bluuebunny/crossref_metadata_2025_split huggingface dataset:
Do Neotropical Migrant Butterflies Navigate using a Solar Compass?
Authors: Oliveira Evandro G. , Srygley Robert B. , Dudley Robert 
Published: April 2021

ABSTRACT
Many tropical butterfly species are well-known for their migratory behaviour. Although these insects can maintain a constant direction throughout the day, the physiological mechanisms of orientation are unknown. It has been argued that tropical migrant butterflies must use a time-compensated sun compass to accomplish their journey, but the crucial experimental manipulations to test this hypothesis have not been conducted. This study reports the results of clock-shift experiments performed with two species of migrating butterflies (Pieridae: Aphrissa statira and Phoebis argante) captured during flight across Lake Gatún, Panamá. The observed constant flight bearing of natural controls suggests that these species are capable of performing time-compensated celestial navigation. Our clock-shift experiments suggest that a sun compass is involved. Individuals submitted to a 4 h advance shift took significantly different mean orientations on release compared with control butterflies. The direction of this difference was consistent with the use of a sun compass. The magnitude was approximately half the predicted value if the vanishing bearing of released butterflies was used as the variable to evaluate the effect of time-shifting and approximately three-quarters of that predicted if the estimated heading was the variable used. Mean vanishing bearings of control and experimental butterflies did not correspond to predicted values. This difference can be attributed largely to the combined effects of wind and handling.
How Body Size Affects Middle-Ear Structure and Function and Auditory Sensitivity in Gekkonoid Lizards
Authors: Werner Yehudah L. , Montgomery Lynda G. , Safford Shawn D. , Igic Petar G. , Saunders James C. 
Published: April 2021

ABSTRACT
Gekkonoid lizards increase in body size throughout life, and the present study investigates whether changes in auditory function accompany these increases. Middle-ear structures in four groups of animals, adults and juveniles of two gekkonoid species (Eublepharis macularius and Oedura marmorata), were examined. Tympanic membrane velocity and phase were also measured in all four groups. An indication of peripheral auditory function was obtained for each group by measuring compound action potentials (CAPs) from the round window membrane. The middle-ear contribution to CAP thresholds was obtained by comparing threshold levels of the CAP response with and without an intact middle-ear system. The results from these studies indicated that significant changes occurred in middle-ear structure, tympanic membrane velocity and CAP threshold between the younger and older animals. In addition, the adults of both species exhibited better auditory function when the acoustic stimulus was delivered to the tympanic membrane than when it was delivered to the columella footplate. The findings show clearly that increased body size (or age) is accompanied by functional changes in the auditory periphery.
L-Type Ca2+ Current in Fish Cardiac Myocytes: Effects of Thermal Acclimation and β-Adrenergic Stimulation
Authors: Vornanen Matti 
Published: April 2021

ABSTRACT
A patch-clamp analysis of L-type Ca2+ current in ventricular myocytes of cold- and warm-acclimated rainbow trout (Oncorhynchus mykiss) and crucian carp (Carassius carassius) hearts was performed. Trout were acclimated at 4 and 17°C and carp at 4 and 24°C for a minimum of 4 weeks. Ventricular myocytes were isolated by enzymatic dissociation using collagenase and trypsin. Marked species-specific differences were noted in Ca2+ current density and its β -adrenergic regulation. The density of basal Ca2+ current in crucian carp (6.9–7.4 pA pF−1) was almost double that of trout (4.2–4.5 pA pF−1) ventricular myocytes. Maximal β-adrenergic stimulation increased Ca2+ current by approximately 2.3-fold in trout but by only 1.4-fold in crucian carp, so that Ca2+ current densities in the presence of 10 μmol l−1 isoprenaline were almost equal in trout (8.6–10.5 pA pF−1) and carp (9.6–10.4 pA pF−1) cardiac cells. Direct activation of adenylate cyclase by forskolin (10 μmol l−1) was also associated with similar interspecies differences in the stimulation of Ca2+ current.
Thermal acclimation did not change either the density or the kinetics of L-type Ca2+ current in crucian carp ventricular myocytes. In trout cardiac cells, thermal acclimation had no effects on the density of Ca2+ current, but the rate of current inactivation was accelerated after acclimation to cold temperature. As a consequence of faster current decay, the contribution of sarcolemmal Ca2+ current to total cellular [Ca2+] was smaller in cold-acclimated than in warm-acclimated trout. The responses of Ca2+ current to maximal β-adrenergic stimulation by isoprenaline or to direct activation of adenylate cyclase by forskolin were not changed by thermal acclimation in either species. It is concluded (1) that the density of sarcolemmal Ca2+ current is not increased after acclimation to cold, (2) that sarcolemmal Ca2+ influx through L-type Ca2+ channels can make a significant contribution to contractile [Ca2+] in both teleost species studied and (3) that β-adrenergic stimulation of Ca2+ current is more important in modulating cardiac contractility in trout than in carp.
Non-Myotendinous Force Transmission in Rat Extensor Digitorum Longus Muscle
Authors: Huijing Peter A. , Baan Guus C. , Rebel Guido T. 
Published: April 2021

