Humans have the remarkable ability to run over variable terrains. During locomotion, however, humans are unstable in the mediolateral direction and this instability must be controlled actively—a goal ...that could be achieved in more ways than one. Walking research indicates that the subtalar joint absorbs energy in early stance and returns it in late stance, an attribute that is credited to the tibialis posterior muscle-tendon unit. The purpose of this study was to determine how humans (n = 11) adapt to mediolateral perturbations induced by custom-made 3D-printed “footwear” that either enhanced or reduced pronation of the subtalar joint (modeled as motion in 3 planes) while running (3 m/s). In all conditions, the subtalar joint absorbed energy (ie, negative mechanical work) in early stance followed by an immediate return of energy (ie, positive mechanical work) in late stance, demonstrating a “spring-like” behavior. These effects increased and decreased in footwear conditions that enhanced or reduced pronation (
P
≤ .05), respectively. Of the recorded muscles, the tibialis posterior (
P
≤ .05) appeared to actively change its activation in concert with the changes in joint energetics. We suggest that the “spring-like” behavior of the subtalar joint may be an inherent function that enables the lower limb to respond to mediolateral instabilities during running.
The objective of this article is to provide an historical perspective on a review of “Heat production and chemical change in muscle” written by Roger C. Woledge and published in Progress in ...Biophysics and Molecular Biology 50 years ago. We first provide a brief but broad summary of the history of muscle chemistry prior to 1971 and then address the central theme of the 1971 review - that of energy balance. Energy balance is a method to establish whether all the energetically significant biochemical reactions accompanying muscle contraction have been identified. Woledge adopted the method to compare the measured enthalpy output (i.e., the sum of the heat output and work output) to that expected from the extent of known biochemical reactions. Prior work had suggested that the observed and expected enthalpy outputs were similar but Woledge proposed that the expected heat had been overestimated and that, hence, there must be an unidentified reaction that accounted for as much as half the heat produced by a contracting muscle. We describe investigations carried out after the review that vindicated that view, ultimately characterising the processes producing the unexplained enthalpy which, in turn, led to identification of the hitherto unknown reaction. Those experiments and a more recent resurrection of the approach using fluorescent probes to monitor ATP turnover have now accounted for the processes that underlie the complex time courses of muscle heat production and ATP turnover during contraction, at least in the classical frog sartorius muscle preparation. However, the few studies performed on mammalian muscles since then have produced results that are difficult to reconcile with the ideas derived from energy balance studies of amphibian and fish muscles, thereby suggesting a new objective for energy balance studies.
Muscle energetics encompasses the relationships between mechanical performance and the biochemical and thermal changes that occur during muscular activity. The biochemical reactions that underpin ...contraction are described and the way in which these are manifest in experimental recordings, as initial and recovery heat, is illustrated. Energy use during contraction can be partitioned into that related to cross-bridge force generation and that associated with activation by Ca2+. Activation processes account for 25–45% of ATP turnover in an isometric contraction, varying amongst muscles. Muscle energy use during contraction depends on the nature of the contraction. When shortening muscles produce less force than when contracting isometrically but use energy at a greater rate. These characteristics reflect more rapid cross-bridge cycling when shortening. When lengthening, muscles produce more force than in an isometric contraction but use energy at a lower rate. In that case, cross-bridges cycle but via a pathway in which ATP splitting is not completed. Shortening muscles convert part of the free energy available from ATP hydrolysis into work with the remainder appearing as heat. In the most efficient muscle studied, that of a tortoise, cross-bridges convert a maximum of 47% of the available energy into work. In most other muscles, only 20–30% of the free energy from ATP hydrolysis is converted into work.
