bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pharmacological blockade of the dive response: effects on heart rate and diving behaviour in the harbour seal (Phoca vitulina)
Authors: Elliott Nicole M. , Andrews Russel D. , Jones David R. 
Published: April 2021

SUMMARYWhile diving, harbour seals (Phoca vitulina) manage their oxygen stores through cardiovascular adjustments, including bradycardia, a concurrent reduction in cardiac output, and peripheral vasoconstriction. At the surface,post-dive tachycardia facilitates rapid reloading of oxygen stores. Although harbour seals can tolerate &gt;20 min of submergence, the majority of their natural dives are only 2-6 min and are usually followed by surface intervals that are &lt;1 min, so they spend approximately 80% of their time submerged. Given that harbour seals meet their ecological needs through repetitive short aerobic dives, we were interested in the functional role, if any, of the dive response during these short dives. During voluntary diving in an 11 m deep tank, the cardiovascular responses to submergence of five harbour seals were manipulated using specific pharmacological antagonists, and the effects on diving behaviour were observed. Effects of pharmacological blockade on heart rate were also examined to assess the autonomic control of heart rate during voluntary diving. Heart rate was recorded using subcutaneous electrodes and data loggers, while diving behaviour was monitored using a video camera. The muscarinic blocker methoctramine blocked diving bradycardia, theα-adrenergic blocker prazosin blocked diving vasoconstriction, and theβ-adrenergic blocker metoprolol blocked post-dive tachycardia. Heart-rate analysis indicated that diving bradycardia is primarily modulated by the vagus, while post-dive tachycardia results from parasympathetic withdrawal as well as increased sympathetic stimulation of the heart. None of the pharmacological blockers had any effect on average dive or surface interval duration. Seals maintained a high percentage of time spent diving in all treatments. Thus, harbour seals do not appear to need the dive response during short dives in order to maintain an efficient dive strategy.
Stroke frequencies of emperor penguins diving under sea ice
Authors: van Dam R. P. , Ponganis P. J. , Ponganis K. V. , Levenson D. H. , Marshall G. 
Published: April 2021

SUMMARYDuring diving, intermittent swim stroke patterns, ranging from burst/coast locomotion to prolonged gliding, represent potential energy conservation mechanisms that could extend the duration of aerobic metabolism and, hence,increase the aerobic dive limit (ADL, dive duration associated with onset of lactate accumulation). A 5.6 min ADL for emperor penguins had been previously determined with lactate measurements after dives of &lt;50 m depth. In order to assess locomotory patterns during such dives, longitudinal acceleration was measured with an attached accelerometer in 44 dives of seven adult birds diving from an isolated dive hole in the sea ice of McMurdo Sound, Antarctica. Detection of wing strokes in processed accelerometer data was verified in selected birds with analysis of simultaneous Crittercam underwater video footage. Mean dive duration of birds equipped with the accelerometer and a time-depth recorder (TDR) was 5.7±2.2 min; 48% of these dives were greater than the measured 5.6 min ADL (ADLM). Highest stroke frequencies (0.92±0.31 Hz, N=981) occurred during the initial descent to 12 m depth. Swimming effort was reduced to a mean stroke frequency&lt;0.70 Hz during other phases of the dive (while traveling below 12 m depth,during foraging ascents/descents to and from the sub-ice surface, and during final ascents to exit). The longest stroke interval (8.6 s) occurred during a feeding excursion to the undersurface of the ice. In dives&gt;ADLM, mean stroke frequency during travel segments was significantly less than that in dives &lt;ADLM(P&lt;0.05). Mean stroke frequency of the entire dive correlated inversely (P&lt;0.05) with diving duration (r=-0.67) and with mean dive depth (r=-0.43). Emperor penguins did not exhibit any significant (&gt;10 s) periods of prolonged gliding during these shallow(&lt;60 m) foraging dives. However, a stroke/glide pattern was evident with more than 50% of strokes associated with a stroke interval &gt;1.6 s, and with lower stroke frequency associated with increased dive duration.
The ilio-marsupialis muscle in the dasyurid marsupial Sminthopsis douglasi: form, function and fibre-type profiles in females with and without suckling young
Authors: Woolley P. A. , Patterson M. F. , Stephenson G. M. , Stephenson D. G. 
Published: April 2021

