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13582165

10.1007/S00360-012-0696-1

The capacity for paracellular absorption in the insectivorous bat Tadarida brasiliensis

Water-soluble nutrients are absorbed by the small intestine via transcellular and paracellular processes. The capacity for paracellular absorption seems greater in fliers than in nonfliers, although that conclusion rests mainly on a comparison of flying birds and nonflying mammals because only two frugivorous bat species have been studied. Furthermore, the bats studied so far were relatively large (>85 g, compared with most bat species which are <20 g) and were not insectivores (like about 70 % of bat species). We studied the small (11 g) insectivorous bat Tadarida brasiliensis and tested the prediction that the capacity for paracellular absorption would be as high as in the other bat and avian species studied so far, well above that in terrestrial, nonflying mammals. Using standard pharmacokinetic technique, we measured the extent of absorption (fractional absorption = f) of inert carbohydrate probes: L-arabinose (MM = 150.13) absorbed exclusively by paracellular route and 3OMD-glucose (MM = 194) absorbed both paracellularly and transcellularly. As predicted, the capacity of paracellular absorption in this insectivorous bat was high (L-arabinose f = 1.03 ± 0.14) as in other frugivorous bats and small birds. Absorption of 3OMD-glucose was also complete (f = 1.09 ± 0.17), but >80 % was accounted for by paracellular absorption. We conclude that passive paracellular absorption of molecules of the size of amino acids and glucose is extensive in this bat and, generally in bats, significantly higher than that in nonflying mammals, although the exact extent can be somewhat lower or higher depending on molecule size, polarity and charge.

Journal of Comparative Physiology B

7183877

10.1007/S00360-012-0691-6

Assessing the impact of thermal acclimation on physiological condition in the zebrafish model

The zebrafish has become a valuable vertebrate model organism in a wide range of scientific disciplines, but current information concerning the physiological temperature response of adult zebrafish is rather scarce. In this study, zebrafish were experimentally acclimated for 28 days to 18, 26 or 34 °C and a suite of non-invasive and invasive methods was applied to determine the thermal dependence of zebrafish physiological condition. With decreasing temperature, the metabolic rate of zebrafish decreased, as shown by the decreasing oxygen uptake and ammonia excretion rates, limiting the critical swimming speed, probably due to a decreased muscle fibre power output. In response to exercise, fuel stores were mobilized to the liver as shown by the increased hepatosomatic index, liver total absolute energetic value and liver carbohydrate concentration but due to the low metabolic rate they could not be adequately addressed to power swimming activity at 18 °C. Conversely, the increased metabolic performance at high temperature came with an increased metabolic cost resulting in decreased energy status reflected particularly well by the non-invasive condition factor and invasive measures of carcass protein concentration, carcass total absolute energetic value and liver carbohydrate concentration. We showed that the combined measurement of the relative condition factor and critical swimming speed is a powerful non-invasive tool for long-term follow-up studies. Invasive methods were redundant for measuring general energy status but they provided detailed information concerning metabolic reorganization. With this study we proved that the usefulness of the zebrafish as a model organism can easily be expanded to include physiological studies and we provided a reference dataset for the selection of measures of physiological responses for future studies using the zebrafish.

Journal of Comparative Physiology B

370598

10.1007/S00360-012-0698-Z

Determinants of intra-specific variation in basal metabolic rate

Basal metabolic rate (BMR) provides a widely accepted benchmark of metabolic expenditure for endotherms under laboratory and natural conditions. While most studies examining BMR have concentrated on inter-specific variation, relatively less attention has been paid to the determinants of within-species variation. Even fewer studies have analysed the determinants of within-species BMR variation corrected for the strong influence of body mass by appropriate means (e.g. ANCOVA). Here, we review recent advancements in studies on the quantitative genetics of BMR and organ mass variation, along with their molecular genetics. Next, we decompose BMR variation at the organ, tissue and molecular level. We conclude that within-species variation in BMR and its components have a clear genetic signature, and are functionally linked to key metabolic process at all levels of biological organization. We highlight the need to integrate molecular genetics with conventional metabolic field studies to reveal the adaptive significance of metabolic variation. Since comparing gene expressions inter-specifically is problematic, within-species studies are more likely to inform us about the genetic underpinnings of BMR. We also urge for better integration of animal and medical research on BMR; the latter is quickly advancing thanks to the application of imaging technologies and ‘omics’ studies. We also suggest that much insight on the biochemical and molecular underpinnings of BMR variation can be gained from integrating studies on the mammalian target of rapamycin (mTOR), which appears to be the major regulatory pathway influencing the key molecular components of BMR.

Journal of Comparative Physiology B

8724152

10.1007/S00360-012-0693-4

Body regional distribution and stratification of fatty acids in the blubber of New Zealand sea lions: implications for diet predictions

Fatty acids (FAs) from blubber are often analysed to assess the diet of marine mammals. However, distribution of blubber FAs is not necessarily uniform along the body. It is therefore important to understand the deposition of dietary fat to be able to estimate the diet. We analysed the FA compositions of the thoracic ventral (T region) blubber of 28 New Zealand (NZ) sea lions Phocarctos hookeri by-caught by the southern arrow squid Nototodarus sloani fishery. Each blubber sample was divided into an inner and an outer layer. For 16 of these 28 animals, the pelvic dorsal (P) region was also sampled. The influence of body region and layer was statistically tested on the distribution of blubber FAs. We found minimal differences between the P and T regions (3 out of 29 FAs). The outer blubber layer was more concentrated in short-chain monounsaturated FAs, and less concentrated in saturated FAs, but the degree of stratification was small. Diet predictions from quantitative FA signature analysis (QFASA) applied on different body regions were similar. When applied to different blubber layers, QFASA gave some variation in the contribution of rattails (~25 % in outer blubber vs. ~12 % in inner blubber). Nonetheless, diet predicted from both layers was dominated by similar prey species: octopus, hoki and rattails. Hoki and rattails shared a similar ecological niche. Therefore, feeding ecology of NZ sea lions inferred from the inner or the outer blubber would lead to the same conclusions. In the case of NZ sea lions, the outer layer of blubber, if the only sample accessible, could be a useful tissue for diet inference from FAs.

Journal of Comparative Physiology B

17094893

10.1007/S00360-012-0692-5

Differential effects of thyroid status on regional H2O2 production in slow- and fast-twitch muscle of ducklings

Birds seem to employ powerful physiological strategies to curb the harmful effects of reactive oxygen species (ROS) because they generally live longer than predicted by the free radical theory of aging. However, little is known about the physiological mechanisms that confer protection to birds against excessive ROS generation. Hence, we investigated the ability of birds to control mitochondrial ROS generation during physiologically stressful periods. In our study, we analyzed the relationship between the thyroid status and the function of intermyofibrillar and subsarcolemmal mitochondria located in glycolytic and oxidative muscles of ducklings. We found that the intermyofibrillar mitochondria of both glycolytic and oxidative muscles down regulate ROS production when plasma T3 levels rise. The intermyofibrillar mitochondria of the gastrocnemius muscle (an oxidative muscle) produced less ROS and were more sensitive than the pectoralis muscle (a glycolytic muscle) to changes in plasma T3. Such differences in the ROS production by glycolytic and oxidative muscles were associated with differences in the membrane proton permeability and in the rate of free radical leakage within the respiratory chain. This is the first evidence which shows that in birds, the amount of ROS that the mitochondria release is dependent on: (1) their location within the muscle; (2) the type of muscle (glycolytic or oxidative) and (3) on the thyroid status. Reducing muscle mitochondrial ROS generation might be an important mechanism in birds to limit oxidative damage during periods of physiological stress.

Journal of Comparative Physiology B

16625080

10.1007/S00360-012-0700-9

Evidence for a role of tight junctions in regulating sodium permeability in zebrafish (Danio rerio) acclimated to ion-poor water

Freshwater teleosts are challenged by diffusive ion loss across permeable epithelia including gills and skin. Although the mechanisms regulating ion loss are poorly understood, a significant component is thought to involve paracellular efflux through pathways formed via tight junction proteins. The mammalian orthologue (claudin-4) of zebrafish (Danio rerio) tight junction protein, claudin-b, has been proposed to form a cation-selective barrier regulating the paracellular loss of Na+. The present study investigated the cellular localization and regulation of claudin-b, as well as its potential contribution to Na+ homeostasis in adult zebrafish acclimated to ion-poor water. Using a green fluorescent protein-expressing line of transgenic zebrafish, we found that claudin-b was expressed along the lamellar epithelium as well as on the filament in the inter-lamellar regions. Co-localization of claudin-b and Na+/K+-ATPase was observed, suggesting its interaction with mitochondrion-rich cells. Claudin-b also appeared to be associated with other cell types, including the pavement cells. In the kidney, claudin-b was expressed predominantly in the collecting tubules. In addition, exposure to ion-poor water caused a significant increase in claudin-b abundance as well as a decrease in Na+ efflux, suggesting a possible role for claudin-b in regulating paracellular Na+ loss. Interestingly, the whole-body uptake of a paracellular permeability marker, polyethylene glycol-400, increased significantly after prolonged exposure to ion-poor water, indicating that an increase in epithelial permeability is not necessarily coupled with an increase in passive Na+ loss. Overall, our study suggests that in ion-poor conditions, claudin-b may contribute to a selective reduction in passive Na+ loss in zebrafish.

Journal of Comparative Physiology B

14702210

10.1007/S00360-012-0699-Y

Effect of central and peripheral leucine on energy metabolism in the Djungarian hamster (Phodopus sungorus)

Branched-chain amino acids, particularly leucine, are thought to activate nutrient sensing pathways in the hypothalamus that regulate food intake and energy homeostasis. In the light of recent controversial findings of leucine’s effect on energy homeostasis further clarification of the metabolic impact of dietary leucine supplementation is required. We examined the pharmacological and dietary effects of leucine on energy metabolism in the Djungarian hamster (Phodopus sungorus), a well-established model for studies of alterations in leptin sensitivity and energy metabolism. We acutely administered leucine into the lateral ventricle (1.1 μg) of hamsters to characterize whether leucine exhibits anorexigenic properties in this species as has been described in other rodents. Next the catabolic effect of dietary administered leucine via supplemented rodent diet (15 % leucine), drinking water (17 g/L leucine) and oral gavages (10 mg/day); as well as the effect of subcutaneously (0.1 and 3 mg/day) and intraperitoneally (0.1, 3 and 6 mg/day) injected leucine which avoids the gastrointestinal-track was analyzed. Centrally administered leucine reduced 24 h food intake (by 32 %) and body weight. Both parameters were also reduced in hamsters with leucine supplemented diet, but this catabolic response was based on a pronounced taste aversion to the leucine-diet. In all other experiments, dietary leucine and peripheral injections of leucine had no effect on food intake, body weight and basal blood glucose levels. Our data suggest that in the Djungarian hamster dietary leucine fails to exhibit catabolic effects that would override the evolutionary conserved adaptations of the species which is critical for its survival.

Journal of Comparative Physiology B

17677492

10.1007/S00360-012-0689-0

Changes in diet, body mass and fatty acid composition during pre-hibernation in a subtropical bat in relation to NPY and AgRP expression

Prior to hibernation, mammals accumulate large amounts of fat in their bodies. In temperate mammalian species, hibernation is improved by increasing the levels of poly-unsaturated fatty acids (PUFA) in the body. The saturation of fatty acids (FA) in both white adipose tissue (WAT) and membrane phospholipids of mammals often reflects their diet composition. We found that the greater mouse-tailed bat (Rhinopoma microphyllum) accumulates large amounts of fat at the end of summer by gradually shifting to a fat-rich diet (queen carpenter ants, Camponotus felah). PUFA are almost absent in this diet (<1 % of total FA), which contains a high fraction of saturated (SFA) and mono-unsaturated (MUFA) fatty acids. We found similar low levels of PUFA in mouse-tailed bat WAT, but not in their heart total lipids. The expression of two appetite-stimulating (orexigenic) hypothalamic neuropeptides, AgRP and NPY, increased in parallel to the shift in diet and with fat gain in these bats. To the best of our knowledge, this is the only documented example of specific pre-hibernation diet in bats, and one which reveals the most saturated FA composition ever documented in a mammal. We suggest that the increase in expression levels of NPY and AgRP may contribute to the observed diet shift and mass gain, and that the FA composition of the bat’s specialized diet is adaptive in the relatively high temperatures we recorded in both their winter and summer roosts.

Journal of Comparative Physiology B

17294698

10.1007/S00360-012-0697-0

The ability of the Antarctic nematode Panagrolaimus davidi to survive intracellular freezing is dependent upon nutritional status

The Antarctic nematode Panagrolaimus davidi is the best documented example of an animal surviving intracellular freezing and the only animal so far shown to survive such freezing throughout its tissues. However, a recent study found that after exposure to a freezing stress that produced intracellular freezing in a proportion of nematodes, the resulting survival levels could be explained if those nematodes that froze intracellularly had died. We have thus re-examined the survival of intracellular freezing in this nematode. The ability to survive a freezing exposure that is likely to produce intracellular freezing (freezing at −10 °C) declines with culture age. In cultures that are fed regularly, the ability to survive freezing at −10 °C increases, but in starved cultures freezing survival declines. Survival of intracellular freezing in fed cultures was confirmed using cryomicroscopy, staining of cells with vital dyes and by freeze substitution and transmission electron microscopy. We have thus confirmed that P. davidi can survive intracellular freezing and shown that this ability is dependent upon them being well fed. The effect of culture conditions on the nutrient status of the nematodes should thus be an important factor in the design of experiments.

Journal of Comparative Physiology B

18756352

10.1007/S00360-012-0694-3

Discontinuous ammonia excretion and glutamine storage in littoral Oniscidea (Crustacea: Isopoda): testing tidal and circadian models

A key evolutionary development facilitating land colonization in terrestrial isopods (Isopoda: Oniscidea) is the intermittent liberation of waste nitrogen as volatile ammonia. Intermittent ammonia release exploits glutamine (Gln) as an intermediary nitrogen store. Here, we explore the relationship between temporal patterns of ammonia release and Gln accumulation in three littoral oniscideans from Southern California. Results are interpreted in terms of water availability, habitat, activity patterns, and ancestry. A two-way experimental design was used to test whether ammonia excretion and Gln accumulation follow a tidal or diel periodicity. Ammonia excretion was studied in the laboratory using chambers with or without available seawater and using an acid trap to collect volatile ammonia. Ligia occidentalis releases ammonia directly into seawater and accumulates Gln during low tide (48.9 ± 6.5 μmol g−1 at low tide, 24.1 ± 3.0 μmol g−1 at high tide), indicating that excretion is tidally constrained. Alloniscus perconvexus and Tylos punctatus can excrete ammonia directly into seawater or utilize volatilization. Both species burrow in sand by day and show a diel excretory pattern, accumulating Gln nocturnally (31.8 ± 2.7 μmol g−1 at dawn and 21.8 ± 2.3 μmol g−1 at dusk for A. perconvexus; 85.7 ± 15.1 μmol g−1 at dawn and 25.4 ± 2.9 μmol g−1 at dusk for T. punctatus) and liberating ammonia diurnally. Glutaminase shows higher activity in terrestrial (0.54–0.86 U g−1) compared to intertidal (0.25–0.31 U g−1) species, consistent with the need to generate high PNH3 for volatilization. The predominant isoform in Armadillidium vulgare is phosphate dependent and maleate independent; phosphate is a plausible regulator in vivo.

Journal of Comparative Physiology B

6785758

10.1007/S00359-012-0742-1

Interspecifc variation in eye shape and retinal topography in seven species of galliform bird (Aves: Galliformes: Phasianidae)

Eye morphology and the retinal topography of animals that live in either ‘open’ (e.g., grassland) or ‘enclosed’ (e.g., forest) terrestrial habitats show common adaptations to constraints imposed by these different habitat types. Although relationships between habitat and the visual system are well documented in most vertebrates, relatively few studies have examined this relationship in birds. Here, we compare eye shape and retinal topography across seven species from the family Phasianidae (Galliformes) that are diurnally active in either open or enclosed habitats. Species from enclosed habitats have significantly larger corneal diameters, relative to transverse diameters, than species from open habitats, which we predict serves to enhance visual sensitivity. Retinal topography, however, was similar across all seven species and consisted of a centrally positioned area centralis and a weak horizontal visual streak, with no discernible fovea. In the Japanese quail (Coturnix japonica), there was also a dorso-temporal extension of increased neuron density and, in some specimens, a putative area dorsalis. The total number of neurons in the retinal ganglion cell layer was correlated with retinal whole-mount area. Average and peak neuron densities were similar across species, with the exception of the Japanese quail, which had greater average and peak densities. Peak anatomical spatial resolving power was also similar among species, ranging from approximately 10–13 cycles/°. Overall, the pattern of retinal topography we found in phasianids is associated with ground-foraging in birds and presumably facilitates the identification of small food items on the ground as well as other visually guided behaviors, irrespective of habitat type.

