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12689364

10.1007/S00359-014-0977-0

Clutter and conspecifics: a comparison of their influence on echolocation and flight behaviour in Daubenton’s bat, Myotis daubentonii

We compared the influence of conspecifics and clutter on echolocation and flight speed in the bat Myotis daubentonii. In a large room, actual pairs of bats exhibited greater disparity in peak frequency (PF), minimum frequency (FMIN) and call period compared to virtual pairs of bats, each flying alone. Greater inter-individual disparity in PF and FMIN may reduce acoustic interference and/or increase signal self-recognition in the presence of conspecifics. Bats flying alone in a smaller flight room, to simulate a more cluttered habitat as compared to the large flight room, produced calls of shorter duration and call period, lower intensity, and flew at lower speeds. In cluttered space, shorter call duration should reduce masking, while shorter call period equals more updates to the bat’s auditory scene. Lower intensity likely reflects reduced range detection requirements, reduced speed the demands of flying in clutter. Our results show that some changes (e.g. PF separation) are associated with conspecifics, others with closed habitat (e.g. reduced call intensity). However, we demonstrate that call duration, period, and flight speed appear similarly influenced by conspecifics and clutter. We suggest that some changes reduce conspecific interference and/or improve self-recognition, while others demonstrate that bats experience each other like clutter.

Journal of Comparative Physiology A

458497

10.1007/S00359-014-0975-2

How can motor systems retain performance over a wide temperature range? Lessons from the crustacean stomatogastric nervous system

Abstract Marine invertebrates, such as lobsters and crabs, deal with a widely and wildly fluctuating temperature environment. Here, we describe the effects of changing temperature on the motor patterns generated by the stomatogastric nervous system of the crab, Cancer borealis. Over a broad range of “permissive” temperatures, the pyloric rhythm increases in frequency but maintains its characteristic phase relationships. Nonetheless, at more extreme high temperatures, the normal triphasic pyloric rhythm breaks down, or “crashes”. We present both experimental and computational approaches to understanding the stability of both single neurons and networks to temperature perturbations, and discuss data that shows that the “crash” temperatures themselves may be environmentally regulated. These approaches provide insight into how the nervous system can be stable to a global perturbation, such as temperature, in spite of the fact that all biological processes are temperature dependent.

Journal of Comparative Physiology A

16760483

10.1007/S00360-014-0881-5

Cardiovascular function in large to small hibernators: bears to ground squirrels

Mammalian hibernation has intrigued scientists due to extreme variations in normal seasonal physiological homeostasis. Numerous species manifest a hibernation phenotype although the characteristics of the hypometabolic state can be quite different. Ground squirrels (e.g., Sciuridae) are often considered the prototypical hibernator as individuals in this genus transition from an active, euthermic state (37 °C) to a nonresponsive hibernating state where torpid body temperature commonly falls to 3–5 °C. However, the hibernating state is not continuous as periodic warming and arousals occur. In contrast, the larger hibernators of genus Ursus are less hypothermic (body temperatures decline from approximately 37°–33 °C), are more reactive, and cyclical arousals do not occur. Both species dramatically reduce cardiac output during hibernation from the active state (bears ~75 % reduction in bears and ~97 % reduction in ground squirrels), and both species demonstrate hypokinetic atrial chamber activity. However, there are several important differences in cardiac function between the two groups during hibernation. Left ventricular diastolic filling volumes and stroke volumes do not differ in bears between seasons, but increased diastolic and stroke volumes during hibernation are important contributors to cardiac output in ground squirrels. Decreased cardiac muscle mass and increased ventricular stiffness have been found in bears, whereas ground squirrels have increased cardiac muscle mass and decreased ventricular stiffness during hibernation. Molecular pathways of cardiac muscle plasticity reveal differences between the species in the modification of sarcomeric proteins such as titin and α myosin heavy chain during hibernation. The differences in hibernation character are likely to account for the alternative cardiac phenotypes and functional strategies manifested by the two species. Molecular investigation coupled with better knowledge of seasonal physiological alterations is dramatically advancing our understanding of small and large hibernators and their evolutionary differences.

Journal of Comparative Physiology B

10654242

10.1007/S00359-014-0973-4

Eight-choice sound localization by manatees: performance abilities and head related transfer functions

Two experiments investigated the ability and means by which two male Florida manatees (Trichechus manatus latirostris) may determine the direction of a sound source. An eight-choice discrimination paradigm was used to determine the subjects’ sound localization abilities of five signal conditions covering a range of frequencies, durations, and levels. Subjects performed above the 12.5 % chance level for all broadband frequencies and were able to localize sounds over a large level range. Errors were typically located to either side of the signal source location when presented in the front 180° but were more dispersed when presented from locations behind the subject. Front-to-back confusions were few and accuracy was greater when signals originated from the front 180°. Head-related transfer functions were measured to determine if frequencies were filtered by the manatee body to create frequency-specific interaural level differences (ILDs). ILDs were found for all frequencies as a function of source location, although they were largest with frequencies above 18 kHz and when signals originated to either side of the subjects. Larger ILDs were found when the signals originated behind the subjects. A shadowing-effect produced by the body may explain the relatively low occurrence of front-back confusions in the localization study.

Journal of Comparative Physiology A

2784884

10.1007/S00360-014-0883-3

Using biochemical markers to assess the effects of imposed temperature stress on freshwater decapod crustaceans: Cherax quadricarinatus as a test case

The effects of thermal stress can impact negatively on the abundance and distribution of temperature-sensitive species, particularly freshwater crustaceans. This study investigated the effects of thermal stress on physiological and biochemical parameters at five treatment temperatures resulting in minimal (25 °C), moderate (27, 29 °C) or severe (31, 33 °C) thermal stress in the common tropical freshwater crayfish Cherax quadricarinatus. The aim was to develop a suite of stress-sensitive assays to use on threatened populations of freshwater crustaceans, particularly those restricted to cooler temperatures and only found in high altitude refugia. Significant increases in indicators of oxidative and metabolic stress were observed at 29 °C and were elevated further at 33 °C. After a 50-day acclimation to an imposed temperature stress, significant changes in the level of total glutathione, total lipids, muscular protein, total haemocyte count, lipid peroxidation and protein carbonyls were observed between treatments while superoxide dismutase activity and haemolymph protein concentrations did not change. The data provided proof of concept that measuring key biochemical responses to high temperature can provide a means of contrasting the level of thermal stress experienced between individuals of the same species adapted to different temperatures. The methods developed are expected to be of use in research on wild populations of other freshwater poikilothermic organisms, particularly those susceptible to increased environmental temperatures associated with climate change.

Journal of Comparative Physiology B

400096

10.1007/S00360-014-0879-Z

Gut transport characteristics in herbivorous and carnivorous serrasalmid fish from ion-poor Rio Negro water

Three closely related characids, Tambaqui (omnivore), black Piranha (carnivore), and Pacu (herbivore), all Serrasalmidae, inhabit the ion-poor, acidic Rio Negro. We compared O2-consumption and N excretion rates in vivo, and sodium, chloride, glucose, and ammonia transport characteristics of gut sac preparations in vitro. The Pacu had a significantly higher weight-specific oxygen consumption, and a lower N/Q ratio than the omnivorous Tambaqui, and a significantly lower urea-N excretion rate than the carnivorous black Piranha, suggesting N-limitation in the herbivorous Pacu. With a value of 2.62 ± 0.15, gut to fork length ratio in the Pacu was about 2.5 times higher than in the black Piranha, and 2.0 times higher than in the Tambaqui. Anterior intestinal activities of three enzymes involved in N-fixation for amino acid synthesis (glutamate dehydrogenase, glutamate–oxaloacetate transferase, and glutamate–pyruvate transferase) were generally greatest in the carnivore and lowest in the herbivore species. In all three species, sodium, chloride, glucose, and ammonia were taken up at high rates from the intestine, resulting in an isosmotic fluid flux. Comparing the area-specific fluid flux of the anterior, mid, and posterior gut sections, no difference was detected between the three sections of the Pacu, while in the Tambaqui, it was highest in the anterior section, and in the black Piranha highest in the middle section. Overall, the area-specific uptake rates for sodium, chloride, glucose, and ammonia of anterior, mid, and posterior sections were similar in all three species, indicating that there is no difference in the area-specific transport rates associated with trophic position. The net ammonia uptake flux from gut interior was not significantly different from the net ammonia efflux to the serosal fluid, so that the ammonia removed from the intestine by the mucosal epithelium was quantitatively transferred through the tissue to the serosal side in all three species. Thus, metabolic activity of gut tissue did not significantly influence the net ammonia transfer. Due to the much higher gut to fork length ratio, the overall transport capacity of the gut of the herbivorous Pacu by far exceeded the transport capacity of their carnivorous and omnivorous relatives, thus compensating for the lower digestibility and the low Na+, Cl−, and N-content of the plant diet. Accordingly, in order to cope with the more difficult digestible plant material and the very low nitrogen content of plants, herbivorous fish have not evolved more effective area-specific transport capacities, but rather have increased the length of the gut.

Journal of Comparative Physiology B

16933917

10.1007/S00360-014-0882-4

Spontaneous daily torpor and fasting-induced torpor in Djungarian hamsters are characterized by distinct patterns of metabolic rate

The Djungarian hamster is a rodent species that expresses both spontaneous daily torpor (SDT) when acclimated to winter conditions as well as fasting-induced torpor (FIT) during summer. In an earlier report we argued that these two thermoregulatory phenomena differ in several parameters. In the present study, we further complete this comparison by showing that metabolic rate patterns differ between both SDT and FIT. SDT bouts were significantly longer and deeper compared to FIT bouts. Additionally, respiratory quotient measures support the view that SDT is entered from a state of energetic balance while FIT appears to be an emergency shutdown of energy demanding thermogenesis due to a shortage of energy sources. In a second experiment, we also confirm that brief periods of food restriction during the hamsters’ torpor season increase the frequency of SDT, but do not affect its depth or duration. Although winter-acclimated animals could flexibly alter torpor frequency in order to stay in energetic balance, we also found evidence for torpor expression patterns that resembled FIT, rather than SDT. Consequently, if energetic challenges cannot be compensated with increased SDT expression any longer, the hamsters seem to be driven in a negative energy balance resulting in FIT as a last resort.

Journal of Comparative Physiology B

13303111

10.1007/S00360-014-0874-4

Oxygen-dependent heat tolerance and developmental plasticity in turtle embryos

Oxygen and temperature have previously been treated as different environmental stresses and studied separately in most cases. Although the oxygen–temperature interaction may provide new insight into proximate and evolutionary constraints on embryonic development and offspring fitness, it has rarely been studied in oviparous amniotes. We used a two-factor experiment [three oxygen concentrations (12, 22 and 30 %) × two temperatures (26.5 and 34 °C)] to identify the effect of the oxygen–temperature interaction on embryonic development and hatchling traits in the Chinese soft-shelled turtle, Pelodiscus sinensis. When eggs were incubated at the critically high temperature, hatching success of turtle eggs was enhanced by hyperoxia but reduced by hypoxia; this result was not observed in eggs incubated at the benign temperature. Hypoxia retarded embryonic development, and reduced body size, locomotor performance and survival rate of hatchings at the critically high temperature. However, the effects of hypoxia were greatly reduced at the benign temperature. Our study demonstrates that oxygen and temperature interact to affect not only the heat tolerance and developmental rate of embryos but also the fitness-related traits of hatchlings, suggesting that interactions among environmental factors impose significant ecological constraints on embryonic development in oviparous amniotes.

Journal of Comparative Physiology B

13680779

10.1007/S00359-014-0976-1

Biomechanics of hearing in katydids

Animals have evolved a vast diversity of mechanisms to detect sounds. Auditory organs are thus used to detect intraspecific communicative signals and environmental sounds relevant to survival. To hear, terrestrial animals must convert the acoustic energy contained in the airborne sound pressure waves into neural signals. In mammals, spectral quality is assessed by the decomposition of incoming sound waves into elementary frequency components using a sophisticated cochlear system. Some insects like katydids (or bushcrickets) have evolved biophysical mechanisms for auditory processing that are remarkably equivalent to those of mammals. Located on their front legs, katydid ears are small, yet are capable of performing several of the tasks usually associated with mammalian hearing. These tasks include air-to-liquid impedance conversion, signal amplification, and frequency analysis. Impedance conversion is achieved by a lever system, a mechanism functionally analogous to the mammalian middle ear ossicles, yet morphologically distinct. In katydids, the exact mechanisms supporting frequency analysis seem diverse, yet are seen to result in dispersive wave propagation phenomenologically similar to that of cochlear systems. Phylogenetically unrelated katydids and tetrapods have evolved remarkably different structural solutions to common biophysical problems. Here, we discuss the biophysics of hearing in katydids and the variations observed across different species.

Journal of Comparative Physiology A

17566456

10.1007/S00360-014-0877-1

The evolution of nitric oxide signalling in vertebrate blood vessels

Nitric oxide is one of the most important signalling molecules involved in the regulation of physiological function. It first came to prominence when it was discovered that the vascular endothelium of mammals synthesises and releases nitric oxide (NO) to mediate a potent vasodilation. Subsequently, it was shown that NO is synthesised in the endothelium by a specific isoform of nitric oxide synthase (NOS) called NOS3. Following this discovery, it was assumed that an endothelial NO/NOS3 system would be present in all vertebrate blood vessels. This review will discuss the latest genomic, anatomical and physiological evidence which demonstrates that an endothelial NO/NOS3 signalling is not ubiquitous in non-mammalian vertebrates, and that there have been key evolutionary steps that have led to the endothelial NO signalling system being a regulatory system found only in reptiles, birds and mammals. Furthermore, the emerging role of nitrite as an endocrine source of NO for vascular regulation is discussed.

Journal of Comparative Physiology B

15312848

10.1007/S00360-014-0880-6

Activity, abundance and expression of Ca2+-activated proteases in skeletal muscle of the aestivating frog, Cyclorana alboguttata

In most mammals, prolonged muscle disuse (e.g. bed-rest, limb casting or spaceflight) results in atrophy of muscle fibres which is largely due to unregulated proteolysis. Although numerous proteolytic pathways are known to participate in muscle disuse atrophy, recent evidence suggests that activation of Ca2+-dependent cysteine proteases (calpains) is required for disuse atrophy in limb skeletal muscles. In contrast to typical models of muscle disuse (humans and rodents), animals that experience natural bouts of chronic muscle inactivity, such as hibernating mammals and aestivating frogs, consistently exhibit limited or no change in skeletal muscle size. In the current study, we examined enzyme activity, protein abundance and gene expression levels of calpain isoforms in gastrocnemius muscle of the aestivating frog, Cyclorana alboguttata. We predicted that in aestivating C. alboguttata there would be a downregulation of the abundance, activity and gene expression of calpain 1 and calpain 2. In contrast to our hypothesis, there was no significant decrease in the enzyme activity levels or the relative protein abundances of calpain 1 and calpain 2. Similarly, gene expression assays (both qRT-PCR and RNA Seq data) indicated that calpains were unaffected by aestivation. Western blotting of ‘muscle-specific’ calpain 3, which is consistently downregulated during atrophic conditions, indicated that this isoform is present in C. alboguttata muscle where it appears to be in its autolysed state. The absence of any increase in enzyme activity, protein and mRNA abundance of calpains in aestivators is consistent with the protection of gastrocnemius muscle against uncontrolled proteolysis throughout aestivation.

Journal of Comparative Physiology B

1755045

10.1007/S00359-014-0970-7

Pectoral sound generation in the blue catfish Ictalurus furcatus

Catfishes produce pectoral stridulatory sounds by “jerk” movements that rub ridges on the dorsal process against the cleithrum. We recorded sound synchronized with high-speed video to investigate the hypothesis that blue catfish Ictalurus furcatus produce sounds by a slip–stick mechanism, previously described only in invertebrates. Blue catfish produce a variably paced series of sound pulses during abduction sweeps (pulsers) although some individuals (sliders) form longer duration sound units (slides) interspersed with pulses. Typical pulser sounds are evoked by short 1–2 ms movements with a rotation of 2°–3°. Jerks excite sounds that increase in amplitude after motion stops, suggesting constructive interference, which decays before the next jerk. Longer contact of the ridges produces a more steady-state sound in slides. Pulse pattern during stridulation is determined by pauses without movement: the spine moves during about 14 % of the abduction sweep in pulsers (~45 % in sliders) although movement appears continuous to the human eye. Spine rotation parameters do not predict pulse amplitude, but amplitude correlates with pause duration suggesting that force between the dorsal process and cleithrum increases with longer pauses. Sound production, stimulated by a series of rapid movements that set the pectoral girdle into resonance, is caused by a slip–stick mechanism.