SUMMARY
The form, function and fibre-type profiles of the ilio-marsupialis muscles,branches of which insert on to the skin of the nipples and pouch, have been investigated in the small dasyurid marsupial Sminthopsis douglasi. Single fibres from the branches of muscles associated with unsuckled nipples in non-lactating females and with both unsuckled and suckled nipples at four stages during the 70-day suckling period were typed according to their sensitivity to the activators strontium (Sr2+) and calcium(Ca2+) into fast-twitch, slow-twitch and composite types. An unusual finding was the predominance of composite fibres in the resting state(unsuckled nipples). Changes in fibre-type composition were observed during the suckling period and these changes correlated with events in the development of the suckling young. Composite fibres declined during the suckling period and, at the stage when the young can no longer be accommodated in the pouch but must still be carried by the mother while she is foraging, an increase in fast-twitch fibres that are associated with dynamic muscular activity was seen. Later in the suckling period, when the mammary tissue is greatly enlarged but the mother does not carry the young while out feeding,there was an increase in the proportion of slow-twitch (fatigue-resistant)fibres. The high proportion of fast-twitch fibres present late in the suckling period may be associated with vibratory movements that result in the young relinquishing the nipples.
Localisation of an acoustic signal in a noisy environment: the display call of the king penguinAptenodytes patagonicus
Authors: Aubin Thierry , Jouventin Pierre 
Published: April 2021

SUMMARYKing penguin chicks identify their parents by an acoustic signal, the display call. This call consists of a succession of similar syllables. Each syllable has two harmonic series, strongly modulated in frequency and amplitude, with added beats of varying amplitude generated by a two-voice system. Previous work showed that only one syllable of the call is needed for the chick to identify the calling adult. Both the frequency modulation pattern of the syllable and the two-voice system play a role in the call identification. The syllabic organisation of the call, the harmonic structure and the amplitude modulations of the syllables apparently do not contribute to individual recognition. Are these acoustic features useless? To answer to this question, playback experiments were conducted using three categories of experimental signals: (i) signal with only the fundamental frequencies of the natural call, (ii) signal with the amplitude of each syllable kept at a constant level and (iii) signals with only one syllable, repeated or not. The responses of chicks to these experimental signals were compared to those obtained with the calls of their natural parents. We found that these acoustic features, while not directly implicated in the individual recognition process,help the chicks to better localise the signal of their parents. In addition,the redundant syllabic organisation of the call is a means of counteracting the masking effect of the background noise of the colony.
Magnetic compass orientation in European robins is dependent on both wavelength and intensity of light
Authors: Muheim Rachel , Bäckman Johan , Åkesson Susanne 
Published: April 2021

SUMMARYMagnetic compass orientation in birds has been shown to be light dependent. Results from behavioural studies indicate that magnetoreception capabilities are disrupted under light of peak wavelengths longer than 565 nm, and shifts in orientation have been observed at higher light intensities(43-44×1015 quanta s-1 m-2). To investigate further the function of the avian magnetic compass with respect to wavelength and intensity of light, we carried out orientation cage experiments with juvenile European robins, caught during their first autumn migration,exposed to light of 560.5 nm (green), 567.5 nm (green-yellow) and 617 nm (red)wavelengths at three different intensities (1 mW m-2, 5 mW m-2 and 10 mW m-2). We used monochromatic light of a narrow wavelength range (half bandwidth of 9-11 nm, compared with half bandwidths ranging between 30 nm and 70 nm used in other studies) and were thereby able to examine the magnetoreception mechanism in the expected transition zone between oriented and disoriented behaviour around 565 nm in more detail. We show (1) that European robins show seasonally appropriate migratory directions under 560.5 nm light, (2) that they are completely disoriented under 567.5 nm light under a broad range of intensities, (3) that they are able to orient under 617 nm light of lower intensities, although into a direction shifted relative to the expected migratory one, and (4) that magnetoreception is intensity dependent, leading to disorientation under higher intensities. Our results support the hypothesis that birds possess a light-dependent magnetoreception system based on magnetically sensitive,antagonistically interacting spectral mechanisms, with at least one high-sensitive short-wavelength mechanism and one low-sensitive long-wavelength mechanism.
Vision in the peafowl (Aves:Pavo cristatus)
Authors: Hart Nathan S. 
Published: April 2021

