Additional Metabolic Costs Research Articles

Metagenomics reveals effects of fluctuating water conditions on functional pathways in plant litter microbial community

Climate change modifies environmental conditions, resulting in altered precipitation patterns, moisture availability and nutrient distribution for microbial communities. Changes in water availability are projected to affect a range of ecological processes, including the decomposition of plant litter and carbon cycling. However, a detailed understanding of microbial stress response to drought/flooding is missing. In this study, an intermittent lake is taken up as a model for changes in water availability and how they affect the functional pathways in microbial communities of the decomposing Phragmites australis litter. The results show that most enriched functions in both habitats belonged to the classes of Carbohydrates and Clustering-based subsystems (terms with unknown function) from SEED subsystems classification. We confirmed that changes in water availability resulted in altered functional makeup of microbial communities. Our results indicate that microbial communities under more frequent water stress (due to fluctuating conditions) could sustain an additional metabolic cost due to the production or uptake of compatible solutes to maintain cellular osmotic balance. Nevertheless, although prolonged submergence seemed to have a negative impact on several functional traits in the fungal community, the decomposition rate was not affected.

Phasmid species that inhabit colder environments are less likely to have the ability to fly.

A vast majority of insects can fly, but some cannot. Flight generally increases how far an individual can travel to access mates, enables the exploitation of additional food resources, and aids in predator avoidance. Despite its functional significance, much remains unknown about the factors that influence the evolution of flight. Here, I use phylogenetic comparative methods to investigate whether average annual temperature or wind speed, two components of the flying environment, is correlated with the evolution of flight using data from 107 species of stick and leaf insects (Insecta: Phasmatodea). I find no association between wind speed and flying ability in this clade. However, I find that colder temperatures are associated with the lack of flying ability. This pattern may be explained by the additional metabolic costs required for insects to fly when it is cold. This finding contradicts previous patterns observed in other insect groups and supports the hypothesis that cold temperatures can influence the evolution of flight.

The Development of an Innovative Occupational Passive Upper Extremity Exoskeleton and an Investigation of Its Effects on Muscles

Work-related musculoskeletal disorders are one of the main problems reducing the life quality of workers. Occupational exoskeletons are one of the most promising solutions for solving this issue. In this study, an innovative and passive upper-extremity exoskeleton design was presented and tested by measuring ten different muscle activities for two tasks: Task 1, for over-the-head tool handling, and Task 2, for completely stretched forearm tool handling. The special optimized switch mechanism design allowed for free motion when it was not active, which provided design advantages in comparison to the currently available designs. The muscle activity levels were measured via EMG for both tasks and the results were compared and evaluated with and without the exoskeleton on the human body. It was shown that the muscle activity for Task 1 was reduced by 55% for the middle deltoid, 37% for the posterior deltoid, and 27% for the anterior deltoid muscles, in comparison to no exoskeleton for Task 1. For Task 2, the muscle activity was reduced by 48% for the middle deltoid, 20% for the posterior deltoid, and 38% for the anterior deltoid. The exoskeleton presented in this study is an efficient design that significantly increases shoulder comfort, especially in working conditions, without bringing an additional metabolic cost for the secondary muscles.

A Semi-active Exoskeleton Based on EMGs Reduces Muscle Fatigue When Squatting.

