bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diapause in tardigrades: a study of factors involved in encystment
Authors: Guidetti Roberto , Boschini Deborah , Altiero Tiziana , Bertolani Roberto , Rebecchi Lorena 
Published: June 2008

SUMMARY
Stressful environmental conditions limit survival, growth and reproduction,or these conditions induce resting stages indicated as dormancy. Tardigrades represent one of the few animal phyla able to perform both forms of dormancy:quiescence and diapause. Different forms of cryptobiosis (quiescence) are widespread and well studied, while little attention has been devoted to the adaptive meaning of encystment (diapause). Our goal was to determine the environmental factors and token stimuli involved in the encystment process of tardigrades. The eutardigrade Amphibolus volubilis, a species able to produce two types of cyst (type 1 and type 2), was considered. Laboratory experiments and long-term studies on cyst dynamics of a natural population were conducted. Laboratory experiments demonstrated that active tardigrades collected in April produced mainly type 2 cysts, whereas animals collected in November produced mainly type 1 cysts, indicating that the different responses are functions of the physiological state at the time they were collected. The dynamics of the two types of cyst show opposite seasonal trends: type 2 cysts are present only during the warm season and type 1 cysts are present during the cold season. Temperature represents the environmental factor involved in induction, maintenance and termination of the cyst. We also obtained evidence that A. volubilis is able to perform both diapause and cryptobiosis,even overlapping the two phenomena. The induction phase of tardigrade encystment can be compared to the induction phase of insect diapause, also indicating an involvement of endogenous factors in tardigrade encystment. As in insect diapause, tardigrade encystment can be considered a diapausing state controlled by exogenous and endogenous stimuli.
Phylogeny, scaling, and the generation of extreme forces in trap-jaw ants
Authors: Spagna Joseph C. , Vakis Antonis I. , Schmidt Chris A. , Patek Sheila N. , Zhang Xudong , Tsutsui Neil D. , Suarez Andrew V. 
Published: June 2008

SUMMARYTrap-jaw ants of the genus Odontomachus produce remarkably fast predatory strikes. The closing mandibles of Odontomachus bauri, for example, can reach speeds of over 60 m s–1. They use these jaw strikes for both prey capture and locomotion – by striking hard surfaces, they can launch themselves into the air. We tested the hypothesis that morphological variation across the genus is correlated with differences in jaw speeds and accelerations. We video-recorded jaw-strikes at 70 000–100 000 frames s–1 to measure these parameters and to model force production. Differences in mean speeds ranged from 35.9±7.7 m s–1 for O. chelifer, to 48.8±8.9 m s–1 for O. clarus desertorum. Differences in species' accelerations and jaw sizes resulted in maximum strike forces in the largest ants (O. chelifer) that were four times those generated by the smallest ants (O. ruginodis). To evaluate phylogenetic effects and make statistically valid comparisons, we developed a phylogeny of all sampled Odontomachus species and seven outgroup species (19 species total) using four genetic loci. Jaw acceleration and jaw-scaling factors showed significant phylogenetic non-independence, whereas jaw speed and force did not. Independent contrast (IC) values were used to calculate scaling relationships for jaw length, jaw mass and body mass, which did not deviate significantly from isometry. IC regression of angular acceleration and body size show an inverse relationship, but combined with the isometric increase in jaw length and mass results in greater maximum strike forces for the largest Odontomachus species. Relatively small differences (3%) between IC and species-mean based models suggest that any deviation from isometry in species' force production may be the result of recent selective evolution, rather than deep phylogenetic signal.
Light and peptidergic eclosion hormone neurons stimulate a rapid eclosion response that masks circadian emergence inDrosophila
Authors: McNabb Susan L. , Truman James W. 
Published: June 2008

SUMMARYLight signals can entrain circadian clocks, but they can also mask aspects of the circadian output. We have analyzed the masking effects of a lights-on(LOn) signal on Drosophila eclosion. The LOn response results in 12–21% of the flies that emerge on a given day eclosing within 10 min of the LOn signal. Flies that lack the neuropeptide eclosion hormone (EH), or in which its release is inhibited by the tetanus toxin light chain, lack the response. Optic photoreceptors in both the ocelli and the compound eyes appear to be required for the response. The LOn signal has two effects: (1) it drastically reduces the interval between EH release and eclosion, presumably by suppressing a transient descending inhibition that immediately follows EH release, and (2) it stimulates premature EH release. The LOn signal does not influence the latency of wing spreading, an EH-regulated post-ecdysis behavior.
Effects of altering flow and odor information on plume tracking behavior in walking cockroaches, Periplaneta americana (L.)
Authors: Willis Mark A. , Avondet Jennifer L. , Finnell Andrew S. 
Published: June 2008