Lactating Steller sea lions (SSL; Eumetopias jubatus) are income breeders, which balance the energetic cost of provisioning a pup with alternating periods of foraging at sea and nursing onshore ...during a 12–36 month dependency period. Foraging dives may be benthic or epipelagic, and the diverse diet varies seasonally and geographically. The objective of this study was to use animal-borne video and data recorders (VDRs) to record prey captures and characterize the three-dimensional movements, dive performance, and foraging strategies of female SSL while rearing a pup on Lovushki Island, located in the Kuril Island Archipelago in Far Eastern Russia. Female SSL made short foraging trips (8.7 h) and remained relatively close to the rookery (< 15 km) with an average swim speed of 1.5 m sec−1 and metabolic rate of 3.15 W kg−1, which was 1.8-fold greater than their estimated resting metabolic rate. We identified two types of dives representing shallow (Type 3) and deep (Type 4) benthic foraging, primarily on Atka mackerel (Pleurogrammus monopterygius) at night when they rest on the seafloor. The estimated Field Metabolic Rate (FMR; 2.31 W kg−1) for a mean 31.7 h foraging-nursing cycle was only 1.3-fold greater than their estimated resting metabolic rate, primarily because the females spent 73% of their time onshore nursing the pup. The short foraging trips near the rookery and low FMR indicated abundant prey. On average, female SSL captured 35.4 fish during a foraging trip, which represented an estimated 20.8 kg of prey. This was sufficient to remain in energy balance and provision a pup during early lactation. However, a 10–20% reduction in the size or abundance of prey would result in a 38–76% reduction in milk production, respectively, which would cause reduced growth or death of the pup. These calculations indicate the thin margin for energy balance in SSL during early lactation. Hence, any reduction in the size or abundance of prey could have serious consequences for reproductive success and fitness.
•Female SSL made short foraging trips (8.7 h) and remained relatively close to the rookery (< 15 km).•Average swim speed was1.5 m sec−1, and metabolic rate was 3.15 W kg−1.•Two types of dives were identified representing shallow (Type 3) and deep (Type 4) benthic foraging, primarily on Atka mackerel at night.•Estimated Field Metabolic Rate (FMR; 2.31 W kg−1) for a mean 31.7 h foraging-nursing cycle was only 1.3-fold greater than their estimated resting metabolic rate.•The short foraging trips near the rookery and low FMR indicated abundant prey.•On average, female SSL captured 35.4 fish during a foraging trip, which represented an estimated 20.8 kg of prey and sufficient to remain in energy balance and provision a pup during early lactation.•A 10–20% reduction in the size or abundance of prey would result in a 38–76% reduction in milk production, respectively.
Metabolic rates are fundamental to many biological processes, and commonly scale with body size with an exponent ( b
) between 2/3 and 1 for reasons still debated. According to the 'metabolic-level ...boundaries hypothesis', b
depends on the metabolic level ( L
). We test this prediction and show that across cephalopod species intraspecific b
correlates positively with not only L
but also the scaling of body surface area with body mass. Cephalopod species with high L
maintain near constant mass-specific metabolic rates, growth and probably inner-mantle surface area for exchange of respiratory gases or wastes throughout their lives. By contrast, teleost fish show a negative correlation between b
and L
. We hypothesize that this striking taxonomic difference arises because both resource supply and demand scale differently in fish and cephalopods, as a result of contrasting mortality and energetic pressures, likely related to different locomotion costs and predation pressure. Cephalopods with high L
exhibit relatively steep scaling of growth, locomotion, and resource-exchange surface area, made possible by body-shape shifting. We suggest that differences in lifestyle, growth and body shape with changing water depth may be useful for predicting contrasting metabolic scaling for coexisting animals of similar sizes. This article is part of the theme issue 'Physiological diversity, biodiversity patterns and global climate change: testing key hypotheses involving temperature and oxygen'.
The tortuosity of the track taken by an animal searching for food profoundly affects search efficiency, which should be optimised to maximise net energy gain. Models examining this generally describe ...movement as a series of straight steps interspaced by turns, and implicitly assume no turn costs. We used both empirical‐ and modelling‐based approaches to show that the energetic costs for turns in both terrestrial and aerial locomotion are substantial, which calls into question the value of conventional movement models such as correlated random walk or Lévy walk for assessing optimum path types. We show how, because straight‐line travel is energetically most efficient, search strategies should favour constrained turn angles, with uninformed foragers continuing in straight lines unless the potential benefits of turning offset the cost.