In dynamic manufacturing and warehousing environments, the work scene made it impossible for workers to sit, so workers suffer from muscle fatigue of the lower limb caused by standing or squatting for a long period of time. In this paper, a semi-active exoskeleton used to reduce the muscle fatigue of the lower limb was designed and evaluated. (i) Background: The advantages and disadvantages of assistive exoskeletons developed for industrial purposes were introduced. (ii) Simulation: The process of squatting was simulated in the AnyBody.7.1 software, the result showed that muscle activity of the gluteus maximus, rectus femoris, vastus medialis, vastus lateralis, vastus intermedius, and erector spinae increased with increasing of knee flexion angle. (iii) Design: The exoskeleton was designed with three working modes: rigid-support mode, elastic-support mode and follow mode. Rigid-support mode was suitable for scenes where the squatting posture is stable, while elastic-support mode was beneficial for working environments where the height of squatting varied frequently.The working environments were identified intelligently based on the EMGs of the gluteus maximus, and quadriceps, and the motor was controlled to switch the working mode between rigid-support mode and elastic-support mode. In follow mode, the exoskeleton moves freely with users without interfering with activities such as walking, ascending and descending stairs. (iv) Experiments: Three sets of experiments were conducted to evaluate the effect of exoskeleton. Experiment one was conducted to measure the surface electromyography signal (EMGs) in both condition of with and without exoskeleton, the root mean square of EMGs amplitude of soleus, vastus lateralis, vastus medialis, gastrocnemius, vastus intermedius, rectus femoris, gluteus maximus, and erector spinae were reduced by 98.5, 97.89, 80.09, 77.27, 96.73, 94.17, 70.71, and 36.32%, respectively, with the assistance of the exoskeleton. The purpose of experiment two was aimed to measure the plantar pressure with and without exoskeleton. With exoskeleton, the percentage of weight through subject's feet was reduced by 63.94, 64.52, and 65.61% respectively at 60°, 90°, and 120° of knee flexion angle, compared to the condition of without exoskeleton. Experiment three was purposed to measure the metabolic cost at a speed of 4 and 5 km/h with and without exoskeleton. Experiment results showed that the average additional metabolic cost introduced by exoskeleton was 2.525 and 2.85%. It indicated that the exoskeleton would not interfere with the movement of the wearer Seriously in follow mode. (v) Conclusion: The exoskeleton not only effectively reduced muscle fatigue, but also avoided interfering with the free movement of the wearer.

Sub-lethal temperature thresholds indicate acclimation and physiological limits in brook trout Salvelinus fontinalis.

The upper thermal tolerance of brook trout Salvelinus fontinalis was estimated using critical thermal maxima (CTmax ) experiments on fish acclimated to temperatures that span the species' thermal range (5-25°C). The CTmax increased with acclimation temperature but plateaued in fish acclimated to 20, 23 and 25°C. Plasma lactate was highest, and the hepato-somatic index (IH ) was lowest at 23 and 25°C, which suggests additional metabolic costs at those acclimation temperatures. The results suggest that there is a sub-lethal threshold between 20 and 23°C, beyond which the fish experience reduced physiological performance.

ROS production and its detoxification in early and late sown cultivars of wheat under future O3 concentration

The present field study was planned with an objective to unravel the mechanisms behind the differential responses of early and late sown wheat cultivars with respect to their defense capacity to scavenge ROS induced under elevated O3 (EO3). Experiments were performed under ambient and elevated levels of O3 (ambient + 20 ppb) to plants inside open-top chambers (OTCs). Ozone concentrations, stomatal flux of O3 and meteorological parameters were measured throughout the experiment. Contents of superoxide radicals (O2−) and hydrogen peroxide (H2O2) and their localization, lipid peroxidation, antioxidative enzyme activities, ascorbic acid and total phenolic contents were measured at vegetative and reproductive developmental stages. EO3 exposure induced higher stomatal flux of O3 in early sown cultivars. Higher contents of O2−, H2O2 and lipid peroxidation were noticed under EO3 in all the cultivars but the magnitude of increases was higher in late sown cultivars at the reproductive stage. Activities of glutathione reductase (GR) and ascorbate peroxidase (APX) were higher in late sown cultivars under EO3. Ascorbic acid and total phenolic contents were significantly higher in early sown than late sown cultivars under EO3 treatment. The present study concludes that early sown cultivars are more efficient in their defense response due to higher induction of enzymatic and non-enzymatic antioxidants, while the induction of enzymatic antioxidants was more distinct in late sown cultivars. Non-enzymatic linked defense mechanism requires additional metabolic cost than enzymatic defense, making early sown cultivars more susceptible to EO3. Differential response of early and late sown cultivars with respect to antioxidative defense against O3 stress suggests that yield responses are governed by the time of sowing and intrinsic defense responses of the cultivars. In future with rising trend of O3, early sown cultivars are expected to be more vulnerable to oxidative stress compared to late sown cultivars.