SUMMARYThe visual sense of the Indian blue-shouldered peafowl Pavo cristatus was investigated with respect to the spectral absorption characteristics of the retinal photoreceptors, the spectral transmittance of the ocular media and the topographic distribution of cells in the retinal ganglion cell layer. Microspectrophotometry revealed a single class of rod,four spectrally distinct types of single cone and a single class of double cone. In the case of the single cone types, which contained visual pigments with wavelengths of maximum absorbance (λmax) at 424, 458,505 and 567 nm, spectral filtering by the ocular media and the different cone oil droplets with which each visual pigment is associated gives predicted peak spectral sensitivities of 432, 477, 537 and 605 nm, respectively. Topographic analysis of retinal ganglion cell distribution revealed a large central area of increased cell density (at peak, 35,609 cells mm-2) with a poorly defined visual streak extending nasally. The peafowl has a calculated maximum spatial resolution (visual acuity) in the lateral visual field of 20.6 cycles degrees-1. These properties of the peafowl eye are discussed with respect to its visual ecology and are compared with those of other closely related species.
Effects of intestinal nematodes during lactation: consequences for host morphology, physiology and offspring mass
Authors: Kristan Deborah M. 
Published: April 2021

SUMMARYSublethal parasites are often assumed to have no detrimental effects on their host. However, the sublethal intestinal nematode Heligmosomoides polygyrus affects both the morphology and the physiology of its laboratory mouse (Mus musculus) host and therefore has the potential to affect host life history. The objectives of the present study were to determine (1) whether lactating and non-lactating mice responded similarly to experimental infection with H. polygyrus and (2) whether the changes in morphology and physiology that occurred with parasite infection affected host reproductive performance. Parasitized mice had greater whole body mass as a result of greater lean mass compared with unparasitized mice. Parasitized mice had larger organs (spleen, stomach, cecum and small intestine) and a diminished rate of glucose transport by the small intestine compared with unparasitized mice. Lactating mice had larger organs (liver, kidney, spleen,heart, stomach, large intestine, cecum and small intestine), lean mass and whole body mass, but a similar rate of glucose transport compared with virgin mice. Resting metabolism increased with lactation but not with parasitism. Lactating and non-lactating mice responded similarly to parasite infection for most measured variables. Production of large litters was followed by production of small litters for parasitized but not unparasitized females. After adjusting for parity and litter size, parasitized mothers produced female pups that were 6% smaller at weaning than female pups from unparasitized mothers, but there was no effect of maternal parasite infection on mass at weaning for male pups. Other measures of reproductive output were not affected by parasite infection.
Trimethylamine oxide accumulation in marine animals: relationship to acylglycerol storagej
Authors: Seibel Brad A. , Walsh Patrick J. 
Published: April 2021

SUMMARYTrimethylamine oxide (TMAO) is a common and compatible osmolyte in muscle tissues of marine organisms that is often credited with counteracting protein-destabilizing forces. However, the origin and synthetic pathways of TMAO are actively debated. Here, we examine the distribution of TMAO in marine animals and report a correlation between TMAO and acylglycerol storage. We put forward the hypothesis that TMAO is derived, at least in part, from the hydrolysis of phosphatidylcholine, endogenous or dietary, for storage as diacylglycerol ethers and triacylglycerols. TMAO is synthesized from the trimethylammonium moiety of choline, thus released, and is retained as a compatible solute in concentrations reflecting the amount of lipid stored in the body. A variation on this theme is proposed for sharks.
A motor and a brake: two leg extensor muscles acting at the same joint manage energy differently in a running insect
Authors: Ahn A. N. , Full R. J. 
Published: April 2021