Journal of Comparative Physiology A

1256692

10.1007/S00359-012-0743-0

Effects of aversive experience on the behavior within a custom-made plus maze in the short-tailed fruit bat, Carollia perspicillata

Stress exposure evokes a variety of physiological and behavioral responses in an organism, enabling it to cope with stressful situations and changes in the environment. In a previous study, we found that subjecting individuals of Carollia perspicillata to a chronic immobilization stress paradigm resulted in a significant increase of fecal cortisol concentrations. In the present study, we investigated the influence of stress on the behavior of C. perspicillata, by adapting a commonly used behavioral paradigm for characterizing coping styles of animals (i.e., the elevated-plus maze) to bats. Adult bats were subjected 1 h/day to immobilization over a period of 10 days. On the subsequent day, the behavior of each animal was analyzed in a custom-made plus maze, consisting of four arms (two open and two enclosed ones) and designed 3D because of the bats’ ability to fly. In this newly invented design, we compared the behaviors of stressed animals and controls. Changes in locomotor and exploratory behavior suggest two divergent adaptive behaviors in C. perspicillata following the chronic stress paradigm, possibly indicating different stress coping styles.

Journal of Comparative Physiology A

16758475

10.1007/S00359-012-0744-Z

Echolocation behavior of the Japanese horseshoe bat in pursuit of fluttering prey

Echolocation sounds of Rhinolophus ferrumequinum nippon as they approached a fluttering moth (Goniocraspidum pryeri) were investigated using an on-board telemetry microphone (Telemike). In 40 % of the successful moth-capture flights, the moth exhibited distinctive evasive flight behavior, but the bat pursued the moth by following its flight path. When the distance to the moth was approximately 3–4 m, the bats increased the duration of the pulses to 65–95 ms, which is 2–3 times longer than those during landing flight (30–40 ms). The mean of 5.8 long pulses were emitted before the final buzz phase of moth capture, without strengthening the sound pressure level. The mean duration of long pulses (79.9 ± 7.9 ms) corresponded to three times the fluttering period of G. pryeri (26.5 × 3 = 79.5 ms). These findings indicate that the bats adjust the pulse duration to increase the number of temporal repetitions of fluttering information rather than to produce more intense sonar sounds to receive fine insect echoes. The bats exhibited Doppler-shift compensation for echoes returning from large static objects ahead, but not for echoes from target moths, even though the bats were focused on capturing the moths. Furthermore, the echoes of the Telemike recordings from target moths showed spectral glints of approximately 1–1.5 kHz caused by the fluttering of the moths but not amplitude glints because of the highly acoustical attenuation of ultrasound in the air, suggesting that spectral information may be more robust than amplitude information in echoes during moth capturing flight.

Journal of Comparative Physiology A

18763907

10.1007/S00360-012-0688-1

A comparative meta-analysis of maximal aerobic metabolism of vertebrates: implications for respiratory and cardiovascular limits to gas exchange

Maximal aerobic metabolic rates (MMR) in vertebrates are supported by increased conductive and diffusive fluxes of O2 from the environment to the mitochondria necessitating concomitant increases in CO2 efflux. A question that has received much attention has been which step, respiratory or cardiovascular, provides the principal rate limitation to gas flux at MMR? Limitation analyses have principally focused on O2 fluxes, though the excess capacity of the lung for O2 ventilation and diffusion remains unexplained except as a safety factor. Analyses of MMR normally rely upon allometry and temperature to define these factors, but cannot account for much of the variation and often have narrow phylogenetic breadth. The unique aspect of our comparative approach was to use an interclass meta-analysis to examine cardio-respiratory variables during the increase from resting metabolic rate to MMR among vertebrates from fish to mammals, independent of allometry and phylogeny. Common patterns at MMR indicate universal principles governing O2 and CO2 transport in vertebrate cardiovascular and respiratory systems, despite the varied modes of activities (swimming, running, flying), different cardio-respiratory architecture, and vastly different rates of metabolism (endothermy vs. ectothermy). Our meta-analysis supports previous studies indicating a cardiovascular limit to maximal O2 transport and also implicates a respiratory system limit to maximal CO2 efflux, especially in ectotherms. Thus, natural selection would operate on the respiratory system to enhance maximal CO2 excretion and the cardiovascular system to enhance maximal O2 uptake. This provides a possible evolutionary explanation for the conundrum of why the respiratory system appears functionally over-designed from an O2 perspective, a unique insight from previous work focused solely on O2 fluxes. The results suggest a common gas transport blueprint, or Bauplan, in the vertebrate clade.

Journal of Comparative Physiology B

18327707

10.1007/S00360-012-0685-4

Water absorption and bicarbonate secretion in the intestine of the sea bream are regulated by transmembrane and soluble adenylyl cyclase stimulation

In the marine fish intestine luminal, HCO3− can remove divalent ions (calcium and magnesium) by precipitation in the form of carbonate aggregates. The process of epithelial HCO3− secretion is under endocrine control, therefore, in this study we aimed to characterize the involvement of transmembrane (tmACs) and soluble (sACs) adenylyl cyclases on the regulation of bicarbonate secretion (BCS) and water absorption in the intestine of the sea bream (Sparus aurata). We observed that all sections of sea bream intestine are able to secrete bicarbonate as measured by pH–Stat in Ussing chambers. In addition, gut sac preparations reveal net water absorption in all segments of the intestine, with significantly higher absorption rates in the anterior intestine that in the rectum. BCS and water absorption are positively correlated in all regions of the sea bream intestinal tract. Furthermore, stimulation of tmACs (10 μM FK + 500 μM IBMX) causes a significant decrease in BCS, bulk water absorption and short circuit current (Isc) in a region dependent manner. In turn, stimulation of sACs with elevated HCO3− results in a significant increase in BCS, and bulk water absorption in the anterior intestine, an action completely reversed by the sAC inhibitor KH7 (200 μM). Overall, the results reveal a functional relationship between BCS and water absorption in marine fish intestine and modulation by tmACs and sAC. In light of the present observations, it is hypothesized that the endocrine effects on intestinal BCS and water absorption mediated by tmACs are locally and reciprocally modulated by the action of sACs in the fish enterocyte, thus fine-tuning the process of carbonate aggregate production in the intestinal lumen.

Journal of Comparative Physiology B

1957604

10.1007/S00360-012-0684-5

K+-dependent 3H-d-glucose transport by hepatopancreatic brush border membrane vesicles of a marine shrimp

The effects of sodium, potassium, sugar inhibitors, and membrane potential on 3H-d-glucose uptake by hepatopancreatic epithelial brush border membrane vesicles (BBMV) of the Atlantic marine shrimp, Litopenaeus setiferus, were investigated. Brush border membrane vesicles were prepared using a MgCl2/EGTA precipitation method and uptake experiments were conducted using a high speed filtration technique. 3H-d-Glucose uptake was stimulated by both sodium and potassium and these transport rates were almost doubled in the presence of an inside-negative-induced membrane potential. Kinetics of 3H-d-glucose influx were hyperbolic functions of both external Na+ or K+, and an induced membrane potential increased influx Jmax and lowered Km in both salts. 3H-d-Glucose influx versus [glucose] in both Na+ or K+ media also displayed Michaelis–Menten properties that were only slightly affected by induced membrane potential. Phloridzin was a poor inhibitor of 0.5 mM 3H-d-glucose influx, requiring at least 5 mM in NaCl and 10 mM in KCl to significantly reduce hexose transport. Several sugars (d-galactose, α-methyl-d-gluco-pyranoside, unlabeled d-glucose, d-fructose, and d-mannose) were used at 75 mM as potential inhibitors of 0.1 mM 3H-d-glucose influx. Only unlabeled d-glucose, d-fructose, and d-mannose significantly (p < 0.05) reduced labeled glucose transport. An additional experiment using increasing concentrations of d-mannose (0, 10, 25, 75, and 100 mM) showed this hexose to be an effective inhibitor of 0.1 mM 3H-d-glucose uptake at concentrations of 75 mM and higher. As a whole these results suggest that 3H-d-glucose transport by hepatopancreatic BBMV occurs by a carrier system that is able to use both Na+ and K+ as drivers, is enhanced by membrane potential, is relatively refractory to phloridzin, and is only inhibited by itself, d-fructose, and d-mannose. These properties are similar to those exhibited by the mammalian SLC5A9/SGLT4 transporter, suggesting that an invertebrate analogue of this protein may occur in shrimp.

Journal of Comparative Physiology B

2614707

10.1007/S00359-012-0741-2

Increased bursting glutamatergic neurotransmission in an auditory forebrain area of the zebra finch (Taenopygia guttata) induced by auditory stimulation

The caudomedial nidopallium (NCM) is a telencephalic area involved in auditory processing and memorization in songbirds, but the synaptic mechanisms associated with auditory processing in NCM are largely unknown. To identify potential changes in synaptic transmission induced by auditory stimulation in NCM, we used a slice preparation for path-clamp recordings of synaptic currents in the NCM of adult zebra finches (Taenopygia guttata) sacrificed after sound isolation followed by exposure to conspecific song or silence. Although post-synaptic GABAergic and glutamatergic currents in the NCM of control and song-exposed birds did not present any differences regarding their frequency, amplitude and duration after song exposure, we observed a higher probability of generation of bursting glutamatergic currents after blockade of GABAergic transmission in song-exposed birds as compared to controls. Both song-exposed males and females presented an increase in the probability of the expression of bursting glutamatergic currents, however bursting was more commonly seen in males where they appeared even without blocking GABAergic transmission. Our data show that song exposure changes the excitability of the glutamatergic neuronal network, increasing the probability of the generation of bursts of glutamatergic currents, but does not affect basic parameters of glutamatergic and GABAergic synaptic currents.

Journal of Comparative Physiology A

9667627

10.1007/S00360-012-0686-3

Ontogeny of hypoxic modulation of cardiac performance and its allometry in the African clawed frog Xenopus laevis

The ontogeny of cardiac hypoxic responses, and how such responses may be modified by rearing environment, are poorly understood in amphibians. In this study, cardiac performance was investigated in Xenopus laevis from 2 to 25 days post-fertilization (dpf). Larvae were reared under either normoxia or moderate hypoxia (PO2 = 110 mmHg), and each population was assessed in both normoxia and acute hypoxia. Heart rate (fh) of normoxic-reared larvae exhibited an early increase from 77 ± 1 beats min−1 at 2 dpf to 153 ± 1 beats min−1 at 4 dpf, followed by gradual decreases to 123 ± 3 beats min−1 at 25 dpf. Stroke volume (SV), 6 ± 1 nl, and cardiac output (CO), 0.8 ± 0.1 μl min−1, at 5 dpf both increased by more than 40-fold to 25 dpf with rapid larval growth (~30-fold increase in body mass). When exposed to acute hypoxia, normoxic-reared larvae increased fh and CO between 5 and 25 dpf. Increased SV in acute hypoxia, produced by increased end-diastolic volume (EDV), only occurred before 10 dpf. Hypoxic-reared larvae showed decreased acute hypoxic responses of EDV, SV and CO at 7 and 10 dpf. Over the period of 2–25 dpf, cardiac scaling with mass showed scaling coefficients of −0.04 (fh), 1.23 (SV) and 1.19 (CO), contrary to the cardiac scaling relationships described in birds and mammals. In addition, fh scaling in hypoxic-reared larvae was altered to a shallower slope of −0.01. Collectively, these results indicate that acute cardiac hypoxic responses develop before 5 dpf. Chronic hypoxia at a moderate level can not only modulate this cardiac reflex, but also changes cardiac scaling relationship with mass.

Journal of Comparative Physiology B

16017439

10.1007/S00360-012-0687-2

Osmoregulatory response to low salinities in the European sea bass embryos: a multi-site approach

Embryonic osmoregulation effected by embryonic ionocytes in the European sea bass Dicentrarchus labrax has been studied at several sites, including the yolk sac membrane, the first gill slits and the gut ionocytes. D. labrax embryos, spawned in seawater (SW) (39 ‰), were exposed to dilute seawater (DSW) (5 ‰) during 48 h, from stage 10 pairs of somites (10S) to hatching time (HT). Control embryos originating from the same spawn were maintained in SW. Both SW and DSW embryos were examined after 24- and 48-h exposure. Nanoosmometric measurements of the embryonic fluids osmolality suggest that late embryos are confronted with the variations in external salinity and that they were able to slightly regulate their osmolality. Immunolocalization of Na+/K+ ATPase, NKCC and CFTR has shown that DSW-exposed embryos can limit ion losses due to compensatory physiological mechanisms. CFTR and NKCC were not observed in DSW embryos in the yolk sac ionocytes and in the tegumentary ionocytes of the gill slits. The quantification of mRNA indicated that NKA, NKCC1 and CFTR transcript levels increased from stage 10S to stage HT. At stage HT, following 48 h of DSW- or SW-exposure, different responses were observed according to salinity. These results, when compared to those obtained in D. labrax juveniles and adults long-term exposed to fresh water (FW), show that in embryos the physiological response following a short-term DSW exposure is different. The mechanisms of hyper-osmoregulation observed in D. labrax embryos, although not fully efficient, allow their survival for several days in DSW.

Journal of Comparative Physiology B

5642496

10.1007/S00360-012-0683-6

Interspecific variation in thermoregulation among three sympatric bats inhabiting a hot, semi-arid environment

Bats in hot roosts experience some of the most thermally challenging environments of any endotherms, but little is known about how heat tolerance and evaporative cooling capacity vary among species. We investigated thermoregulation in three sympatric species (Nycteris thebaica, Taphozous mauritianus and Sauromys petrophilus) in a hot, semi-arid environment by measuring body temperature (Tb), metabolic rate and evaporative water loss (EWL) at air temperatures (Ta) of 10–42 °C. S. petrophilus was highly heterothermic with no clear thermoneutral zone, and exhibited rapid increases in EWL at high Ta to a maximum of 23.7 ± 7.4 mg g−1 h−1 at Ta ≈ 42 °C, with a concomitant maximum Tb of 43.7 ± 1.0 °C. T. mauritianus remained largely normothermic at Tas below thermoneutrality and increased EWL to 14.7 ± 1.3 mg g−1 h−1 at Ta ≈ 42 °C, with a maximum Tb of 42.9 ± 1.6 °C. In N. thebaica, EWL began increasing at lower Ta than in either of the other species and reached a maximum of 18.6 ± 2.1 mg g−1 h−1 at Ta = 39.4 °C, with comparatively high maximum Tb values of 45.0 ± 0.9 °C. Under the conditions of our study, N. thebaica was considerably less heat tolerant than the other two species. Among seven species of bats for which data on Tb as well as roost temperatures in comparison to outside Ta are available, we found limited evidence for a correlation between overall heat tolerance and the extent to which roosts are buffered from high Ta.