Algal oxygen boost could help hot rock pool dwellers on sunny days

If you're down on the beach poking around in a rock pool, it's often the start of a summer holiday, but for Tristan McArley, from the University of Auckland, New Zealand, it's just another day at the office. He collects fish from rock pools to learn how the animals cope as the temperatures soar and the water oxygen levels dwindle, usually impairing the ability of fish to go about their daily chores. However, on one particularly brilliant summer day, McArley noticed that the rock pools were literally fizzing. Algae trapped in the pools were photosynthesising and pumping out oxygen, boosting the gas in the stagnant water to the point where it could hold no more and the oxygen escaped as bubbles. It occurred to McArley that a surfeit of oxygen is just another situation that the fish encounter naturally when it is sunny, ‘[yet] very few studies had looked into the influence of higher than normal levels of oxygen in rock pool fish’, he says.Knowing that European perch are able to extend their metabolic capacity (the difference between their maximum and minimum metabolic rates, which permits them to perform routine activities) when oxygen levels are boosted, McArley and his colleagues Anthony Hickey and Neill Herbert, also from Auckland, wondered how local triplefin fish deal with an overabundance of oxygen on blistering summer days.‘These fish often occupy quite small rock pools so they are easily caught with hand nets’, says McArley, who transported 2 g mottled twisters (Bellapiscis medius) and common triplefins (Forsterygion lapillum) back to the Leigh Marine Laboratory. McArley then began measuring the fish's oxygen consumption – initially when swimming at their top speed in 21°C water at either normal (100% air saturation) or 200% air saturation (super oxygenated) to record their maximum oxygen consumption. Next, he allowed the fish to settle down gradually until they reached the minimum oxygen consumption necessary for survival. After that, McArley increased the temperature gradually from 21°C to 29°C to find out how the fish's oxygen consumption increased as the temperature rose. Finally, he logged when the fish toppled over as they were warmed in normal and super-oxygenated water, to find the highest temperature that they can tolerate.The metabolic capacity of the fish in 200% air saturated water increased, allowing them to continue going about their lives despite the higher temperatures, which usually impair fish activities. Considering the sunny conditions that cause oxygen levels to increase in rock pools, McArley says, ‘It may be that whenever these species face acutely high temperatures, they do so under super-oxygenated conditions’. At the highest temperatures, the super-oxygenated fish were barely more resilient than the fish in normally oxygenated water, toppling over at about 31°C, ‘pointing to factors other than the ability to supply oxygen to tissues as being responsible for setting the absolute thermal limits in these species’, says McArley. However, he was surprised when he measured the metabolic rates of the super-oxygenated twisters and triplefins at rest; the metabolic rates were higher than those of the fish in normal water. ‘This suggests there are also some additional metabolic costs of super-oxygenation to these fish’, he says.It seems that fish in hot rock pools on sunny days may not be as compromised as everyone had thought and McArley adds, ‘It is important to study the impacts of stressors such as acute heat stress under ecologically relevant conditions’. However, he warns that the algal oxygen boost is unlikely to protect sizzling rock pool species in the long run as climate change takes an unrelenting grip.

Starvation rates in larval and juvenile Atlantic silversides (Menidia menidia) are unaffected by high CO2 conditions

Over the past decade, laboratory experiments on fish early life stages have found many traits that are evidently sensitive to elevated CO2 levels. With respect to larval growth, high CO2 environments are commonly assumed to increase acid–base regulation and other plastic responses, thus incurring additional metabolic costs that reduce the scope for growth. This assumption is not well supported by empirical evidence. One reason might be that experiments often provide unrestricted feeding conditions, which could allow larvae to compensate for higher costs by increased food intake. To remove potentially confounding effects of larval feeding, we conducted a series of starvation trials on offspring of the Atlantic silverside (Menidia menidia), predicting faster starvation at high compared to ambient CO2 treatments. We compiled observations from five separate experiments spanning different years, laboratories, temperatures (17–26 °C), life stages (newly hatched larvae, previously fed larvae, early juveniles), and CO2 levels (300–6500 µatm). Contrary to expectation, we found that starvation rates were largely independent of the CO2 environment in this fish species. The one exception occurred at the lowest temperature and most extreme CO2 treatment, which resulted in slower not faster starvation in newly hatched larvae at high compared to ambient CO2 treatments. The apparent failure of starvation rate as a proxy for CO2 effects on larval fish metabolism may have several reasons, including potential CO2 tolerance of offspring, observed large stochasticity in early life survival masking small metabolic costs of high CO2, and the general depression and reconfiguration of fish metabolism in response to food deprivation.

