The metabolic cost of turning right side up in the Mediterranean spur-thighed tortoise (Testudo graeca)

Armoured, rigid bodied animals, such as Testudines, must self-right should they find themselves in an inverted position. The ability to self-right is an essential biomechanical and physiological process that influences survival and ultimately fitness. Traits that enhance righting ability may consequently offer an evolutionary advantage. However, the energetic requirements of self-righting are unknown. Using respirometry and kinematic video analysis, we examined the metabolic cost of self-righting in the terrestrial Mediterranean spur-thighed tortoise and compared this to the metabolic cost of locomotion at a moderate, easily sustainable speed. We found that self-righting is, relatively, metabolically expensive and costs around two times the mass-specific power required to walk. Rapid movements of the limbs and head facilitate successful righting however, combined with the constraints of breathing whilst upside down, contribute a significant metabolic cost. Consequently, in the wild, these animals should favour environments or behaviours where the risk of becoming inverted is reduced.

The Influence of snow properties on speed and gait choice in the Svalbard rock ptarmigan (Lagopus muta hyperborea)

Substrate supportiveness is linked to the metabolic cost of locomotion, as it influences the depth to which the foot of a moving animal will sink. As track depth increases animals typically reduce their speed to minimise any potential energetic imbalance. Here we examine how self-selected speed in the Svalbard rock ptarmigan is affected by snow supportiveness and subsequent footprint depth measured using thin-blade penetrometry and 3D photogrammetry, respectively. Our findings indicate that snow supportiveness and footprint depth are poor predictors of speed (r2 = 0.149) and stride length (r2 = 0.106). The ptarmigan in our study rarely sunk to depths beyond the intertarsal joint, regardless of the speed, suggesting that at this relatively shallow depth any increased cost is manageable. 3D reconstructions also indicate that the ptarmigan may exploit the compressive nature of snow to generate thrust during stance, as a trend towards greater foot rotations in deeper footprints was found. It remains unclear if the Svalbard ptarmigan are deliberately avoiding unsupportive snowy substrates. However, if they do, these results would be consistent with the idea that animals should choose routes that minimise energy costs of locomotion. Resumen La firmeza del sustrato se asocial al costo metabólico de la locomoción ya que influencia cuán profundo las extremidades de un animal se hunden al moverse. A medida hundimiento aumenta, usualmente los animales reducen su velocidad para minimizar potenciales desbalances energéticos. En este estudio examinamos cómo la velocidad de la perdiz de la roca de Svalbard es afectada por la firmeza del sustrato y la profundidad de hundimiento de sus patas, usando penetrometría y fotogrametría 3D, respectivamente. Nuestros resultados indican que la firmeza de la nieve y la profundidad de hundimiento de las patas no son buenos predictores de la velocidad (r2 = 0.149) y de la longitud de la zancada (r2 = 0.106). La profundidad de las huellas de las perdices de nuestro estudio rara vez sobrepasó la altura de la articulación intertarsal, independientemente de la velocidad de locomoción, sugiriendo que a profundidades relativamente menores los costos energéticos son manejables. Las reconstrucciones 3D también indican que las perdices podrían aprovechar la naturaleza compresiva de la nieve para generar suficiente empuje durante la fase de soporte, ya que se encontró una tendencia hacia mayores rotaciones de la pata en huellas más profundas. Es incierto si las perdices de Svalbard deliberadamente evitan áreas con nieve más blanda. Sin embargo, si lo hacen, estos resultados serían consistentes con la idea de que los animales deberían seleccionar rutas que minimizan los gastos energéticos en locomoción.

Sexual Mismatch Between Vessel-Associated Foraging and Discard Consumption in a Marine Top Predator

Sex differences in diet and foraging behaviour are common in sexually dimorphic species, often driven by differences in the cost of locomotion or ability to exploit different ecological niches. However, sex-specific foraging strategies also occur in monomorphic or slightly dimorphic species where the drivers are poorly understood. Here, we study sex differences in foraging of northern gannets (Morus bassanus), where females are only slightly heavier than males. Using concurrently tracked gannets (298 full foraging trips from 81 individuals) and fishing vessels across 5 years, we quantify individual-based vessel-associated putative foraging, and relate this to discard consumption. We found a significant positive relationship between time spent in vessel-associated foraging and discard consumption for both sexes. However, while females showed greater proportions of vessel-associated foraging than males, discarded fish contributed less to the diet of females in all years. These results contrast with previous suggestions that female gannets interact with vessels less often than males, and are consistent with competitive exclusion of females from trawler-associated discards. Our findings give insight into sexual differences in foraging behaviour in the absence of dimorphism that are necessary to predict their response to environmental and anthropogenic changes.