ABSTRACT
The extensor digitorum longus muscle (EDL) of the rat hindleg consists of four heads. The heads are named after their insertions on the digits of toes II, III, IV and V. The EDL heads share a proximal tendon and aponeurosis, but have separate distal aponeuroses and tendons. By cutting the distal tendons of selected heads, direct myotendinous force transmission within these heads is prevented. Therefore, force exerted by the muscle would be expected to decrease according to the physiological cross-sectional area disconnected if myotendinous force transmission were the only mechanism of force transmission.
The results indicate that EDL force production remained at high levels after acute tenotomy: muscle length–force curves did not alter significantly following cutting of the tendons of heads II and III. Cutting the tendon of head IV as well leaves only head V in its original condition. After tenotomy of head IV, length–force characteristics were altered significantly, but optimum force was maintained at 84 % of that of the intact muscle. After separation of head IV from head V intramuscularly for some distance along their interface, the force dropped to much lower levels, with optimum force approaching 50 % of that of the intact muscle.
The length of active proximal fibres (located within head II) did not remain constant but increased with increasing muscle lengths after tenotomy as well as after partial separation of heads IV and V. The amount of length change decreased after intramuscular separation of the heads, indicating declining reactive forces.
It is concluded that force transmission occurred from tenotomized heads to their intact neighbours and vice versa. The magnitude of the force transmitted from head to head was dependent on the degree of integrity of the connective tissue at the interface between heads.
The Importance of Atmospheric Odours for the Homing Performance of Pigeons in the Sonoran Desert of the Southwestern United States
Authors: Bingman V. P. , Alyan S. , Benvenuti S. 
Published: April 2021

ABSTRACT
The importance of atmospheric odours for homing pigeon navigation in a desert environment was tested using birds from two lofts located in the Sonoran desert near Tucson, Arizona, USA. When released from a familiar training site, experienced control pigeons and pigeons given intranasal injections of zinc sulphate to produce anosmia both displayed good homeward orientation and homed rapidly. When released from two unfamiliar locations, in contrast, the controls continued to display good homing performance while the zinc-sulphate-treated pigeons homed poorly. Significant differences in vanishing bearings, homing time and homing success were recorded. When a group of control and a group of zinc-sulphate-treated inexperienced pigeons were released from two unfamiliar locations, both groups homed poorly. Nonetheless, the controls still outperformed the zinc-sulphate-treated birds, the most notable result being a significant difference in homing success. Taken together, these results highlight the importance of atmospheric odours for the operation of the navigational map of the homing pigeon in a desert environment and, together with previous experiments, demonstrate that the role of atmospheric odours in homing does not seem to vary in any salient way with ambient climatic conditions.
Chemotactic responses of Dictyostelium discoideum amoebae to a cyclic AMP concentration gradient: evidence to support a spatial mechanism for sensing cyclic AMP
Authors: Tani Tomomi , Naitoh Yutaka 
Published: April 2021