Integrating spatio-temporal variation in resource availability and herbivore movements into rangeland management: RaMDry—An agent-based model on livestock feeding ecology in a dynamic, heterogeneous, semi-arid environment

Fast growth of the human population puts high pressure on pasture habitats due to increasingly high grazing intensities on shrinking grazing land. Adapted herbivore management is needed to maintain the long term productivity of the rangeland ecosystem, especially in dry climates where precipitation is highly erratic and where forage yield and quality of the pasture are highly dynamic. We used an agent-based approach to develop a spatially explicit model for a case study region in Madagascar. Our model “RaMDry” integrates the movements and feeding metabolism of domesticated ruminants in order to assess the potential of adaptive livestock production in a highly dynamic, heterogeneous, semi-arid rangeland system. It evaluates the additional metabolic energy costs due to pastoral herd movements in search of forage, incorporates seasonal dynamics in forage quality in terms of feed digestibility and relates forage availability and quality to climatic conditions. In the presented study, we focused on describing the processes simulated in RaMDry in detail, simplifying model conditions by implying free-ranging conditions. We verified the results of the model through global and local sensitivity analysis and pattern-oriented modeling and compared findings with observed patterns and existing data from literature. Our model provides a useful tool to assess strategies and effects of locally adapted herd and rangeland utilization for sustained food security and household economy of livestock keepers in the semi-arid tropics and sub-tropics. Subject for further analysis of the model is its capability to simulate different management strategies and climatic conditions as well as the development of the models’ capacity to predict accumulative effects of environmental degradation.

Failing to meet relative humidity targets for incubated neonates causes higher heat loss and metabolic costs in the first week of life.

Frequent nursing procedures can modify a newborn infant's thermal environment when their incubator is opened. This study evaluated the impact of relative humidity (RH) on preterm infants in closed incubators and calculated their heat loss and additional metabolic cost. We studied 45 preterm infants born before 32 + 0 weeks, nursed at the neonatal intensive care unit at Amiens University Hospital, France from January 2009 to November 2011. Their body, skin and air temperatures and the incubator's RH were continuously recorded from day 1 to 8 of life, and the differences between the measured and target RH were calculated. Body heat loss (BHL) was also calculated. On day one, the measured RH (68.7 ± 1.0%) was significantly lower than the target RH (75%, p < 0.05), but this difference, together with BHL (p < 0.001) and evaporative heat loss (p < 0.001), fell significantly over time (p < 0.05). The additional metabolic cost correlated with the difference between measured and target RH (p < 0.001). RH from day 1 to 8 was below the recommended target value for preterm infants and resulted in high evaporative and greater total BHL and additional metabolic cost. The findings pose numerous challenges, including nursing care and incubator design.

The contribution of geometry to the human connectome

The human connectome is a topologically complex, spatially embedded network. While its topological properties have been richly characterized, the constraints imposed by its spatial embedding are poorly understood. By applying a novel resampling method to tractography data, we show that the brain's spatial embedding makes a major, but not definitive, contribution to the topology of the human connectome. We first identify where the brain's structural hubs would likely be located if geometry was the sole determinant of brain topology. Empirical networks show a widespread shift away from this geometric center toward more peripheral interconnected skeletons in each hemisphere, with discrete clusters around the anterior insula, and the anterior and posterior midline regions of the cortex. A relatively small number of strong inter-hemispheric connections assimilate these intra-hemispheric structures into a rich club, whose connections are locally more clustered but globally longer than predicted by geometry. We also quantify the extent to which the segregation, integration, and modularity of the human brain are passively inherited from its geometry. These analyses reveal novel insights into the influence of spatial geometry on the human connectome, highlighting specific topological features that likely confer functional advantages but carry an additional metabolic cost.

Cell-intrinsic mechanisms of temperature compensation in a grasshopper sensory receptor neuron.