Journal of Comparative Physiology A

16968997

10.1007/S00359-014-0969-0

Active amplification in insect ears: mechanics, models and molecules

Active amplification in auditory systems is a unique and sophisticated mechanism that expends energy in amplifying the mechanical input to the auditory system, to increase its sensitivity and acuity. Although known for decades from vertebrates, active auditory amplification was only discovered in insects relatively recently. It was first discovered from two dipterans, mosquitoes and flies, who hear with their light and compliant antennae; only recently has it been observed in the stiffer and heavier tympanal ears of an orthopteran. The discovery of active amplification in two distinct insect lineages with independently evolved ears, suggests that the trait may be ancestral, and other insects may possess it as well. This opens up extensive research possibilities in the field of acoustic communication, not just in auditory biophysics, but also in behaviour and neurobiology. The scope of this review is to establish benchmarks for identifying the presence of active amplification in an auditory system and to review the evidence we currently have from different insect ears. I also review some of the models that have been posited to explain the mechanism, both from vertebrates and insects and then review the current mechanical, neurobiological and genetic evidence for each of these models.

Journal of Comparative Physiology A

16980282

10.1007/S00360-014-0878-0

Tubular localization and expressional dynamics of aquaporins in the kidney of seawater-challenged Atlantic salmon

Most vertebrate nephrons possess an inherited ability to secrete fluid in normal or pathophysiological states. We hypothesized that renal aquaporin expression and localization are functionally regulated in response to seawater and during smoltification in Atlantic salmon and thus reflect a shift in renal function from filtration towards secretion. We localized aquaporins (Aqp) in Atlantic salmon renal tubular segments by immunohistochemistry and monitored their expressional dynamics using RT-PCR and immunoblotting. Three aquaporins: Aqpa1aa, Aqp1ab and Aqp8b and two aquaglyceroporins Aqp3a and Aqp10b were localized in the kidney of salmon. The staining for all aquaporins was most abundant in the proximal kidney tubules and there was no clear effect of salinity or developmental stage on localization pattern. Aqp1aa and Aqp3a were abundant apically but extended throughout the epithelial cells. Aqp10b was expressed apically and along the lateral membrane. Aqp8b was mainly basolateral and Aqp1ab was located in sub-apical intracellular compartments. mRNAs of aqp8b and aqp10b were higher in FW smolts compared to FW parr, whereas the opposite was true for aqp1aa. Aqp mRNA levels changed in response to both SW and sham transfer. Protein levels, however, were stable for most paralogs. In conclusion, aquaporins are abundant in salmon proximal renal tubules and may participate in water secretion and thus urine modification as suggested for other vertebrates. Further studies should seek to couple functional measurements of single nephrons to expression and localization of Aqps in the salmonid kidney.

Journal of Comparative Physiology B

706640

10.1007/S00359-014-0971-6

Activation of muscarinic acetylcholine receptors elevates intracellular Ca2+ concentrations in accessory lobe neurons of the chick

Accessory lobes are protrusions located at the lateral sides of the spinal cord of chicks and it has been proposed that they play a role as a sensory organ for equilibrium during walking. We have reported that functional neurons exist in the accessory lobe. As there is histological evidence that synaptic terminals of cholinergic nerves exist near the somata of accessory lobe neurons, we examined the effects of acetylcholine on changes in intracellular Ca2+ concentrations ([Ca2+]i), as an index of cellular activities. Acetylcholine (0.1–100 µM) caused a transient rise in the [Ca2+]i. Acetylcholine-evoked [Ca2+]i rises were observed in the absence of extracellular Ca2+, and they were abolished in the presence of cyclopiazonic acid, an inhibitor of Ca2+-ATPase of intracellular Ca2+ stores or atropine, a muscarinic receptor antagonist. mRNAs coding M3 and M5 isoforms of the muscarinic receptors were detected in accessory lobes by the RT-PCR. These results indicate that chick accessory lobe neurons express functional muscarinic acetylcholine receptors, and that acetylcholine stimulates Ca2+ mobilization from intracellular Ca2+ stores, which elevates the [Ca2+]i in the somata of accessory lobe neurons, through activation of these receptors. Cholinergic synaptic transmission to the accessory lobe neurons may regulate some cellular functions through muscarinic receptors.

Journal of Comparative Physiology A

14546681

10.1007/S00359-014-0967-2

Seeing double: visual physiology of double-retina eye ontogeny in stomatopod crustaceans

Stomatopod eye development is unusual among crustaceans. Just prior to metamorphosis, an adult retina and associated neuro-processing structures emerge adjacent to the existing material in the larval compound eye. Depending on the species, the duration of this double-retina eye can range from a few hours to several days. Although this developmental process occurs in all stomatopod species observed to date, the retinal physiology and extent to which each retina contributes to the animal’s visual sensitivity during this transition phase is unknown. We investigated the visual physiology of stomatopod double retinas using microspectrophotometry and electroretinogram recordings from different developmental stages of the Western Atlantic species Squilla empusa. Though microspectrophotometry data were inconclusive, we found robust ERG responses in both larval and adult retinas at all sampled time points indicating that the adult retina responds to light from the very onset of its emergence. We also found evidence of an increase in the response dynamics with ontogeny as well as an increase in sensitivity of retinal tissue during the double-retina phase relative to single retinas. These data provide an initial investigation into the ontogeny of vision during stomatopod double-retina eye development.

Journal of Comparative Physiology A

1963964

10.1007/S00359-014-0968-1

Sensory feedback in cockroach locomotion: current knowledge and open questions

The American cockroach, Periplaneta americana, provides a successful model for the study of legged locomotion. Sensory regulation and the relative importance of sensory feedback vs. central control in animal locomotion are key aspects in our understanding of locomotive behavior. Here we introduce the cockroach model and describe the basic characteristics of the neural generation and control of walking and running in this insect. We further provide a brief overview of some recent studies, including mathematical modeling, which have contributed to our knowledge of sensory control in cockroach locomotion. We focus on two sensory mechanisms and sense organs, those providing information related to loading and unloading of the body and the legs, and leg-movement-related sensory receptors, and present evidence for the instrumental role of these sensory signals in inter-leg locomotion control. We conclude by identifying important open questions and indicate future perspectives.

Journal of Comparative Physiology A

15186326

10.1007/S00360-014-0876-2

Functional characterization of a putative disaccharide membrane transporter in crustacean intestine

Transepithelial absorption of dietary sucrose in the American lobster, Homarus americanus, was investigated by mounting an intestine in a perfusion chamber to characterize mucosal to serosal (MS) 14C-sucrose transport. These fluxes were measured by adding varying concentrations of 14C-sucrose to the perfusate and monitoring their appearance in the bathing solution. Transepithelial 14C-sucrose transport was the combination of a hyperbolic function of luminal concentration, following Michaelis–Menten kinetics, and apparent diffusion. The kinetic constants of the putative sucrose transporter were KM = 20.50 ± 6.00 µM and Jmax = 1.81 ± 0.50 pmol/cm2 × min. Phloridzin, an inhibitor of Na+-dependent mucosal glucose transport, decreased MS 14C-sucrose transport. Decreased MS 14C-sucrose transport also occurred in the presence of luminal trehalose, a disaccharide containing d-glucose moieties. Thin-layer chromatography (TLC) identified the chemical nature of radioactively labeled sugars in the bath following transepithelial transport. TLC revealed 14C-sucrose was transported across the intestine largely intact with no 14C-glucose or 14C-fructose appearing in the serosal bath or luminal perfusate. Only 13 % of bath radioactivity was volatile metabolites. Results suggest that disaccharide sugars can be transported intact across crustacean intestine and support the occurrence of a functional disaccharide membrane transporter.

Journal of Comparative Physiology B

16307749

10.1007/S00359-014-0966-3

Insect hearing: from physics to ecology

broad range of anatomical variation in both types of hearing organs. As Regen’s experiment with field crickets already indicates, hearing research has strongly benefited from the fact that many species of insects respond so reliably to acoustic playbacks, and that they do so under very different experimental paradigms, from open-loop laboratory conditions on a trackball to the disturbed and noisy conditions in the field. Moreover, with the advent of neurophysiological techniques hearing and sound communication in insects has become one of the classical areas in neuroethology, aiming to understand the proximate mechanisms of behavior in signalers and receivers (Huber et al. 1989; Gerhardt and Huber 2002; Greenfield 2002; Hedwig 2013). Finally, the refinement of methods such as scanning Laser Doppler Vibrometry for measuring sound-induced vibrations down to the nanometer range has greatly improved our understanding of the biophysics of hearing in recent years. This issue of JCP-A presents a synopsis of what is currently known about insect hearing. Its title, Insect hearing: from physics to ecology, reflects its broad thematic scope. We have to keep in mind that natural selection may act on virtually all aspects of hearing, from molecules associated with the transduction and amplification process in receptor cells, to sound guides that provide directionality in the small insect receivers, or to the complex behavior in large choruses of singing insects. The contributions to this issue are guided by four basic themes: (1) ears and receptor mechanisms, (2) pattern recognition and directional hearing, (3) ecology of sound communication, and (4) evolution. Since the first recordings from locust auditory receptor neurons it was established that locusts’ ears are, in principle, able to discriminate different frequencies. However, the biophysical and or physiological basis of this capacity Almost exactly 100 years ago, Johann Regen performed an ingenious simple experiment where he arranged a male cricket calling in one room and transmitted its song via telephone to another room. There a female could be attracted to the earpiece of a second telephone (Regen 1913). Given the poor frequency characteristics of the early (and contemporary) telephones, one could already speculate about the nature of (temporal) cues that guided the female s phonotactic approach. In the meantime a tremendous progress has been made regarding our understanding of insect hearing (Gerhardt and Huber 2002; Hedwig 2013). This is partly due to the bewildering variety of insect ears having evolved independently many times, and virtually anywhere on the insect body such as on the tibia, abdomen, thorax, wing, mouthparts or the base of the neck (reviews: Hoy and Robert 1996; Yack 2004; Straus and Stumpner 2015). Insect hearing organs exist as two basic forms: (1) either as tympanal ears with a thin cuticular membrane, an air-filled cavity behind it and a chordotonal organ directly or indirectly coupled mechanically to the tympanum (Robert and Hoy 1998)—these ears respond to sound pressure changes; or (2) as nontympanal hearing organs which respond to the air particle velocity. These are represented by filiform hairs or antennae, such as those in mosquitoes or fruit flies. The collection of articles in this special issue of JCP-A covers a

Journal of Comparative Physiology A

1837011

10.1007/S00359-014-0960-9

Prestin is an anion transporter dispensable for mechanical feedback amplification in Drosophila hearing

In mammals, the membrane-based protein Prestin confers unique electromotile properties to cochlear outer hair cells, which contribute to the cochlear amplifier. Like mammals, the ears of insects, such as those of Drosophila melanogaster, mechanically amplify sound stimuli and have also been reported to express Prestin homologs. To determine whether the D. melanogaster Prestin homolog (dpres) is required for auditory amplification, we generated and analyzed dpres mutant flies. We found that dpres is robustly expressed in the fly’s antennal ear. However, dpres mutant flies show normal auditory nerve responses, and intact non-linear amplification. Thus we conclude that, in D. melanogaster, auditory amplification is independent of Prestin. This finding resonates with prior phylogenetic analyses, which suggest that the derived motor function of mammalian Prestin replaced, or amended, an ancestral transport function. Indeed, we show that dpres encodes a functional anion transporter. Interestingly, the acquired new motor function in the phylogenetic lineage leading to birds and mammals coincides with loss of the mechanotransducer channel NompC (=TRPN1), which has been shown to be required for auditory amplification in flies. The advent of Prestin (or loss of NompC, respectively) may thus mark an evolutionary transition from a transducer-based to a Prestin-based mechanism of auditory amplification.

Journal of Comparative Physiology A

17011933

10.1007/S00360-014-0872-6

Regional thermal specialisation in a mammal: temperature affects power output of core muscle more than that of peripheral muscle in adult mice (Mus musculus)

In endotherms, such as mammals and birds, internal organs can specialise to function within a narrow thermal range. Consequently, these organs should become more sensitive to changes in body temperature. Yet, organs at the periphery of the body still experience considerable fluctuations in temperature, which could select for lower thermal sensitivity. We hypothesised that the performance of soleus muscle taken from the leg would depend less on temperature than would the performance of diaphragm muscle taken from the body core. Soleus and diaphragm muscles were isolated from mice and subjected to isometric and work-loop studies to analyse mechanical performance at temperatures between 15 and 40 °C. Across this thermal range, soleus muscle took longer to generate isometric force and longer to relax, and tended to produce greater normalised maximal force (stress) than did diaphragm muscle. The time required to produce half of maximal force during isometric tetanus and the time required to relax half of maximal force were both more sensitive to temperature in soleus than they were in diaphragm. However, thermal sensitivities of maximal force during isometric tetani were similar for both muscles. Consistent with our hypothesis, power output (the product of speed and force) was greater in magnitude and more thermally sensitive in diaphragm than it was in soleus. Our findings, when combined with previous observations of muscles from regionally endothermic fish, suggest that endothermy influences the thermal sensitivities of power output in core and peripheral muscles.

Journal of Comparative Physiology B

15662079

10.1007/S00360-014-0870-8

Dietary fatty acids affect mitochondrial phospholipid compositions and mitochondrial gene expression of rainbow trout liver at different ages

Mitochondria are among the first responders to various stressors that challenge the homeostasis of cells and organisms. Mitochondrial decay is generally associated with impairment in the organelle bioenergetics function and increased oxidative stress, and it appears that deterioration of mitochondrial inner membrane phospholipids (PL), particularly cardiolipin (CL), and accumulation of mitochondrial DNA (mtDNA) mutations are among the main mechanisms involved in this process. In the present study, liver mitochondrial membrane PL compositions, lipid peroxidation, and mtDNA gene expression were analyzed in rainbow trout fed three diets with the same base formulation but with lipid supplied either by fish oil (FO), rapeseed oil (RO), or high DHA oil (DHA) during 6 weeks. Specifically, two feeding trials were performed using fish from the same population of two ages (1 and 3 years), and PL class compositions of liver mitochondria, fatty acid composition of individual PL classes, TBARS content, and mtDNA expression were determined. Dietary fatty acid composition strongly affected mitochondrial membrane composition from trout liver but observed changes did not fully reflect the diet, particularly when it contained high DHA. The changes were PL specific, CL being particularly resistant to changes in DHA. Some significant differences observed in expression of mtDNA with diet may suggest long-term dietary effects in mitochondrial gene expression which could affect electron transport chain function. All the changes were influenced by fish age, which could be related to the different growth rates observed between 1- and 3-year-old trout but that could also indicate age-related changes in the ability to maintain structural homeostasis of mitochondrial membranes.

Journal of Comparative Physiology B

14846074

10.1007/S00359-014-0965-4

Spider joint hair sensilla: adaptation to proprioreceptive stimulation

Adding to previous efforts towards a better understanding of the remarkable diversity of spider mechanosensitive hair sensilla, this study examines hairs of Cupiennius salei most likely serving a proprioreceptive function. At the tibia–metatarsus joint of all walking legs, there are two opposing groups of hairs ventrally on the tibia (20 hairs) and metatarsus (75 hairs), respectively. These hairs deflect each other when the joint flexes during locomotion, reversibly interlocking by microtrichs on their hair shafts. The torque resisting the hair deflection into the direction of natural stimulation is smaller by up to two powers of ten than that for the other directions. The torsional restoring constant S of the hair suspension is about 10−10 Nm rad−1 in the preferred direction, up to a hair deflection angle of 30° (mean of natural deflection angles). Joint movements were imposed in ranges and at rates measured in walking spiders and sensory action potentials recorded. Within the natural step frequencies (0.3–3 Hz) the rate of action potentials follows the velocity of hair deflection. All findings point to the morphological, mechanical, and physiological adaptedness of the joint hair sensilla to their proprioreceptive stimulation during locomotion.

Journal of Comparative Physiology A

15836436

10.1007/S00359-014-0964-5

Eye movements of vertebrates and their relation to eye form and function

The types of eye movements shown by all vertebrates originated in the earliest fishes. These consisted of compensatory movements, both vestibular and visual, to prevent image motion, and saccades to relocate gaze. All vertebrates fixate food items with their heads to enable ingestion, but from teleosts onwards some species also use eye movements to target particular objects, especially food. Eye movement use is related to the resolution distribution in the retina, with eyes that contain foveas, or areas of high ganglion cell density, being more likely to make targeting eye movements, not seen in animals with more uniform retinas. Birds, in particular, tend mainly to use head movements when shifting gaze. Many birds also make translatory head saccades (head bobbing) when walking. It is common for animals to use both eyes when locating food items ahead, but the use of binocular disparity for distance judgment is rare, and has only been demonstrated in toads, owls, cats and primates. Smooth tracking with eyes alone is probably confined to primates. The extent of synchrony and directional symmetry in the movements of the two eyes varies greatly, from complete independence in the sandlance and chameleon, to perfect coordination in primates.

Journal of Comparative Physiology A

926330

10.1007/S00359-014-0963-6

Choosiness, a neglected aspect of preference functions: a review of methods, challenges and statistical approaches

Animals are faced with many choices and a very important one is the choice of a mating partner. Inter-individual differences in mating preferences have been studied for some time, but most studies focus on the location of the peak preference rather than on other aspects of preference functions. In this review, we discuss the role of variation in choosiness in inter-sexual selection. We define individual-level choosiness as the change in mating propensity in response to different stimulus signals. We illustrate general issues in estimating aspects of preference functions and discuss experimental setups for quantifying variation in choosiness with a focus on choices based on acoustic signals in insects. One important consideration is whether preferences are measured sequentially one stimulus at a time or in competitive multiple-choice setups; the suitability of these alternatives depends on the ecology of the study species. Furthermore, we discuss the usefulness of behavioural proxies for determining preference functions, which can be misleading if the proxies are not linearly related to mating propensity. Finally, we address statistical approaches, including the use of function-valued trait analysis, for studying choosiness. Most of the conclusions can be generalized beyond acoustic signals in insects and to choices in non-sexual contexts.