Journal of Comparative Physiology B

16543884

10.1007/S00360-012-0682-7

Hepatic carbamoyl phosphate synthetase (CPS) I and urea contents in the hylid tree frog, Litoria caerulea: transition from CPS III to CPS I

The complete cDNA sequence of CPS I obtained from the liver of the hylid tree frog, Litoria caerulea, consisted of 4,485 bp which coded for 1,495 amino acids with an estimated molecular mass of 163.7 kDa. The deduced CPS I consisted of a mitochondrial targeting sequence of 33 amino acid residues, a glutaminase amidotransferase component spanning from tyrosine 95 to leucine 425, and a methylglyoxal synthetase-like component spanning from valine 441 to lysine 1566. It also comprised two cysteine residues (cysteine 1360 and cysteine 1370) that are characteristic of N-acetyl-l-glutamate dependency. Similar to the CPS I of Ranacatesbeiana and Cps III of lungfishes and teleosts, it contained the Cys–His–Glu catalytic triad (cysteine 304, histidine 388 and glutamate 390). All Cps III contain methionine 305 and glutamine 308, which are essential for the Cys–His–Glu triad to react with glutamine, but the CPS I of R.catesbeiana contains lysine 305 and glutamate 308, and therefore cannot effectively utilize glutamine as a substrate. However, the CPS I of L. caerulea, unlike that of R.catesbeiana, contained besides glutamate 308, methionine 305 instead of lysine 305, and thus represented a transitional form between Cps III and CPS I. Indeed, CPS I of L. caerulea could utilize glutamine or NH4+ as a substrate in vitro, but the activity obtained with glutamine + NH4+ reflected that obtained with NH4+ alone. Furthermore, only <5 % of the glutamine synthetase activity was present in the hepatic mitochondria, indicating that CPS I of L. caerulea did not have an effective supply of glutamine in vivo. Hence, our results confirmed that the evolution of CPS I from Cps III occurred in amphibians. Since L. caerulea contained high levels of urea in its muscle and liver, which increased significantly in response to desiccation, its CPS I had the dual functions of detoxifying ammonia to urea and producing urea to reduce evaporative water loss.

Journal of Comparative Physiology B

15019636

10.1007/S00359-012-0740-3

Auditory change detection by a single neuron in an insect

The detection of novel signals in the auditory scene is an elementary task of any hearing system. In Neoconocephalus katydids, a primary auditory interneuron (TN-1) with broad spectral sensitivity, responded preferentially to rare deviant pulses (7 pulses/s repetition rate) embedded among common standard pulses (140 pulses/s repetition rate). Eliminating inhibitory input did not affect the detection of the deviant pulses. Detection thresholds for deviant pulses increased significantly with increasing amplitude of standard pulses. Responses to deviant pulses occurred when the carrier frequencies of deviant and standard were sufficiently different, both when the deviant had a higher or lower carrier frequency than the standard. Recordings from receptor neurons revealed that TN-1 responses to the deviant pulses did not depend on the population response strength of the receptors, but on the distribution of the receptor cell activity. TN-1 responses to the deviant pulse occurred only when the standard and deviant pulses were transmitted by different groups of receptor cells. TN-1 responses parallel stimulus specific adaptation (SSA) described in mammalian auditory system. The results support the hypothesis that the mechanisms underlying SSA and change-detection are located in the TN-1 dendrite, rather than the receptor cells.

Journal of Comparative Physiology A

18448605

10.1007/S00359-012-0739-9

Convergence of reference frequencies by multiple CF–FM bats (Rhinolophus ferrumequinum nippon) during paired flights evaluated with onboard microphones

The constant frequency component of the second harmonic (CF2) of echolocation sounds in Rhinolophus ferrumequinum nippon were measured using onboard telemetry microphones while the bats exhibited Doppler-shift compensation during flights with conspecifics. (1) The CF2 frequency of pulses emitted by individual bats at rest (Frest) showed a long-term gradual decline by 0.22 kHz on average over a period of 3 months. The mean neighboring Frest (interindividual differences in Frest between neighboring bats when the bats were arranged in ascending order according to Frest) ranged from 0.08 to 0.11 kHz among 18 bats in a laboratory colony. (2) The standard deviation of observed echo CF2 (reference frequency) for bats during paired flights ranged from 50 to 90 Hz, which was not significantly different from that during single flights. This finding suggests that during paired flights, bats exhibit Doppler-shift compensation with the same accuracy as when they fly alone. (3) In 60 % (n = 29) of the cases, the difference in the reference frequency between two bats during paired flights significantly decreased compared to when the bats flew alone. However, only 15 % of the cases (n = 7) showed a significant increase during paired flights. The difference in frequency between two bats did not increase even when the reference frequencies of the individuals were not statistically different during single flights.

Journal of Comparative Physiology A

7100467

10.1007/S00360-012-0680-9

Sex-specific impact of prenatal stress on growth and reproductive parameters of guinea pigs

Body condition and reproductive maturation are parameters of reproductive success that are influenced by sexual hormones rising in the circulation during the time of puberty. Various endocrine systems can be programmed by conditions experienced during early life. Stress for instance is supposed to be capable of influencing fetal development, leading to adjustments of offspring’s later physiology. We examined whether prenatal stress (induced by exposure to strobe light) during early- to mid-gestation was capable of affecting later reproductive parameters in guinea pigs (Cavia aperea f. porcellus). Therefore, we measured the levels of testosterone and progesterone from the age of day 12–124 in prenatally stressed (PS, n = 20) and unaffected control animals (n = 24). Furthermore, we determined the timing of puberty and growth. Body weight development revealed significantly faster growth in PS females compared to control animals. The onset of first estrus was slightly earlier in PS females, however not significantly so. Cycle lengths and levels of progesterone differed between groups over the course of time with higher progesterone levels and more constant cycles among PS females compared to control females who displayed marked differences between first and subsequent cycles. Levels of testosterone did not differ between groups. We conclude that prenatal stress accelerates growth and maturity in females, but not in males.

Journal of Comparative Physiology B

15079854

10.1007/S00360-012-0679-2

Aquaporin homologs and water transport in the anal papillae of the larval mosquito, Aedes aegypti

The hemolymph osmolarity of the freshwater mosquito larvae (Aedes aegypti) is greater than that of their habitat. To combat the influx of water, larvae cycle water entering through the gut and anal papillae to the Malpighian tubules for secretion. The presence of aquaporins (AQPs, water channels) may facilitate the movement of water across these tissues. Tissue distribution of mRNA transcripts of putative aquaporins from mosquito larvae, using quantitative PCR, revealed expression of transcripts in the Malpighian tubules and anal papillae. Four putative aquaporin transcripts are expressed in the Malpighian tubules and provide a basis for further work aimed at discovering the elusive water transporters functioning during diuresis. Transcripts of putative AQPs (AaAQP4 and AaAQP1b) are expressed in the anal papillae. Immunoreactivity to a human AQP1-antibody was found in the anal papillae and mercury inhibits tritiated water uptake in isolated anal papillae. Together, the results suggest that AQP(s) could be responsible for facilitating water transport at the papillae epithelium.

Journal of Comparative Physiology B

1349989

10.1007/S00359-012-0737-Y

Integration of binocular optic flow in cervical neck motor neurons of the fly

Global visual motion elicits an optomotor response of the eye that stabilizes the visual input on the retina. Here, we analyzed the neck motor system of the blowfly to understand binocular integration of visual motion information underlying a head optomotor response. We identified and characterized two cervical nerve motor neurons (called CNMN6 and CNMN7) tuned precisely to an optic flow corresponding to pitch movements of the head. By means of double recordings and dye coupling, we determined that these neurons are connected ipsilaterally to two vertical system cells (VS2 and VS3), and contralaterally to one horizontal system cell (HSS). In addition, CNMN7 turned out to be connected to the ipsilateral CNMN6 and to its contralateral counterpart. To analyze a potential function of this circuit, we performed behavioral experiments and found that the optomotor pitch response of the fly head was only observable when both eyes were intact. Thus, this neural circuit performs two visuomotor transformations: first, by integrating binocular visual information it enhances the tuning to the optic flow resulting from pitch movements of the head, and second it could assure an even head declination by coordinating the activity of the CNMN7 neurons on both sides.

Journal of Comparative Physiology A

7617982

10.1007/S00360-012-0677-4

Molecular diversity, metabolic transformation, and evolution of carotenoid feather pigments in cotingas (Aves: Cotingidae)

Carotenoid pigments were extracted from 29 feather patches from 25 species of cotingas (Cotingidae) representing all lineages of the family with carotenoid plumage coloration. Using high-performance liquid chromatography (HPLC), mass spectrometry, chemical analysis, and 1H-NMR, 16 different carotenoid molecules were documented in the plumages of the cotinga family. These included common dietary xanthophylls (lutein and zeaxanthin), canary xanthophylls A and B, four well known and broadly distributed avian ketocarotenoids (canthaxanthin, astaxanthin, α-doradexanthin, and adonixanthin), rhodoxanthin, and seven 4-methoxy-ketocarotenoids. Methoxy-ketocarotenoids were found in 12 species within seven cotinga genera, including a new, previously undescribed molecule isolated from the Andean Cock-of-the-Rock Rupicola peruviana, 3′-hydroxy-3-methoxy-β,β-carotene-4-one, which we name rupicolin. The diversity of cotinga plumage carotenoid pigments is hypothesized to be derived via four metabolic pathways from lutein, zeaxanthin, β-cryptoxanthin, and β-carotene. All metabolic transformations within the four pathways can be described by six or seven different enzymatic reactions. Three of these reactions are shared among three precursor pathways and are responsible for eight different metabolically derived carotenoid molecules. The function of cotinga plumage carotenoid diversity was analyzed with reflectance spectrophotometry of plumage patches and a tetrahedral model of avian color visual perception. The evolutionary history of the origin of this diversity is analyzed phylogenetically. The color space analyses document that the evolutionarily derived metabolic modifications of dietary xanthophylls have resulted in the creation of distinctive orange-red and purple visual colors.

Journal of Comparative Physiology B

7205327

10.1007/S00359-012-0738-X

Micro-scale fluid and odorant transport to antennules of the crayfish, Procambarus clarkii

A numerical model was developed to determine advective–diffusive transport of odorant molecules to olfactory appendages of the crayfish, Procambarus clarkii. We tested the extent of molecule transport to the surfaces of aesthetasc sensilla during an antennule flick and the degree of odorant exchange during subsequent flicks. During the rapid downstroke of a flick, odorant molecules are advected between adjacent aesthetascs, while during the slower return stroke, these odorants are trapped between the sensilla and molecular diffusion occurs over a sufficient time period to transport odorants to aesthetasc surfaces. During subsequent flicks, up to 97.6 % of these odorants are replaced with new odorant molecules. The concentration of molecules captured along aesthetasc surfaces was found to increase with increased gap spacing between aesthetascs, flick speed, and distance from the proximal end of the aesthetasc, but these changes in morphology and flicking kinematics reduce the animal’s ability to take discrete samples of the odorant-laden fluid environment with each flick. Results suggest that antennule flicking allows discrete sampling of the time- and space-varying odorant signal, and high concentration odorant filaments can be distinguished from more diffuse, low concentration filaments through changes in both the timing and the encounter rate of odorant molecules to aesthetasc surfaces.

Journal of Comparative Physiology A

17967808

10.1007/S00359-012-0736-Z

Toral lateral line units of goldfish, Carassius auratus, are sensitive to the position and vibration direction of a vibrating sphere

We recorded the responses of lateral line units in the midbrain torus semicircularis of goldfish, Carassius auratus, to a 50-Hz vibrating sphere and determined the unit’s spatial receptive fields for various distances between fish and sphere and for different directions of sphere vibration. All but one unit responded to the vibrating sphere with an increase in discharge rate. Only a proportion (25 %) of the units exhibited phase-locked responses. Receptive fields were narrow or broad and contained one, two or more areas of increased discharge rate. The data show that the receptive fields of toral lateral line units are in many respects similar to those of brainstem units but differ from those of afferent nerve fibres. The responses of primary afferents represent the pressure gradient pattern generated by a vibrating sphere and provide information about sphere location and vibration direction. Across the array of lateral line neuromasts, the fish brain in principle can derive this information. Nevertheless, toral units tuned to a distinct sphere location or sensitive to a distinct sphere vibration direction were not found. Therefore, it is conceivable that the torus semicircularis uses a population code to determine spatial location and vibration direction of a vibrating sphere.

Journal of Comparative Physiology A

17529985

10.1007/S00360-012-0678-3

Should I stay or should I go?: Physiological, metabolic and biochemical consequences of voluntary emersion upon aquatic hypoxia in the scaleless fish Galaxias maculatus

Hypoxia represents a significant challenge to most fish, forcing the development of behavioural, physiological and biochemical adaptations to survive. It has been previously shown that inanga (Galaxias maculatus) display a complex behavioural repertoire to escape aquatic hypoxia, finishing with the fish voluntarily emerging from the water and aerially respiring. In the present study we evaluated the physiological, metabolic and biochemical consequences of both aquatic hypoxia and emersion in inanga. Inanga successfully tolerated up to 6 h of aquatic hypoxia or emersion. Initially, this involved enhancing blood oxygen-carrying capacity, followed by the induction of anaerobic metabolism. Only minor changes were noted between emersed fish and those maintained in aquatic hypoxia, with the latter group displaying a higher mean cell haemoglobin content and a reduced haematocrit after 6 h. Calculations suggest that inanga exposed to both aquatic hypoxia and air reduced oxygen uptake and also increased anaerobic contribution to meet energy demands, but the extent of these changes was small compared with hypoxia-tolerant fish species. Overall, these findings add to previous studies suggesting that inanga are relatively poorly adapted to survive aquatic hypoxia.

Journal of Comparative Physiology B

11173125

10.1007/S00359-012-0734-1

Probing cochlear tuning and tonotopy in the tiger using otoacoustic emissions

Otoacoustic emissions (sound emitted from the ear) allow cochlear function to be probed noninvasively. The emissions evoked by pure tones, known as stimulus-frequency emissions (SFOAEs), have been shown to provide reliable estimates of peripheral frequency tuning in a variety of mammalian and non-mammalian species. Here, we apply the same methodology to explore peripheral auditory function in the largest member of the cat family, the tiger (Panthera tigris). We measured SFOAEs in 9 unique ears of 5 anesthetized tigers. The tigers, housed at the Henry Doorly Zoo (Omaha, NE), were of both sexes and ranged in age from 3 to 10 years. SFOAE phase-gradient delays are significantly longer in tigers—by approximately a factor of two above 2 kHz and even more at lower frequencies—than in domestic cats (Felis catus), a species commonly used in auditory studies. Based on correlations between tuning and delay established in other species, our results imply that cochlear tuning in the tiger is significantly sharper than in domestic cat and appears comparable to that of humans. Furthermore, the SFOAE data indicate that tigers have a larger tonotopic mapping constant (mm/octave) than domestic cats. A larger mapping constant in tiger is consistent both with auditory brainstem response thresholds (that suggest a lower upper frequency limit of hearing for the tiger than domestic cat) and with measurements of basilar-membrane length (about 1.5 times longer in the tiger than domestic cat).

Journal of Comparative Physiology A

9492702

10.1007/S00359-012-0735-0

Structural coloration signals condition, parental investment, and circulating hormone levels in Eastern bluebirds (Sialia sialis)

Many of the brilliant plumage coloration displays of birds function as signals to conspecifics. One species in which the function of plumage ornaments has been assessed is the Eastern bluebird (Sialia sialis). Studies of a population breeding in Alabama (USA) have established that plumage ornaments signal quality, parental investment, and competitive ability in both sexes. Here we tested the additional hypotheses that (1) Eastern bluebird plumage ornamentation signals nest defense behavior in heterospecific competitive interactions and (2) individual variation in plumage ornamentation reflects underlying differences in circulating hormone levels. We also tested the potential for plumage ornaments to signal individual quality and parental investment in a population breeding in Oklahoma (USA). We found that Eastern bluebirds with more ornamented plumage are in better condition, initiate breeding earlier in the season, produce larger clutches, have higher circulating levels of the stress hormone corticosterone, and more ornamented males have lower circulating androgen levels. Plumage coloration was not related to nest defense behavior. Thus, plumage ornamentation may be used by both sexes to assess the physiological condition and parental investment of prospective mates. Experimental manipulations of circulating hormone levels during molt are needed to define the role of hormones in plumage ornamentation.