Changes in temperature affect biochemical reaction rates and, consequently, neural processing. The nervous systems of poikilothermic animals must have evolved mechanisms enabling them to retain their functionality under varying temperatures. Auditory receptor neurons of grasshoppers respond to sound in a surprisingly temperature-compensated manner: firing rates depend moderately on temperature, with average Q10 values around 1.5. Analysis of conductance-based neuron models reveals that temperature compensation of spike generation can be achieved solely relying on cell-intrinsic processes and despite a strong dependence of ion conductances on temperature. Remarkably, this type of temperature compensation need not come at an additional metabolic cost of spike generation. Firing rate-based information transfer is likely to increase with temperature and we derive predictions for an optimal temperature dependence of the tympanal transduction process fostering temperature compensation. The example of auditory receptor neurons demonstrates how neurons may exploit single-cell mechanisms to cope with multiple constraints in parallel.DOI: http://dx.doi.org/10.7554/eLife.02078.001.

Gallium-mediated siderophore quenching as an evolutionarily robust antibacterial treatment

Conventional antibiotics select strongly for resistance and are consequently losing efficacy worldwide. Extracellular quenching of shared virulence factors could represent a more promising strategy because (i) it reduces the available routes to resistance (as extracellular action precludes any mutations blocking a drug's entry into cells or hastening its exit) and (ii) it weakens selection for resistance, as fitness benefits to emergent mutants are diluted across all cells in a cooperative collective. Here, we tested this hypothesis empirically. We used gallium to quench the iron-scavenging siderophores secreted and shared among pathogenic Pseudomonas aeruginosa bacteria, and quantitatively monitored its effects on growth in vitro. We assayed virulence in acute infections of caterpillar hosts (Galleria mellonella), and tracked resistance emergence over time using experimental evolution. Gallium strongly inhibited bacterial growth in vitro, primarily via its siderophore quenching activity. Moreover, bacterial siderophore production peaked at intermediate gallium concentrations, indicating additional metabolic costs in this range. In vivo, gallium attenuated virulence and growth-even more so than in infections with siderophore-deficient strains. Crucially, while resistance soon evolved against conventional antibiotic treatments, gallium treatments retained their efficacy over time. Extracellular quenching of bacterial public goods could offer an effective and evolutionarily robust control strategy.

Update on Energy Homeostasis and Insufficient Sleep

Driven by the demands and opportunities of modern life, many people habitually sleep less than 6 h a night. In the sleep clinic, chronic sleep restriction is recognized by the diagnosis of insufficient sleep syndrome (ICSD-9, 307.49-4), which is receiving increased scrutiny as a potential risk to metabolic health. Its relevance for the practicing endocrinologist is highlighted by a stream of epidemiological data that show an association of insufficient sleep with increased incidence of obesity and related morbidities. A central theme of this update is the notion that sleep loss incurs additional metabolic cost, which triggers a set of neuroendocrine, metabolic, and behavioral adaptations aimed at increasing food intake and conserving energy. Although this coordinated response may have evolved to offset the metabolic demands of extended wakefulness in natural habitats with limited food availability, it can be maladaptive in the context of a modern environment that allows many to overeat while maintaining a sedentary lifestyle without sufficient sleep. Importantly, such sleep loss-related metabolic adaptation may undermine the success of behavioral interventions based on reduced caloric intake and increased physical activity to lower metabolic risk in obesity-prone individuals. This emerging perspective is based on data from recently published human interventional studies and requires further experimental support. Nevertheless, it now seems prudent to recommend that overweight and obese individuals attempting to reduce their caloric intake and maintain increased physical activity should obtain adequate sleep and, if needed, seek effective treatment for any coexisting sleep disorders.