ABSTRACT
The motile responses of Dictyostelium discoideum amoebae to a cyclic AMP (cAMP) concentration gradient were examined using a novel assay system. In this system, a cAMP concentration gradient was generated, while the overall cAMP concentration could be either increased or decreased in a chamber containing amoebae. The chemotactic responses of amoebae were examined immediately after they had been subjected to the cAMP concentration gradient. Amoebae moving in random directions in a reference solution ascended a cAMP concentration gradient after they had been exposed to the gradient irrespective of whether there was an increase or a decrease in the overall cAMP concentration. This strongly supports the idea that D. discoideum amoebae can sense a spatial cAMP gradient around them and that this causes their chemoaccumulation behavior. Ascending locomotion became less conspicuous when the amoebae were treated with a homogeneous cAMP solution for approximately 8 min before exposure to a cAMP gradient. This cAMP pretreatment reduced the sensitivity of the amoeba to a cAMP concentration gradient. The cAMP concentration gradient could be reversed in less than 30 s in this assay system, allowing the generation of a cAMP wave by accumulating amoebae to be mimicked. The ascending amoebae continued to move in the same direction for 1–2 min after the gradient had been reversed. This is consistent with the well-known observation that reversal of a cAMP concentration gradient experienced by the amoebae passing through a cAMP wave does not negate their chemotactic movement towards the accumulation center.
Metabolic opportunists: feeding and temperature influence the rate and pattern of respiration in the high arcticwoollybear caterpillar Gynaephora groenlandica (Lymantriidae)
Authors: Bennett Valerie A. , Kukal Olga , Lee Richard E. 
Published: April 2021

ABSTRACT
Arctic woollybear caterpillars, Gynaephora groenlandica, had the capacity to rapidly and dramatically increase respiration rates up to fourfold within 12–24 h of feeding and exhibited similar decreases in respiration of 60–85 % in as little as 12 h of starvation. At the peak of their feeding season, the respiration rates of caterpillars also increased significantly with temperature from 0.5 to 22 °C for both fed and starved caterpillars (Q10=1–5). Indicative of diapause, late season caterpillars had depressed respiration rates which were less sensitive to temperature changes (Q10≈1.5), while respiration rates for caterpillars that had spun hibernacula were even lower. G. groenlandica did not appear to demonstrate metabolic cold adaptation compared with other temperate lepidopteran larvae. The seasonal capacity to adjust metabolic rate rapidly in response to food consumption and temperature (which can be elevated by basking) may promote the efficient acquisition of energy during the brief (1 month) summer growing and feeding season, while conserving energy by entering diapause when conditions are less favorable. These adaptations, along with their long 15–20 year life cycle and the retention of freeze tolerance year-round, promote the survival of G. groenlandica in this harsh polar environment.
Cardiovascular effects of angiotensin-II-mediated adrenaline release in rainbow trout Oncorhynchus mykiss
Authors: Bernier Nicholas J. , Perry Steve F. 
Published: April 2021

ABSTRACT
To determine the contribution of plasma catecholamines to the cardiovascular effects of elevated levels of angiotensin II (Ang II) in trout, this study investigated (1) the stimulatory effects of [Asn1-Val5]-Ang II on plasma catecholamine levels, (2) the cardiovascular effects of Ang II with and without α-adrenoceptor blockade and (3) the relationship between plasma adrenaline concentrations and their cardiovascular effects. Bolus intravascular injections of Ang II (25–1200 pmol kg−1) elicited dose-dependent (between 75 and 1200 pmol kg−1) increases in plasma adrenaline levels; mean plasma noradrenaline levels only increased in response to a dose of 1200 pmol kg−1. Ang-II-elicited increases in plasma adrenaline levels ranged from 3.3±0.3 nmol l−1 for 75 pmol kg−1 Ang II to 125.1±40.0 nmol l−1 for 1200 pmol kg−1 Ang II. Injections of Ang II (25–1200 pmol kg−1) also elicited dose-dependent increases in dorsal aortic pressure (PDA), systemic resistance (RS), cardiac output (Q̇) and stroke volume (VS). In fish first treated with the α-adrenoceptor blocker phenoxybenzamine, Ang II injections elicited a decrease in Q̇ and VS, and the increases in PDA and RS following administration of the 600 and 1200 pmol kg−1 Ang II doses were significantly reduced. Bolus injections of adrenaline (1.8×10−10 to 1.4×10−8 mol kg−1) elicited dose-dependent increases in PDA at a plasma adrenaline concentration of 16.5 nmol l−1 and in RS at a plasma adrenaline concentration of 50.5 nmmol l−1. Adrenaline injections also elicited increases in Q̇ and VS at plasma adrenaline concentrations of 50.5 nmol l−1; however, higher plasma adrenaline concentrations were not associated with further increases in either Q̇ or VS. These results demonstrate that, in vivo, Ang II can act as a potent non-cholinergic secretagogue of humoral adrenaline in trout and that some of the cardiovascular effects of exogenous Ang II can be attributed to increased levels of plasma adrenaline. Our data also indicate that the cardiovascular effects of Ang-II-mediated humoral catecholamines are recruited in a dose-dependent manner and, as such, may require an acute stimulation of the renin–angiotensin system to contribute significantly to the pressor activity of endogenous angiotensins.
Osmoregulation in Marine Mammals
Authors: Ortiz Rudy M. 
Published: April 2021