Journal of Comparative Physiology A

12867679

10.1007/S00359-014-0961-8

The nervous and the immune systems: conspicuous physiological analogies

From all biological constituents of complex organisms, two are highly sophisticated: the nervous and the immune systems. Interestingly, their goals and processes appear to be distant from each other; however, their physiological mechanisms keep notorious similarities. Both construct intelligence, learn from experience, and keep memory. Their precise responses to innumerable stimuli are delicately modulated, and the exposure of the individual to thousands of potential challenges integrates their functionality; they use a large part of their constituents not in excitatory activities but in the maintenance of inhibitory mechanisms to keep silent vast intrinsic potentialities. The nervous and immune systems are integrated by a basic cell lineage (neurons and lymphocytes, respectively) but each embodies countless cell subgroups with different and specialized deeds which, in contrast with cells from other organs, labyrinthine molecular arrangements conduct to “one cell, one function”. Also, nervous and immune actions confer identity that differentiates every individual from countless others in the same species. Both systems regulate and potentiate their responses aided by countless biological resources of variable intensity: hormones, peptides, cytokines, pro-inflammatory molecules, etc. How the immune and the nervous systems buildup memory, learning capability, and exquisite control of excitatory/inhibitory mechanisms constitute major intellectual challenges for contemporary research.

Journal of Comparative Physiology A

14762693

10.1007/S00360-014-0875-3

Synergistic effects of acute warming and low pH on cellular stress responses of the gilthead seabream Sparus aurata

The present study assesses the resilience of the Mediterranean gilthead seabream (Sparus aurata) to acute warming and water acidification, using cellular indicators of systemic to molecular responses to various temperatures and CO2 concentrations. Tissue metabolic capacity derived from enzyme measurements, citrate synthase, 3-hydroxyacyl CoA dehydrogenase (HOAD), as well as lactate dehydrogenase. Cellular stress and signaling responses were identified from expression patterns of Hsp70 and Hsp90, the phosphorylation of p38 MAPK, JNKs and ERKs, from protein ubiquitylation and finally from the levels of transcription factor Hif-1α as an indicator of systemic hypoxemia. Exposure to elevated CO2 levels at temperatures higher than 24 °C generally caused an increase in fish mortality above the rate caused by warming alone, indicating effects of the two factors and a failure of acclimation and thus the limits of phenotypic plasticity to be reached. As a potential reason, tissue-dependent induction and stabilization of Hif-1α indicate hypoxemic conditions. Their exacerbation by enhanced CO2 levels is linked to the persistent expression of Hsp70 and Hsp90, oxidative stress and activation of MAPK and ubiquitin pathways. Antioxidant defence is enhanced by expression of catalase and glutathione reductase, however, leaving superoxide dismutase suppressed by elevated CO2 levels. On longer timescales in specimens surviving warming and CO2 exposures, various metabolic adjustments initiate a preference to oxidize lipid via HOAD for energy supply. These processes indicate significant acclimation up to a limit and a time-limited capacity to survive extreme conditions passively by exploiting mechanisms of cellular resilience.

Journal of Comparative Physiology B

17025264

10.1007/S00360-014-0873-5

Electrocardiogram, heart movement and heart rate in the awake gecko (Hemidactylus mabouia)

Abstract The electrocardiogram (ECG) is the simplest and most effective non-invasive method to assess the electrical activity of the heart and to obtain information on the heart rate (HR) and rhythm. Because information on the HR of very small reptiles (body mass <10 g) is still scarce in the literature, in the present work we describe a procedure for recording the ECG in non-anesthetized geckos (Hemidactylus mabouia, Moreau de Jonnès, 1818) under different conditions, namely manual restraint (MR), spontaneous tonic immobility (TI), and in the non-restrained condition (NR). In the gecko ECG, the P, QRS and T waves were clearly distinguishable. The HR was 2.83 ± 0.02 Hz under MR, which was significantly greater (p < 0.001) than the HR under the TI (1.65 ± 0.09 Hz) and NR (1.60 ± 0.10 Hz) conditions. Spontaneously beating isolated gecko hearts contracted at 0.84 ± 0.03 Hz. The in vitro beating rate was affected in a concentration-dependent fashion by adrenoceptor stimulation with noradrenaline, as well as by the muscarinic cholinergic agonist carbachol, which produced significant positive and negative chronotropic effects, respectively (p < 0.001). To our knowledge, this is the first report on the ECG morphology and HR values in geckos, particularly under TI. The methodology and instrumentation developed here are useful for non-invasive in vivo physiological and pharmacological studies in small reptiles without the need of physical restraint or anesthesia.

Journal of Comparative Physiology B

14792535

10.1007/S00360-014-0871-7

Acclimation to different environmental salinities induces molecular endocrine changes in the GH/IGF-I axis of juvenile gilthead sea bream (Sparus aurata L.)

AbstractTo assess the role of the GH/IGF-I axis in osmotic acclimation of the gilthead seabream Sparus aurata, juvenile specimens were acclimated to four environmental salinities: hyposmotic (5 ‰), isosmotic (12 ‰) and hyperosmotic (40 and 55 ‰). The full-length cDNAs for both pituitary adenylate cyclase-activating peptide (PACAP) and prepro-somatostatin-I (PSS-I), the precursor for mature somatostatin-I (SS-I), were cloned. Hypothalamic PACAP and PSS-I, hypophyseal growth hormone (GH) and prolactin (PRL), and hepatic insulin-like growth factor-I (IGF-I) mRNA expression levels were analyzed in the four rearing salinities tested. PACAP and IGF-I mRNA values increased significantly in response to both 5 and 55 ‰ salinities, showing a U-shaped curve relationship with the basal level in the 40 ‰ group. Hypothalamic PSS-I expression increased strongly in the 55 ‰ environment. GH mRNA levels did not change in any of the tested environmental salinities. PRL mRNA maximum levels were encountered in the 5 and 12 ‰ environments, but significantly down-regulated in the 40 ‰. Plasma cortisol levels significantly increased in the 40 ‰ environment. These results are discussed in relation to the well-known high adaptability of Sparus aurata to different environmental salinities and the role of the GH/IGF-I axis in this process.

Journal of Comparative Physiology B

5565338

10.1007/S00360-014-0869-1

The thermal plasticity of locomotor performance has diverged between northern and southern populations of the eastern newt (Notophthalmus viridescens)

Abstract Many temperate ectotherms undergo thermal acclimation to remain functional over a wide range of body temperatures, but few studies have investigated whether populations of a single species have evolved differences in the thermal plasticity of locomotor performance. Therefore, we asked whether the thermal plasticity of locomotor performance has diverged between northern and southern populations of eastern newts (Notophthalmus viridescens). We acclimated eastern newts from Florida and Maine to cold (6 °C) or warm (28 °C) conditions for 12 weeks. Following acclimation, we measured the burst speed of newts at 6, 11.5, 17, 22.5, 28, and 33.5 °C. We also measured the activities of creatine kinase (CK) and lactate dehydrogenase (LDH) in skeletal muscle of newts. The newts from Maine were better able to acclimate to low temperature compared to newts from Florida. Regardless of acclimation, the thermal sensitivity of burst speed was higher in the Florida compared to the Maine population. In general, newts from Maine performed better at low temperatures, whereas newts from Florida performed better at high temperatures. The activities of CK and LDH were lower in cold compared to warm-acclimated newts in the Florida population, but acclimation did not affect the activities of these enzymes in the Maine population. The activities of CK and LDH do not explain differences in the thermal plasticity of locomotor performance between populations. Our results demonstrate that the thermal sensitivity and plasticity of locomotor performance differ between northern and southern populations of eastern newts, suggesting that these traits readily adapt to the thermal environment.

Journal of Comparative Physiology B

13992655

10.1007/S00359-014-0962-7

Selective forces on origin, adaptation and reduction of tympanal ears in insects

Insect ears evolved many times independently. As a consequence, a striking diversity exists in the location, construction and behavioural implementation of ears. In this review, we first summarise what is known about the evolutionary origin of ears and the presumed precursor organs in the various insect groups. Thereafter, we focus on selective forces for making and keeping an ear: we discuss detecting and localising predators and conspecifics, including establishing new “private” channels for intraspecific communication. More advanced aspects involve judging the distance of conspecifics, or assessing individual quality from songs which makes auditory processing a means for exerting sexual selection on mating partners. We try to identify negative selective forces, mainly in the context of energy expenditure for developing and keeping an ear, but also in conjunction with acoustic communication, which incorporates risks like eavesdropping by predators and parasitoids. We then discuss balancing pressures, which might oppose optimising an ear for a specific task (when it serves different functions, for example). Subsequently, we describe various scenarios that might have led to a reduction or complete loss of ears in evolution. Finally, we describe cases of sex differences in ears and potential reasons for their appearance.

Journal of Comparative Physiology A

9109953

10.1007/S00359-014-0957-4

Flow sensing in developing Xenopus laevis is disrupted by visual cues and ototoxin exposure

We explored how lateral line cues interact with visual cues to mediate flow sensing behaviors in the nocturnal developing frog, Xenopus laevis, by exposing animals to current flows under different lighting conditions and after exposure to the ototoxin gentamicin. Under dark conditions, Xenopus tadpoles move downstream at the onset of current flow, then turn, and orient toward the direction of the flow with high accuracy. Postmetamorphic froglets also exhibit positive rheotaxis but with less accuracy and longer latency. The addition of discrete light cues to an otherwise dark environment disrupts rheotaxis and positioning. Orientation is less accurate, latency to orient is longer, and animals do not move as far downstream in the presence of light. Compared with untreated tadpoles tested in the dark, tadpoles exposed to gentamicin show less accurate rheotaxis with longer latency and do not move as far downstream in response to flow. These effects are compounded by the presence of light cues. The disruptive effects of light on flow sensing in Xenopus emphasize the disturbances to natural behaviors that may be produced by anthropogenic illumination in nocturnal habitats.

Journal of Comparative Physiology A

16390465

10.1007/S00360-014-0868-2

Heat loss in air of an Antarctic marine mammal, the Weddell seal

The conflicting needs of homeostasis in air versus water complicate our understanding of thermoregulation in marine mammals. Large-scale modeling efforts directed at predicting the energetic impact of changing sea ice conditions on polar ecosystems require a better understanding of thermoregulation in air of free-ranging animals. We utilized infrared imaging as an indirect approach to determine surface temperatures of dry, hauled-out Weddell seals (Leptonychotes weddellii, n = 35) of varying age and body condition during the Antarctic summer. The study groups provided a fivefold range in body mass and a threefold range in blubber depth. Surface temperature (Ts) did not vary by body region (head, shoulder, axilla, torso, hip, flippers). Average seal Ts (mean 13.9 ± 11.2 °C) was best described through a combination of the physical traits of body mass and environmental variables of ambient temperature Tair, and wind speed. Additional factors of ice temperature (Tice), relative humidity and cloud cover did not improve the model. Heat transfer model estimates suggested that radiation contributed 56.6 ± 7.7 % of total heat loss. Convection and conduction accounted for the remaining 15.7 ± 12.3 and 27.7 ± 9.3 %, respectively. Heat loss by radiation was primarily influenced by body mass and wind speed, whereas convective heat loss was influenced primarily by blubber depth and wind speed. Conductive heat loss was modeled largely as a function of physical traits of mass and blubber depth rather than any environmental covariates, and therefore was substantially higher in animals in leaner condition.

Journal of Comparative Physiology B

10436448

10.1007/S00360-014-0866-4

Sex differences in the long-term repeatability of the acute stress response in long-lived, free-living Florida scrub-jays (Aphelocoma coerulescens)

There is increasing evidence that individual differences in the physiological stress response are persistent traits in many animals. To test the hypothesis that the stress-induced CORT (SI-CORT) response is repeatable over the adult life span of Florida scrub-jays (Aphelocoma coerulescens), we sampled 32 male and 25 female free-living scrub-jays (aged 2–13 years) during a 9-year period (2004–2012). Each individual was sampled two to five times and samples were collected one or more years apart during the pre-breeding season (Jan–March). In addition, individuals sampled over the greatest time period (6–8 years) were analyzed separately to more closely assess long-term repeatability. SI-CORT was repeatable in females, but not males, when values were not corrected for confounding variables (agreement repeatability). However, when the year and time of day of sample collection were controlled (adjusted repeatability), SI-CORT was repeatable in both sexes. SI-CORT was also repeatable in the males and females sampled 6–8 years apart. Finally, baseline CORT levels of males, but not females, exhibited low but significant repeatability when adjusted for year. The results of this study demonstrate that differences in SI-CORT levels were repeatable within adult scrub-jays sampled up to 8 years apart. Further, the female SI-CORT response was more consistent between pre-breeding seasons than males, which may have resulted from males having higher SI-CORT plasticity in response to environmental conditions. These data support the hypothesis that the SI-CORT response of Florida scrub-jays develops before adulthood and persists throughout much, if not all, of their natural adult life span.

Journal of Comparative Physiology B

18410139

10.1007/S00360-014-0862-8

Oxygen-induced plasticity in tracheal morphology and discontinuous gas exchange cycles in cockroaches Nauphoeta cinerea

The function and mechanism underlying discontinuous gas exchange in terrestrial arthropods continues to be debated. Three adaptive hypotheses have been proposed to explain the evolutionary origin or maintenance of discontinuous gas exchange cycles (DGCs), which may have evolved to reduce respiratory water loss, facilitate gas exchange in high CO2 and low O2 micro-environments, or to ameliorate potential damage as a result of oversupply of O2. None of these hypotheses have unequivocal support, and several non-adaptive hypotheses have also been proposed. In the present study, we reared cockroaches Nauphoeta cinerea in selected levels of O2 throughout development, and examined how this affected growth rate, tracheal morphology and patterns of gas exchange. O2 level in the rearing environment caused significant changes in tracheal morphology and the exhibition of DGCs, but the direction of these effects was inconsistent with all three adaptive hypotheses: water loss was not associated with DGC length, cockroaches grew fastest in hyperoxia, and DGCs exhibited by cockroaches reared in normoxia were shorter than those exhibited by cockroaches reared in hypoxia or hyperoxia.

Journal of Comparative Physiology B

15481147

10.1007/S00359-014-0959-2

Nycthemeral variation in melatonin receptor expression in the lymphoid organs of a tropical seasonal breeder Funambulus pennanti

Seasonal variations in immune functions point toward the involvement of melatonin in its regulation. These chronobiotic effects are exerted by receptors present on the immunocompetent cells. The present study investigated daily/nycthemeral variation in expression of melatonin receptor subtypes MT1/MT2 in the lymphoid organs (spleen/thymus) of a tropical squirrel, Funambulus pennanti. The receptor expression was noted every 4 h interval over 24 h under natural light–dark cycle, during two seasons and was correlated with peripheral level of melatonin. The MT1/MT2 receptor expression displayed higher levels at the time of dusk (light–dark transition; 1800 hours), while plasma melatonin was still low compared to the preceding time point. The receptors were downregulated during the nighttime with a minimum expression at 0200 hours. Thymus, during the long day length, showed a tissue-specific pattern of receptor expression with a minimum expression at 0600 hours. Results suggest that photoperiod by modulation of melatonin level inversely regulates the receptor expression. The observations imply that there exists a temporal window of sensitivity in the target organs to the melatonin signal that is regulated by modulation of melatonin receptor expression which might be involved in mediating the photoperiodic effects of melatonin in the control of seasonal immune physiology.

Journal of Comparative Physiology A

15558396

10.1007/S00359-014-0958-3

Parasitoid flies exploiting acoustic communication of insects—comparative aspects of independent functional adaptations

Two taxa of parasitoid Diptera have independently evolved tympanal hearing organs to locate sound producing host insects. Here we review and compare functional adaptations in both groups of parasitoids, Ormiini and Emblemasomatini. Tympanal organs in both groups originate from a common precursor organ and are somewhat similar in morphology and physiology. In terms of functional adaptations, the hearing thresholds are largely adapted to the frequency spectra of the calling song of the hosts. The large host ranges of some parasitoids indicate that their neuronal filter for the temporal patterns of the calling songs are broader than those found in intraspecific communication. For host localization the night active Ormia ochracea and the day active E. auditrix are able to locate a sound source precisely in space. For phonotaxis flight and walking phases are used, whereby O. ochracea approaches hosts during flight while E. auditrix employs intermediate landings and re-orientation, apparently separating azimuthal and vertical angles. The consequences of the parasitoid pressure are discussed for signal evolution and intraspecific communication of the host species. This natural selection pressure might have led to different avoidance strategies in the hosts: silent males in crickets, shorter signals in tettigoniids and fluctuating population abundances in cicadas.