Discrete thermal windows cause opposite response of sympatric cold-water fish species to annual temperature variability

Cold-water fish populations in lakes are predicted to be most vulnerable to global warming due to their geographical isolation and their requirement for habitats with low temperatures. In contrast, higher fisheries catches of cold-water species often correlate with warmer winter and spring temperatures. Mechanistic understanding of the relationships between annual temperatures and population densities can only be achieved by integrating physiology and behavioral ecology of the focal species, an approach that has so far not been applied to freshwater fish populations. We took advantage from a unique biological system, the coexistence of two cold-water Coregonus species in a deep lake. These fish species show discrete thermal windows (4–5°C vs. 7–9°C) and life histories (spring- vs. autumn-spawning). We analyzed short (6–11 years) time series of pelagic fish densities obtained by hydroacoustics and trawl catches, their zooplankton prey densities, and water temperature in Lake Stechlin (Germany). Young-of-year fish densities increased after warm winters. In contrast, densities of juveniles and adults were correlated with metalimnetic June temperatures, but an opposite response direction of the sympatric species was caused by their discrete thermal windows. Densities of the species with a 4–5°C thermal optimum increased in years with warm June, whereas densities of the other species with a 7–9°C optimum declined in these warm years. The occupied depths of both populations at night shifted towards less suitable water temperatures if densities of the competing species increased, suggesting interactive niche segregation. Therefore, growth of fishes may be reduced and hence mortality increased by additional metabolic costs induced by occurrence in layers outside of the metabolic optima. Temperature-driven inter- and intra-specific competition in the metalimnetic layer may cause a complex response of cold-water fish assemblages in lakes to warming. More approaches testing the relative performance of interacting species are needed to improve predictions on the consequences of global change on lake ecosystems.

Biophysical Aspects of Resource Acquisition and Competition in Algal Mixotrophs

Mixotrophic organisms combine autotrophic and heterotrophic nutrition and are abundant in both freshwater and marine environments. Recent observations indicate that mixotrophs constitute a large fraction of the biomass, bacterivory, and primary production in oligotrophic environments. While mixotrophy allows greater flexibility in terms of resource acquisition, any advantage must be traded off against an associated increase in metabolic costs, which appear to make mixotrophs uncompetitive relative to obligate autotrophs and heterotrophs. Using an idealized model of cell physiology and community competition, we identify one mechanism by which mixotrophs can effectively outcompete specialists for nutrient elements. At low resource concentrations, when the uptake of nutrients is limited by diffusion toward the cell, the investment in cell membrane transporters can be minimized. In this situation, mixotrophs can acquire limiting elements in both organic and inorganic forms, outcompeting their specialist competitors that can utilize only one of these forms. This advantage can be enough to offset as much as a twofold increase in additional metabolic costs incurred by mixotrophs. This mechanism is particularly relevant for the maintenance of mixotrophic populations and productivity in the highly oligotrophic subtropical oceans.

Metabolic Cost of Wheelchair Propulsion Using an Ergonomic Hand Drive Mechanism

Conventional manual wheelchair (CMW) use is associated with a high prevalence of shoulder and wrist pain, which may interfere with mobility and lead to increased risk of cardiovascular problems. Previous lever-activated propulsion designs have been shown to shift and reduce shoulder muscular demands, decreasing the risk of incurring repetitive strain injuries. However, these designs do not consider the anthropometrics of the user (height, arm length, etc.). The novel ergonomic hand drive mechanism (EHDM) used in this study was designed to shift awkward postures while accommodating different users without additional metabolic cost. PURPOSE: To evaluate metabolic cost (VO2 and HR) while using an EHDM. METHODS: Eight adult full-time manual wheelchair users participated (46.8±21.8 yrs, 74.0±12.7 kg, 174.6±13.6 cm). All participants were medically and functionally stable and at least six months post injury. Participants propelled around a circuit for three and a half minutes at a self-selected pace in a CMW and then again in the same chair fitted with the hand drive mechanism for a total of two trials. VO2 and HR were recorded using a portable device while distance, velocity and push frequency were measured manually. Velocity, distance traveled, push frequency, VO2 per meter, and heart rate were compared by wheelchair condition for the last 30 seconds of each trial using paired t-tests (α=0.05). RESULTS: The CMW condition resulted in more distance traveled (28.7±15.1 m vs. 20.0±8.7 m, p=0.049) as well as greater velocity (0.957±0.5 m/s vs. 0.667±0.3 m/s, p=0.049) than the EHDM condition. No significant differences were found between the two conditions for number of pushes (26.3±5.8 vs. 27.0±5.3, p=0.683), VO2 efficiency (0.24±0.1 ml/kg/min/m vs. 0.31±0.1 ml/kg/min/m, p=0.08), or HR (102.6±14.2 bpm vs. 105.5±15.7 bpm, p=0.635). CONCLUSION: The results demonstrate that participants avoided additional metabolic costs although performance (velocity and distance) was sacrificed with the EHDM. Modifications to the EHDM (e.g. addition of gearing) could rectify the performance decrement. Supported by the Clinical and Translational Science Institute Pilot & Collaborative Research Projects (NIH). The hand drive mechanism used in this study is the intellectual property of Shands Healthcare.