SUMMARY
Animals using odor plumes to locate resources are activated to track these plumes by the presence of an attractive odor, and typically steer toward the source using directional cues from the flowing air or water bearing the odor. We challenged freely walking virgin male cockroaches, Periplaneta americana, to track plumes of airborne female pheromone and then video-recorded and analyzed their responses as the odor plume and wind were independently manipulated. Plume tracking males that experienced the total loss of directional air flow halfway to the odor source showed little change in their performance, and 100% were able to quickly locate the pheromone source. By contrast, males experiencing a sudden loss of odor while tracking a plume rapidly changed their behavior; often turning downwind and retracing their steps to the release point, or walking in loops, but rarely moving upwind to the previous location of the source. In a subsequent experiment, in order to determine whether a memory of the previously experienced wind direction could provide the directional information necessary to locate an odor source, we challenged males to track plumes in zero wind after pre-exposing them to: (1) wind and pheromone, (2) wind only, and (3) neither wind nor pheromone. These were compared to males tracking a wind-borne pheromone plume, in which case, all males were able to locate the pheromone source. Our results show that males require the detection of wind and pheromone simultaneously during plume tracking in order to quickly and efficiently locate the odor source. These results are consistent with those reported from flying moths tracking wind-borne pheromone plumes, and suggest that the control system underlying this behavior requires ongoing simultaneous experience with wind and odor information during the performance of the behavior to operate efficiently.
Integration within and between muscles during terrestrial locomotion:effects of incline and speed
Authors: Higham Timothy E. , Biewener Andrew A. 
Published: June 2008

SUMMARYAnimals must continually adapt to varying locomotor demands when moving in their natural habitat. Despite the dynamic nature of locomotion, little is known about how multiple muscles, and different parts of a muscle, are functionally integrated as demand changes. In order to determine the extent to which synergist muscles are functionally heterogeneous, and whether this heterogeneity is altered with changes in demand, we examined the in vivo function of the lateral (LG) and medial (MG) gastrocnemius muscles of helmeted guinea fowl (Numida meleagris) during locomotion on different inclines (level and uphill at 14°) and at different speeds (0.5 and 2.0 m s–1). We also quantified function in the proximal(pMG) and distal (dMG) regions of the MG to examine the extent to which a single muscle is heterogeneous. We used electromyography, sonomicrometry and tendon force buckles to quantify activation, length change and force patterns of both muscles, respectively. We show that the LG and MG exhibited an increase in force and stress with a change in gait and an increase in locomotor speed, but not with changes in incline. While the LG and MG exhibited similar levels of stress when walking at 0.5 m s–1,stress in the LG was 1.8 times greater than in the MG when running at 2.0 m s–1. Fascicle shortening increased with an increase in speed on both inclines for the LG, but only on the level for the pMG. Positive work performed by the LG exceeded that of the pMG and dMG for all conditions, and this difference was magnified when locomotor speed increased. Within the MG,the pMG shortened more, and at a faster rate than the dMG, resulting in a greater amount of positive work performed by the pMG. Mean spike amplitude of the electromyogram (EMG) bursts increased for all muscle locations with an increase in speed, but changes with incline were more variable. The functional differences between the LG and MG are likely due to the different moments each exerts at the knee, as well as differences in motor unit recruitment. The differences within the MG are likely due to motor unit recruitment differences, but also differences in architecture. Fascicles within the dMG insert into an extensive aponeurosis, which results in a higher apparent dynamic stiffness relative to fascicles operating within the pMG. On the level surface, the greater compliance of the pMG leads to increased stretch of its fascicles at the onset of force, further enhancing force production. Our results demonstrate the capacity for functional diversity between and within muscle synergists, which occur with changes in gait, speed and grade.
The contribution of axial fiber extensibility to the adhesion of viscous capture threads spun by orb-weaving spiders
Authors: Opell Brent D. , Markley Brian J. , Hannum Charles D. , Hendricks Mary L. 
Published: June 2008

SUMMARYThe viscous capture threads produced by over 4000 species of orb-weaving spiders are formed of regularly spaced aqueous droplets supported by a pair of axial fibers. These threads register increased stickiness when spans of increasing lengths contact a surface, indicating that adhesion is recruited from multiple droplets. This study examined threads produced by five species to test the hypothesis that axial fiber extensibility is crucial for this summation of adhesion. It did so by comparing the stickiness of unstretched threads with threads that had been elongated to reduce the extensibility of their axial fibers. As stretching these threads also increased the distance between their droplets, we measured the stickiness of stretched threads with contact plates whose widths were increased in proportion to the degree of thread elongation. We then accounted for the actual thread elongation achieved for each individual's threads and for differences in the five species'absolute thread extensibility. The results showed that in four species thread extensibility contributed positively to adhesion. For three species, thread extensibility and droplet volume together explained the mean per droplet adhesion of threads. Models based on these three species show that, as threads were elongated, increasing amounts of potential adhesion were lost to diminished axial fiber extensibility. These models indicate that approximately one-third of an unstretched viscous thread's stickiness accrues from the adhesive recruitment made possible by axial fiber extensibility.
Bumble bees heat up for high quality pollen
Authors: Mapalad Katherine S. , Leu Daniel , Nieh James C. 
Published: June 2008