Journal of Comparative Physiology A

5662496

10.1007/S00359-014-0956-5

Computational themes of peripheral processing in the auditory pathway of insects

Hearing in insects serves to gain information in the context of mate finding, predator avoidance or host localization. For these goals, the auditory pathways of insects represent the computational substrate for object recognition and localization. Before these higher level computations can be executed in more central parts of the nervous system, the signals need to be preprocessed in the auditory periphery. Here, we review peripheral preprocessing along four computational themes rather than discussing specific physiological mechanisms: (1) control of sensitivity by adaptation, (2) recoding of amplitude modulations of an acoustic signal into a labeled-line code (3) frequency processing and (4) conditioning for binaural processing. Along these lines, we review evidence for canonical computations carried out in the peripheral auditory pathway and show that despite the vast diversity of insect hearing, signal processing is governed by common computational motifs and principles.

Journal of Comparative Physiology A

15653302

10.1007/S00359-014-0955-6

Ecology of acoustic signalling and the problem of masking interference in insects

The efficiency of long-distance acoustic signalling of insects in their natural habitat is constrained in several ways. Acoustic signals are not only subjected to changes imposed by the physical structure of the habitat such as attenuation and degradation but also to masking interference from co-occurring signals of other acoustically communicating species. Masking interference is likely to be a ubiquitous problem in multi-species assemblages, but successful communication in natural environments under noisy conditions suggests powerful strategies to deal with the detection and recognition of relevant signals. In this review we present recent work on the role of the habitat as a driving force in shaping insect signal structures. In the context of acoustic masking interference, we discuss the ecological niche concept and examine the role of acoustic resource partitioning in the temporal, spatial and spectral domains as sender strategies to counter masking. We then examine the efficacy of different receiver strategies: physiological mechanisms such as frequency tuning, spatial release from masking and gain control as useful strategies to counteract acoustic masking. We also review recent work on the effects of anthropogenic noise on insect acoustic communication and the importance of insect sounds as indicators of biodiversity and ecosystem health.

Journal of Comparative Physiology A

14653970

10.1007/S00359-014-0953-8

Influence of double stimulation on sound-localization behavior in barn owls

Barn owls do not immediately approach a source after they hear a sound, but wait for a second sound before they strike. This represents a gain in striking behavior by avoiding responses to random incidents. However, the first stimulus is also expected to change the threshold for perceiving the subsequent second sound, thus possibly introducing some costs. We mimicked this situation in a behavioral double-stimulus paradigm utilizing saccadic head turns of owls. The first stimulus served as an adapter, was presented in frontal space, and did not elicit a head turn. The second stimulus, emitted from a peripheral source, elicited the head turn. The time interval between both stimuli was varied. Data obtained with double stimulation were compared with data collected with a single stimulus from the same positions as the second stimulus in the double-stimulus paradigm. Sound-localization performance was quantified by the response latency, accuracy, and precision of the head turns. Response latency was increased with double stimuli, while accuracy and precision were decreased. The effect depended on the inter-stimulus interval. These results suggest that waiting for a second stimulus may indeed impose costs on sound localization by adaptation and this reduces the gain obtained by waiting for a second stimulus.

Journal of Comparative Physiology A

15128916

10.1007/S00360-014-0867-3

Ammonia exposure increases the expression of Na+:K+:2Cl− cotransporter 1a in the gills of the giant mudskipper, Periophthalmodon schlosseri

The giant mudskipper, Periophthalmodon schlosseri, is an obligate air-breathing teleost that can actively excrete ammonia against high concentrations of environmental ammonia. This study aimed to clone and sequence the Na+:K+:2Cl−cotransporter1 (nkcc1) from the gills of P. schlosseri, and to determine the effects of ammonia exposure on its mRNA expression and protein abundance after pre-acclimation to slightly brackish water (salinity 3; SBW) for 2 weeks. The complete coding cDNA sequences of nkcc1a consisted of 3453 bp, coding for 1151 amino acid with an estimated molecular mass of 125.4 kDa. Exposure to 75 mmol l−1 NH4Cl in SBW had no effect on the mRNA expression of nkcc1a. However, western blotting revealed a significant increase in the protein abundance of multiple T4-immunoreactive bands of molecular mass 170–250 kDa in the gills of P. schlosseri exposed to ammonia. Furthermore, immunofluorescence microscopy demonstrated the colocalization of the increased T4-immunoreactive protein with Na+/K+-ATPase (Nka) α-subunit to the basolateral membrane of certain ionocytes in the gills of the ammonia-exposed fish. As Nkcc1 is known to have a basolateral localization, it can be concluded that ammonia exposure led to an increase in the expression of glycosylated Nkcc1, the molecular masses of which were reduced upon enzymatic deglycosylation, in the gills of P. schlosseri. The dependency on post-transcriptional and post-translational regulation of branchial Nkcc1 in P. schlosseri would facilitate prompt responses to changes in environmental condition. As NH4+ can replace K+, NH4+ could probably enter ionocytes through the basolateral Nkcc1a during active ammonia excretion, but increased influx of Na+, NH4+ and 2Cl− would alter the transmembrane Na+ gradient. Consequently, exposure of P. schlosseri to ammonia would also result in an increase in branchial activity of Nka with decreased NH4+ affinity so as to maintain intracellular Na+ and K+ homeostasis as reported elsewhere.

Journal of Comparative Physiology B

18127037

10.1007/S00359-014-0949-4

Pattern recognition in field crickets: concepts and neural evidence

Since decades the acoustic communication behavior of crickets is in the focus of neurobiology aiming to analyze the neural basis of male singing and female phonotactic behavior. For temporal pattern recognition several different concepts have been proposed to elucidate the possible neural mechanisms underlying the tuning of phonotaxis in females. These concepts encompass either some form of a feature detecting mechanism using cross-correlation processing, temporal filter properties of brain neurons or an autocorrelation processing based on a delay-line and coincidence detection mechanism. Current data based on intracellular recordings of auditory brain neurons indicate a sequential processing by excitation and inhibition in a local auditory network within the protocerebrum. The response properties of the brain neurons point towards the concept of an autocorrelation-like mechanism underlying female pattern recognition in which delay-lines by long lasting inhibition may be involved.

Journal of Comparative Physiology A

11431298

10.1007/S00359-014-0952-9

Glia in Drosophila behavior

Glial cells constitute about 10 % of the Drosophila nervous system. The development of genetic and molecular tools has helped greatly in defining different types of glia. Furthermore, considerable progress has been made in unraveling the mechanisms that control the development and differentiation of Drosophila glia. By contrast, the role of glia in adult Drosophila behavior is not well understood. We here summarize recent work describing the role of glia in normal behavior and in Drosophila models for neurological and behavioral disorders.

Journal of Comparative Physiology A

18404146

10.1007/S00359-014-0954-7

Photo-tropotaxis based on projection through the cerebral commissure in the terrestrial slug Limax

In the terrestrial slug, Limax, eyes are located at the tip of the superior tentacles. This animal has long been believed to show negative phototaxis through tropotaxis, i.e., it compares the two light intensities detected by bilateral eyes to move away from a light source. As one of the possible manifestations of such negative phototaxis, a circling movement has been observed: if one of the superior tentacles is removed, the slugs continuously move in the direction of the removed side. However, there has been no evidence demonstrating that this behavior is actually based on negative phototropotaxis. In this study, we showed that the slugs do not exhibit the circling behavior in the absence of light, and that amputation of the cerebral commissure also diminishes the circling behavior under light. We could detect light-evoked responses during electrical recording from the cut edge of the cerebral commissure. Labeling of the optic nerve with neurobiotin also revealed the presence of the commissural fibers that potentially transmit the light information to the contralateral cerebral ganglion. Our study suggests that the slug’s circling behavior is based on phototropotaxis in which the light intensities detected by the bilateral eyes are compared through the cerebral commissure.

Journal of Comparative Physiology A

12167082

10.1007/S00359-014-0951-X

Dichromatic vision in a fruit bat with diurnal proclivities: the Samoan flying fox (Pteropus samoensis)

A nocturnal bottleneck during mammalian evolution left a majority of species with two cone opsins, or dichromatic color vision. Primate trichromatic vision arose from the duplication and divergence of an X-linked opsin gene, and is long attributed to tandem shifts from nocturnality to diurnality and from insectivory to frugivory. Opsin gene variation and at least one duplication event exist in the order Chiroptera, suggesting that trichromatic vision could evolve under favorable ecological conditions. The natural history of the Samoan flying fox (Pteropus samoensis) meets these conditions—it is a large bat that consumes nectar and fruit and demonstrates strong diurnal proclivities. It also possesses a visual system that is strikingly similar to that of primates. To explore the potential for opsin gene duplication and divergence in this species, we sequenced the opsin genes of 11 individuals (19 X-chromosomes) from three South Pacific islands. Our results indicate the uniform presence of two opsins with predicted peak sensitivities of ca. 360 and 553 nm. This result fails to support a causal link between diurnal frugivory and trichromatic vision, although it remains plausible that the diurnal activities of P. samoensis have insufficient antiquity to favor opsin gene renovation.

Journal of Comparative Physiology A

16281703

10.1007/S00359-014-0950-Y

Spectral sensitivity, luminous sensitivity, and temporal resolution of the visual systems in three sympatric temperate coastal shark species

We used electroretinography (ERG) to determine spectral and luminous sensitivities, and the temporal resolution (flicker fusion frequency, FFF) in three sympatric (but phylogenetically distant) coastal shark species: Carcharhinus plumbeus (sandbar shark), Mustelus canis (smooth dogfish), and Squalus acanthias (spiny dogfish). Spectral sensitivities were similar (range ~400–600 nm, peak sensitivity ~470 nm), with a high likelihood of rod/cone dichromacy enhancing contrast discrimination. Spiny dogfish were significantly less light sensitive than the other species, whereas their FFF was ~19 Hz at maximum intensities; a value equal to that of sandbar shark and significantly above that of smooth dogfish (~9–12 Hz). This occurred even though experiments on spiny dogfish were conducted at 12 versus 25 °C and 20 °C for experiments on sandbar shark and smooth dogfish, respectively. Although spiny dogfish have a rod-dominated retina (rod:cone ratio 50:1), their visual system appears to have evolved for a relatively high temporal resolution (i.e., high FFF) through a short integration time, with the requisite concomitant reduction in luminous sensitivity. Our results suggest adaptive plasticity in the temporal resolution of elasmobranch visual systems which reflects the importance of the ability to track moving objects such as mates, predators, or prey.

Journal of Comparative Physiology A

14531611

10.1007/S00359-014-0948-5

Neurobiology of acoustically mediated predator detection

Ultrasound-driven avoidance responses have evolved repeatedly throughout the insecta as defenses against predation by echolocating bats. Although the auditory mechanics of ears and the properties of auditory receptor neurons have been studied in a number of groups, central neural processing of ultrasound stimuli has been examined in only a few cases. In this review, I summarize the neuronal basis for ultrasound detection and predator avoidance in crickets, tettigoniids, moths, and mantises, where central circuits have been studied most thoroughly. Several neuronal attributes, including steep intensity–response functions, high firing rates, and rapid spike conduction emerge as common themes of avoidance circuits. I discuss the functional consequences of these attributes, as well as the increasing complexity with which ultrasound stimuli are represented at successive levels of processing.

Journal of Comparative Physiology A

1133234

10.1007/S00359-014-0947-6

Extracellular recordings reveal absence of magneto sensitive units in the avian optic tectum

There is a consensus that birds detect the earth’s magnetic field and use some of its features for orientation and homing purposes. Since the late 1960s, when the first solid behavioral evidence of magnetoreception was obtained, much research has been devoted to describing the ethological aspects of this behavior. The neurophysiological basis of magnetoreception has been much less studied, although a frequently cited 1986 report described a high prevalence (70 %) of magneto-sensitive neurons in the pigeon optic tectum with high signal-to-noise ratios (Semm and Demaine, J Comp Physiol A 159:619–625, 1986). Here, we repeated these neurophysiological experiments using anesthetized as well as awake pigeons and new recording techniques. Our data indicate that magneto-sensitive units do not exist in the avian tectum.

Journal of Comparative Physiology A

14653768

10.1007/S00360-014-0861-9

Thermal plasticity of skeletal muscle mitochondrial activity and whole animal respiration in a common intertidal triplefin fish, Forsterygion lapillum (Family: Tripterygiidae)

Oxygen demand generally increases in ectotherms as temperature rises in order to sustain oxidative phosphorylation by mitochondria. The thermal plasticity of ectotherm metabolism, such as that of fishes, dictates a species survival and is of importance to understand within an era of warming climates. Within this study the whole animal O2 consumption rate of a common New Zealand intertidal triplefin fish, Forsterygion lapillum, was investigated at different acclimation temperatures (15, 18, 21, 24 or 25 °C) as a commonly used indicator of metabolic performance. In addition, the mitochondria within permeabilised skeletal muscle fibres of fish acclimated to a moderate temperature (18 °C Cool acclimation group—CA) and a warm temperature (24 °C. Warm acclimation group—WA) were also tested at 18, 24 and 25 °C in different states of coupling and with different substrates. These two levels of analysis were carried out to test whether any peak in whole animal metabolism reflected the respiratory performance of mitochondria from skeletal muscle representing the bulk of metabolic tissue. While standard metabolic rate (SMR- an indicator of total maintenance metabolism) and maximal metabolic rate ($$\dot{M}$$M˙O2max) both generally increased with temperature, aerobic metabolic scope (AMS) was maximal at 24 °C, giving the impression that whole animal (metabolic) performance was optimised at a surprisingly high temperature. Mitochondrial oxygen flux also increased with increasing assay temperature but WA fish showed a lowered response to temperature in high flux states, such as those of oxidative phosphorylation and in chemically uncoupled states of respiration. The thermal stability of mitochondria from WA fish was also noticeably greater than CA fish at 25 °C. However, the predicted contribution of respirational flux to ATP synthesis remained the same in both groups and WA fish showed higher anaerobic activity as a result of high muscle lactate loads in both rested and exhausted states. CA fish had a comparably lower level of resting lactate and took 30 % longer to fatigue than WA fish. Despite some apparent acclimation capacity of skeletal muscle mitochondria, the ATP synthesis capacity of this species is constrained at high temperatures, and that a greater fraction of metabolism in skeletal muscle appears to be supported anaerobically at higher temperatures. The AMS peak at 24 °C does not therefore represent utilisation efficiency of oxygen but, rather, the temperature where scope for oxygen flow is greatest.  

Journal of Comparative Physiology B

14761453

10.1007/S00359-014-0945-8

Moth hearing and sound communication

Active echolocation enables bats to orient and hunt the night sky for insects. As a counter-measure against the severe predation pressure many nocturnal insects have evolved ears sensitive to ultrasonic bat calls. In moths bat-detection was the principal purpose of hearing, as evidenced by comparable hearing physiology with best sensitivity in the bat echolocation range, 20–60 kHz, across moths in spite of diverse ear morphology. Some eared moths subsequently developed sound-producing organs to warn/startle/jam attacking bats and/or to communicate intraspecifically with sound. Not only the sounds for interaction with bats, but also mating signals are within the frequency range where bats echolocate, indicating that sound communication developed after hearing by “sensory exploitation”. Recent findings on moth sound communication reveal that close-range (~ a few cm) communication with low-intensity ultrasounds “whispered” by males during courtship is not uncommon, contrary to the general notion of moths predominantly being silent. Sexual sound communication in moths may apply to many eared moths, perhaps even a majority. The low intensities and high frequencies explain that this was overlooked, revealing a bias towards what humans can sense, when studying (acoustic) communication in animals.

Journal of Comparative Physiology A

18027176

10.1007/S00359-014-0944-9

How aquatic water-beetle larvae with small chambered eyes overcome challenges of hunting under water

A particularly unusual visual system exists in the visually guided aquatic predator, the Sunburst Diving Beetle, Thermonectus marmoratus (Coleoptera: Dytiscidae). The question arises: how does this peculiar visual system function? A series of experiments suggests that their principal eyes (E1 and E2) are highly specialized for hunting. These eyes are tubular and have relatively long focal lengths leading to high image magnification. Their retinae are linear, and are divided into distinct green-sensitive distal and UV and polarization-sensitive proximal portions. Each distal retina, moreover, has many tiers of photoreceptors with rhabdomeres the long axis of which are peculiarly oriented perpendicular to the light path. Based on detailed optical investigations, the lenses of these eyes are bifocal and project focused images onto specific retinal tiers. Behavioral experiments suggest that these larvae approach prey within their eyes’ near-fields, and that they can correctly gauge prey distances even when conventional distance-vision mechanisms are unavailable. In the near-field of these eyes object distance determines which of the many retinal layers receive the best-focused images. This retinal organization could facilitate an unusual distance-vision mechanism. We here summarize past findings and discuss how these eyes allow Thermonectus larvae to be such successful predators.

