissipation to metabolic heat production was 1.58, a value towards the lower end of the range reported for passerines. Our data support the prediction that C. burra shows metabolic traits similar to those of other larks inhabiting extremely arid climates, but not the notion that evaporative cooling at high Ta in this species is more efficient than in most passerines.
Lipid acquisition and tissue storage in hagfish: new insights from an ancient vertebrate
Venue: Journal of Comparative Physiology B

Hagfishes are ancient vertebrates, which have the ability to tolerate nearly a year of food deprivation with energy during fasting maintained using lipid stores. While lipid transporters are evolutionarily conserved, there are relatively few studies examining mechanisms of lipid acquisition in teleosts and no reports in the primitive and evolutionarily important agnathans. We examined tissue lipid droplet distribution and used gut sac preparations to characterize uptake mechanisms of the monounsaturated fatty acid, oleic acid (OA; 18:1 cis-9), in the Pacific hagfish. OA absorption was carrier-mediated and demonstrated saturable concentration-dependent uptake with an affinity constant of 55 ± 7 µM, and a maximal rate of uptake of 1311 ± 97 pmol cm− 2 h− 1. Additionally, regulation of intestinal transport was demonstrated as feeding significantly increased uptake. To further examine post-prandial effects on fatty acid transport, hagfish were dosed with bovine insulin, which had no effect on OA intestinal acquisition, but did lower plasma glucose. Overall, this is the first evidence for intestinal fatty acid acquisition in an agnathan, which are ideal models for understanding the evolution of nutrient transport processes in vertebrates, and are particularly suited to lipid research owing to their dependence upon this energy source during prolonged periods of fasting.