Journal of Comparative Physiology A

14738198

10.1007/S00359-012-0733-2

IP3-mediated octopamine-induced synaptic enhancement of crayfish LG neurons

The biogenic amines, octopamine and serotonin, modulate the synaptic activity of the lateral giant interneuron (LG) circuitry of the crayfish escape behavior. Bath application of both octopamine and serotonin enhances the synaptic responses of LG to sensory stimulation. We have shown previously (Araki et al. J Neurophysiol 94:2644–2652, 2005) that a serotonin-induced enhancement of the LG response was mediated by an increase in cAMP levels following activation of adenylate cyclase; however, octopamine acts independently. Here, we clarify how octopamine enhances the LG response during sensory stimulation using physiological and pharmacological analyses. When phospholipase C inhibitor U-73122 was directly injected into the LG before biogenic amine application, it abolished the enhancing effect of octopamine on direct sensory input to the LG, but did not block indirect input via sensory interneurons or the effect of serotonin. Direct injection of IP3, and its analogue adenophostin A, into the LG increased the synaptic response of the LG to sensory stimulation. Thus, IP3 mediates octopamine-induced synaptic enhancement of the LG, but serotonin acts independently. These results indicate that both octopamine and serotonin enhance the synaptic responses of the LG to sensory stimulation, but that they activate two different signaling cascades in the LG.

Journal of Comparative Physiology A

6878131

10.1007/S00360-012-0675-6

Maximal thermogenic capacity and non-shivering thermogenesis in the South American subterranean rodent Ctenomystalarum

Subterranean rodents inhabit closed tunnel systems that are hypoxic and hypercapnic and buffer aboveground ambient temperature. In contrast to other strictly subterranean rodents, Ctenomys talarum exhibits activity on the surface during foraging and dispersion and hence, is exposed also to the aboveground environment. In this context, this species is a valuable model to explore how the interplay between underground and aboveground use affects the relationship among basal metabolic rate (BMR), cold-induced maximum metabolic rate (MMR), shivering (ST), and non-shivering thermogenesis (NST). In this work, we provide the first evidence of the presence of NST, including the expression of uncoupling proteins in brown adipose tissue (BAT), and shivering thermogenesis in Ctenomys talarum, a species belonging to the most numerous subterranean genus, endemic to South America. Our results show no differences in BMR, cold-induced MMR, and NST between cold- (15 °C) and warm- (25 °C) acclimated individuals. Furthermore, thermal acclimation had no effect on the expression of mitochondrial uncoupling protein 1 (UCP1) in BAT. Only cytochrome c oxidase (COX) content and activity increased during cold acclimation. When interscapular BAT was removed, NST decreased more than 30 %, whereas cold-induced MMR remained unchanged. All together, these data suggest that cold-induced MMR reaches a maximum in warm-acclimated individuals and so a probable ceiling in NST and UCP1 expression in BAT. Possible thermogenic mechanisms explaining the increase in the oxidative capacity, mediated by COX in BAT of cold-acclimated individuals and the role of ST in subterranean life habits are proposed.

Journal of Comparative Physiology B

13514427

10.1007/S00360-012-0674-7

Hair cortisol: a parameter of chronic stress? Insights from a radiometabolism study in guinea pigs

Measurement of hair cortisol has become popular in the evaluation of chronic stress in various species. However, a sound validation is still missing. Therefore, deposition of radioactivity in hair and excretion into feces and urine after repeated injection of 3H-cortisol was studied in guinea pigs (n = 8). Each animal was given intraperitoneally 243.6 kBq 3H-cortisol/day on 3 successive days. After the first injection, all voided excreta were collected for 3 days. After the second injection, hair was shaved off the animals’ back and newly grown hair was obtained on day 7. Following methanol extraction, radiolabeled and unlabeled glucocorticoid metabolites (GCM) in fecal and hair samples were characterized by high-performance liquid chromatography (HPLC) and enzyme immunoassays (EIA). In feces, maximum radioactivity was reached 8 h (median) post each injection, whereas maxima in urine were detected in the first samples (median 2.5 h). Metabolites excreted into feces (13.3 % ± 3.7) or urine (86.7 %) returned nearly to background levels. HPLC of fecal extracts showed minor variation between individuals and sexes. In hair, small amounts of radioactivity were present. However, two EIAs detected large amounts of unlabeled GCM, including high levels at the position of the cortisol standard; radioactivity was absent in this fraction, demonstrating that 3H-cortisol was metabolized. Furthermore, large amounts of immunoreactivity coinciding with a radioactive peak at the elution position of cortisone were found. These results show for the first time that only small amounts of systemically administered radioactive glucocorticoids are deposited in hair of guinea pigs, while measurement of large amounts of unlabeled GCM strongly suggests local production of glucocorticoids in hair follicles.

Journal of Comparative Physiology B

15449583

10.1007/S00359-012-0732-3

Magnetic field perception in the rainbow trout Oncorynchus mykiss: magnetite mediated, light dependent or both?

In the present study, we demonstrate the role of the trigeminal system in the perception process of different magnetic field parameters by heartbeat conditioning, i.e. a significantly longer interval between two consecutive heartbeats after magnetic stimulus onset in the salmonid fish Oncorhynchus mykiss. The electrocardiogram was recorded with subcutaneous silver wire electrodes in freely swimming fish. Inactivation of the ophthalmic branch of the trigeminal nerve by local anaesthesia revealed its role in the perception of intensity/inclination of the magnetic field by abolishing the conditioned response (CR). In contrast, experiments with 90° direction shifts clearly showed the normal conditioning effect during trigeminal inactivation. In experiments under red light and in darkness, CR occurred in case of both the intensity/inclination stimulation and 90° direction shifts, respectively. With regard to the data obtained, we propose the trigeminal system to perceive the intensity/inclination of the magnetic field in rainbow trouts and suggest the existence of another light-independent sensory structure that enables fish to detect the magnetic field direction.

Journal of Comparative Physiology A

6866587

10.1007/S00360-012-0673-8

The interactive effects of exercise and gill remodeling in goldfish (Carassius auratus)

Gill remodeling in goldfish (Carassius auratus) is accomplished by the appearance or retraction of a mass of cells (termed the interlamellar cell mass or ILCM) between adjacent lamellae. Given the presumed effects of gill remodeling on diffusing capacity, the goals of the current study were (1) to determine the consequences of increased aerobic O2 demand (swimming) on gill remodelling and (2) to assess the consequences of the presence or absence of the ILCM on aerobic swimming capacity. Fish acclimated to 7 °C exhibited a marked increase in the ILCM which occupied, on average, 70.0 ± 4.1 % of the total interlamellar channel area in comparison to an average ILCM area of only 28.3 ± 0.9 % in fish acclimated to 25 °C. Incrementally increasing swimming velocity in fish at 7 °C to achieve a maximum aerobic swimming speed (UCRIT) within approximately 3 h resulted in a marked loss of the ILCM area to 44.8 ± 3.5 %. Fish acclimated to 7 °C were subjected to 35 min swimming trials at 30, 60 or 80 % UCRIT revealing that significant loss of the ILCM occurred at swimming speeds exceeding 60 % UCRIT. Prior exposure of cold water-acclimated fish to hypoxia to induce shedding of the ILCM did not affect swimming performance when assessed under normoxic conditions (control fish UCRIT = 2.34 ± 0.30 body lengths s−1; previously hypoxic fish UCRIT = 2.99 ± 0.14 body lengths s−1) or the capacity to raise rates of O2 consumption with increasing swimming speeds. Because shedding of ILCM during UCRIT trials complicated the interpretation of experiments designed to evaluate the impact of the ILCM on swimming performance, additional experiments using a more rapid ‘ramp’ protocol were performed to generate swimming scores. Neither prior hypoxia exposure nor a previous swim to UCRIT (both protocols are known to cause loss of the ILCM) affected swimming scores (the total distance swum during ramp UCRIT trials). However, partitioning all data based on the extent of ILCM coverage upon cessation of the swimming trial revealed that fish with less than 40 % ILCM coverage exhibited a significantly greater swimming score (539 ± 86 m) than fish with greater than 50 % ILCM coverage (285 ± 70 m). Thus, while loss of the ILCM at swimming speeds exceeding 60 % UCRIT confounds the interpretation of experiments designed to assess the impact of the ILCM on swimming performance, we suggest that the shedding of the ILCM, in itself, coupled with improved swimming scores in fish exhibiting low ILCM coverage (<40 %), provide evidence that the ILCM in goldfish acclimated to cold water (7 °C) is indeed an impediment to aerobic swimming capacity.

Journal of Comparative Physiology B

17732654

10.1007/S00359-012-0731-4

The marine mammal dive response is exercise modulated to maximize aerobic dive duration

When aquatically adapted mammals and birds swim submerged, they exhibit a dive response in which breathing ceases, heart rate slows, and blood flow to peripheral tissues and organs is reduced. The most intense dive response occurs during forced submersion which conserves blood oxygen for the brain and heart, thereby preventing asphyxiation. In free-diving animals, the dive response is less profound, and energy metabolism remains aerobic. However, even this relatively moderate bradycardia seems diametrically opposed to the normal cardiovascular response (i.e., tachycardia and peripheral vasodilation) during physical exertion. As a result, there has been a long-standing paradox regarding how aquatic mammals and birds exercise while submerged. We hypothesized based on cardiovascular modeling that heart rate must increase to ensure adequate oxygen delivery to active muscles. Here, we show that heart rate (HR) does indeed increase with flipper or fluke stroke frequency (SF) during voluntary, aerobic dives in Weddell seals (HR = 1.48SF − 8.87) and bottlenose dolphins (HR = 0.99SF + 2.46), respectively, two marine mammal species with different evolutionary lineages. These results support our hypothesis that marine mammals maintain aerobic muscle metabolism while swimming submerged by combining elements of both dive and exercise responses, with one or the other predominating depending on the level of exertion.

Journal of Comparative Physiology A

15012554

10.1007/S00360-012-0670-Y

Temperature-dependent toxicity in mammals with implications for herbivores: a review

Diet selection in mammalian herbivores is thought to be primarily governed by intrinsic properties of food, such as nutrient and plant secondary compound (PSC) contents, and less so by environmental factors. However, several independent lines of evidence suggest that the toxicity of PSCs is mediated, in part, by ambient temperature and that the effect of small changes in ambient temperature is on par with several fold changes in PSC concentration. This review describes the disparate lines of evidence for temperature-dependent toxicity and the putative mechanisms causing this phenomenon. A model is described that integrates thermal physiology with temperature-dependent toxicity to predict maximal dietary intake of plant secondary compounds by mammalian herbivores. The role of temperature-dependent toxicity is considered with respect to the observed changes in herbivorous species attributed to climate change. Possible future investigations and the effects of temperature-dependent toxicity on other endotherms are presented. Temperature-dependent toxicity has the potential to apply to all endotherms that consume toxins. The effects of temperature-dependent toxicity will likely be exacerbated with increasing ambient temperatures caused by climate change.

Journal of Comparative Physiology B

8723092

10.1007/S00360-012-0668-5

Impacts of ocean acidification on respiratory gas exchange and acid–base balance in a marine teleost, Opsanus beta

The oceanic carbonate system is changing rapidly due to rising atmospheric CO2, with current levels expected to rise to between 750 and 1,000 μatm by 2100, and over 1,900 μatm by year 2300. The effects of elevated CO2 on marine calcifying organisms have been extensively studied; however, effects of imminent CO2 levels on teleost acid–base and respiratory physiology have yet to be examined. Examination of these physiological processes, using a paired experimental design, showed that 24 h exposure to 1,000 and 1,900 μatm CO2 resulted in a characteristic compensated respiratory acidosis response in the gulf toadfish (Opsanus beta). Time course experiments showed the onset of acidosis occurred after 15 min of exposure to 1,900 and 1,000 μatm CO2, with full compensation by 2 and 4 h, respectively. 1,900-μatm exposure also resulted in significantly increased intracellular white muscle pH after 24 h. No effect of 1,900 μatm was observed on branchial acid flux; however, exposure to hypercapnia and HCO3− free seawater compromised compensation. This suggests branchial HCO3− uptake rather than acid extrusion is part of the compensatory response to low-level hypercapnia. Exposure to 1,900 μatm resulted in downregulation in branchial carbonic anhydrase and slc4a2 expression, as well as decreased Na+/K+ ATPase activity after 24 h of exposure. Infusion of bovine carbonic anhydrase had no effect on blood acid–base status during 1,900 μatm exposures, but eliminated the respiratory impacts of 1,000 μatm CO2. The results of the current study clearly show that predicted near-future CO2 levels impact respiratory gas transport and acid–base balance. While the full physiological impacts of increased blood HCO3− are not known, it seems likely that chronically elevated blood HCO3− levels could compromise several physiological systems and furthermore may explain recent reports of increased otolith growth during exposure to elevated CO2.

Journal of Comparative Physiology B

8719717

10.1007/S00360-012-0669-4

Hypoxia associated NMDA receptor 2 subunit composition: developmental comparison between the hypoxia-tolerant subterranean mole-rat, Spalax, and the hypoxia-sensitive rat

Vertebrate brains are sensitive to oxygen depletion, which may lead to cell death. Hypoxia sensitivity originates from the high intrinsic rate of ATP consumption of brain tissue, accompanied by the release of glutamate, leading to the opening of ionotropic glutamate receptors, such as N-methyl-d-aspartate (NMDA) receptors (NMDARs). The relative expression levels of the four NMDAR-2 (NR2) subunits change during mammalian development with higher levels of units NR2B and NR2D observed during early development and correlated with hypoxic tolerance during embryonic and neonatal stages of development. Higher levels of NR2D are also abundant in brains of hypoxia tolerant species such as the crucian carp. The subterranean mole-rat, Spalax spends its life underground in sealed burrows and has developed a wide range of adaptations to this special niche including hypoxia-tolerance. In this study, we compared the in vivo mRNA expression of NR2 subunits in the brains of embryonic, neonatal and adult Spalax and rat. Our results demonstrate that under normoxic conditions, mRNA levels of NR2D are higher in Spalax than in rat at all developmental stages studied and are similar to levels in neonatal rat and in other hypoxia/anoxia tolerant species. Furthermore, under hypoxia SpalaxNR2D mRNA levels increase while no response was observed in rat. Similarly, hypoxia induces an increase in mRNA levels of Spalax NR2A, claimed to promote neuronal survival. We suggest that indeed the proportional combinations of NMDAR-2 subunits contribute to the ability of the Spalax brain to cope with hypoxic environments.

Journal of Comparative Physiology B

1164665

10.1007/S00359-012-0730-5

Centrally patterned rhythmic activity integrated by a peripheral circuit linking multiple oscillators

The central pattern generator for heartbeat in the medicinal leech, Hirudo generates rhythmic activity conveyed by heart excitor motor neurons in segments 3–18 to coordinate the bilateral tubular hearts and side vessels. We focus on behavior and the influence of previously un-described peripheral nerve circuitry. Extracellular recordings from the valve junction (VJ) where afferent vessels join the heart tube were combined with optical recording of contractions. Action potential bursts at VJs occurred in advance of heart tube and afferent vessel contractions. Transections of nerves were performed to reduce the output of the central pattern generator reaching the heart tube. Muscle contractions persisted but with a less regular rhythm despite normal central pattern generator rhythmicity. With no connections between the central pattern generator and heart tube, a much slower rhythm became manifest. Heart excitor neuron recordings showed that peripheral activity might contribute to the disruption of centrally entrained contractions. In the model presented, peripheral activity would normally modify the activity actually reaching the muscle. We also propose that the fundamental efferent unit is not a single heart excitor neuron, but rather is a functionally defined unit of about three adjacent motor neurons and the peripheral assembly of coupled peripheral oscillators.

Journal of Comparative Physiology A

16194759

10.1007/S00360-012-0671-X

High levels of liver antioxidants are associated with life-history strategies characteristic of slow growth and high survival rates in birds

Antioxidants have a large potential to coevolve with life-histories because of their capacity to counteract the negative effects of free radicals on fitness. However, only a few studies have explored the association between antioxidant levels and life-history strategies comparing a large number of species. Here we used an extensive dataset of 125 species of birds to investigate the association between concentrations of antioxidants (carotenoids and vitamin E) in the liver, which is the main storage organ for fat-soluble antioxidants, and life-history and morphology. We found that high liver antioxidant concentrations were associated with life-history strategies characterized by “live slow, die old”, in clear contrast to previous studies reporting a relationship between high plasma antioxidants and life-histories characterized by “live fast, die young”. Thus, high carotenoid concentrations were present in species with large body, brain and egg sizes, high absolute metabolic rate and a resident lifestyle, while high vitamin E concentrations were present in species with large brain size and long life span and incubation period. Our results indicate that antioxidants and life-histories coevolve, and that this may be mediated by positive fitness consequences of the accumulation of liver antioxidants, as species with higher antioxidant levels live longer.