SUMMARYThe individual muscles of a multiple muscle group at a given joint are often assumed to function synergistically to share the load during locomotion. We examined two leg extensors of a running cockroach to test the hypothesis that leg muscles within an anatomical muscle group necessarily manage (i.e. produce, store, transmit or absorb) energy similarly during running. Using electromyographic and video motion-analysis techniques, we determined that muscles 177c and 179 are both active during the first half of the stance period during muscle shortening. Using the in vivo strain and stimulation patterns determined during running, we measured muscle power output. Although both muscles were stimulated during the first half of shortening, muscle 177c generated mechanical energy (28 W kg–1) like a motor, while muscle 179 absorbed energy (–19 W kg–1) like a brake. Both muscles exhibited nearly identical intrinsic characteristics including similar twitch kinetics and force–velocity relationships. Differences in the extrinsic factors of activation and relative shortening velocity caused the muscles to operate very differently during running. Presumed redundancy in a multiple muscle group may, therefore, represent diversity in muscle function. Discovering how muscles manage energy during behavior requires the measurement of a large number of dynamically interacting variables.
Morphology, swimming performance and propulsive mode of six co-occurring hydromedusae
Authors: Colin Sean P. , Costello John H. 
Published: April 2021

SUMMARYJet propulsion, based on examples from the Hydrozoa, has served as a valuable model for swimming by medusae. However, cnidarian medusae span several taxonomic classes (collectively known as the Medusazoa) and represent a diverse array of morphologies and swimming styles. Does one mode of propulsion appropriately describe swimming by all medusae? This study examined a group of co-occurring hydromedusae collected from the waters of Friday Harbor, WA, USA, to investigate relationships between swimming performance and underlying mechanisms of thrust production. The six species examined encompassed a wide range of bell morphologies and swimming habits. Swimming performance (measured as swimming acceleration and velocity) varied widely among the species and was positively correlated with bell streamlining (measured as bell fineness ratio) and velar structure development (measured as velar aperture ratio). Calculated thrust production due to jet propulsion adequately explained acceleration patterns of prolate medusae (Aglantha digitale, Sarsia sp. and Proboscidactyla flavicirrata) possessing well-developed velums. However, acceleration patterns of oblate medusae (Aequorea victoria, Mitrocoma cellularia and Phialidium gregarium) that have less developed velums were poorly described by jet thrust production. An examination of the wakes behind swimming medusae indicated that, in contrast to the clearly defined jet structures produced by prolate species, oblate medusae did not produce defined jets but instead produced prominent vortices at the bell margins. These vortices are consistent with a predominantly drag-based, rowing mode of propulsion by the oblate species. These patterns of propulsive mechanics and swimming performance relate to the role played by swimming in the foraging ecology of each medusa. These patterns appear to extend beyond hydromedusae and thus have important implications for other members of the Medusazoa.
Why did some ichthyosaurs have such large eyes?
Authors: Humphries Stuart , Ruxton Graeme D. 
Published: April 2021

SUMMARYMany species of extinct marine ichthyosaurs had much larger eyes for their body size than would be expected of extant marine mammals and reptiles. Sensitivity to low light at great depth for the deep-diving genus Ophthalmosaurus has recently been suggested as the reason for the large eyes of these animals. Here, we discuss the implications for vision at such depths and consider other optical factors determining eye size. We suggest that the large eyes of ichthyosaurs are more likely to be the result of simultaneous selection for both sensitivity to low light and visual acuity. The importance of the evolutionary history of extant marine mammals and extinct ichthyosaurs is discussed, as are ecological factors driving both acuity and sensitivity.
Hyperosmotic and thermal stresses activate p38-MAPK in the perfused amphibian heart
Authors: Aggeli Ioanna-Katerina S. , Gaitanaki Catherine , Lazou Antigone , Beis Isidoros 
Published: April 2021