Determining where, when and how much animals eat is fundamental to understanding their ecology. We developed a technique to identify a prey capture signature for little penguins from accelerometry, ...in order to quantify food intake remotely. We categorised behaviour of captive penguins from HD video and matched this to time-series data from back-mounted accelerometers. We then trained a support vector machine (SVM) to classify the penguins' behaviour at 0.3 s intervals as either 'prey handling' or 'swimming'. We applied this model to accelerometer data collected from foraging wild penguins to identify prey capture events. We compared prey capture and non-prey capture dives to test the model predictions against foraging theory. The SVM had an accuracy of 84.95±0.26% (mean ± s.e.) and a false positive rate of 9.82±0.24% when tested on unseen captive data. For wild data, we defined three independent, consecutive prey handling observations as representing true prey capture, with a false positive rate of 0.09%. Dives with prey captures had longer duration and bottom times, were deeper, had faster ascent rates, and had more 'wiggles' and 'dashes' (proxies for prey encounter used in other studies). The mean (±s.e.) number of prey captures per foraging trip was 446.6±66.28. By recording the behaviour of captive animals on HD video and using a supervised machine learning approach, we show that accelerometry signatures can classify the behaviour of wild animals at unprecedentedly fine scales.
Landscapes of fear describe a spatial representation of an animal's perceived risk of predation and the associated foraging costs, while energy landscapes describe the spatial representation of their ...energetic cost of moving and foraging. Fear landscapes are often dynamic and change based on predator presence and behaviour, and variation in abiotic conditions that modify risk. Energy landscapes are also dynamic and can change across diel, seasonal, and climatic timescales based on variability in temperature, snowfall, wind/current speeds, etc.
Recently, it was suggested that fear and energy landscapes should be integrated. In this paradigm, the interaction between landscapes relates to prey being forced to use areas of the energy landscape they would avoid if risk were not a factor. However, dynamic energy landscapes experienced by predators must also be considered since they can affect their ability to forage, irrespective of variation in prey behaviour. We propose an additional component to the fear and dynamic energy landscape paradigm that integrates landscapes of both prey and predators, where predator foraging behaviour is modulated by changes in their energyscape.
Specifically, we integrate the predator's energy landscape into foraging theory that predicts prey patch‐leaving decisions under the threat of predation. We predict that as a predator's energetic cost of foraging increases in a habitat, then the prey's foraging cost of predation and patch quitting harvest rate, will decrease. Prey may also decrease their vigilance in response to increased energetic foraging costs for predators, which will lower giving‐up densities of prey.
We then provide examples in terrestrial, aerial, and marine ecosystems where we might expect to see these effects. These include birds and sharks which use updrafts that vary based on wind and current speeds, tidal state, or temperature, and terrestrial predators (e.g. wolves) whose landscapes vary seasonally with snow depth or ice cover which may influence their foraging success and even diet selection.
A predator perspective is critical to considering the combination of these landscapes and their ecological consequences. Dynamic predator energy landscapes could add an additional spatiotemporal component to risk effects, which may cascade through food webs.
Read the free Plain Language Summary for this article on the Journal blog.
Read the free Plain Language Summary for this article on the Journal blog.
Performance of eight rice (Oryza sativa L.) genotypes (IR 83383–B–B–129–4, IR 83387–B–B–27–4, IR88867– 9–1–1–4, IR88964–24–2–1–4, IR88964–11–2–2–4, ...IR88966–39–1–4–4, Rajendra Sweta and Rajendra Bhagwati) were evaluated in different levels of nitrogen (N) application, i.e. control, 50% RDN (60 kg N/ha), 100% RDN (120 kg N/ha) and 150% RDN (180 kg N/ha) during the rainy season of 2016–17 in lowland transplanted condition of Patna, Bihar. Significantly higher grain yields (5.19 t/ha) and net returns (` 52260/ha) were recorded with application of 180 kg N/ha. Grain yields and net returns were noted higher with IR 83383–B–B–129–4 (4.27 t/ha and ` 38181/ ha). Carbohydrate equivalent yield (4.06 t/ha) and carbon output (6.42 t CE/ha) were also higher with 150% RDN. IR83383–B–B–129–4 had significantly higher carbohydrate equivalent yield (3.34 t/ha) and carbon output (5.23 t CE/ ha). Gross energy output, net energy return, energy use efficiency, energy profitability, energy productivity, energy intensity in economic terms and energy output efficiency were markedly higher with 180 kg N/ha. These attributes were higher with IR83383–B–B–129–4 but being on a par with IR83387–B–B–27–4. Therefore, growing of IR 83383–B–B–129–4 along with application of 180 kg N/ha is an ideal approach to achieve the higher productivity, profitability and energetics in lowland transplanted condition of Bihar.
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