Journal of Comparative Physiology B

9799131

10.1007/S00360-012-0672-9

Cell cycle arrest associated with anoxia-induced quiescence, anoxic preconditioning, and embryonic diapause in embryos of the annual killifish Austrofundulus limnaeus

Embryos of the annual killifish Austrofundulus limnaeus can enter into dormancy associated with diapause and anoxia-induced quiescence. Dormant embryos are composed primarily of cells arrested in the G1/G0 phase of the cell cycle based on flow cytometry analysis of DNA content. In fact, most cells in developing embryos contain only a diploid complement of DNA, with very few cells found in the S, G2, or M phases of the cell cycle. Diapause II embryos appear to be in a G0-like state with low levels of cyclin D1 and p53. However, the active form of pAKT is high during diapause II. Exposure to anoxia causes an increase in cyclin D1 and p53 expression in diapause II embryos, suggesting a possible re-entry into the cell cycle. Post-diapause II embryos exposed to anoxia or anoxic preconditioning have stable levels of cyclin D1 and stable or reduced levels of p53. The amount of pAKT is severely reduced in 12 dpd embryos exposed to anoxia or anoxic preconditioning. This study is the first to evaluate cell cycle control in embryos of A. limnaeus during embryonic diapause and in response to anoxia and builds a foundation for future research on the role of cell cycle arrest in supporting vertebrate dormancy.

Journal of Comparative Physiology B

10670820

10.1007/S00360-012-0666-7

Adaptation to thermally variable environments: capacity for acclimation of thermal limit and heat shock response in the shrimp Palaemonetes varians

In the context of climate change, there is a sustained interest in understanding better the functional mechanisms by which marine ectotherms maintain their physiological scope and define their ability to cope with thermal changes in their environment. Here, we present evidence that the variable shrimp Palaemonetes varians shows genuine acclimation capacities of both the thermal limit (CTmax) and the heat shock response (hsp70 induction temperature). During cold acclimation to 10 °C, the time lag to adjust the stress gene expression to the current environmental temperature proved to exceed 1 week, thereby highlighting the importance of long-term experiments in evaluating the species’ acclimation capacities. Cold and warm-acclimated specimens of P. varians can mobilise the heat shock response (HSR) at temperatures above those experienced in nature, which suggests that the species is potentially capable of expanding its upper thermal range. The shrimp also survived acute heat shock well above its thermal limit without subsequent induction of the HSR, which is discussed with regard to thermal adaptations required for life in highly variable environments.

Journal of Comparative Physiology B

14948091

10.1007/S00359-012-0728-Z

Role of wing pronation in evasive steering of locusts

Evasive steering is crucial for flying in a crowded environment such as a locust swarm. We investigated how flying locusts alter wing-flapping symmetry in response to a looming object approaching from the side. Desert locusts (Schistocerca gregaria) were tethered to a rotatable shaft that allowed them to initiate a banked turn. A visual stimulus of an expending disk on one side of the locust was used to evoke steering while recording the change in wingbeat kinematics and electromyography (EMG) of metathoracic wing depressors. Locusts responded to the looming object by rolling to the contralateral direction. During turning, EMG of hindwing depressors showed an omission of one action potential in the subalar depressor (M129) of the hindwing inside the turn. This omission was associated with increased pronation of the same wing, reducing its angle-of-attack during the downstroke. The link between spike-omission in M129 and wing pronation was verified by stimulating the hindwing depressor muscles with an artificial motor pattern that included the misfire of M129. These results suggest that hindwing pronation is instrumental in rotating the body to the side opposite of the approaching threat. Turning away from the threat would be highly adaptive for collision avoidance when flying in dense swarms.

Journal of Comparative Physiology A

12529782

10.1007/S00360-012-0667-6

Analysis of cutaneous and internal gill gas exchange morphology in early larval amphibians, Pseudophryne bibronii and Crinia georgiana

This study uses stereological techniques to examine body, internal gill and cardiovascular morphology of two larval amphibians, Pseudophryne bibronii and Crinia georgiana, to evaluate the roles of diffusive and convective gas exchange. Gosner stage 27 specimens were prepared for light microscopy and six parallel sections of equal distance taken through the body as well as a further six through the heart and internal gills. Body, internal gill and heart volume as well as body and internal gill surface areas were determined. The harmonic mean distance across the internal gills was also measured and used to estimate oxygen diffusive conductance, DO2. The species were of similar body size and surface area, but the heart and internal gills were larger in P. bibronii, which may represent precursors for greater growth of the species beyond stage 27. The much larger surface area of the skin compared to the internal gills in both species suggests it is the main site for gas exchange, with the gills supplementing oxygen uptake. The sparse cutaneous capillary network suggests diffusion is the main oxygen transport mechanism across the skin and directly into deeper tissues. A numerical model that simplifies larval shape, and has an internal (axial vessels) and external oxygen source, confirms that diffusion is able to maintain tissue oxygen with limited convective input.

Journal of Comparative Physiology B

1794151

10.1007/S00360-012-0665-8

Evolution of osmoregulatory patterns and gill ion transport mechanisms in the decapod Crustacea: a review

Decapod crustaceans exhibit a wide range of osmoregulatory patterns and capabilities from marine osmoconformers to brackish and freshwater hyperregulators to terrestrial hyporegulators. The principal gill salt transport mechanisms proposed to underlie the ability of the better-known taxa to occupy these specific habitats are examined here. Traditional thinking suggests that a graduated series of successively stronger adaptive mechanisms may have driven the occupation of ever more dilute osmotic niches, culminating in the conquest of freshwater and dry land. However, when habitat and osmoregulatory parameters are analyzed quantitatively against the phylogenies of the taxa examined, as illustrated here using a palaemonid shrimp clade, their association becomes questionable and may hold true only in specific cases. We also propose a putative evolution for gill epithelial ion pump and transporter arrangement in a eubrachyuran crab clade whose lineages occupy distinct osmotic niches. By including the systematics of these selected groups, this review incorporates the notion of a protracted time scale, here termed ‘phylophysiology’, into decapod osmoregulation, allowing the examination of putative physiological transformations and their underlying evolutionary processes. This approach assumes that species are temporally linked, a factor that can impart phylogenetic structuring, which must be considered in comparative studies. Future experimental models in decapod osmoregulatory physiology should contemplate the phylogenetic relationships among the taxa chosen to better allow comprehension of the transformations arising during their evolution.

Journal of Comparative Physiology B

16157940

10.1007/S00359-012-0729-Y

Behavioral response to antennal tactile stimulation in the field cricket Gryllus bimaculatus

We examined behavioral responses of the field cricket Gryllus bimaculatus to tactile stimuli to the antennae. Three stimulants of similar shape and size but different textures were used: a tibia from the hunting spider Heteropoda venatoria (potential predator), a tibia from the orb-web spider Argiope bruennichi (less likely predator), and a glass rod. Each stimulus session comprised a first gentle contact and a second strong contact. The evoked behavioral responses were classified into four categories: aversion, aggression, antennal search, and no response. Regardless of the stimulants, the crickets exhibited antennal search and aversion most frequently in response to the first and second stimuli, respectively. The frequency of aversion was significantly higher to the tibia of H. venatoria than to other stimulants. The most striking observation was that aggressive responses were exclusive to the H. venatoria tibia. To specify the hair type that induced aggression, we manipulated two types of common hairs (bristle and fine) on the tibia of the predatory spider. When bristle hairs were removed from the H. venatoria tibia, aggression was significantly reduced. These results suggest that antennae can discriminate the tactile texture of external objects and elicit adaptive behavioral responses.

Journal of Comparative Physiology A

11283862

10.1007/S00359-012-0727-0

Involvement of Na+/K+pump in fine modulation of bursting activity of the snail Br neuron by 10 mT static magnetic field

The spontaneously active Br neuron from the brain-subesophageal ganglion complex of the garden snail Helix pomatia rhythmically generates regular bursts of action potentials with quiescent intervals accompanied by slow oscillations of membrane potential. We examined the involvement of the Na+/K+ pump in modulating its bursting activity by applying a static magnetic field. Whole snail brains and Br neuron were exposed to the 10-mT static magnetic field for 15 min. Biochemical data showed that Na+/K+-ATPase activity increased almost twofold after exposure of snail brains to the static magnetic field. Similarly, 31P NMR data revealed a trend of increasing ATP consumption and increase in intracellular pH mediated by the Na+/H+ exchanger in snail brains exposed to the static magnetic field. Importantly, current clamp recordings from the Br neuron confirmed the increase in activity of the Na+/K+ pump after exposure to the static magnetic field, as the magnitude of ouabain’s effect measured on the membrane resting potential, action potential, and interspike interval duration was higher in neurons exposed to the magnetic field. Metabolic pathways through which the magnetic field influenced the Na+/K+ pump could involve phosphorylation and dephosphorylation, as blocking these processes abolished the effect of the static magnetic field.

Journal of Comparative Physiology A

14259372

10.1007/S00359-012-0724-3

Ultraviolet visual sensitivity in three avian lineages: paleognaths, parrots, and passerines

Ultraviolet (UV) light-transmitted signals play a major role in avian foraging and communication, subserving functional roles in feeding, mate choice, egg recognition, and nestling discrimination. Sequencing functionally relevant regions of the short wavelength sensitive type 1 (SWS1) opsin gene that is responsible for modulating the extent of SWS1 UV sensitivity in birds allows predictions to be made about the visual system’s UV sensitivity in species where direct physiological or behavioral measures would be impractical or unethical. Here, we present SWS1 segment sequence data from representative species of three avian lineages for which visually based cues for foraging and communication have been investigated to varying extents. We also present a preliminary phylogenetic analysis and ancestral character state reconstructions of key spectral tuning sites along the SWS1 opsin based on our sequence data. The results suggest ubiquitous ultraviolet SWS1 sensitivity (UVS) in both paleognaths, including extinct moa (Emeidae), and parrots, including the nocturnal and flightless kakapo (Strigops habroptilus), and in most, but not all, songbird (oscine) lineages, and confirmed violet sensitivity (VS) in two suboscine families. Passerine hosts of avian brood parasites were included both UVS and VS taxa, but sensitivity did not co-vary with egg rejection behaviors. The results should stimulate future research into the functional parallels between the roles of visual signals and the genetic basis of visual sensitivity in birds and other taxa.

Journal of Comparative Physiology A

2626797

10.1007/S00360-012-0664-9

Cystic fibrosis transmembrane conductance regulator in the gills of the climbing perch, Anabas testudineus, is involved in both hypoosmotic regulation during seawater acclimation and active ammonia excretion during ammonia exposure

This study aimed to clone and sequence the cystic fibrosis transmembrane conductance regulator (cftr) from, and to determine the effects of seawater acclimation or exposure to 100 mmol l−1 NH4Cl in freshwater on its mRNA and protein expressions in, the gills of Anabas testudineus. There were 4,530 bp coding for 1,510 amino acids in the cftr cDNA sequence from A. testudineus. The branchial mRNA expression of cftr in fish kept in freshwater was low (<50 copies of transcript per ng cDNA), but significant increases were observed in fish acclimated to seawater for 1 day (92-fold) or 6 days (219-fold). Branchial Cftr expression was detected in fish acclimated to seawater but not in the freshwater control, indicating that Cl− excretion through the apical Cftr of the branchial epithelium was essential to seawater acclimation. More importantly, fish exposed to ammonia also exhibited a significant increase (12-fold) in branchial mRNA expression of cftr, with Cftr being expressed in a type of Na+/K+-ATPase-immunoreactive cells that was apparently different from the type involved in seawater acclimation. It is probable that Cl− excretion through Cftr generated a favorable electrical potential across the apical membrane to drive the excretion of $$ {\text{NH}}_{4}^{ + } $$ against a concentration gradient through a yet to be determined transporter, but it led to a slight loss of endogenous Cl−. Since ammonia exposure also resulted in significant decreases in blood pH, [HCO3−] and [total CO2] in A. testudineus, it can be deduced that active $$ {\text{NH}}_{4}^{ + } $$ excretion could also be driven by the exit of HCO3− through the apical Cftr. Furthermore, A. testudineus uniquely responded to ammonia exposure by increasing the ambient pH and decreasing the branchial bafilomycin-sensitive V-type H+-ATPase activity, which suggests that its gills might have low NH3 permeability.

Journal of Comparative Physiology B

11174102

10.1007/S00360-012-0663-X

‘No cost of echolocation for flying bats’ revisited

Echolocation is energetically costly for resting bats, but previous experiments suggested echolocation to come at no costs for flying bats. Yet, previous studies did not investigate the relationship between echolocation, flight speed, aerial manoeuvres and metabolism. We re-evaluated the ‘no-cost’ hypothesis, by quantifying the echolocation pulse rate, the number of aerial manoeuvres (landings and U-turns), and the costs of transport in the 5-g insectivorous bat Rhogeessa io (Vespertilionidae). On average, bats (n = 15) travelled at 1.76 ± 0.36 m s−1 and performed 11.2 ± 6.1 U-turns and 2.8 ± 2.9 ground landings when flying in an octagonal flight cage. Bats made more U-turns with decreasing wing loading (body weight divided by wing area). At flight, bats emitted 19.7 ± 2.7 echolocation pulses s−1 (range 15.3–25.8 pulses s−1), and metabolic rate averaged 2.84 ± 0.95 ml CO2 min−1, which was more than 16 times higher than at rest. Bats did not echolocate while not engaged in flight. Costs of transport were not related to the rate of echolocation pulse emission or the number of U-turns, but increased with increasing number of landings; probably as a consequence of slower travel speed when staying briefly on ground. Metabolic power of flight was lower than predicted for R. io under the assumption that energetic costs of echolocation call production is additive to the aerodynamic costs of flight. Results of our experiment are consistent with the notion that echolocation does not add large energetic costs to the aerodynamic power requirements of flight in bats.

Journal of Comparative Physiology B

7365164

10.1007/S00360-012-0662-Y

HIF-1α regulation in mammalian hibernators: role of non-coding RNA in HIF-1α control during torpor in ground squirrels and bats

A potential role for non-coding RNAs, miR-106b and antisense hypoxia inducible transcription factor-1 (HIF-1α), in HIF-1α regulation during mammalian hibernation was investigated in two species, the thirteen-lined ground squirrel (Ictidomys tridecemlineatus) and the little brown bat (Myotis lucifugus). Both species showed differential regulation of HIF-1α during hibernation. HIF-1α protein levels increased significantly in skeletal muscle of both species when animals entered torpor, as well as in bat liver. HIF-1α mRNA levels correlated with the protein increase in bat skeletal muscle and liver but not in squirrel skeletal muscle. Antisense HIF-1α transcripts were identified in skeletal muscle of both hibernators. The expression of antisense HIF-1α was reduced in skeletal muscle of torpid bats compared with euthermic controls, suggesting that release of inhibition by the antisense RNA contributes to regulating HIF-1α translation in this tissue during torpor. The expression of miR-106b, a microRNA associated with HIF-1α regulation, also decreased during torpor in both skeletal muscle and liver of bats and in ground squirrel skeletal muscle. These data present the first evidence that non-coding RNA provides novel post-transcriptional mechanisms of HIF-1α regulation when hibernators descend into deep cold torpor, and also demonstrate that these mechanisms are conserved in two divergent mammalian orders (Rodentia and Chiroptera).