SUMMARYWe assessed the activation of p38-MAPK (mitogen-activated protein kinase) by osmotic and thermal stresses in the isolated perfused amphibian (Rana ridibunda) heart. Hyperosmotic stress induced the rapid activation of the kinase. In particular, in the presence of 0.5 mol l–1 sorbitol, p38-MAPK was maximally phosphorylated (by approximately twelvefold) at 15 min, while excess of NaCl (206 mmol l–1 final concentration) or KCl (16 mmol l–1 final concentration) stimulated a less potent activation, maximised (by approximately eightfold and fourfold) within 2 min and 30 s, respectively, relative to control values. The effect of all three compounds examined was reversible, since the kinase phosphorylation levels decreased upon reperfusion of the heart with normal bicarbonate-buffered saline. Conversely, hypotonicity did not induce any p38-MAPK activation. Furthermore, both hypothermia and hyperthermia induced considerable phosphorylation of the kinase, by four- and 7.5-fold, respectively, relative to control values. Immunohistochemical studies elucidated the localisation pattern of phospho-p38-MAPK and also revealed enhanced atrial natriuretic peptide (ANP) immunoreactivity in osmotically stressed hearts. Interestingly, SB 203580 (1 μmol l–1) not only completely blocked the activation of p38-MAPK by all these interventions, but also abolished the enhanced ANP immunoreactivity induced by 0.5 mol l–1 sorbitol. These findings indicate the possible involvement of ANP in the mechanisms regulating responses under such stressful conditions.
Insect egg deposition induces Pinus sylvestris to attract egg parasitoids
Authors: Hilker Monika , Kobs Carsten , Varama Martti , Schrank Kai 
Published: April 2021

SUMMARY
Plant volatiles released in response to feeding insects are known to attract enemies of the feeding herbivores. In this study, egg deposition by a herbivorous insect was shown to induce a gymnosperm plant to emit volatiles that attract egg parasitoids. Odour from twigs of Pinus sylvestris laden with egg masses of the pine sawfly Diprion pini attracts the eulophid egg parasitoid Chrysonotomyia ruforum. Volatiles released from pine twigs without diprionid eggs are not attractive. Oviposition by the sawfly onto pine needles induces not only a local response in pine needles laden with eggs but also a systemic reaction. Needles without eggs but adjacent to those bearing diprionid eggs also release the volatiles that attract the egg parasitoid. The elicitor of the attractive volatiles was shown to be present in the oviduct secretion coating the eggs of D. pini. When pine twigs are treated with jasmonic acid, a well-known plant wound signal, they emit volatiles that attract the egg parasitoid. These results show, for the first time, that a gymnosperm plant is able to attract parasitoids as soon as a herbivore has deposited its eggs on it. Thus, the plant appears to defend itself against herbivores prior to being damaged by feeding larvae.
Physiological responses of Houbara bustards to high ambient temperatures
Authors: Tieleman B. Irene , Williams Joseph B. , LaCroix Frédéric , Paillat Patrick 
Published: April 2021

SUMMARYDesert birds often experience a scarcity of drinking water and food and must survive episodes of high ambient temperature (Ta). The physiological mechanisms that promote survival during extended periods of high Ta have received little attention. We investigated the physiological responses of wild-caught and captive-reared Houbara bustards, Chlamydotis macqueenii, to Ta values ranging from below 0°C to 55°C, well above those in most previous studies of birds. Captive-reared Houbara bustards (mass 1245±242 g, N=7, mean ± s.d.) in summer have a resting metabolic rate (RMR) of 261.4 kJ day–1, 26 % below allometric predictions, and a total evaporative water loss (TEWL) at 25°C of 25.8 g day–1, 31 % below predictions. When Ta exceeded body temperature (Tb), the dry heat transfer coefficient decreased, a finding supporting the prediction that birds should minimize dry heat gain from the environment at high Ta values. Houbara bustards withstand high Ta values without becoming hyperthermic; at 45°C, Tb was on average 0.9°C higher than at 25°C. RMR and TEWL of captive-bred Houbara bustards were 23 % and 46 % higher in winter than in summer, respectively. Captive-reared Houbara bustards had a 17 % lower RMR and a 28 % lower TEWL than wild-born birds with similar genetic backgrounds. Differences in body composition between wild-caught and captive-reared birds were correlated with differences in physiological performance.