Journal of Comparative Physiology A

9700382

10.1007/S00360-014-0863-7

Analysis of glycylsarcosine transport by lobster intestine using gas chromatography

Gas chromatography was used to measure transepithelial transport of glycylsarcosine (Gly-Sar) by perfused lobster (Homarus americanus) intestine. Unidirectional and net fluxes of dipeptide across the tissue and luminal factors affecting their magnitude and direction were characterized by perfusing the lumen with the dipeptide and measuring its appearance in saline on the serosal side of the organ. Transmural transport of 10 mM Gly-Sar resulted in serosal accumulation of only the dipeptide; no appearance of corresponding monomeric amino acids glycine or sarcosine was observed. Carrier-mediated and diffusional transmural intestinal transport of Gly-Sar was estimated at 1–15 mM luminal concentrations and followed a curvilinear equation providing a Km = 0.44 ± 0.17 mM, a Jmax = 1.27 ± 0.12 nmol cm−2 min−1, and a diffusional coefficient = 0.026 ± 0.008 nmol cm−2 min−1 mM−1. Unidirectional mucosal to serosal and serosal to mucosal fluxes of 10 mM Gly-Sar provided a significant (p < 0.05) net absorptive flux toward the serosa of 3.54 ± 0.77 nmol cm−2 min−1, further supporting carrier-mediated dipeptide transport across the gut. Alkaline (pH 8.5) luminal pH more than doubled transmural Gly-Sar transport as compared to acidic (pH 5.5) luminal pH, while luminal amino acid-metal chelates (e.g., Leu-Zn-Leu), and high concentrations of amino acids alone significantly (p < 0.001) reduced intestinal Gly-Sar transfer by inhibiting carrier transport of the dipeptide. Proposed mechanisms accounting for intestinal dipeptide transport and luminal factors affecting this process are discussed.

Journal of Comparative Physiology B

1624475

10.1007/S00359-014-0946-7

Computational principles underlying recognition of acoustic signals in grasshoppers and crickets

Grasshoppers and crickets independently evolved hearing organs and acoustic communication. They differ considerably in the organization of their auditory pathways, and the complexity of their songs, which are essential for mate attraction. Recent approaches aimed at describing the behavioral preference functions of females in both taxa by a simple modeling framework. The basic structure of the model consists of three processing steps: (1) feature extraction with a bank of ‘LN models’—each containing a linear filter followed by a nonlinearity, (2) temporal integration, and (3) linear combination. The specific properties of the filters and nonlinearities were determined using a genetic learning algorithm trained on a large set of different song features and the corresponding behavioral response scores. The model showed an excellent prediction of the behavioral responses to the tested songs. Most remarkably, in both taxa the genetic algorithm found Gabor-like functions as the optimal filter shapes. By slight modifications of Gabor filters several types of preference functions could be modeled, which are observed in different cricket species. Furthermore, this model was able to explain several so far enigmatic results in grasshoppers. The computational approach offered a remarkably simple framework that can account for phenotypically rather different preference functions across several taxa.

Journal of Comparative Physiology A

16423535

10.1007/S00359-014-0943-X

Hearing in the sea otter (Enhydra lutris): auditory profiles for an amphibious marine carnivore

In this study we examine the auditory capabilities of the sea otter (Enhydra lutris), an amphibious marine mammal that remains virtually unstudied with respect to its sensory biology. We trained an adult male sea otter to perform a psychophysical task in an acoustic chamber and at an underwater apparatus. Aerial and underwater audiograms were constructed from detection thresholds for narrowband signals measured in quiet conditions at frequencies from 0.125–40 kHz. Aerial hearing thresholds were also measured in the presence of octave-band masking noise centered at eight signal frequencies (0.25–22.6 kHz) so that critical ratios could be determined. The aerial audiogram of the sea otter resembled that of sea lions and showed a reduction in low-frequency sensitivity relative to terrestrial mustelids. Best sensitivity was −1 dB re 20 µPa at 8 kHz. Under water, hearing sensitivity was significantly reduced when compared to sea lions and other pinniped species, demonstrating that sea otter hearing is primarily adapted to receive airborne sounds. Critical ratios were more than 10 dB higher than those measured for pinnipeds, suggesting that sea otters are less efficient than other marine carnivores at extracting acoustic signals from background noise, especially at frequencies below 2 kHz.

Journal of Comparative Physiology A

15955028

10.1007/S00359-014-0942-Y

Motor skill learning enhances the expression of activity-regulated cytoskeleton-associated protein in the rat cerebellum

Abstract Motor skill learning is essential for environmental adaptations during everyday life. It has been shown that the cerebellum plays an important role in both the adaptation of eye movements and the motor skill learning. However, the neuronal substrates responsible for consolidation of complex motor skills rather than simple reflexes are still uncertain. Because the induction of immediate-early genes activity-regulated cytoskeleton-associated protein (Arc) and zinc finger binding protein clone 268 (Zif268) has been regarded as a marker for recent neuronal activity, therefore, in the present study, a rat paradigm of motor skill learning was used to investigate the protein expression of Arc and zif268 in the cerebellum after motor skill learning. Rats were trained to traverse the runway apparatus for 5 days. Protein samples were collected from the cerebellar cortices 1 hour after the training on days 1, 3, and 5, and analyzed by western blotting. The results showed that the expression of Arc, but not zif268, was significantly increased in the cerebellum following motor skill learning. These findings suggest that motor skill learning induces Arc expression in the cerebellum, which may play a role in acquiring complex motor skills.

Journal of Comparative Physiology A

15764405

10.1007/S00359-014-0940-0

No rainbow for grey bamboo sharks: evidence for the absence of colour vision in sharks from behavioural discrimination experiments

Despite convincing data collected by microspectrophotometry and molecular biology, rendering sharks colourblind cone monochromats, the question of whether sharks can perceive colour had not been finally resolved in the absence of any behavioural experiments compensating for the confounding factor of brightness. The present study tested the ability of juvenile grey bamboo sharks to perceive colour in an experimental design based on a paradigm established by Karl von Frisch using colours in combination with grey distractor stimuli of equal brightness. Results showed that contrasts but no colours could be discriminated. Blue and yellow stimuli were not distinguished from a grey distractor stimulus of equal brightness but could be distinguished from distractor stimuli of varying brightness. In addition, different grey stimuli were distinguished significantly above chance level from one another. In conclusion, the behavioural results support the previously collected physiological data on bamboo sharks, which mutually show that the grey bamboo shark, like several marine mammals, is a cone monochromate and colourblind.

Journal of Comparative Physiology A

16524728

10.1007/S00360-014-0864-6

Parental environmental exposure leads to glycometabolic disturbances that affect fertilization of eggs in the silkworm Bombyx mori: the parental transcript legacy

Parental transcript legacy plays an important role in fertilization and development of the early embryo. Parental environmental exposure affects the fertilization of eggs, but the underlying biochemical mechanism is largely unresolved. In this study, the parental environmental effects on fertilization of eggs were explored in the silkworm Bombyx mori (B. mori), an ideal lepidopteran animal model. The results showed that the rate of fertilization decreased after the parents were exposed to a poor environment at 32 °C with continuous illumination for 72 h on days 6–9 of the pupal stage, which is a key period for germ cell maturation. This was likely attributable to lower energy charge values, obstructed nicotinamide adenine dinucleotide (NAD+) regeneration and inactive tricarboxylic acid cycle (TCA), leading to accumulation of large amounts of pyruvic acid and lactic acid. This effect was related to energy metabolism via glycolysis; in particular disruption of pyruvate metabolism. In conclusion, this study showed parental exposure to an abnormal environment during germ cell maturation affected glycolysis and the subsequent fertilization of eggs via the parental transcript legacy in B. mori.

Journal of Comparative Physiology B

18857571

10.1007/S00359-014-0941-Z

Differences in lens optical plasticity in two gadoid fishes meeting in the Arctic

Arctic and boreal/temperate species are likely to be evolutionary adapted to different light regimes. Currently, the boreal/temperate Atlantic cod (Gadus morhua) is coexisting with the native polar cod (Boreogadus saida) in the Arctic waters around Svalbard, Norway. Here, we studied light/dark adaptative optical plasticity of their eye lenses by exposing fish to bright light during the polar night. Schlieren photography, high-definition laser scanning and ray tracing were used to determine the optical properties of excised crystalline lenses. Both species have multifocal lenses, an optical adaptation for improved color vision. In polar cod, the optical properties of the lens were independent of light exposure. In the more southern Atlantic cod, the optical properties of the lens changed within hours upon exposure to light, even after months of darkness. Such fast optical adjustment has previously only been shown in a tropical cichlid. During the polar night the Atlantic cod lens seems to be unregulated and dysfunctional since it had an unsuitable focal length and severe spherical aberration. We present a system, to our knowledge unique, for studying visual plasticity on different timescales in relation to evolutionary history and present the first study on the polar cod visual system.

Journal of Comparative Physiology A

9286258

10.1007/S00359-014-0938-7

Signal interactions and interference in insect choruses: singing and listening in the social environment

Acoustic insects usually sing amidst conspecifics, thereby creating a social environment—the chorus—in which individuals communicate, find mates, and avoid predation. A temporal structure may arise in a chorus because of competitive and cooperative factors that favor certain signal interactions between neighbors. This temporal structure can generate significant acoustic interference among singers that pose problems for communication, mate finding, and predator detection. Acoustic insects can reduce interference by means of selective attention to only their nearest neighbors and by alternating calls with neighbors. Alternatively, they may synchronize, allowing them to preserve call rhythm and also to listen for predators during the silent intervals between calls. Moreover, males singing in choruses may benefit from reduced per capita predation risk as well as enhanced vigilance. They may also enjoy greater per capita attractiveness to females, particularly in the case of synchronous choruses. In many cases, however, the overall temporal structure of the chorus is only an emergent property of simple, pairwise interactions between neighbors. Nonetheless, the chorus that emerges can impose significant selection pressure on the singing of those individual males. Thus, feedback loops may occur and potentially influence traits at both individual and group levels in a chorus.

Journal of Comparative Physiology A

14804480

10.1007/S00359-014-0936-9

Genetic dissection of sleep–metabolism interactions in the fruit fly

Dysregulation of sleep and metabolism has enormous health consequences. Sleep loss is linked to increased appetite and insulin insensitivity, and epidemiological studies link chronic sleep deprivation to obesity-related disorders including type II diabetes and cardiovascular disease. Interactions between sleep and metabolism involve the integration of signaling from brain regions regulating sleep, feeding, and metabolic function. Investigating the relationship between these processes provides a model to address more general questions of how the brain prioritizes homeostatically regulated behaviors. The availability of powerful genetic tools in the fruit fly, Drosophila melanogaster, allows for precise manipulation of neural function in freely behaving animals. There is a strong conservation of genes and neural circuit principles regulating sleep and metabolic function, and genetic screens in fruit flies have been effective in identifying novel regulators of these processes. Here, we review recent findings in the fruit fly that further our understanding of how the brain modulates sleep in accordance with metabolic state.

Journal of Comparative Physiology A

8400639

10.1007/S00359-014-0939-6

Directional hearing: from biophysical binaural cues to directional hearing outdoors

When insects communicate by sound, or use acoustic cues to escape predators or detect prey or hosts they have to localize the sound in most cases, to perform adaptive behavioral responses. In the case of particle velocity receivers such as the antennae of mosquitoes, directionality is no problem because such receivers are inherently directional. Insects equipped with bilateral pairs of tympanate ears could principally make use of binaural cues for sound localization, like all other animals with two ears. However, their small size is a major problem to create sufficiently large binaural cues, with respect to both interaural time differences (ITDs, because interaural distances are so small), but also with respect to interaural intensity differences (IIDs), since the ratio of body size to the wavelength of sound is rather unfavorable for diffractive effects. In my review, I will only shortly cover these biophysical aspects of directional hearing. Instead, I will focus on aspects of directional hearing which received relatively little attention previously, the evolution of a pressure difference receiver, 3D-hearing, directional hearing outdoors, and directional hearing for auditory scene analysis.

Journal of Comparative Physiology A

103970

10.1007/S00360-014-0860-X

Protective effects of ectoine on heat-stressed Daphnia magna

Ectoine (ECT) is an amino acid produced and accumulated by halophilic bacteria in stressful conditions in order to prevent the loss of water from the cell. There is a lack of knowledge on the effects of ECT in heat-stressed aquatic animals. The purpose of our study was to determine the influence of ECT on Daphnia magna subjected to heat stress with two temperature gradients: 1 and 0.1 °C/min in the range of 23–42 °C. Time to immobilisation, survival during recovery, swimming performance, heart rate, thoracic limb movement and the levels of heat shock protein 70 kDa 1A (HSP70 1A), catalase (CAT) and nitric oxide species (NOx) were determined in ECT-exposed and unexposed daphnids; we showed protective effects of ECT on Daphnia magna subjected to heat stress. Time to immobilisation of daphnids exposed to ECT was longer when compared to the unexposed animals. Also, survival rate during the recovery of daphnids previously treated with ECT was higher. ECT significantly attenuated a rapid increase of mean swimming velocity which was elevated in the unexposed daphnids. Moreover, we observed elevation of thoracic limb movement and modulation of heart rate in ECT-exposed animals. HSP70 1A and CAT levels were reduced in the presence of ECT. On the other hand, NOx level was slightly elevated in both ECT-treated and unexposed daphnids, however slightly higher NOx level was found in ECT-treated animals. We conclude that the exposure to ectoine has thermoprotective effects on Daphnia magna, however their mechanisms are not associated with the induction of HSP70 1A.

Journal of Comparative Physiology B

18104835

10.1007/S00359-014-0937-8

Neural functions of long noncoding RNAs in Drosophila

Long noncoding RNA (lncRNA) is an emerging category of transcript, and comprises the majority of the transcriptome of various complex organisms. The biological functions of only a handful of lncRNAs have been investigated in detail, showing involvement in a wide range of biological processes through different functional paradigms. However, most lncRNAs remain to be identified. Many lncRNAs are predicted to function, often preferentially, in the nervous system, potentially playing roles in mediating neural functions such as development, behavior, and cognition. To examine the biological significance and potential mechanisms of the remaining unknown neural lncRNAs, certain tractable model organisms, such as Drosophila, can provide advantages including the use of numerous genetic tools. Herein, we summarize recent progress on the in vivo or potential functions of Drosophila lncRNAs, in particular, behavior and development-related lncRNAs.

Journal of Comparative Physiology A

10801553

10.1007/S00360-014-0851-Y

Trypsin isozymes in the lobster Panulirus argus (Latreille, 1804): from molecules to physiology

Trypsin enzymes have been studied in a wide variety of animal taxa due to their central role in protein digestion as well as in other important physiological and biotechnological processes. Crustacean trypsins exhibit a high number of isoforms. However, while differences in properties of isoenzymes are known to play important roles in regulating different physiological processes, there is little information on this aspect for decapod trypsins. The aim of this review is to integrate recent findings at the molecular level on trypsin enzymes of the spiny lobster Panulirus argus, into higher levels of organization (biochemical, organism) and to interpret those findings in relation to the feeding ecology of these crustaceans. Trypsin in lobster is a polymorphic enzyme, showing isoforms that differ in their biochemical features and catalytic efficiencies. Molecular studies suggest that polymorphism in lobster trypsins may be non-neutral. Trypsin isoenzymes are differentially regulated by dietary proteins, and it seems that some isoenzymes have undergone adaptive evolution coupled with a divergence in expression rate to increase fitness. This review highlights important but poorly studied issues in crustaceans in general, such as the relation among trypsin polymorphism, phenotypic (digestive) flexibility, digestion efficiency, and feeding ecology.

Journal of Comparative Physiology B

17294137

10.1007/S00360-014-0853-9

The energetics of a Malagasy rodent, Macrotarsomys ingens (Nesomyinae): a test of island and zoogeographical effects on metabolism

This study provides first insights into the energetics of the Nesomyinae, a subfamily of rodents endemic to Madagascar. The ancestral nesomyine colonized Madagascar from Africa ca. 30–15 mya at the onset of Oligocene global cooling. We tested the hypothesis that, contrary to what might be expected from Island Biogeography theory, post-colonization character displacement of thermoregulatory traits was constrained by phylogenetic inertia through climate adaptation. The study was conducted in the Parc National d’Ankarafantsika, Madagascar. We measured the basal metabolic rate (BMR) and body temperature (Tb) patterns of naturally warm-acclimated, freshly captured adult long-tailed big-footed mice Macrotarsomys ingens (67.4 g). The mean ± SD BMR of M. ingens was 0.298 ± 0.032 Watts (n = 12), 31.7 % lower than that predicted by a phylogenetically independent allometric equation. Body mass was correlated with BMR. The lower critical limit of thermoneutrality (Tlc) was 30.7 °C. The mean ± SD Tb = 36.1 ± 0.8 °C (n = 12) compared well with the mean Tb values for myomorph rodents from the Afrotropical zone, but was lower than those of the Neotropical and Palearctic zones. M. ingens became pathologically hypothermic when exposed to ambient temperatures lower than 18 °C. The soil temperature at depths of 250 mm and deeper did not decrease below 22 °C throughout the austral winter. The thermoregulatory data for M. ingens did not differ from those that characterize mainland Afrotropical rodents. However, BMR and Tb were lower than those of Holarctic rodents. Thus, contrary to expectations of Island Biogeography theory that rapid character displacement often occurs in morphological and behavioural traits when mammals colonize islands, M. ingens displayed climate-related physiological traits indicative of phylogenetic inertia. Presumably the tropical conditions that prevailed on Madagascar at the time of colonisation differed very little from those of the African mainland, and hence there was no strong driving force for change. Unlike small tenrecs and lemurs that radiated on Madagascar prior to the Oligocene, traits associated with an insular existence, such as daily torpor and hibernation, were not evident in M. ingens.