Journal of Comparative Physiology B

13869107

10.1007/S00360-012-0661-Z

Thermoregulatory changes anticipate hibernation onset by 45 days: data from free-living arctic ground squirrels

Hibernation is a strategy of reducing energy expenditure, body temperature (Tb) and activity used by endotherms to escape unpredictable or seasonally reduced food availability. Despite extensive research on thermoregulatory adjustments during hibernation, less is known about transitions in thermoregulatory state, particularly under natural conditions. Laboratory studies on hibernating ground squirrels have demonstrated that thermoregulatory adjustments may occur over short intervals when animals undergo several brief, preliminary torpor bouts prior to entering multiday torpor. These short torpor bouts have been suggested to reflect a resetting of hypothalamic regions that control Tb or to precondition animals before they undergo deep, multiday torpor. Here, we examined continuous records of Tb in 240 arctic ground squirrels (Urocitellus parryii) prior to hibernation in the wild and in captivity. In free-living squirrels, Tb began to decline 45 days prior to hibernation, and average Tb had decreased 4.28 °C at the onset of torpor. Further, we found that 75 % of free-living squirrels and 35 % of captive squirrels entered bouts of multiday torpor with a single Tb decline and without previously showing short preliminary bouts. This study provides evidence that adjustments in the thermoregulatory component of hibernation begin far earlier than previously demonstrated. The gradual reduction in Tb is likely a component of the suite of metabolic and behavioral adjustments, controlled by an endogenous, circannual rhythm, that vary seasonally in hibernating ground squirrels.

Journal of Comparative Physiology B

17087318

10.1007/S00359-012-0726-1

Testosterone dynamics during encounter: role of emotional factors

This study attempts to develop a new theory to explain the varying dynamics of testosterone levels in dominant (winners) and subordinate (losers) males, both pre- and post-encounter. The crux of our new theory consists of the following four theses: (1) the strengthening of testosterone synthesis is a result of not only the existence of challenges, but also of a positive mood before an encounter that is associated with the anticipation of a victory; (2) in situations where the anticipation of victory is present but the positive mood is absent, no rise in testosterone levels will occur; (3) testosterone acts as a “pleasure” hormone and usually releases in situations where the individual achieves or anticipates possible satisfaction; (4) an increased release of testosterone to the blood not only decreases anxiety but also elevates the mood, which increases animal’s/human’s assertiveness and consequently aggressiveness.

Journal of Comparative Physiology A

15750983

10.1007/S00359-012-0725-2

Modulation of network pacemaker neurons by oxygen at the anaerobic threshold

Previous in vitro and in vivo studies showed that the frequency of rhythmic pyloric network activity in the lobster is modulated directly by oxygen partial pressure (PO2). We have extended these results by (1) increasing the period of exposure to low PO2 and by (2) testing the sensitivity of the pyloric network to changes in PO2 that are within the narrow range normally experienced by the lobster (1 to 6 kPa). We found that the pyloric network rhythm was indeed altered by changes in PO2 within the range typically observed in vivo. Furthermore, a previous study showed that the lateral pyloric constrictor motor neuron (LP) contributes to the O2 sensitivity of the pyloric network. Here, we expanded on this idea by testing the hypothesis that pyloric pacemaker neurons also contribute to pyloric O2 sensitivity. A 2-h exposure to 1 kPa PO2, which was twice the period used previously, decreased the frequency of an isolated group of pacemaker neurons, suggesting that changes in the rhythmogenic properties of these cells contribute to pyloric O2 sensitivity during long-term near-anaerobic (anaerobic threshold, 0.7–1.2 kPa) conditions.

Journal of Comparative Physiology A

16760980

10.1007/S00359-012-0723-4

Ants swimming in pitcher plants: kinematics of aquatic and terrestrial locomotion in Camponotus schmitzi

Camponotus schmitzi ants live in symbiosis with the Bornean pitcher plant Nepenthes bicalcarata. Unique among ants, the workers regularly dive and swim in the pitcher’s digestive fluid to forage for food. High-speed motion analysis revealed that C. schmitzi ants swim at the surface with all legs submerged, with an alternating tripod pattern. Compared to running, swimming involves lower stepping frequencies and larger phase delays within the legs of each tripod. Swimming ants move front and middle legs faster and keep them more extended during the power stroke than during the return stroke. Thrust estimates calculated from three-dimensional leg kinematics using a blade-element approach confirmed that forward propulsion is mainly achieved by the front and middle legs. The hind legs move much less, suggesting that they mainly serve for steering. Experiments with tethered C. schmitzi ants showed that characteristic swimming movements can be triggered by submersion in water. This reaction was absent in another Camponotus species investigated. Our study demonstrates how insects can use the same locomotory system and similar gait patterns for moving on land and in water. We discuss insect adaptations for aquatic/amphibious lifestyles and the special adaptations of C. schmitzi to living on an insect-trapping pitcher plant.

Journal of Comparative Physiology A

16701563

10.1007/S00359-012-0722-5

Evidence of red sensitive photoreceptors in Pygopleurus israelitus (Glaphyridae: Coleoptera) and its implications for beetle pollination in the southeast Mediterranean

A very well-documented case of flower-beetle interaction is the association in the Mediterranean region between red bowl-shaped flowers and beetles of the family Glaphyridae. The present study examines the visual mechanisms by which Pygopleurus israelitus (Glaphyridae: Scarabaeoidea: Coleoptera) would perceive the colors of flowers they visit by characterizing the spectral sensitivity of its photoreceptors. Our measurements revealed the presence of three types of photoreceptors, maximally sensitive in the UV, green and red areas of the spectrum. Using color vision space diagrams, we calculated the distribution of beetle-visited flower colors in the glaphyrid and honeybee color space and evaluated whether chromatic discrimination differs between the two types of pollinators. Respective color loci in the beetle color space are located on one side of the locus for green foliage background, whereas in the honeybee the flower color loci surround the locus occupied by green foliage. Our results represent the first evidence of a red sensitive photoreceptor in a flower-visiting coleopteran species, highlighting Glaphyridae as an interesting model group to study the role of pollinators in flower color evolution.

Journal of Comparative Physiology A

15960839

10.1007/S00359-012-0720-7

Nematocytes’ activation in Pelagia noctiluca (Cnidaria, Scyphozoa) oral arms

Nematocytes’ discharge is triggered to perform both defense and predation strategies in cnidarians and occurs under chemico-physical stimulation. In this study, different compounds such as amino acids and proteins (mucin, albumin, poly-l-lysine, trypsin), sugars and N-acetylate sugars (N-acetyl neuraminic acid, N-acetyl galactosamine, sucrose, glucose, agarose and trehalose), nucleotides (ATP and cAMP), were tested as chemosensitizers of nematocyte discharge in the oral arms of the scyphozoan Pelagia noctiluca, particularly abundant in the Strait of Messina (Italy). Excised oral arms were submitted to a combined chemico-physical stimulation by treatment with different compounds followed by mechanical stimulation by a non-vibrating test probe. Discharge induced by a chemico-physical stimulation was more significant than that obtained after mechanical stimulation alone. A chemosensitizing mechanism, with a dose-dependent effect, was observed after treatment with sugars, amino compounds such as glutathione, nucleotides and mucin, according to that already seen in sea anemones. Such findings suggest that, though Anthozoa and Scyphozoa exhibit different divergence times during the evolutionary process, the discharge activation exhibits common features, probably derived from their last common ancestor.

Journal of Comparative Physiology A

10210760

10.1007/S00359-012-0721-6

Adult neurogenesis in the brain of the Mozambique tilapia, Oreochromis mossambicus

Although the generation of new neurons in the adult nervous system (‘adult neurogenesis’) has been studied intensively in recent years, little is known about this phenomenon in non-mammalian vertebrates. Here, we examined the generation, migration, and differentiation of new neurons and glial cells in the Mozambique tilapia (Oreochromis mossambicus), a representative of one of the largest vertebrate taxonomic orders, the perciform fish. The vast majority of new cells in the brain are born in specific proliferation zones of the olfactory bulb; the dorsal and ventral telencephalon; the periventricular nucleus of the posterior tuberculum, optic tectum, and nucleus recessi lateralis of the diencephalon; and the valvula cerebelli, corpus cerebelli, and lobus caudalis of the cerebellum. As shown in the olfactory bulb and the lateral part of the valvula cerebelli, some of the young cells migrate from their site of origin to specific target areas. Labeling of mitotic cells with the thymidine analog 5-bromo-2′-deoxyuridine, combined with immunostaining against the neuron-specific marker protein Hu or against the astroglial marker glial fibrillary acidic protein demonstrated differentiation of the adult-born cells into both neurons and glia. Taken together, the present investigation supports the hypothesis that adult neurogenesis is an evolutionarily conserved vertebrate trait.

Journal of Comparative Physiology A

16168088

10.1007/S00360-012-0659-6

Molecular and physicochemical characterization of hemoglobin from the high-altitude Taiwanese brown-toothed shrew (Episoriculus fumidus)

Red-toothed shrews (subfamily Soricinae) exhibit the highest mass-specific rates of O2 consumption recorded among eutherian mammals, though surprisingly no data appears to be available on the functional characteristics of their hemoglobin (Hb). As a first step in addressing this shortcoming, we investigated the O2 binding characteristics of Taiwanese brown-toothed shrew (Episoriculusfumidus) Hb and its temperature and pH dependence in the absence and presence of anionic red blood cell effectors. Although comparative data regarding the intrinsic O2 affinity of other shrew species are currently unavailable, our data suggest that the sensitivity of this high-elevation endemic species’ Hb to allosteric effector molecules is similar to that of the two lowland species of white-toothed (crocidurine) shrews examined to date. The efficient exploitation of blood O2 reserves by E. fumidus appears to be achieved via synergistic modulation of O2 affinity by Cl− and organic phosphates that moreover dramatically lowers the overall enthalpy of oxygenation of their Hb. Oxygen unloading is presumably further enhanced by a relatively high Bohr effect (ΔLog P50/ΔpH = −0.69) and marked reduction in the titratable histidine content (predicted low proton buffering value) of the component globin chains relative to human HbA. Notably, however, the limited data available suggest these latter attributes may be widespread among shrews and hence likely are not adaptations to chronic altitudinal hypoxia per se.

Journal of Comparative Physiology B

17346869

10.1007/S00360-012-0658-7

Glucose metabolism in fish: a review

Teleost fishes represent a highly diverse group consisting of more than 20,000 species living across all aquatic environments. This group has significant economical, societal and environmental impacts, yet research efforts have concentrated primarily on salmonid and cyprinid species. This review examines carbohydrate/glucose metabolism and its regulation in these model species including the role of hormones and diet. Over the past decade, molecular tools have been used to address some of the downstream components of these processes and these are incorporated to better understand the roles played by carbohydrates and their regulatory paths. Glucose metabolism remains a contentious area as many fish species are traditionally considered glucose intolerant and, therefore, one might expect that the use and storage of glucose would be considered of minor importance. However, the actual picture is not so clear since the apparent intolerance of fish to carbohydrates is not evident in herbivorous and omnivorous species and even in carnivorous species, glucose is important for specific tissues and/or for specific activities. Thus, our aim is to up-date carbohydrate metabolism in fish, placing it to the context of these new experimental tools and its relationship to dietary intake. Finally, we suggest that new research directions ultimately will lead to a better understanding of these processes.

Journal of Comparative Physiology B

11390539

10.1007/S00360-012-0660-0

Water balance trumps ion balance for early marine survival of juvenile pink salmon (Oncorhynchus gorbuscha)

Smolting salmonids typically require weeks to months of physiological preparation in freshwater (FW) before entering seawater (SW). Remarkably, pink salmon (Oncorhynchus gorbuscha) enter SW directly following yolk absorption and gravel emergence at a size of 0.2 g. To survive this exceptional SW migration, pink salmon were hypothesized to develop hypo-osmoregulatory abilities prior to yolk absorption and emergence. To test this, alevins (pre-yolk absorption) and fry (post-yolk absorption) were transferred from FW in darkness to SW under simulated natural photoperiod (SNP). Ionoregulatory status was assessed at 0, 1 and 5 days post-transfer. SW alevins showed no evidence of hypo-osmoregulation, marked by significant water loss and no increase in gill Na+/K+-ATPase (NKA) activity or Na+:K+:2Cl− cotransporter (NKCC) immunoreactive (IR) cell frequency. Conversely, fry maintained water balance, upregulated gill NKA activity by 50 %, increased the NKA α1b/α1a mRNA expression ratio by sixfold and increased NKCC IR cell frequency. We also provide the first evidence of photoperiod-triggered smoltification in pink salmon, as fry exposed to SNP in FW exhibited preparatory changes in gill NKA activity and α1 subunit expression similar to fry exposed to SNP in SW. Interestingly, fry incurred larger increases in whole body Na+ than alevins following both SW and FW + SNP exposure (40 and 20 % in fry vs. 0 % in alevins). The ability to incur and tolerate large ion loads may underlie a novel mechanism for maintaining water balance in SW prior to completing hypo-osmoregulatory development. We propose that pink salmon represent a new form of anadromy termed “precocious anadromy”.

Journal of Comparative Physiology B

16892182

10.1007/S00359-012-0719-0

Saccadic tracking of targets mediated by the anterior-lateral eyes of jumping spiders

The modular visual system of jumping spiders (Salticidae) divides characteristics such as high spatial acuity and wide-field motion detection between different pairs of eyes. A large pair of telescope-like anterior-median (AM) eyes is supported by 2–3 pairs of ‘secondary’ eyes, which provide almost 360 degrees of visual coverage at lower resolution. The AM retinae are moveable and can be pointed at stimuli within their range of motion, but salticids have to turn to bring targets into this frontal zone in the first place. We describe how the front-facing pair of secondary eyes (anterior lateral, AL) mediates this through a series of whole-body ‘tracking saccades’ in response to computer-generated stimuli. We investigated the ‘response area’ of the AL eyes and show a clear correspondence between the physical margins of the retina and stimulus position at the onset of the first saccade. Saccade frequency is maximal at the margin of AL and AM fields of view. Furthermore, spiders markedly increase the velocity with which higher magnitude tracking saccades are carried out. This has the effect that the time during which vision is impaired due to motion blur is kept at an almost constant low level, even during saccades of large magnitude.

Journal of Comparative Physiology A

16522622

10.1007/S00360-012-0654-Y

Mitochondrial adaptations to utilize hydrogen sulfide for energy and signaling

Sulfur is a versatile molecule with oxidation states ranging from −2 to +6. From the beginning, sulfur has been inexorably entwined with the evolution of organisms. Reduced sulfur, prevalent in the prebiotic Earth and supplied from interstellar sources, was an integral component of early life as it could provide energy through oxidization, even in a weakly oxidizing environment, and it spontaneously reacted with iron to form iron–sulfur clusters that became the earliest biological catalysts and structural components of cells. The ability to cycle sulfur between reduced and oxidized states may have been key in the great endosymbiotic event that incorporated a sulfide-oxidizing α-protobacteria into a host sulfide-reducing Archea, resulting in the eukaryotic cell. As eukaryotes slowly adapted from a sulfidic and anoxic (euxinic) world to one that was highly oxidizing, numerous mechanisms developed to deal with increasing oxidants; namely, oxygen, and decreasing sulfide. Because there is rarely any reduced sulfur in the present-day environment, sulfur was historically ignored by biologists, except for an occasional report of sulfide toxicity. Twenty-five years ago, it became evident that the organisms in sulfide-rich environments could synthesize ATP from sulfide, 10 years later came the realization that animals might use sulfide as a signaling molecule, and only within the last 4 years did it become apparent that even mammals could derive energy from sulfide generated in the gastrointestinal tract. It has also become evident that, even in the present-day oxic environment, cells can exploit the redox chemistry of sulfide, most notably as a physiological transducer of oxygen availability. This review will examine how the legacy of sulfide metabolism has shaped natural selection and how some of these ancient biochemical pathways are still employed by modern-day eukaryotes.

Journal of Comparative Physiology B

12616412

10.1007/S00359-012-0718-1

Acoustic signal perception in a noisy habitat: lessons from synchronising insects

Acoustically communicating animals often have to cope with ambient noise that has the potential to interfere with the perception of conspecific signals. Here we use the synchronous display of mating signals in males of the tropical katydid Mecopoda elongata in order to assess the influence of nocturnal rainforest noise on signal perception. Loud background noise may disturb chorus synchrony either by masking the signals of males or by interaction of noisy events with the song oscillator. Phase-locked synchrony of males was studied under various signal-to-noise ratios (SNRs) using either native noise or the audio component of noise (<9 kHz). Synchronous entrainment was lost at a SNR of −3 dB when native noise was used, whereas with the audio component still 50 % of chirp periods matched the pacer period at a SNR of −7 dB. Since the chirp period of solo singing males remained almost unaffected by noise, our results suggest that masking interference limits chorus synchrony by rendering conspecific signals ambiguous. Further, entrainment with periodic artificial signals indicates that synchrony is achieved by ignoring heterospecific signals and attending to a conspecific signal period. Additionally, the encoding of conspecific chirps was studied in an auditory neuron under the same background noise regimes.