SUMMARY
Osmoregulation in marine mammals has been investigated for over a century; however, a review of recent advances in our understanding of water and electrolyte balance and of renal function in marine mammals is warranted. The following topics are discussed: (i) kidney structure and urine concentrating ability, (ii) sources of water, (iii) the effects of feeding, fasting and diving, (iv) the renal responses to infusions of varying salinity and (v) hormonal regulation. The kidneys of pinnipeds and cetaceans are reniculate in structure, unlike those of terrestrial mammals (except bears), but this difference does not confer any greater concentrating ability. Pinnipeds, cetaceans, manatees and sea otters can concentrate their urine above the concentration of sea water, but only pinnipeds and otters have been shown to produce urine concentrations of Na+ and Cl−1 that are similar to those in sea water. This could afford them the capacity to drink sea water and not lose fresh water. However, with few exceptions, drinking is not a common behavior in pinnipeds and cetaceans. Water balance is maintained in these animals via metabolic and dietary water, while incidental ingestion and dietary salt may help maintain electrolyte homeostasis. Unlike most other aquatic mammals, sea otters commonly drink sea water and manatees frequently drink fresh water. Among the various taxonomic groups of marine mammals, the sensitivity of the renin–angiotensin–aldosterone system appears to be influenced by the availability of Na+. The antidiuretic role of vasopressin remains inconclusive in marine mammals, while the natriuretic function of atrial natriuretic peptide has yet to be examined. Ideas on the direction of future studies are presented.
Dynamics of Pavement Cell–Chloride Cell Interactions During Abrupt Salinity Change in FUNDULUS HETEROCLITUS
Authors: Daborn K. , Cozzi R. R. F. , Marshall W. S. 
Published: April 2021

SUMMARY
Freshwater-adapted killifish (Fundulus heteroclitus) opercular epithelia were dissected and subjected to blood-side hypertonic bathing solution in Ussing-style chambers to simulate the increase in blood osmolality during migration to sea water. Conversely, seawater-acclimated killifish opercular epithelia were subjected to hypotonic bathing solutions to simulate the initial stages of migration to fresh water. Freshwater-acclimation (hypertonic stress) induced a rapid (approximately 30min) increase in membrane conductance (Gt) from 3.10±0.56 to 7.52±1.15mScm−2 (P&lt;0.01, N=27), whereas seawater-acclimation (hypotonic stress) induced a rapid decrease in Gt from 8.22±1.15 to 4.41±1.00mScm−2 (P&lt;0.01, N=27; means ± s.e.m.). Control seawater-acclimated membranes had a density of apical crypts (where chloride cells are exposed to the environment; detected by scanning electron microscopy) of 1133±96.4cryptsmm−2 (N=12), whereas the hypotonically shocked specimens had a lower crypt density of 870±36.7cryptsmm−2 (P&lt;0.01 N=10; means ± s.e.m.). Hypertonic shock of freshwater membranes increased crypt density from 383.3±73.9 (N=12) to 630±102.9cryptsmm−2 (P&lt;0.05; N=11; means ± s.e.m.). There was no change in density of chloride cells, as detected by fluorescence microscopy; hence, osmotic stress changes the degree of exposure, not the number of chloride cells. Cytochalasin D (5.0μmoll−1) completely blocked the conductance response to hypotonic shock and the reduction in apical crypt density measured by scanning electron microscopy, while phalloidin (33μmoll−1), colchicine (3×10−4moll−1) and griseofulvin (1.0μmoll−1) were ineffective. Actin imaging by phalloidin staining and confocal microscopy revealed extensive actin cords in pavement cell microridges and a ring of actin at the apex of chloride cells. We conclude that the actin cytoskeleton of chloride cells is required to maintain crypt opening and that osmotic shock causes chloride cells to adjust their apical crypt size.
Limits to sustained energy intake
Authors: Johnson M. S. , Thomson S. C. , Speakman J. R. 
Published: April 2021