Journal of Comparative Physiology B

16075271

10.1007/S00360-014-0856-6

Chronic mitochondrial uncoupling treatment prevents acute cold-induced oxidative stress in birds

Endotherms have evolved two major types of thermogenesis that allow them to actively produce heat in response to cold exposure, either through muscular activity (i.e. shivering thermogenesis) or through futile electro-chemical cycles (i.e. non-shivering thermogenesis). Amongst the latter, mitochondrial uncoupling is of key importance because it is suggested to drive heat production at a low cost in terms of oxidative stress. While this has been experimentally shown in mammals, the oxidative stress consequences of cold exposure and mitochondrial uncoupling are clearly less understood in the other class of endotherms, the birds. We compared metabolic and oxidative stress responses of zebra finches chronically treated with or without a chemical mitochondrial uncoupler (2,4-dinitrophenol: DNP), undergoing an acute (24 h) and a chronic (4 weeks) cold exposure (12 °C). We predicted that control birds should present at least a transient elevation of oxidative stress levels in response to cold exposure. This oxidative stress cost should be more pronounced in control birds than in DNP-treated birds, due to their lower basal uncoupling state. Despite similar increase in metabolism, control birds presented elevated levels of DNA oxidative damage in response to acute (but not chronic) cold exposure, while DNP-treated birds did not. Plasma antioxidant capacity decreased overall in response to chronic cold exposure. These results show that acute cold exposure increases oxidative stress in birds. However, uncoupling mitochondrial functioning appears as a putative compensatory mechanism preventing cold-induced oxidative stress. This result confirms previous observations in mice and underlines non-shivering thermogenesis as a putative key mechanism for endotherms in mounting a response to cold at a low oxidative cost.

Journal of Comparative Physiology B

14305715

10.1007/S00360-014-0855-7

An in vitro investigation of gastrointestinal Na+ uptake mechanisms in freshwater rainbow trout

In vitro gut-sac preparations of all four sections (stomach, anterior, mid, and posterior intestine) of the gastrointestinal tract (GIT) of freshwater rainbow trout, together with radiotracer (22Na) techniques, were used to study unidirectional Na+ uptake rates (UR, mucosal → blood space) and net absorptive fluid transport rates (FTR) under isosmotic conditions (mucosal = serosal osmolality). On an area-specific basis, unidirectional Na+ UR was highest in the mid-intestine, but when total gut area was taken into account, the three intestinal sections contributed equally, with very low rates in the stomach. The theoretical capacity for Na+ uptake across the whole GIT is sufficient to supply all of the animal’s nutritive requirements for Na+. Transport occurs by low affinity systems with apparent Km values 2–3 orders of magnitude higher than those in the gills, in accord with comparably higher Na+ concentrations in chyme versus fresh water. Fluid transport appeared to be Na+-dependent, such that treatments which altered unidirectional Na+ UR generally altered FTR in a comparable fashion. Pharmacological trials (amiloride, EIPA, phenamil, bafilomycin, furosemide, hydrochlorothiazide) conducted at a mucosal Na+ concentration of 50 mmol L−1 indicated that GIT Na+ uptake occurs by a variety of apical mechanisms (NHE, Na+ channel/H+ ATPase, NCC, NKCC) with relative contributions varying among sections. However, at a mucosal Na+ concentration of 10 mmol L−1, EIPA, phenamil, bafilomycin, and hydrochlorothiazide were no longer effective in inhibiting unidirectional Na+ UR or FTR, suggesting the contribution of unidentified mechanisms under low Na+ conditions. A preliminary model is presented.

Journal of Comparative Physiology B

15483740

10.1007/S00360-014-0859-3

Androgen receptor-mediated regulation of adrenocortical activity in the sand rat, Psammomys obesus

The wild sand rat, Psammomys obesus, displays seasonal variations in adrenocortical activity that parallel those of testicular activity, indicating functional cross-talk between the hypothalamo-pituitary-adrenal and hypothalamo-pituitary–gonadal axes. In the present study, we examined androgen receptor (AR)-mediated actions of testicular steroids in the regulation of adrenocortical function in the sand rat. Specifically, we examined the expression of AR in the adrenal cortex, as well as adrenal apoptosis in male sand rats that had been surgically castrated or castrated and supplemented with testosterone; biochemical indices of adrenocortical function and hormone profiles were also measured. Orchiectomy was followed by an increase in adrenocorticotropic hormone secretion from the anterior pituitary and subsequently, increased adrenocortical activity; the latter was evidenced by orchiectomy-induced increases in the adrenal content of cholesterol and lipids as well as adrenal hypertrophy (seen as an elevation of the RNA/DNA ratio). Further, androgen deprivation respectively up- and downregulated the incidence of apoptosis within the glucocorticoid-producing zona fasciculata and sex steroid-producing zona reticularis. Interestingly, orchiectomy resulted in increased expression of AR in the zona fasciculata. All of the orchiectomy-induced cellular and biochemical responses were reversible after testosterone substitution therapy. Together, these data suggest that adrenocortical activity in the sand rat is seasonally modulated by testicular androgens that act through AR located in the adrenal cortex itself.

Journal of Comparative Physiology B

13735072

10.1007/S00359-014-0933-Z

Hearing in the crepuscular owl butterfly (Caligo eurilochus, Nymphalidae)

Tympanal organs are widespread in Nymphalidae butterflies, with a great deal of variability in the morphology of these ears. How this variation reflects differences in hearing physiology is not currently understood. This study provides the first examination of hearing organs in the crepuscular owl butterfly, Caligo eurilochus. We examined the tuning and sensitivity of the C. eurilochus hearing organ, called Vogel’s organ, using laser Doppler vibrometry and extracellular neurophysiology. We show that the C. eurilochus ear responds to sound and is most sensitive to frequencies between 1 and 4 kHz, as confirmed by both the vibration of the tympanal membrane and the physiological response of the associated nerve branches. In comparison to the hearing of its diurnally active relative, Morpho peleides, C. eurilochus has a narrower frequency range with higher auditory thresholds. Hypotheses explaining the function of hearing in this crepuscular butterfly are discussed.

Journal of Comparative Physiology A

1290596

10.1007/S00360-014-0844-X

Osmoregulatory bicarbonate secretion exploits H+-sensitive haemoglobins to autoregulate intestinal O2 delivery in euryhaline teleosts

AbstractMarine teleost fish secrete bicarbonate (HCO3−) into the intestine to aid osmoregulation and limit Ca2+ uptake by carbonate precipitation. Intestinal HCO3− secretion is associated with an equimolar transport of protons (H+) into the blood, both being proportional to environmental salinity. We hypothesized that the H+-sensitive haemoglobin (Hb) system of seawater teleosts could be exploited via the Bohr and/or Root effects (reduced Hb-O2 affinity and/or capacity with decreasing pH) to improve O2 delivery to intestinal cells during high metabolic demand associated with osmoregulation. To test this, we characterized H+ equilibria and gas exchange properties of European flounder (Platichthys flesus) haemoglobin and constructed a model incorporating these values, intestinal blood flow rates and arterial–venous acidification at three different environmental salinities (33, 60 and 90). The model suggested red blood cell pH (pHi) during passage through intestinal capillaries could be reduced by 0.14–0.33 units (depending on external salinity) which is sufficient to activate the Bohr effect (Bohr coefficient of −0.63), and perhaps even the Root effect, and enhance tissue O2 delivery by up to 42 % without changing blood flow. In vivo measurements of intestinal venous blood pH were not possible in flounder but were in seawater-acclimated rainbow trout which confirmed a blood acidification of no less than 0.2 units (equivalent to −0.12 for pHi). When using trout-specific values for the model variables, predicted values were consistent with measured in vivo values, further supporting the model. Thus this system is an elegant example of autoregulation: as the need for costly osmoregulatory processes (including HCO3− secretion) increases at higher environmental salinity, so does the enhancement of O2 delivery to the intestine via a localized acidosis and the Bohr (and possibly Root) effect.

Journal of Comparative Physiology B

5931793

10.1007/S00360-014-0858-4

Effects of reproductive status and high ambient temperatures on the body temperature of a free-ranging basoendotherm

Tenrecs (Order Afrosoricida) exhibit some of the lowest body temperatures (Tb) of any eutherian mammal. They also have a high level of variability in both active and resting Tbs and, at least in cool temperatures in captivity, frequently employ both short- and long-term torpor. The use of heterothermy by captive animals is, however, generally reduced during gestation and lactation. We present data long-term Tb recordings collected from free-ranging S. setosus over the course of two reproductive seasons. In general, reproductive females had slightly higher (~32 °C) and less variable Tb, whereas non-reproductive females and males showed both a higher propensity for torpor as well as lower (~30.5 °C) and more variable rest-phase Tbs. Torpor expression defined using traditional means (using a threshold or cut-off Tb) was much lower than predicted based on the high degree of heterothermy in captive tenrecs. However, torpor defined in this manner is likely to be underestimated in habitats where ambient temperature is close to Tb. Our results caution against inferring metabolic states from Tb alone and lend support to the recent call to define torpor in free-ranging animals based on mechanistic and not descriptive variables. In addition, lower variability in Tb observed during gestation and lactation confirms that homeothermy is essential for reproduction in this species and probably for basoendothermic mammals in general. The relatively low costs of maintaining homeothermy in a sub-tropical environment might help shed light on how homeothermy could have evolved incrementally from an ancestral heterothermic condition.

Journal of Comparative Physiology B

3121126

10.1007/S00360-014-0850-Z

Behavioral and ecological factors account for variation in the mass-independent energy expenditures of endotherms

A persistent controversy has concerned the identification of the factors that influence the quantitative variation in the physiological characters of species, an example of which is the basal rate of metabolism of endotherms. The most important factor accounting for its variation is body mass as long as the range in mass is appreciable. But mass never accounts for all of the variation and none if species have the same mass. Most of the residual variation around the mass curve is associated with behavioral characters, ecological factors, and phylogeny, i.e., history. These agents influence energy expenditure by different means and at different stages in the life history of species. Phylogeny describes the historic origin, evolution, and distribution of character states in contemporary species. However, the level of energy expenditure is quantitatively determined by the collective of realized states in combination with conditions in the environment. Therefore, two stages determine energy expenditure: (1) the evolution of character states and (2) their impact in conjunction with conditions on the environment. Behavioral characters and ecological factors, when coupled with log10 mass, usually account for >94 % of the variation in the log10 basal rates of birds and mammals, a capacity not found in phylogenetic analyses. The difficulty of determining a direct impact of phylogeny on physiological characters results from its correlation with behavioral characters. When appropriate, the passerine/non-passerine dichotomy in birds and the sub/infraclass dichotomy in mammals combine with behavioral characters, ecological factors, and log10 mass to increase r2 to account for 96–99 % of the variation in log10 basal rate. This occurs because dichotomies incorporate factors other than those already in the analyses. The clearest demonstration of the direct impact of character states is the equality of energy expenditure in species convergent with species from other clades without any evidence of the clade to which the species belong. A multifactorial approach depends on the inclusion of life history characteristics of species, but this analysis applies only to continuous, quantitative relationships, which are often modified by discontinuous agents. Distinctive character states distinguish species and therefore must be included in any attempt to account for differences in their level of energy expenditure. No analysis that ignores life history characteristics can account for the quantitative variation in energy expenditure beyond that associated with body mass.

Journal of Comparative Physiology B

913105

10.1007/S00359-014-0935-X

Which way is up? Asymmetric spectral input along the dorsal–ventral axis influences postural responses in an amphibious annelid

Medicinal leeches are predatory annelids that exhibit countershading and reside in aquatic environments where light levels might be variable. They also leave the water and must contend with terrestrial environments. Yet, leeches generally maintain a dorsal upward position despite lacking statocysts. Leeches respond visually to both green and near-ultraviolet (UV) light. I used LEDs to test the hypothesis that ventral, but not dorsal UV would evoke compensatory movements to orient the body. Untethered leeches were tested using LEDs emitting at red (632 nm), green (513 nm), blue (455 nm) and UV (372 nm). UV light evoked responses in 100 % of trials and the leeches often rotated the ventral surface away from it. Visible light evoked no or modest responses (12–15 % of trials) and no body rotation. Electrophysiological recordings showed that ventral sensilla responded best to UV, dorsal sensilla to green. Additionally, a higher order interneuron that is engaged in a variety of parallel networks responded vigorously to UV presented ventrally, and both the visible and UV responses exhibited pronounced light adaptation. These results strongly support the suggestion that a dorsal light reflex in the leech uses spectral comparisons across the dorsal–ventral axis rather than, or in addition to, luminance.

Journal of Comparative Physiology A

6777212

10.1007/S00359-014-0934-Y

Cross-modal interaction between visual and olfactory learning in Apis cerana

The power of the small honeybee brain carrying out behavioral and cognitive tasks has been shown repeatedly to be highly impressive. The present study investigates, for the first time, the cross-modal interaction between visual and olfactory learning in Apis cerana. To explore the role and molecular mechanisms of cross-modal learning in A. cerana, the honeybees were trained and tested in a modified Y-maze with seven visual and five olfactory stimulus, where a robust visual threshold for black/white grating (period of 2.8°–3.8°) and relatively olfactory threshold (concentration of 50–25 %) was obtained. Meanwhile, the expression levels of five genes (AcCREB, Acdop1, Acdop2, Acdop3, Actyr1) related to learning and memory were analyzed under different training conditions by real-time RT-PCR. The experimental results indicate that A. cerana could exhibit cross-modal interactions between visual and olfactory learning by reducing the threshold level of the conditioning stimuli, and that these genes may play important roles in the learning process of honeybees.

Journal of Comparative Physiology A

18304217

10.1007/S00360-014-0857-5

Aging alters contractile properties and fiber morphology in pigeon skeletal muscle

In this study, we tested the hypothesis that skeletal muscle from pigeons would display age-related alterations in isometric force and contractile parameters as well as a shift of the single muscle fiber cross-sectional area (CSA) distribution toward smaller fiber sizes. Maximal force output, twitch contraction durations and the force–frequency relationship were determined in tensor propatagialis pars biceps muscle from young 3-year-old pigeons, middle-aged 18-year-old pigeons, and aged 30-year-old pigeons. The fiber CSA distribution was determined by planimetry from muscle sections stained with hematoxylin and eosin. Maximal force output of twitch and tetanic contractions was greatest in muscles from young pigeons, while the time to peak force of twitch contractions was longest in muscles from aged pigeons. There were no changes in the force–frequency relationship between the age groups. Interestingly, the fiber CSA distribution in aged muscles revealed a greater number of larger sized muscle fibers, which was verified visually in histological images. Middle-aged and aged muscles also displayed a greater amount of slow myosin containing muscle fibers. These data demonstrate that muscles from middle-aged and aged pigeons are susceptible to alterations in contractile properties that are consistent with aging, including lower force production and longer contraction durations. These functional changes were supported by the appearance of slow myosin containing muscle fibers in muscles from middle-aged and aged pigeons. Therefore, the pigeon may represent an appropriate animal model for the study of aging-related alterations in skeletal muscle function and structure.

Journal of Comparative Physiology B

17910462

10.1007/S00360-014-0854-8

Living in the fast lane: rapid development of the locomotor muscle in immature harbor porpoises (Phocoena phocoena)

Cetaceans (dolphins and whales) are born into the aquatic environment and are immediately challenged by the demands of hypoxia and exercise. This should promote rapid development of the muscle biochemistry that supports diving, but previous research on two odontocete (toothed whales and dolphins) species showed protracted postnatal development for myoglobin content and buffering capacity. A minimum of 1 and 1.5 years were required for Fraser’s (Lagenodelphis hosei) and bottlenose (Tursiops truncatus) dolphins to obtain mature myoglobin contents, respectively; this corresponded to their lengthy 2 and 2.5-year calving intervals (a proxy for the dependency period of cetacean calves). To further examine the correlation between the durations for muscle maturation and maternal dependency, we measured myoglobin content and buffering capacity in the main locomotor muscle (longissimus dorsi) of harbor porpoises (Phocoenaphocoena), a species with a comparatively short calving interval (1.5 years). We found that at birth, porpoises had 51 and 69 % of adult levels for myoglobin and buffering capacity, respectively, demonstrating greater muscle maturity at birth than that found previously for neonatal bottlenose dolphins (10 and 65 %, respectively). Porpoises achieved adult levels for myoglobin and buffering capacity by 9–10 months and 2–3 years postpartum, respectively. This muscle maturation occurred at an earlier age than that found previously for the dolphin species. These results support the observation that variability in the duration for muscular development is associated with disparate life history patterns across odontocetes, suggesting that the pace of muscle maturation is not solely influenced by exposure to hypoxia and exercise. Though the mechanism that drives this variability remains unknown, nonetheless, these results highlight the importance of documenting the species-specific physiological development that limits diving capabilities and ultimately defines habitat utilization patterns across age classes.