Journal of Comparative Physiology A

11234009

10.1007/S00360-012-0657-8

Osmoregulatory strategies in natural populations of the black-chinned tilapia Sarotherodon melanotheron exposed to extreme salinities in West African estuaries

The effect of salinity was studied in natural populations of the black-chinned tilapia (Sarotherodon melanotheron) from West Africa. This euryhaline species colonizes nearly all coastal environments from bays to lagoons characterized by salinities ranging from fresh water to hypersaline water over 100 ‰. Individuals were sampled during the dry season at several locations characterized by different levels of salinity (3–102 ‰). Their osmotic status and their gills were analyzed. The branchial mitochondria-rich cells (MRC), localized at the basis of the filaments and along the lamellae in fish taken from the saline stations, showed a wide plasticity with significant differences in their number and size. The most striking results were a significant larger area (≈3x) and a higher number (≈55x) of MRC at high salinity (102 ‰) compared to low salinity (3 ‰). The major ion transporters and channels were localized by immunocytochemistry and different expression patterns have been recorded between stations. Despite an increased Na+/K+-ATPase (NKA) α-subunit expression and NKA activity, pointing to an increased monovalent ion excretion, a severe osmotic imbalance was recorded in animals living in hypersaline environments.

Journal of Comparative Physiology B

2295427

10.1007/S00360-012-0656-9

Interpreting indices of physiological stress in free-living vertebrates

When vertebrate physiological ecologists use the terms ‘stress’ or ‘physiological stress’, they typically mean the level of hypothalamus–pituitary–adrenal (HPA-) axis activation. Measurements of stress hormone concentrations (e.g. glucocorticoids in blood, urine or faeces), leukocytes (e.g. the neutrophil–lymphocyte ratio or heterophil equivalent), immunofunction (e.g. innate, cell-mediated or humoral immunity measures) and regenerative anaemia (e.g. mean erythrocyte volume and red blood cell distribution width) have all been used to estimate HPA-axis activity in free-living vertebrates. Stress metrics have provided insights into aspects of autecology or population regulation that could not have been easily obtained using other indices of population wellbeing, such as body condition or relative abundance. However, short- and long-term stress (often problematically termed acute and chronic stress, respectively) can interact in unpredictable ways. When animals experience trapping and handling stress before blood, faeces and/or urine is sampled, the interaction of short- and long-term stress can confound interpretation of the data, a fact not always acknowledged in studies of stress in free-living vertebrates. This review examines how stress metrics can be confounded when estimates of HPA-axis activation are collected for free-living vertebrates and outlines some approaches that can be used to help circumvent the influence of potentially confounding factors.

Journal of Comparative Physiology B

9292821

10.1007/S00359-012-0716-3

Columnar cells necessary for motion responses of wide-field visual interneurons in Drosophila

Wide-field motion-sensitive neurons in the lobula plate (lobula plate tangential cells, LPTCs) of the fly have been studied for decades. However, it has never been conclusively shown which cells constitute their major presynaptic elements. LPTCs are supposed to be rendered directionally selective by integrating excitatory as well as inhibitory input from many local motion detectors. Based on their stratification in the different layers of the lobula plate, the columnar cells T4 and T5 are likely candidates to provide some of this input. To study their role in motion detection, we performed whole-cell recordings from LPTCs in Drosophila with T4 and T5 cells blocked using two different genetically encoded tools. In these flies, motion responses were abolished, while flicker responses largely remained. We thus demonstrate that T4 and T5 cells indeed represent those columnar cells that provide directionally selective motion information to LPTCs. Contrary to previous assumptions, flicker responses seem to be largely mediated by a third, independent pathway. This work thus represents a further step towards elucidating the complete motion detection circuitry of the fly.

Journal of Comparative Physiology A

7320203

10.1007/S00360-012-0655-X

Divergent strategies for adaptation to desiccation stress in two Drosophila species of immigrans group

Water balance mechanisms have been investigated in desert Drosophila species of the subgenus Drosophila from North America, but changes in mesic species of subgenus Drosophila from other continents have received lesser attention. We found divergent strategies for coping with desiccation stress in two species of immigrans group—D. immigrans and D. nasuta. In contrast to clinal variation for body melanization in D. immigrans, cuticular lipid mass showed a positive cline in D. nasuta across a latitudinal transect (10°46′–31°43′N). Based on isofemale lines variability, body melanization showed positive correlation with desiccation resistance in D. immigrans but not in D. nasuta. The use of organic solvents has supported water proofing role of cuticular lipids in D. nasuta but not in D. immigrans. A comparative analysis of water budget of these two species showed that higher water content, reduced rate of water loss and greater dehydration tolerance confer higher desiccation resistance in D. immigrans while the reduced rate of water loss is the only possible mechanism to enhance desiccation tolerance in D. nasuta. We found that carbohydrates act as metabolic fuel during desiccation stress in both the species, whereas their rates of utilization differ significantly between these two species. Further, acclimation to dehydration stress improved desiccation resistance due to increase in the level of carbohydrates in D. immigrans but not in D. nasuta. Thus, populations of D. immigrans and D. nasuta have evolved different water balance mechanisms under shared environmental conditions. Multiple measures of desiccation resistance in D. immigrans but reduction in water loss in D. nasuta are consistent with their different levels of adaptive responses to wet and dry conditions on the Indian subcontinent.

Journal of Comparative Physiology B

16020361

10.1007/S00359-012-0717-2

Calcium buffering and clearance in spider mechanosensory neurons

Spider VS-3 mechanoreceptor neurons have a low-voltage-activated Ca2+ current that raises intracellular calcium concentration [Ca2+] when they are depolarized by agonists of GABAA receptors or fire action potentials. The Ca2+ rise produces negative feedback by modulating the mechanoreceptor current and regulates Ca2+- and voltage-activated K+ currents. However, nothing is known about Ca2+ buffering in VS-3 neurons. Dynamic changes in VS-3 neuron intracellular [Ca2+] were measured using the fluorescent Ca2+ indicator Oregon Green BAPTA-1 (OG488) to understand Ca2+ buffering and clearance. Intracellular OG488 concentration increased slowly over more than 2 h as it diffused through a sharp intracellular microelectrode and spread through the cell. This slow increase was used to measure endogenous Ca2+ buffering and clearance by the added buffer technique, with OG488 acting as both added exogenous buffer and Ca2+ indicator. [Ca2+] was raised for brief periods by regular action potential firing, produced by pulsed electric current injection through the microelectrode. The resulting rise and fall of [Ca2+] were well fitted by the single compartment model of Ca2+ dynamics. With earlier ratiometric [Ca2+] estimates, these data gave an endogenous Ca2+ binding ratio of 684. Strong Ca2+ buffering may assist these neurons to deal with rapid changes in mechanical inputs.

Journal of Comparative Physiology A

17651967

10.1007/S00360-012-0653-Z

Cloning, tissue expression pattern and daily rhythms of Period1, Period2, and Clock transcripts in the flatfish Senegalese sole, Solea senegalensis

An extensive network of endogenous oscillators governs vertebrate circadian rhythmicity. At the molecular level, they are composed of a set of clock genes that participate in transcriptional–translational feedback loops to control their own expression and that of downstream output genes. These clocks are synchronized with the environment, although entrainment by external periodic cues remains little explored in fish. In this work, partial cDNA sequences of clock genes representing both positive (Clock) and negative (Period1, Period2) elements of the molecular feedback loops were obtained from the nocturnal flatfish Senegalese sole, a relevant species for aquaculture and chronobiology. All of the above genes exhibited high identities with their respective teleost clock genes, and Per–Arnt–Sim or basic helix–loop–helix binding domains were recognized in their primary structure. They showed a widespread distribution through the animal body and some of them displayed daily mRNA rhythms in central (retina, optic tectum, diencephalon, and cerebellum) and peripheral (liver) tissues. These rhythms were most robust in retina and liver, exhibiting marked Period1 and Clock daily oscillations in transcript levels as revealed by ANOVA and cosinor analysis. Interestingly, expression profiles were inverted in retina and optic tectum compared to liver. Such differences suggest the existence of tissue-dependent zeitgebers for clock gene expression in this species (i.e., light for retina and optic tectum and feeding time for liver). This study provides novel insight into the location of the molecular clocks (central vs. peripheral) and their different phasing and synchronization pathways, which contributes to better understand the teleost circadian systems and its plasticity.

Journal of Comparative Physiology B

16385689

10.1007/S00359-012-0715-4

Photic resetting of the circadian clock is correlated with photic habitat in Anolis lizards

Circadian rhythms are regulated by an internal clock, which is itself synchronized to environmental cues such as light and temperature. It is widely assumed that the circadian system is adapted to local cues, which vary enormously across habitats, yet the comparative data necessary for testing this idea are lacking. We examined photic and thermal resetting of the circadian clock in five species of Anolis lizards whose microhabitats differ in the amounts of sun and shade. The primary circadian oscillator in Anolis is the pineal gland, which produces the hormone melatonin. A flow-through culture system was employed to measure rhythmic melatonin output from individually cultured pineal glands. All species showed temperature-compensated circadian rhythms of pineal melatonin. Light caused significant phase delays of the melatonin rhythm, and this effect varied among species. Controlling for phylogenetic differences, the results indicate that the pineal glands of shade-dwelling species are more sensitive to photic resetting than species living in more brightly illuminated habitats. The differences were not due to variation in free-running period, but may be due to variation in oscillator phase and/or robustness. Surprisingly, thermal resetting was not statistically significant. Overall, the results suggest that the Anolis circadian system is adapted to photic habitat.

Journal of Comparative Physiology A

16730299

10.1007/S00360-012-0648-9

Low social status impairs hypoxia tolerance in rainbow trout (Oncorhynchus mykiss)

In the present study, chronic behavioural stress resulting from low social status affected the physiological responses of rainbow trout (Oncorhynchus mykiss) to a subsequent acute stressor, exposure to hypoxia. Rainbow trout were confined in fork-length matched pairs for 48–72 h, and social rank was assigned based on behaviour. Dominant and subordinate fish were then exposed individually to graded hypoxia (final water PO2, PwO2 = 40 Torr). Catecholamine mobilization profiles differed between dominant and subordinate fish. Whereas dominant fish exhibited generally low circulating catecholamine levels until a distinct threshold for release was reached (PwO2 = 51.5 Torr corresponding to arterial PO2, PaO2 = 24.1 Torr), plasma catecholamine concentrations in subordinate fish were more variable and identification of a distinct threshold for release was problematic. Among fish that mobilized catecholamines (i.e. circulating catecholamines rose above the 95% confidence interval around the baseline value), however, the circulating levels achieved in subordinate fish were significantly higher (459.9 ± 142.2 nmol L−1, mean ± SEM, N = 12) than those in dominant fish (130.9 ± 37.9 nmol L−1, N = 12). The differences in catecholamine mobilization occurred despite similar P50 values in dominant (22.0 ± 1.5 Torr, N = 6) and subordinate (22.1 ± 2.2 Torr, N = 8) fish, and higher PaO2 values in subordinate fish under severely hypoxic conditions (i.e. PwO2 < 60 Torr). The higher PaO2 values of subordinate fish likely reflected the greater ventilatory rates and amplitudes exhibited by these fish during severe hypoxia. At the most severe level of hypoxia, subordinate fish were unable to defend arterial blood O2 content, which fell to approximately half (0.60 ± 0.13 mL O2 g−1 haemoglobin, N = 9) that of dominant fish (1.08 ± 0.09 mL O2 g−1 haemoglobin, N = 9). Collectively, these data indicate that chronic social stress impacts the ability of trout to respond to the additional, acute stress of hypoxia.

Journal of Comparative Physiology B

16085751

10.1007/S00360-012-0647-X

Seasonal changes in thermogenesis of a free-ranging afrotherian small mammal, the Western rock elephant shrew (Elephantulus rupestris)

We report on the seasonal metabolic adjustments of a small-sized member of the phylogenetically ancient Afrotheria, the Western rock elephant shrew (Elephantulus rupestris). We recorded body temperature (Tb) patterns and compared the capacity for adrenergically induced nonshivering thermogenesis (NST) in E. rupestris captured in the wild in summer and winter. Noradrenaline (NA) treatment (0.4–0.5 mg/kg, s.c.) induced a pronounced elevation in oxygen consumption compared to controls (saline), and the increase in oxygen consumption following injection of NA was 1.8-fold higher in winter compared to summer. This suggests that the smaller members of Afrotheria possess functional brown adipose tissue, which changes in thermogenic capacity depending on the season. Torpor was recorded in both seasons, but in winter the incidence of torpor was higher (n = 205 out of 448 observations) and minimal Tb during torpor was lower (Tbmin: 11.9°C) than in summer (n = 24 out of 674 observations; Tbmin: 26°C). In addition to cold, high air humidity emerged as a likely predictor for torpor entry. Overall, E. rupestris showed a high degree of thermoregulatory plasticity, which was mainly reflected in a variable timing of torpor entry and arousal. We conclude that E. rupestris exhibits seasonal metabolic adjustments comparable to what has been long known for many Holarctic rodents.

Journal of Comparative Physiology B

8294329

10.1007/S00360-012-0651-1

Peripheral circadian rhythms and their regulatory mechanism in insects and some other arthropods: a review

Many physiological functions of insects show a rhythmic change to adapt to daily environmental cycles. These rhythms are controlled by a multi-clock system. A principal clock located in the brain usually organizes the overall behavioral rhythms, so that it is called the “central clock”. However, the rhythms observed in a variety of peripheral tissues are often driven by clocks that reside in those tissues. Such autonomous rhythms can be found in sensory organs, digestive and reproductive systems. Using Drosophila melanogaster as a model organism, researchers have revealed that the peripheral clocks are self-sustained oscillators with a molecular machinery slightly different from that of the central clock. However, individual clocks normally run in harmony with each other to keep a coordinated temporal structure within an animal. How can this be achieved? What is the molecular mechanism underlying the oscillation? Also how are the peripheral clocks entrained by light–dark cycles? There are still many questions remaining in this research field. In the last several years, molecular techniques have become available in non-model insects so that the molecular oscillatory mechanisms are comparatively investigated among different insects, which give us more hints to understand the essential regulatory mechanism of the multi-oscillatory system across insects and other arthropods. Here we review current knowledge on arthropod’s peripheral clocks and discuss their physiological roles and molecular mechanisms.

Journal of Comparative Physiology B

17362233

10.1007/S00360-012-0649-8

Physiological constraints and the influence of diet on fatty acids in the yolk of gentoo penguins, Pygoscelis papua

Avian yolk fatty acids (FA) composition is influenced by two main factors: maternal diet and genetic factors that regulate FA metabolism. However, due to embryonic developmental requirements, yolk FA are thought to be physiologically constrained and less useful for dietary and trophic studies. We assessed the relative contributions of diet and physiological constraints in determining the yolk FA composition of a marine bird, the gentoo penguin (Pygoscelis papua) by comparing FA signatures of yolks and prey between a captive, controlled- feeding experiment and a wild population. Captive and wild yolk FA signatures differed even though both groups’ yolk lipids were composed primarily of three FA (16:0, 18:0 and 18:1n-9). Differences were due to FA occurring in relatively low abundance, but which mirrored differences in the FA composition of diets. However, yolk FA signatures were correlated across three penguin species suggesting that common developmental constraints can be relatively more important than species-specific differences in diet or egg-laying physiology. While yolk FA are constrained, several minor components of yolk FA are reflective of diets and the calibration coefficients resulting from this study have the potential to be incorporated into predictive models and allow for quantitative dietary and trophic studies using FA analysis of penguin egg yolks.