SUMMARYThermoregulation plays a key role in bee foraging, allowing some species to forage in suboptimal temperatures. Recently, bumble bee thoracic temperature(Tth) has been shown to increase with nectar carbohydrate content. However, pollen is also vital to bees and exhibits a greater than 20-fold range in protein quality. We provide the first demonstration that bee Tth is also correlated with pollen quality. We allowed bumble bee, Bombus impatiens, foragers from two colonies to collect pollen varying in quality (25%, 50%, 75% and 100% by mass mixed with indigestible α-cellulose). We used infrared thermography to measure surface Tth when a forager finished collecting feeder pollen and when she returned to the nest. Foragers significantly elevated their Tth over ambient air temperature while collecting pollen and maintained this elevated Tth upon returning to the nest. On average, foragers increased Tth over ambient by 0.4°C per 25% increase in pollen protein content. Bumble bees can therefore adjust their thoracic temperature according to pollen quality.
Effects of salinity on intestinal bicarbonate secretion and compensatory regulation of acid–base balance inOpsanus beta
Authors: Genz Janet , Taylor Josi R. , Grosell Martin 
Published: June 2008

SUMMARYMarine teleosts have extracellular fluids less concentrated than their environment, resulting in continual water loss, which is compensated for by drinking, with intestinal water absorption driven by NaCl uptake. Absorption of Cl– occurs in part by apical Cl–/HCO3– exchange, with HCO3– provided by transepithelial transport and/or by carbonic anhydrase-mediated hydration of endogenous epithelial CO2. Hydration of CO2 also liberates H+,which is transported across the basolateral membrane. In this study, gulf toadfish (Opsanus beta) were acclimated to 9, 35 and 50 ppt. Intestinal HCO3– secretion, water and salt absorption, and the ensuing effects on acid–base balance were examined. Rectal fluid excretion greatly increased with increasing salinity from 0.17±0.05 ml kg–1 h–1 in 9 ppt to 0.70±0.19 ml kg–1 h–1 in 35 ppt and 1.46±0.22 ml kg–1 h–1 in 50 ppt. Rectal fluid composition and excretion rates allowed for estimation of drinking rates, which increased with salinity from 1.38±0.30 to 2.60±0.92 and 3.82±0.58 ml kg–1h–1 in 9, 35 and 50 ppt, respectively. By contrast, the fraction of imbibed water absorbed decreased from 85.9±3.8% in 9 ppt to 68.8±3.2% in 35 ppt and 61.4±1.0% in 50 ppt. Despite large changes in rectal base excretion from 9.3±2.7 to 68.2±20.4 and 193.2±64.9 μmol kg–1 h–1 in 9, 35 and 50 ppt, respectively, acute or prolonged exposure to altered salinities was associated with only modest acid–base balance disturbances. Extra-intestinal, presumably branchial, net acid excretion increased with salinity (62.0±21.0, 229.7±38.5 and 403.1±32.9 μmol kg–1 h–1 at 9, 35 and 50 ppt, respectively),demonstrating a compensatory response to altered intestinal base secretion associated with osmoregulatory demand.
A muscarinic cholinergic mechanism underlies activation of the central pattern generator for locust flight
Authors: Buhl Edgar , Schildberger Klaus , Stevenson Paul A. 
Published: June 2008

SUMMARYA central question in behavioural control is how central pattern generators(CPGs) for locomotion are activated. This paper disputes the key role generally accredited to octopamine in activating the CPG for insect flight. In deafferented locusts, fictive flight was initiated by bath application of the muscarinic agonist pilocarpine, the acetylcholine analogue carbachol, and the acetylcholinesterase blocker eserine, but not by nicotine. Furthermore, in addition to octopamine, various other amines including dopamine, tyramine and histamine all induced fictive flight, but not serotonin or the amine-precursor amino acid tyrosine. However, flight initiation was not reversibly blocked by aminergic antagonists, and was still readily elicited by both natural stimulation (wind) and pilocarpine in reserpinized, amine-depleted locusts. By contrast, the muscarinic antagonists atropine and scopolamine reversibly blocked flight initiated by wind, cholinergic agonists, octopamine, and by selective stimulation of a flight-initiating interneurone (TCG). The short delay from TCG stimulation to flight onset suggests that TCG acts directly on the flight CPG, and accordingly that TCG, or its follower cell within the flight generating circuit, is cholinergic. We conclude that acetylcholine acting via muscarinic receptors is the key neurotransmitter in the mechanism underlying the natural activation of the locust flight CPG. Amines are not essential for this, but must be considered as potential neuromodulators for facilitating flight release and tuning the motor pattern. We speculate that muscarinic activation coupled to aminergic facilitation may be a general feature of behavioural control in insects for ensuring conditional recruitment of individual motor programs in accordance with momentary adaptive requirements.
Carbohydrate regulation in relation to colony growth in ants
Authors: Dussutour A. , Simpson S. J. 
Published: June 2008