Energy management on a nectar diet: can sunbirds meet the challenges of low temperature and dilute food?

Summary 1. Animals commonly experience variation in both food quality and metabolic requirements, and must regulate their food intake to maintain energy balance. 2. We exposed captive whitebellied (Cinnyris talatala) and amethyst (Chalcomitra amethystina) sunbirds (Nectariniidae) to different nectar sugar concentrations (0·25, 0·5 and 1 m sucrose), i.e. food qualities, and ambient temperatures (5, 15 and 25 °C), i.e. energy requirements, to examine the effects on food intake, feeding patterns and body mass of the birds. 3. Both species compensated for decreased dietary sugar concentration by increasing food intake. While whitebellied sunbirds showed a constant sugar intake over the range of diet concentrations, amethyst sunbirds ingested less sugar on 0·25 m than on 0·5 m sucrose. During acute short‐term exposure to 5 °C, birds increased food and thus sugar intake on all diet concentrations by almost 27%, compared to the similar intake at 15 and 25 °C. Despite increased food consumption, all birds lost more body mass at 5 and 15 °C than at 25 °C. 4. Adjustment of food intake in both species took place via changes in feeding frequency, with the duration of feeding events unchanged. 5. Apparent sugar assimilation in whitebellied sunbirds was &gt;99%, irrespective of diet concentration and temperature. A chemical reactor model of digestive capacity based on measurements of intestinal hydrolytic capacity mostly underestimated the maximal food intake of whitebellied sunbirds in the cold, but predicted higher maximal intake for amethyst sunbirds than observed on most diet concentrations. 6. We conclude that physiological constraints impose upper limits on compensatory feeding in sunbirds. These constraints are mainly digestive at low temperature and osmoregulatory on dilute diets, while the combination of both stresses leads to additional metabolic costs. 7. The moderate mass loss of both species when exposed to these energy challenges suggests that behavioural changes and/or hypothermia may be used to reduce energy expenditure.

To go or not to go with the flow: Environmental influences on whale shark movement patterns

Seven whale sharks were tracked using satellite-linked tags from Ningaloo Reef, off northern Western Australia, following tagging in April and June 2002 and April–May 2005. We investigated how the movements of those whale shark tracks were influenced by geostrophic surface currents during sequential one-week periods by using a passive diffusion model parameterised with observed starting locations of the sharks and weekly maps of surface current velocity and direction (derived from altimetry). We compared the outputs from the passive diffusion model and maps of chlorophyll-a concentration (SeaWiFs/MODIS) and with the actual tracks of the sharks using GIS and generalized linear mixed-effects models (GLMM). The GLMM indicated very little support for passive diffusion with sea-surface ocean currents influencing whale shark distributions in the north eastern Indian Ocean. Moreover, the sharks' movements correlated only weakly with the spatial distribution of sea-surface chlorophyll-a concentrations. The seven whale sharks had average swimming speeds comparable with those recorded in other satellite tracking studies of this species. Swimming speeds of the seven sharks were similar to those reported in previous studies and up to three times greater than the maximum sea-surface current velocities that the sharks encountered while traversing into lower southerly latitudes (moving northward towards the equator). Our results indicate that whale sharks departing from Ningaloo travel actively and independently of near-surface currents where they spend most of their time despite additional metabolic costs of this behaviour.

Pound for pound: Working out how obesity influences the energetics of walking

Childhood and adult obesity are both serious health problems that are catalyzed by inadequate physical activity and the resulting chronic energy imbalance. For most people, walking consumes more metabolic energy than any other daily activity. Thus it is important to understand the energetic cost of