Journal of Comparative Physiology B

499244

10.1007/S00360-012-0652-0

Coping with physiological oxidative stress: a review of antioxidant strategies in seals

While diving, seals are exposed to apnea-induced hypoxemia and repetitive cycles of ischemia/reperfusion. While on land, seals experience sleep apnea, as well as prolonged periods of food and water deprivation. Prolonged fasting, sleep apnea, hypoxemia and ischemia/reperfusion increase oxidant production and oxidative stress in terrestrial mammals. In seals, however, neither prolonged fasting nor apnea-induced hypoxemia or ischemia/reperfusion increase systemic or local oxidative damage. The strategies seals evolved to cope with increased oxidant production are reviewed in the present manuscript. Among these strategies, high antioxidant capacity and the oxidant-mediated activation of hormetic responses against hypoxia and oxidative stress are discussed. In addition to expanding our knowledge of the evolution of antioxidant defenses and adaptive responses to oxidative stress, understanding the mechanisms that naturally allow mammals to avoid oxidative damage has the potential to advance our knowledge of oxidative stress-induced pathologies and to enhance the translative value of biomedical therapies in the long term.

Journal of Comparative Physiology B

9677564

10.1007/S00360-012-0650-2

Rainbow trout (Oncorhynchus mykiss) shift the age composition of circulating red blood cells towards a younger cohort when exposed to thermal stress

Freshwater fish, such as the rainbow trout, are commonly exposed to temperature fluctuations in their aquatic environment. Exposure to increased temperatures places fish under respiratory stress and increases the likelihood of protein misfolding and degradation that could eventually lead to cell death. Previously, we showed that genes associated with the cellular stress response, apoptosis and hematopoiesis are upregulated in the red blood cells (RBCs) of rainbow trout post-thermal stress, leading to the hypothesis that a tightly regulated interaction between cell repair and cell death is occurring after heat stress. To test this hypothesis, we tracked changes in age class composition and markers of apoptosis in circulating RBCs within individual trout during exposure to and recovery from acute thermal stress. RBCs did not show any indication of apoptosis or necrosis following acute heat stress; however, we observed significant increases in numbers of early, juvenile and dividing RBCs. We also observed a shift in the composition of the circulating RBCs towards a younger cohort following heat shock through release of stored cells from the spleen and an increase in the maturation rate of early RBCs. These results suggest that the genes activated by increased temperature provided sufficient protection against thermal stress in the RBC, subsequently preventing the triggering of the cell death cascade.

Journal of Comparative Physiology B

17145335

10.1007/S00359-012-0714-5

Discrimination of inclined path segments by the desert ant Cataglyphis fortis

Desert ants (Cataglyphis fortis) navigate by means of path integration, and perform accurately even in undulating terrain. They are able to correctly calculate the ground distance between nest and feeder even if their foraging excursion leads them over corrugated surfaces. To compute the respective ground projection when walking over an inclined surface, ants must measure its slope with sufficient accuracy—but how they do so is still not understood. Using a new behavioural assay that included a negative reinforcement, we investigated how well different slopes are discriminated by the ants. Ants were trained to visit an elevated feeder, via a ramp of fixed inclination (five training inclinations were used: 0°, 15°, 30°, 45°, 60°). The ants discriminated a steeper test slope that differed from the training slope by 12.5°. This discrimination performance was found to be constant for training slopes between 0° and 45°. Ants trained on a 60° slope, however, did not discriminate all steeper slopes, up to a vertical ascent, from the 60° inclination. The consequences of this discrimination accuracy for errors in the path integration process are discussed.

Journal of Comparative Physiology A

18995360

10.1007/S00359-012-0713-6

Effects of castration on aggression and levels of serum sex hormones and their central receptors in mandarin voles (Microtus mandarinus)

Aggression in socially monogamous mandarin vole (Microtus mandarinus) was observed after castration. Levels of serum sex hormones and their central receptors were also measured using enzyme-linked immunosorbent assay and immunohistochemistry methods. The data indicate that adult males showed higher levels of aggression after castration. However, castration significantly reduced levels of serum testosterone, and the number of androgen receptor immunoreactive neurons in the anterior hypothalamus, bed nucleus of the stria terminalis, medial amygdaloid nucleus (P < 0.01) and lateral septal nucleus (P < 0.05). In addition, levels of estrogen receptor β in the anterior hypothalamus and medial amygdaloid nucleus (P < 0.05), bed nucleus of the stria terminalis and lateral septal nucleus (P < 0.01) declined to varying degrees at weekly intervals. In contrast, serum 17β-estradiol concentrations were up-regulated by castration and castration did not change levels of estrogen receptor α in the medial amygdaloid nucleus and lateral septal nucleus, but increased it in the anterior hypothalamus 3 weeks after castration (P < 0.05). We suggest that higher levels of aggression induced by castration may be independent of serum testosterone and androgen receptors, and may be associated with high serum 17β-estradiol concentrations, stable estrogen receptor α immunoreactive neurons in some brain regions and the relative ratio of the two estrogen receptors.

Journal of Comparative Physiology A

6352324

10.1007/S00359-012-0711-8

Vibration detection and discrimination in the masked birch caterpillar (Drepana arcuata)

Leaf-borne vibrations are potentially important to caterpillars for communication and risk assessment. Yet, little is known about the vibratory environment of caterpillars, or how they detect and discriminate between vibrations from relevant and non-relevant sources. We measured the vibratory ‘landscape’ of the territorial masked birch caterpillar Drepana arcuata (Drepanidae), and assessed its ability to detect and respond to vibrations generated by conspecific and predatory intruders, wind and rain. Residents of leaf shelters were shown to respond to low amplitude vibrations generated by a crawling conspecific intruder, since removal of the vibrations through leaf incision prevented the resident’s response. Residents did not respond to large amplitude, low frequency disturbances caused by wind and rain alone, but did respond to approaching conspecifics under windy conditions, indicating an ability to discriminate between these sources. Residents also responded differently in the presence of vibrations generated by approaching predators (Podisus) and conspecifics. An analysis of vibration characteristics suggests that despite significant overlap between vibrations from different sources, there are differences in frequency and amplitude characteristics that caterpillars may use to discriminate between sources. Caterpillars live in a vibration-rich environment that we argue forms a prominent part of the sensory world of substrate bound holometabolous larvae.

Journal of Comparative Physiology A

5685157

10.1007/S00359-012-0712-7

Individual recognition during bouts of antiphonal calling in common marmosets

Many vocalizations are encoded with a diversity of acoustic information about the signal producer. Amongst this information content are social categories related to the identity of the caller that are important for determining if and how a signal receiver may interact with that individual. Here, we employed a novel playback method in common marmosets (Callithrix jacchus) to test individual recognition during bouts of antiphonal calling. These experiments utilized custom, interactive playback software that effectively engaged subjects in antiphonal calling using vocalizations produced by a single individual and presented ‘probe’ vocalization stimuli representing a different individual at specific points within bouts of calling. The aim here was to test whether marmosets would recognize that the probe stimulus was a phee call produced by a different individual. Data indicated that marmosets were able to detect the change in caller identity; subjects produced significantly fewer antiphonal call responses to probe than control stimuli and, in some conditions, exhibited a shorter latency to produce the vocal response. These data suggest that marmosets recognize the identity of the individual during bouts of antiphonal calling. Furthermore, these results provide a methodological foundation for implementing the probe playback procedure to examine a broader range of social categorization during vocal interactions.

Journal of Comparative Physiology A

16341262

10.1007/S00360-012-0646-Y

Do Acartia tonsa (Dana) eggs regulate their volume and osmolality as salinity changes?

Subitaneous eggs from an euryhaline calanoid copepod Acartia tonsa were challenged by changes in salinity within the range from full strength salinity, down to zero and up to >70 psu. Egg volume changed immediately, increasing from 2.8 × 105 μm3 at full strength salinity (35 psu) to 3.8 × 105 μm3 at 0 psu and back to its initial volume when gradually being returned to full strength salinity. Egg osmolality followed the molality of the surrounding water when challenged within a salinity range from 2 to 50 psu. Egg respiration was not affected when eggs kept at 35 psu was exposed to low salinity (2 psu). These results suggest that eggs are unable to regulate their volume or osmolality when challenged with changes in salinity. Gradual changes in salinity from 35 to 2 psu and back did not harm the eggs (embryos), since the hatching success remained unaffected by such changes in salinity. In contrast, extreme hyper-saline conditions (76 psu) made the eggs implode and killed the embryo. We propose that the embryo is protected from salinity stress by its plasma membrane and that water exchange driven by osmosis is restricted to the perivitelline space of the egg, which acts as a perfect osmometer in the salinity range of 5–35 psu. We hypothesize further that the embryo is able to keep its volume and osmolality constant due to the impermeability of the inner plasma membrane of the egg or by a combination of osmoregulation and reduced permeability of the inner plasma membrane.

Journal of Comparative Physiology B

18846348

10.1007/S00359-011-0706-X

Realignment of signal processing within a sensory brainstem nucleus as brain temperature declines in the Syrian hamster, a hibernating species

Crucial for survival, the central nervous system must reliably process sensory information over all stages of a hibernation bout to ensure homeostatic regulation is maintained and well-matched to dramatically altered behavioral states. Comparing neural responses in the nucleus tractus solitarius of rats and euthermic Syrian hamsters, we tested the hypothesis that hamster neurons have adaptations sustaining signal processing while conserving energy. Using patch-clamp techniques, we classified second-order neurons in the nucleus as rapid-onset or delayed-onset spiking phenotypes based on their spiking onset to a depolarizing pulse (following a −80 mV prepulse). As temperature decreased from 33 to 15°C, the excitability of all neurons decreased. However, hamster rapid-onset spiking neurons had the highest spiking response and shortest action potential width at every temperature, while hamster delayed-onset spiking neurons had the most negative resting membrane potential. The frequency of spontaneous excitatory postsynaptic currents in both phenotypes decreased as temperature decreased, yet the amplitudes of tractus solitarius stimulation-evoked currents were greater in hamsters than in rats regardless of phenotype and temperature. Changes were significant (P < 0.05), supporting our hypothesis by showing that, as temperature falls, rapid-onset neurons contribute more to signal processing but less to energy conservation than do delayed-onset neurons.

Journal of Comparative Physiology A

2451352

10.1007/S00359-012-0710-9

The pheromones of laying workers in two honeybee sister species: Apis cerana and Apis mellifera

When a honeybee colony loses its queen, workers activate their ovaries and begin to lay eggs. This is accompanied by a shift in their pheromonal bouquet, which becomes more queen like. Workers of the Asian hive bee Apis cerana show unusually high levels of ovary activation and this can be interpreted as evidence for a recent evolutionary arms race between queens and workers over worker reproduction in this species. To further explore this, we compared the rate of pheromonal bouquet change between two honeybee sister species of Apis cerana and Apis mellifera under queenright and queenless conditions. We show that in both species, the pheromonal components HOB, 9-ODA, HVA, 9-HDA, 10-HDAA and 10-HDA have significantly higher amounts in laying workers than in non-laying workers. In the queenright colonies of A. mellifera and A. cerana, the ratios (9-ODA)/(9-ODA + 9-HDA + 10-HDAA + 10-HDA) are not significantly different between the two species, but in queenless A. cerana colonies the ratio is significant higher than in A. mellifera, suggesting that in A. cerana, the workers’ pheromonal bouquet is dominated by the queen compound, 9-ODA. The amount of 9-ODA in laying A. cerana workers increased by over 585% compared with the non-laying workers, that is 6.75 times higher than in A. mellifera where laying workers only had 86% more 9-ODA compared with non-laying workers.

Journal of Comparative Physiology A

4681459

10.1007/S00360-012-0645-Z

Diversity and function of the avian gut microbiota

The intestinal microbiota have now been shown to largely affect host health through various functional roles in terms of nutrition, immunity, and other physiological systems. However, the majority of these studies have been carried out in mammalian hosts, which differ in their physiological traits from other taxa. For example, birds possess several unique life history traits, such as hatching from eggs, which may alter the interactions with and transmission of intestinal microbes compared to most mammals. This review covers the diversity of microbial taxa hosted by birds. It also discusses how avian microbial communities strongly influence nutrition, immune function, and processing of toxins in avian hosts, in manners similar to and different from mammalian systems. Finally, areas demanding further research are identified, along with descriptions of existing techniques that could be employed to answer these questions.

Journal of Comparative Physiology B

14206217

10.1007/S00359-012-0709-2

Grasshopper calling songs convey information about condition and health of males

Females of the grasshopper Chorthippus biguttulus invest much more in the offspring than do males. As a consequence, females are the more selective sex and exert a sexual selection on males by responding to the songs of certain conspecific males while rejecting others. What kind of information about the sender may a female obtain from a male’s song, in addition to its species identity? We searched for correlations between a series of song features and morphometric parameters of individual males. In addition, also the immunocompetence of males was assessed by implanting small pieces of nylon thread. We found significant, positive correlations between certain song characteristics and indicators of male size and immunocompetence. Thus, grasshopper females may—in principle—be able to judge a male’s condition and health from the acoustic signals he produces.

Journal of Comparative Physiology A

15430108

10.1007/S00360-011-0641-8

Divergence of larval resource acquisition for water conservation and starvation resistance in Drosophila melanogaster

Laboratory selection experiments have evidenced storage of energy metabolites in adult flies of desiccation and starvation resistant strains of D. melanogaster but resource acquisition during larval stages has received lesser attention. For wild populations of D. melanogaster, it is not clear whether larvae acquire similar or different energy metabolites for desiccation and starvation resistance. We tested the hypothesis whether larval acquisition of energy metabolites is consistent with divergence of desiccation and starvation resistance in darker and lighter isofemale lines of D. melanogaster. Our results are interesting in several respects. First, we found contrasting patterns of larval resource acquisition, i.e., accumulation of higher carbohydrates during 3rd instar larval stage of darker flies versus higher levels of triglycerides in 1st and 2nd larval instars of lighter flies. Second, 3rd instar larvae of darker flies showed ~40 h longer duration of development at 21°C; and greater accumulation of carbohydrates (trehalose and glycogen) in fed larvae as compared with larvae non-fed after 150 h of egg laying. Third, darker isofemale lines have shown significant increase in total water content (18%); hemolymph (86%) and dehydration tolerance (11%) as compared to lighter isofemale lines. Loss of hemolymph water under desiccation stress until death was significantly higher in darker as compared to lighter isofemale lines but tissue water loss was similar. Fourth, for larvae of darker flies, about 65% energy content is contributed by carbohydrates for conferring greater desiccation resistance while the larvae of lighter flies acquire 2/3 energy from lipids for sustaining starvation resistance; and such energy differences persist in the newly eclosed flies. Thus, larval stages of wild-caught darker and lighter flies have evolved independent physiological processes for the accumulation of energy metabolites to cope with desiccation or starvation stress.

Journal of Comparative Physiology B

18624451

10.1007/S00360-011-0638-3

Carotenoid supplementation and GnRH challenges influence female endocrine physiology, immune function, and egg-yolk characteristics in Japanese quail (Coturnix japonica)

Androgens and carotenoids circulating in plasma affect the physiology and behavior of vertebrates. Much is known about control mechanisms and functions of each of these substances, yet their interactive effects are not well understood. Here we examine possible additive, multiplicative, and interactive effects of testosterone and carotenoids on female endocrine physiology, immunocompetence, and investment in eggs by simultaneously manipulating levels of testosterone [via gonadotropin releasing hormone (GnRH) challenges] and carotenoids (via diet supplementation) in captive female Japanese quail (Coturnix japonica). Females were randomly assigned to one of four treatments: carotenoid supplementation, GnRH challenge, GnRH challenge + carotenoid supplementation, or control. Carotenoid supplementation significantly increased circulating plasma carotenoid levels and acquired immune system performance, but not innate immunity. GnRH challenges elevated circulating testosterone and carotenoid levels, and induced immunosuppression in females. However, females in the GnRH challenge + carotenoid supplementation treatment had higher cell-mediated immune responses than control females and similar responses to those of carotenoid-supplemented females. Hence, availability of carotenoids in female quail seemed to counteract immunosuppressive effects of GnRH challenges. Our results provide further evidence for synergistic effects of carotenoids and testosterone on endocrine physiology and immune function in female birds. Elevated plasma testosterone or carotenoids levels resulted in increased deposition of those compounds to eggs, respectively. Furthermore, because we found that concentrations of testosterone and carotenoids in yolks were correlated within each treatment group, differential deposition of hormones and carotenoids in eggs may not only respond to surrounding social and environmental conditions, but also to other components of the egg.

Journal of Comparative Physiology B