SUMMARY
Links between resting metabolic rate (RMR) and reproductive output have been previously sought at both inter- and intraspecific levels, but have only been found in some interspecific studies. We aimed to examine correlations between RMR measured both prior to breeding and at peak lactation with litter size and litter mass in Mus musculus. By manipulating the litter size of some females at birth, we aimed to establish the direction of causality in any correlation between litter size and RMR. Correlations between maternal morphology and RMR, litter size and litter mass were also examined. Neither pre-breeding RMR nor mass-independent pre-breeding RMR was correlated with litter size or litter mass. RMR at peak lactation, however, was positively correlated with litter size and negatively correlated with mean pup mass. After correcting for the effects of body mass, residual peak lactation RMR was not correlated with litter size or litter mass. Body size was the major morphological variable influencing litter mass, offspring mass and asymptotic food intake. Mammary tissue mass was correlated with litter size when only the data for mice raising unmanipulated litters were used. RMR at peak lactation was significantly related to the principal component of morphology dominated by carcass mass. This study confirms the findings of previous intraspecific and some interspecific studies that found no correlation between RMR and reproductive output after the effects of body mass had been removed.
Limits to sustained energy intake
Authors: Speakman J. R. , Gidney A. , Bett J. , Mitchell I. P. , Johnson M. S. 
Published: April 2021

SUMMARY
Observations were made on 30 MF1 mice with their litters. The animals were fed either normal pelleted mouse food (SDS BP Nutrition Ltd) containing 13.4kJg−1 digestible energy or a specially formulated diet that provided 25% less digestible energy (9.75kJg−1) but equivalent amounts of protein and essential minerals and vitamins per gram as the normal diet. Half the animals were switched to the low-energy diet during early pregnancy and half after parturition. The food intake of the two groups increased enormously following parturition, reaching an asymptote over the last few days of lactation. In both groups, the asymptotic food intake exceeded that previously observed across 71 litters of this strain of mice fed the normal diet throughout pregnancy and lactation; the intake of the group fed the low-energy diet from early lactation significantly exceeded that of the mice switched to the low-energy diet after parturition. The increased intakes of the experimental groups were, however, insufficient to offset the lower digestible energy content of the food during lactation. The body mass of the mothers at the end of lactation did not differ between the two experimental groups and the controls. Offspring mass at weaning was inversely related to litter size, but also did not differ between the three groups; pup mortality did not differ between the experimental and control groups. Behavioural observations showed that during both the dark and light phases the general activity of the mother declined enormously from early pregnancy to late lactation. In the dark phase, the time spent in general activity was replaced by time spent both feeding and resting (suckling young), but in the light phase it was replaced only by feeding. At peak lactation, the mice fed for 30–50% of the dark phase and for 30–40% of the light phase. The data indicate that a previously observed asymptote in food intake during peak lactation at 23gday−1 is unlikely to be a limit mediated centrally by the alimentary tract. A higher central limit may exist, at 26.9gday−1, but this is unlikely to reflect the time available for feeding. The data are consistent with limits on sustainable daily energy intake being mediated by the performance of the mammary glands. Animals appeared to accommodate the demands for milk production within a constrained total energy budget by compensating their behaviour, most notably by reductions in the time spent in ‘general activity’.