SUMMARYAnts and all social insects are faced with a nutritional challenge: the food entering the colony is brought by only a small number of its workers but is shared among all members of the colony. In this study, we investigated how ants maintain carbohydrates supply at both a collective and an individual level in response to changes in the concentration of available sucrose solution, colony demography and larval growth. We manipulated the concentration of sugar solutions available to ant colonies (dilute, medium and concentrated solutions) over extended periods and measured the capacity of colonies to maintain sugar supply through compensatory feeding. First, we demonstrated that ants regulated carbohydrate intake at a collective and individual level. Initially, ants consumed most and recruited fastest in response to more concentrated than to dilute sugar solutions, but over time this pattern reversed, such that the number of ants that fed and the volume ingested by each ant was a negative function of sugar concentration in the diet. Second, we found that ants became better at regulating their carbohydrate intake with the production of larvae in the nest. When the number of larvae was experimentally doubled, the ants regulated their consumption of carbohydrates more accurately than when the number of adult workers was doubled, suggesting that larvae play an important role in providing nutritional feedback to workers. Finally, we showed that ants defended a carbohydrate `intake target' by allowing them to select among sugar solutions of different concentration.
Female mice respond differently to costly foraging versus food restriction
Authors: Schubert Kristin A. , Vaanholt Lobke M. , Stavasius Fanny , Demas Gregory E. , Daan Serge , Visser G. Henk 
Published: June 2008

SUMMARY
Experimental manipulation of foraging costs per food reward can be used to study the plasticity of physiological systems involved in energy metabolism. This approach is useful for understanding adaptations to natural variation in food availability. Earlier studies have shown that animals foraging on a fixed reward schedule decrease energy intake and expenditure. However, the extent to which these changes depend on decreased food intake or increased foraging costs per se has never been tested. We manipulated foraging costs per food reward in female Hsd:ICR(CD-1) laboratory mice, comparing animals faced with low (L) and high (H) foraging costs to non-foraging animals receiving a food restriction (R) matched to the intake of H animals. Mice in the H group ran as much as L mice did but ate significantly less. They concurrently reduced daily energy expenditure and resting metabolic rate, decreased the size of major metabolic organs and utilized body fat stores; mass-specific resting metabolic rate did not differ between groups. We found evidence that these alterations in energy balance may carry fitness costs. As a secondary response to our experimental treatment, H females and, eventually, some R females ceased to show signs of estrous cyclicity. Surprisingly, results of an immune challenge with keyhole limpet hemocyanin showed that primary immune response did not differ between L and H groups, and was actually higher in R mice. Our results demonstrate that high foraging costs per se –the combination of high activity and low food intake – have pronounced physiological effects in female mice.
Scaling of muscle architecture and fiber types in the rat hindlimb
Authors: Eng Carolyn M. , Smallwood Laura H. , Rainiero Maria Pia , Lahey Michele , Ward Samuel R. , Lieber Richard L. 
Published: June 2008

SUMMARY
The functional capacity of a muscle is determined by its architecture and metabolic properties. Although extensive analyses of muscle architecture and fiber type have been completed in a large number of muscles in numerous species, there have been few studies that have looked at the interrelationship of these functional parameters among muscles of a single species. Nor have the architectural properties of individual muscles been compared across species to understand scaling. This study examined muscle architecture and fiber type in the rat (Rattus norvegicus) hindlimb to examine each muscle's functional specialization. Discriminant analysis demonstrated that architectural properties are a greater predictor of muscle function (as defined by primary joint action and anti-gravity or non anti-gravity role)than fiber type. Architectural properties were not strictly aligned with fiber type, but when muscles were grouped according to anti-gravity versusnon-anti-gravity function there was evidence of functional specialization. Specifically, anti-gravity muscles had a larger percentage of slow fiber type and increased muscle physiological cross-sectional area. Incongruities between a muscle's architecture and fiber type may reflect the variability of functional requirements on single muscles, especially those that cross multiple joints. Additionally, discriminant analysis and scaling of architectural variables in the hindlimb across several mammalian species was used to explore whether any functional patterns could be elucidated within single muscles or across muscle groups. Several muscles deviated from previously described muscle architecture scaling rules and there was large variability within functional groups in how muscles should be scaled with body size. This implies that functional demands placed on muscles across species should be examined on the single muscle level.