Journal of Comparative Physiology B

6524653

10.1007/S00359-014-0932-0

Toxins induce ‘malaise’ behaviour in the honeybee (Apis mellifera)

To avoid poisoning and death when toxins are ingested, the body responds with a suite of physiological detoxification mechanisms accompanied by behaviours that in mammals often include vomiting, nausea, and lethargy. Few studies have characterised whether insects exhibit characteristic ‘malaise-like’ behaviours in response to intoxication. Here, we used the honeybee to investigate how intoxication produced by injection or ingestion with three toxins with different pharmacological modes of action quinine, amygdalin, and lithium chloride affected behaviour. We found that toxin-induced changes in behaviour were best characterised by more time spent grooming. Bees also had difficulty performing the righting reflex and exhibited specific toxin-induced behaviours such as abdomen dragging and curling up. The expression of these behaviours also depended on whether a toxin had been injected or ingested. When toxins were ingested, they were least 10 times less concentrated in the haemolymph than in the ingested food, suggesting that their absorption through the gut is strongly regulated. Our data show that bees exhibit changes in behaviour that are characteristic of ‘malaise’ and suggest that physiological signalling of toxicosis is accomplished by multiple post-ingestive pathways in animals.

Journal of Comparative Physiology A

18720307

10.1007/S00359-014-0931-1

Characterisation of whisker control in the California sea lion (Zalophus californianus) during a complex, dynamic sensorimotor task

Studies in pinniped whisker use have shown that their whiskers are extremely sensitive to tactile and hydrodynamic signals. While pinnipeds position their whiskers on to objects and have some control over their whisker protractions, it has always been thought that head movements are more responsible for whisker positioning than the movement of the whiskers themselves. This study uses ball balancing, a dynamic sensorimotor skill that is often used in human and robotic coordination studies, to promote sea lion whisker movements during the task. For the first time, using tracked video footage, we show that sea lion whisker movements respond quickly (26.70 ms) and mirror the movement of the ball, much more so than the head. We show that whisker asymmetry and spread are both altered to help sense and control the ball during balancing. We believe that by designing more dynamic sensorimotor tasks we can start to characterise the active nature of this specialised sensory system in pinnipeds.

Journal of Comparative Physiology A

5864619

10.1007/S00360-014-0852-X

Dietary effect on immunological energetics in mice

Defense against natural aggressors, such as bacterial infections, requires both energy and an immune-cellular response. However, the question as to how these two components are interconnected in small endotherms by means of the host diet remains only poorly understood. Here, we tested in laboratory mice whether dietary proteins and carbohydrates can modulate the interplay between energy expenditure, food intake and the innate and adaptive immune response when confronting a bacterial challenge (Bacillus Calmette-Guérin, BCG). We observed that mice fed with a high protein diet (HP) developed a better immune response associated to increased numbers of circulating monocytes. In addition, HP diet directly influenced the peripheral blood proportions of both T and B lymphocytes even before the BCG challenge. Interestingly, animals that developed this type of immune response after BCG challenge showed an increased rate of metabolism and food consumption before being challenged. Thus, HP diet induced in non-challenged animals a similar energy expenditure and food intake described by BCG-treated mice. These data suggest that a high amount of proteins in diet can modify the energetic and nutrient dynamic in the host causing a better immune reaction against a microbial challenge.

Journal of Comparative Physiology B

14068738

10.1007/S00360-014-0848-6

Adjustments in cholinergic, adrenergic and purinergic control of cardiovascular function in snapping turtle embryos (Chelydra serpentina) incubated in chronic hypoxia

Adenosine is an endogenous nucleoside that acts via G-protein coupled receptors. In vertebrates, arterial or venous adenosine injection causes a rapid and large bradycardia through atrioventricular node block, a response mediated by adenosine receptors that inhibit adenylate cyclase and decrease cyclic AMP concentration. Chronic developmental hypoxia has been shown to alter cardioregulatory mechanisms in reptile embryos, but adenosine’s role in mediating these responses is not known. We incubated snapping turtle embryos under chronic normoxic (N21; 21 % O2) or chronic hypoxic conditions (H10; 10 % O2) beginning at 20 % of embryonic incubation. H10 embryos at 90 % of incubation were hypotensive relative to N21 embryos in both normoxic and hypoxic conditions. Hypoxia caused a hypotensive bradycardia in both N21 and H10 embryos during the initial 30 min of exposure; however, fH and Pm both trended towards increasing during the subsequent 30 min, and H10 embryos were tachycardic relative to N21 embryos in hypoxia. Following serial ≥1 h exposure to normoxic and hypoxic conditions, a single injection of adenosine (1 mg kg−1) was given. N21 and H10 embryos responded to adenosine injection with a rapid and large hypotensive bradycardia in both normoxia and hypoxia. Gene expression for adenosine receptors were quantified in cardiac tissue, and Adora1 mRNA was the predominant receptor subtype with transcript levels 30–82-fold higher than Adora2A or Adora2B. At 70 % of incubation, H10 embryos had lower Adora1 and Adora2B expression compared to N21 embryos. Expression of Adora1 and Adora2B decreased in N21 embryos during development and did not differ from H10 embryos at 90 % of incubation. Similar to previous results in normoxia, H10 embryos in hypoxia were chronically tachycardic compared to N21 embryos before and after complete cholinergic and adrenergic blockade. Chronic hypoxia altered the development of normal cholinergic and adrenergic tone, as well as adenosine receptor mRNA levels. This study demonstrates that adenosine may be a major regulator of heart rate in developing snapping turtle embryos, and that chronic hypoxic incubation alters the response to hypoxic exposure.

Journal of Comparative Physiology B

16499864

10.1007/S00360-014-0847-7

Mechanisms of Na+ uptake, ammonia excretion, and their potential linkage in native Rio Negro tetras (Paracheirodon axelrodi, Hemigrammus rhodostomus, and Moenkhausia diktyota)

Mechanisms of Na+ uptake, ammonia excretion, and their potential linkage were investigated in three characids (cardinal, hemigrammus, moenkhausia tetras), using radiotracer flux techniques to study the unidirectional influx (Jin), efflux (Jout), and net flux rates (Jnet) of Na+ and Cl−, and the net excretion rate of ammonia (JAmm). The fish were collected directly from the Rio Negro, and studied in their native “blackwater” which is acidic (pH 4.5), ion-poor (Na+, Cl− ~20 µM), and rich in dissolved organic matter (DOM 11.5 mg C l−1). JinNa, JinCl, and JAmm were higher than in previous reports on tetras obtained from the North America aquarium trade and/or studied in low DOM water. In all three species, JinNa was unaffected by amiloride (10−4 M, NHE and Na+ channel blocker), but both JinNa and JinCl were virtually eliminated (85–99 % blockade) by AgNO3 (10−7 M). A time course study on cardinal tetras demonstrated that JinNa blockade by AgNO3 was very rapid (<5 min), suggesting inhibition of branchial carbonic anhydrase (CA), and exposure to the CA-blocker acetazolamide (10−4 M) caused a 50 % reduction in JinNa.. Additionally, JinNa was unaffected by phenamil (10−5 M, Na+ channel blocker), bumetanide (10−4 M, NKCC blocker), hydrochlorothiazide (5 × 10−3 M, NCC blocker), and exposure to an acute 3 unit increase in water pH. None of these treatments, including partial or complete elimination of JinNa (by acetazolamide and AgNO3 respectively), had any inhibitory effect on JAmm. Therefore, Na+ uptake in Rio Negro tetras depends on an internal supply of H+ from CA, but does not fit any of the currently accepted H+-dependent models (NHE, Na+ channel/V-type H+-ATPase), or co-transport schemes (NCC, NKCC), and ammonia excretion does not fit the current “Na+/NH4+ exchange metabolon” paradigm. Na+, K+-ATPase and V-type H+-ATPase activities were present at similar levels in gill homogenates, Acute exposure to high environmental ammonia (NH4Cl, 10−3 M) significantly increased JinNa, and NH4+ was equally or more effective than K+ in activating branchial Na+,(K+) ATPase activity in vitro. We propose that ammonia excretion does not depend on Na+ uptake, but that Na+ uptake (by an as yet unknown H+-dependent apical mechanism) depends on ammonia excretion, driven by active NH4+ entry via basolateral Na+,(K+)-ATPase.

Journal of Comparative Physiology B

18751688

10.1007/S00360-014-0849-5

Modulation of aquaporin 2 expression in the kidney of young goats by changes in nitrogen intake

In ruminants, a decrease of dietary nitrogen (N) is an appropriate feeding concept to reduce environmental pollution and costs. In our previous study, when goats were kept on an N-reduced diet, a decrease of plasma urea concentration and an increase of renal urea transporters were demonstrated. Renal urea absorption plays a crucial role for renal water absorption and urine concentration. Renal collecting duct water absorption is mainly mediated by the water channel aquaporin 1 and 2 (AQP1 and AQP2). Therefore, the aim of the present study was to investigate the effects of a dietary N reduction on expression of renal AQP1 and AQP2 in young goats. Twenty male White Saanen goats, 3 months old, were divided equally into two feeding groups, receiving either a diet with an adequate or a reduced-N supply. Goats fed a reduced-N diet showed significantly higher amounts of AQP1 mRNA in cortical tissue, and the expression of AQP2 mRNA and protein were highly elevated in renal outer medulla. An increase of vasopressin concentrations in plasma were detected for the N-reduced fed goats. Therefore, a stimulation of renal water absorption can be assumed. This might be an advantage for ruminants in times of N reduction due to higher urea concentrations in the tubular fluid and which might result in higher absorption of urea by renal urea transporters. Therefore, interplay of aquaporin water channels and urea transporters in the kidney may occur to maintain urea metabolism in times of N scarcity in young goats.

Journal of Comparative Physiology B

8704977

10.1007/S00360-014-0846-8

Starvation-responsive glycine-rich protein gene in the silkworm Bombyx mori

Four glycine-rich protein (GRP) genes were identified from expressed sequence tags of the maxillary galea of the silkworm. All four genes were expressed in the maxillary pulp, antenna, labrum, and labium, but none of the genes were expressed in most internal organs. Expression of one of the genes, termed bmSIGRP, was further increased approximately fivefold in the mouth region (including the maxilla, antenna, labrum, labium, and mandible) after 24 h of starvation. bmSIGRP expression peaked at 24 h and gradually declined during the subsequent 2 days. When a synthetic diet not containing proteins was fed, bmSIGRP expression increased significantly in the mouth region to levels similar to that observed in starved larvae. Synthetic diets that lacked vitamins or salts but contained amino acids did not significantly affect bmSIGRP expression. These results suggest that amino acid depletion increases bmSIGRP expression.

Journal of Comparative Physiology B

14842736

10.1007/S00359-014-0929-8

Audiogram of the chicken (Gallus gallus domesticus) from 2 Hz to 9 kHz

The pure-tone thresholds of four domestic female chickens were determined from 2 Hz to 9 kHz using the method of conditioned suppression/avoidance. At a level of 60 dB sound pressure level (re 20 μN/m2), their hearing range extends from 9.1 Hz to 7.2 kHz, with a best sensitivity of 2.6 dB at 2 kHz. Chickens have better sensitivity than humans for frequencies below 64 Hz; indeed, their sensitivity to infrasound exceeds that of the homing pigeon. However, when threshold testing moved to the lower frequencies, the animals required additional training before their final thresholds were obtained, suggesting that they may perceive frequencies below 64 Hz differently than higher frequencies.

Journal of Comparative Physiology A

15094150

10.1007/S00360-014-0845-9

Evidence of endoplasmic reticulum stress and liver inflammation in the American mink Neovison vison with benign hepatic steatosis

We investigated the presence of inflammatory signs in the progression of fatty liver disease induced by fasting. Sixty standard black American mink (Neovison vison) were fasted for 0, 1, 3, 5, or 7 days and one group for 7 days followed by re-feeding for 28 days. Liver sections were evaluated histologically and liver mRNA levels indicating endoplasmic reticulum (ER) stress, adipogenic transformation, and inflammation were assessed by quantitative real-time PCR. After 3 days of fasting, the mink had developed moderate liver steatosis. Increased hyaluronan reactivity in lymphocytic foci but no Mallory–Denk bodies were seen in livers of the mink fasted for 5–7 days. Up-regulation of glucose-regulated protein, 78 kDa was observed on day 7 indicating ER stress, especially in the females. Liver lipoprotein lipase and monocyte chemoattractant protein 1 mRNA levels increased in response to 5–7 days of food deprivation, while tumor necrosis factor α (TNF-α) was the highest in the mink fasted for 5 days. The expression of the genes of interest, except for TNF-α, correlated with each other and with the liver fat content. The mRNA levels were found to change more rapidly below n-3/n-6 polyunsaturated fatty acid ratio threshold of 0.15. Following re-feeding, hepatocyte morphology and mRNA abundance returned to pre-fasting levels. Within the studied timeframe, evidence for ER stress, adipogenic transformation, and liver inflammation suggested incipient transition from steatosis to steatohepatitis with potential for development of more severe liver disease. This may present a possibility to influence disease progression before histologically observable steatohepatitis.

Journal of Comparative Physiology B

10065586

10.1007/S00359-014-0928-9

Transfer of directional information between the polarization compass and the sun compass in desert ants

Desert ants, Cataglyphis fortis, perform large foraging excursions during which they continuously compute a home vector that allows them to return to the nest on the shortest way. This type of navigation, termed path integration, needs a compass system and an odometer. Ants use several cues to determine their walking direction, two of the most important ones being the sun position and the polarization pattern of the sky. We tested whether an information transfer is possible from one compass system to the other, which depend on different anatomical substrates. Since the sky’s polarization pattern is detected by UV-photoreceptors located in the dorsal rim area (DRA), we used an orange Perspex filter that eliminated the UV part of the spectrum to prevent the use of the polarization compass. The use of the sun compass could be excluded by appropriate screens. In the critical tests the ants had learned a nest-feeder direction with e.g. the sun compass only, and were later tested with the polarization compass, or vice versa. The results show that a transfer is possible in both directions.

Journal of Comparative Physiology A

8935061

10.1007/S00359-014-0927-X

Simulating natural light and temperature cycles in the laboratory reveals differential effects on activity/rest rhythm of four Drosophilids

Recent studies under semi-natural conditions have revealed various unique features of activity/rest rhythms in Drosophilids that differ from those under standard laboratory conditions. An additional afternoon peak (A-peak) has been reported for Drosophila melanogaster and another species D. malerkotliana while D. ananassae exhibited mostly unimodal diurnal activity. To tease apart the role of light and temperature in mediating these species-specific behaviours of four Drosophilid species D. melanogaster, D. malerkotliana, D. ananassae, and Zaprionus indianus we simulated gradual natural light and/or temperature cycles conditions in laboratory. The pattern observed under semi-natural conditions could be reproduced in the laboratory for all the species under a variety of simulated conditions. D. melanogaster and D. malerkotliana showed similar patterns where as D. ananassae consistently exhibited predominant morning activity under almost all regimes. Z. indianus showed clearly rhythmic activity mostly when temperature cycles were provided. We find that gradually changing light intensities reaching a sufficiently high peak value can elicit A-peak in D. melanogaster, D. malerkotliana, and D. ananassae even at mild ambient temperature. Furthermore, we show that high mid-day temperature could induce A-peak in all species even under constant light conditions suggesting that this A-peak is likely to be a stress response.

Journal of Comparative Physiology A

2110247

10.1007/S00359-014-0926-Y

Temperature effects on the tympanal membrane and auditory receptor neurons in the locust

Poikilothermic animals are affected by variations in environmental temperature, as the basic properties of nerve cells and muscles are altered. Nevertheless, insect sensory systems, such as the auditory system, need to function effectively over a wide range of temperatures, as sudden changes of up to 10 °C or more are common. We investigated the performance of auditory receptor neurons and properties of the tympanal membrane of Locusta migratoria in response to temperature changes. Intracellular recordings of receptors at two temperatures (21 and 28 °C) revealed a moderate increase in spike rate with a mean Q10 of 1.4. With rising temperature, the spike rate–intensity–functions exhibited small decreases in thresholds and expansions of the dynamic range, while spike durations decreased. Tympanal membrane displacement, investigated using microscanning laser vibrometry, exhibited a small temperature effect, with a Q10 of 1.2. These findings suggest that locusts are affected by shifts in temperature at the periphery of the auditory pathway, but the effects on spike rate, sensitivity, and tympanal membrane displacement are small. Robust encoding of acoustic signals by only slightly temperature-dependent receptor neurons and almost temperature-independent tympanal membrane properties might enable locusts and grasshoppers to reliably identify sounds in spite of changes of their body temperature.

Journal of Comparative Physiology A

18996428

10.1007/S00360-014-0842-Z

Molecular characterization of argininosuccinate synthase and argininosuccinate lyase from the liver of the African lungfish Protopterus annectens, and their mRNA expression levels in the liver, kidney, brain and skeletal muscle during aestivation

Argininosuccinate synthase (Ass) and argininosuccinate lyase (Asl) are involved in arginine synthesis for various purposes. The complete cDNA coding sequences of ass and asl from the liver of Protopterus annectens consisted of 1,296 and 1,398 bp, respectively. Phylogenetic analyses revealed that the deduced Ass and Asl of P. annectens had close relationship with that of the cartilaginous fish Callorhinchusmilii. Besides being strongly expressed in the liver, ass and asl expression were detectable in many tissues/organs. In the liver, mRNA expression levels of ass and asl increased significantly during the induction phase of aestivation, probably to increase arginine production to support increased urea synthesis. The increases in ass and asl mRNA expression levels during the prolonged maintenance phase and early arousal phase of aestivation could reflect increased demand on arginine for nitric oxide (NO) production in the liver. In the kidney, there was a significant decrease in ass mRNA expression level after 6 months of aestivation, indicating possible decreases in the synthesis and supply of arginine to other tissues/organs. In the brain, changes in ass and asl mRNA expression levels during the three phases of aestivation could be related to the supply of arginine for NO synthesis in response to conditions that resemble ischaemia and ischaemia–reperfusion during the maintenance and arousal phase of aestivation, respectively. The decrease in ass mRNA expression level, accompanied with decreases in the concentrations of arginine and NO, in the skeletal muscle of aestivating P. annectens might ameliorate the potential of disuse muscle atrophy.

Journal of Comparative Physiology B

11109453

10.1007/S00360-014-0843-Y

Sugar flux through the flight muscles of hovering vertebrate nectarivores: a review

In most vertebrates, uptake and oxidation of circulating sugars by locomotor muscles rises with increasing exercise intensity. However, uptake rate by muscle plateaus at moderate aerobic exercise intensities and intracellular fuels dominate at oxygen consumption rates of 50 % of maximum or more. Further, uptake and oxidation of circulating fructose by muscle is negligible. In contrast, hummingbirds and nectar bats are capable of fueling expensive hovering flight exclusively, or nearly completely, with dietary sugar. In addition, hummingbirds and nectar bats appear capable of fueling hovering flight completely with fructose. Three crucial steps are believed to be rate limiting to muscle uptake of circulating glucose or fructose in vertebrates: (1) delivery to muscle; (2) transport into muscle through glucose transporter proteins (GLUTs); and (3) phosphorylation of glucose by hexokinase (HK) within the muscle. In this review, we summarize what is known about the functional upregulation of exogenous sugar flux at each of these steps in hummingbirds and nectar bats. High cardiac output, capillary density, and blood sugar levels in hummingbirds and bats enhance sugar delivery to muscles (step 1). Hummingbird and nectar bat flight muscle fibers have relatively small cross-sectional areas and thus relatively high surface areas across which transport can occur (step 2). Maximum HK activities in each species are enough for carbohydrate flux through glycolysis to satisfy 100 % of hovering oxidative demand (step 3). However, qualitative patterns of GLUT expression in the muscle (step 2) raise more questions than they answer regarding sugar transport in hummingbirds and suggest major differences in the regulation of sugar flux compared to nectar bats. Behavioral and physiological similarities among hummingbirds, nectar bats, and other vertebrates suggest enhanced capacities for exogenous fuel use during exercise may be more wide spread than previously appreciated. Further, how the capacity for uptake and phosphorylation of circulating fructose is enhanced remains a tantalizing unknown.

Journal of Comparative Physiology B

17690980

10.1007/S00360-014-0839-7

Oxygen removal from water versus arterial oxygen delivery: calibrating the Fick equation in Pacific salmon

While it is well known that O2 is directly removed from the water by skin and gill tissues of fish, the mismatch between O2 removal from water (O2 uptake; $$\dot{V}{\text{O}}_{ 2}$$V˙O2) and the O2 delivered to tissues by the primary circulation (O2 consumption; $$\dot{V}{\text{aO}}_{ 2}$$V˙aO2) has never been measured directly. Using data from four recent studies that simultaneously measured $$\dot{V}{\text{O}}_{ 2}$$V˙O2 and $$\dot{V}{\text{aO}}_{ 2}$$V˙aO2 in 2–5 kg Pacific salmon, our analysis revealed that sockeye salmon can remove an additional 12–48 % more O2 from the water than the primary circulation delivers to the systemic tissues. This percentage did not change significantly during swimming activity, a result that contradicts an earlier prediction that the difference should decrease when $$\dot{V}{\text{O}}_{ 2}$$V˙O2 increases during exercise. In resting Chinook salmon, a similar percentage difference in simultaneously measured $$\dot{V}{\text{O}}_{ 2}$$V˙O2 and $$\dot{V}{\text{O}}_{ 2}$$V˙O2 was observed, yet the difference tended to disappear during acute heat stress to a near lethal temperature. These results emphasize that caution should be exercised when using the Fick equation to estimate cardiac output because the overestimate of cardiac output that results from using the Fick equation in Pacific salmon is not small, may not be fixed and may exist in other teleosts.

Journal of Comparative Physiology B

7892948

10.1007/S00360-014-0841-0

Autonomic control of heart rate during orthostasis and the importance of orthostatic-tachycardia in the snake Python molurus

Orthostasis dramatically influences the hemodynamics of terrestrial vertebrates, especially large and elongated animals such as snakes. When these animals assume a vertical orientation, gravity tends to reduce venous return, cardiac filling, cardiac output and blood pressure to the anterior regions of the body. The hypotension triggers physiological responses, which generally include vasomotor adjustments and tachycardia to normalize blood pressure. While some studies have focused on understanding the regulation of these vasomotor adjustments in ectothermic vertebrates, little is known about regulation and the importance of heart rate in these animals during orthostasis. We acquired heart rate and carotid pulse pressure (PPC) in pythons in their horizontal position, and during 30 and 60° inclinations while the animals were either untreated (control) or upon muscarinic cholinoceptor blockade and a double autonomic blockade. Double autonomic blockade completely eradicated the orthostatic-tachycardia, and without this adjustment, the PPC reduction caused by the tilts became higher than that which was observed in untreated animals. On the other hand, post-inclinatory vasomotor adjustments appeared to be of negligible importance in counterbalancing the hemodynamic effects of gravity. Finally, calculations of cardiac autonomic tones at each position revealed that the orthostatic-tachycardia is almost completely elicited by a withdrawal of vagal drive.

Journal of Comparative Physiology B

14327518

10.1007/S00359-014-0925-Z

Why do green rods of frog and toad retinas look green?

Amphibian “green” rods express a blue-sensitive cone visual pigment, and should look yellow. However, when observing them axially under microscope one sees them as green. We used single-cell microspectrophotometry (MSP) to reveal the basis of the perceived color of these photoreceptors. Conventional side-on MSP recording of the proximal cell segments reveals no selective long-wave absorbing pigment explaining the green color. End-on MSP recording shows, in addition to the green rod visual pigment, an extra 2- to 4-fold attenuation being almost flat throughout the visible spectrum. This attenuation is absent in red (rhodopsin) rods, and vanishes in green rods when the retina is bathed in high-refractive media, and at wide illumination aperture. The same treatments change the color from green to yellow. It seems that the non-visual pigment attenuation is a result of slender green rod myoids operating as non-selective light guides. We hypothesize that narrow myoids, combined with photomechanical movements of melanin granules, allow a wide range of sensitivity regulation supporting the operation of green rods as blue receptors at mesopic-to low-photopic illumination levels. End-on transmittance spectrum of green rods looks similar to the reflectance spectrum of khaki military uniforms. So their greenness is the combined result of optics and human color vision.

Journal of Comparative Physiology A

1543451

10.1007/S00360-014-0840-1

Antioxidative properties of 4-methylumbelliferone are related to antibacterial activity in the silkworm (Bombyx mori) digestive tract

Umbelliferones have gained significant attention due to their tumor-inhibitory effects in vitro. This study was undertaken to examine the impact of umbelliferones in an invertebrate model organism, Bombyx mori, to assess the underlying antimicrobial activities via antioxidation in vivo. Oral administration of 4 mM 4-methylumbelliferone (4-MU), a model umbelliferone drug, in B. Mori larvae caused a rapid increase in reactive oxygen species, such as hydrogen peroxide (H2O2) and antimicrobial activity in the digestive tract. In addition, a significant increase in total antioxidant capacity as well as superoxide anion radical-inhibiting activity and reduced glutathione were detected. The antioxidant defense system was activated following induction of H2O2, resulting in a significant rise in catalase (50–66 %) and glutathione peroxidase (175 %) activities, which were helpful in defending digestive tract cells against oxidative injury. These results help in understanding the anticancer mechanism of 4-MU based on its antioxidation in organisms.

Journal of Comparative Physiology B

11836188

10.1007/S00360-014-0832-1

Feeding and digestive responses to fatty acid intake in two South American passerines with different food habits

Specific fatty acids (FA) such as unsaturated (UFA) and saturated (SFA) fatty acids contained in foods are key factors in the nutritional ecology of birds. By means of a field and experimental approach, we evaluated the effect of diet on the activity of three esterases involved in FA hydrolysis; carboxylesterase (CE: 4-NPA-CE and a-NA-CE) and butyrylcholinesterase, in two South American passerines: the omnivorous rufous-collared sparrow (Zonotrichia capensis) and the granivorous common diuca-finch (Diuca diuca). The activity of the three esterases was measured in the intestines of freshly caught individuals over two distinct seasons and also after a chronic intake of a UFA-rich or SFA-rich diet in the laboratory. In turn, we assessed the feeding responses of the birds choosing amongst diets contrasting in the kind of specific FA (UFA- vs. SFA-treated diets). During summer, field CE activities (4-NPA-CE and a-NA-CE) in the small intestine were higher in the rufous-collared sparrow (25.3 ± 3.3 and 81.4 ± 10.8 µmol min−1 g tissue−1, respectively) than in the common diuca-finch (10.0 ± 3.0 and 33.9 ± 13.1 µmol min−1 g tissue−1, respectively). Two hour feeding trial test indicated that both species exhibited a clear preference for UFA-treated diets. On average, the rufous-collared sparrow consumed 0.46 g 2 h−1 of UFA-rich diets and 0.12 g 2 h−1 of SFA-rich diets. In turn, the consumption pattern of the common diuca-finch averaged 0.73 and 0.16 g 2 h−1 for UFA-rich and SFA-rich diets, respectively. After a month of dietary acclimation to UFA-rich and SFA-rich diets, both species maintained body mass irrespective of the dietary regime. Additionally, the intestinal 4-NPA-CE activity exhibited by birds fed on a UFA-rich or SFA-rich diet was higher in the rufous-collared sparrow (39.0 ± 5.3 and 44.2 ± 7.3 µmol min−1 g tissue−1, respectively) than in the common diuca-finch (13.3 ± 1.9 and 11.2 ± 1.4 µmol min−1 g tissue−1, respectively). Finally, the intestinal a-NA-CE activity exhibited by the rufous-collared sparrow was about two times higher when consuming an UFA-rich diet. Our results suggest that the rufus-collared sparrow exhibits a greater capacity for intestinal FA hydrolysis, which would allow it to better deal with fats from different sources.

Journal of Comparative Physiology B

17947882

10.1007/S00359-014-0924-0

Convergent evolution of anti-bat sounds

Bats and their insect prey rely on acoustic sensing in predator prey encounters—echolocation in bats, tympanic hearing in moths. Some insects also emit sounds for bat defense. Here, we describe a previously unknown sound-producing organ in Geometrid moths—a prothoracic tymbal in the orange beggar moth (Eubaphe unicolor) that generates bursts of ultrasonic clicks in response to tactile stimulation and playback of a bat echolocation attack sequence. Using scanning electron microscopy and high-speed videography, we demonstrate that E. unicolor and phylogenetically distant tiger moths have evolved serially homologous thoracic tymbal organs with fundamentally similar functional morphology, a striking example of convergent evolution. We compared E. unicolor clicks to that of five sympatric tiger moths and found that 9 of 13 E. unicolor clicking parameters were within the range of sympatric tiger moths. Remaining differences may result from the small size of the E. unicolor tymbal. Four of the five sympatric clicking tiger moth species were unpalatable to bats (0–20 % eaten), whereas E. unicolor was palatable to bats (86 % eaten). Based on these results, we hypothesize that E. unicolor evolved tymbal organs that mimic the sounds produced by toxic tiger moths when attacked by echolocating bats.

Journal of Comparative Physiology A

6783482

10.1007/S00360-014-0838-8

Preferential intracellular pH regulation represents a general pattern of pH homeostasis during acid–base disturbances in the armoured catfish, Pterygoplichthys pardalis

Preferential intracellular pH (pHi) regulation, where pHi is tightly regulated in the face of a blood acidosis, has been observed in a few species of fish, but only during elevated blood PCO2. To determine whether preferential pHi regulation may represent a general pattern for acid–base regulation during other pH disturbances we challenged the armoured catfish, Pterygoplichthys pardalis, with anoxia and exhaustive exercise, to induce a metabolic acidosis, and bicarbonate injections to induce a metabolic alkalosis. Fish were terminally sampled 2–3 h following the respective treatments and extracellular blood pH, pHi of red blood cells (RBC), brain, heart, liver and white muscle, and plasma lactate and total CO2 were measured. All treatments resulted in significant changes in extracellular pH and RBC pHi that likely cover a large portion of the pH tolerance limits of this species (pH 7.15–7.86). In all tissues other than RBC, pHi remained tightly regulated and did not differ significantly from control values, with the exception of a decrease in white muscle pHi after anoxia and an increase in liver pHi following a metabolic alkalosis. Thus preferential pHi regulation appears to be a general pattern for acid–base homeostasis in the armoured catfish and may be a common response in Amazonian fishes.

Journal of Comparative Physiology B

18963533

10.1007/S00359-014-0923-1

From uni- to multimodality: towards an integrative view on anuran communication

Undeniably, acoustic signals are the predominant mode of communication in frogs and toads. Acoustically active species are found throughout the vast diversity of anuran families. However, additional or alternative signal modalities have gained increasing attention. In several anurans, seismic, visual and chemical communications have convergently evolved due to ecological constraints such as noisy environments. The production of a visual cue, like the inevitably moving vocal sac of acoustically advertising males, is emphasized by conspicuously coloured throats. Limb movements accompanied by dynamic displays of bright colours are additional examples of striking visual signals independent of vocalizations. In some multimodal anuran communication systems, the acoustic component acts as an alert signal, which alters the receiver attention to the following visual display. Recent findings of colourful glands on vocal sacs, producing volatile species-specific scent bouquets suggest the possibility of integration of acoustic, visual and chemical cues in species recognition and mate choice. The combination of signal components facilitates a broadened display repertoire in challenging environmental conditions. Thus, the complexity of the communication systems of frogs and toads may have been underestimated.

Journal of Comparative Physiology A

12699006

10.1007/S00360-014-0837-9

The influence of reproductive condition and concurrent environmental factors on torpor and foraging patterns in female big brown bats (Eptesicus fuscus)

AbstractUnlike many othe r mammals, bats in temperate regions employ short bouts of torpor throughout the reproductive period to maintain a positive energy balance. In addition to decreasing energy expenditure during the day, they typically alter foraging patterns as well. It is well known that various environmental conditions influence both torpor and foraging patterns, but studies of these factors often have focussed on one element in isolation thus it is not known how the two behaviours are collectively influencing temperate bats. The objective of our study was to assess how reproductive condition and environmental factors concurrently affect energy balance in female big brown bats (Eptesicus fuscus). We equipped pregnant and lactating bats in southwest Saskatchewan, Canada with temperature-sensitive radio-transmitters. While transmitters were active, skin temperature data were collected and foraging patterns were determined using triangulation. Of the various environmental and physiological parameters used to model torpor characteristics, roost type was the most important factor. Bats roosting in trees used deeper and longer torpor bouts than those roosting in buildings. Lactating bats had a tendency to forage for longer durations than pregnant bats, and often made more foraging trips. When taken together, we found that foraging duration and torpor duration were not directly related during pregnancy, but exhibited an inverse relationship during lactation. This provides support for the hypothesis that there are physiological trade-offs for reproductive bats and suggests that how bats compensate is not entirely predictable based on current environmental conditions.

Journal of Comparative Physiology B

15344486

10.1007/S00359-014-0922-2

Inhibitory motoneurons in arthropod motor control: organisation, function, evolution

Miniaturisation of somatic cells in animals is limited, for reasons ranging from the accommodation of organelles to surface-to-volume ratio. Consequently, muscle and nerve cells vary in diameters by about two orders of magnitude, in animals covering 12 orders of magnitude in body mass. Small animals thus have to control their behaviour with few muscle fibres and neurons. Hexapod leg muscles, for instance, may consist of a single to a few 100 fibres, and they are controlled by one to, rarely, 19 motoneurons. A typical mammal has thousands of fibres per muscle supplied by hundreds of motoneurons for comparable behavioural performances. Arthopods—crustaceans, hexapods, spiders, and their kin—are on average much smaller than vertebrates, and they possess inhibitory motoneurons for a motor control strategy that allows a broad performance spectrum despite necessarily small cell numbers. This arthropod motor control strategy is reviewed from functional and evolutionary perspectives and its components are described with a focus on inhibitory motoneurons. Inhibitory motoneurons are particularly interesting for a number of reasons: evolutionary and phylogenetic comparison of functional specialisations, evolutionary and developmental origin and diversification, and muscle fibre recruitment strategies.

Journal of Comparative Physiology A