“Hey, It’s Me, It’s Me!” Courtship and Confusion in the Male Reproductive Strategy

This chapter addresses why male anacondas are so much smaller than females. There are a number of advantages for animals to be small. Small animals have lower metabolic costs since they need to maintain only a small body that requires less food. Animals that need less food have potentially higher survival than those that have a large body to maintain. This is particularly important in droughts or times of food shortages. A small body is also an asset because it lowers the cost of locomotion. Hauling around a large body incurs larger energetic expenditures than if the body is small. This is particularly important for males that move much more than females in the mating season to track receptive females for mating. Being small also offers other benefits, such as being inconspicuous, not being a very coveted meal, and hiding easily from potential predators. Of course, there are also some disadvantages of being small. Small animals cannot fight off predators as well as large ones and are limited by their gape to what kind of prey they can eat. Furthermore, larger males may produce more sperm, which would give them an advantage in siring more offspring, particularly in those cases where the female mates with several males.

Oxygen consumption of drift-feeding rainbow trout: the energetic tradeoff between locomotion and feeding in flow

To forage in fast, turbulent flow environments where prey are abundant, predatory fishes must deal with the high associated costs of locomotion. Prevailing theory suggests that many species exploit hydrodynamic refuges to minimize the cost of locomotion while foraging. Here we challenge this theory based on direct oxygen consumption measurements of drift-feeding trout (Oncorhynchus mykiss) foraging in the freestream and from behind a flow refuge at velocities up to 100 cm s-1. We demonstrate that refuging is not energetically beneficial when foraging in fast flows due to a high attack cost and low prey capture success associated with leaving a station-holding refuge to intercept prey. By integrating optimum foraging theory with empirical data from respirometry and video imaging, we develop a mathematical model to predict when drift-feeding fishes should exploit or avoid refuges based on prey density, size and flow velocity. Our foraging and refuging model provides new mechanistic insights into the locomotor costs, habitat use, and prey selection of fishes foraging in current-swept habitats.

Energetics of Walking With a Robotic Knee Exoskeleton

The authors tested 4 young healthy subjects walking with a powered knee exoskeleton to determine if it could reduce the metabolic cost of locomotion. Subjects walked with a backpack loaded and unloaded, on a treadmill with inclinations of 0° and 15°, and outdoors with varied natural terrain. Participants walked at a self-selected speed (average 1.0 m/s) for all conditions, except incline treadmill walking (average 0.5 m/s). The authors hypothesized that the knee exoskeleton would reduce the metabolic cost of walking uphill and with a load compared with walking without the exoskeleton. The knee exoskeleton reduced metabolic cost by 4.2% in the 15° incline with the backpack load. All other conditions had an increase in metabolic cost when using the knee exoskeleton compared with not using the exoskeleton. There was more variation in metabolic cost over the outdoor walking course with the knee exoskeleton than without it. Our findings indicate that powered assistance at the knee is more likely to decrease the metabolic cost of walking in uphill conditions and during loaded walking rather than in level conditions without a backpack load. Differences in positive mechanical work demand at the knee for varying conditions may explain the differences in metabolic benefit from the exoskeleton.

Swimming mechanics and propulsive efficiency in the chambered nautilus

The chambered nautilus ( Nautilus pompilius ) encounters severe environmental hypoxia during diurnal vertical movements in the ocean. The metabolic cost of locomotion ( C met ) and swimming performance depend on how efficiently momentum is imparted to the water and how long on-board oxygen stores last. While propulsive efficiency is generally thought to be relatively low in jet propelled animals, the low C met in Nautilus indicates that this is not the case. We measured the wake structure in Nautilus during jet propulsion swimming, to determine their propulsive efficiency. Animals swam with either an anterior-first or posterior-first orientation. With increasing swimming speed, whole cycle propulsive efficiency increased during posterior-first swimming but decreased during anterior-first swimming, reaching a maximum of 0.76. The highest propulsive efficiencies were achieved by using an asymmetrical contractile cycle in which the fluid ejection phase was relatively longer than the refilling phase, reducing the volume flow rate of the ejected fluid. Our results demonstrate that a relatively high whole cycle propulsive efficiency underlies the low C met in Nautilus , representing a strategy to reduce the metabolic demands in an animal that spends a significant part of its daily life in a hypoxic environment.

Strength Training for Middle- and Long-Distance Performance: A Meta-Analysis

Purpose: To assess the net effects of strength training on middle- and long-distance performance through a meta-analysis of the available literature. Methods: Three databases were searched, from which 28 of 554 potential studies met all inclusion criteria. Standardized mean differences (SMDs) were calculated and weighted by the inverse of variance to calculate an overall effect and its 95% confidence interval (CI). Subgroup analyses were conducted to determine whether the strength-training intensity, duration, and frequency and population performance level, age, sex, and sport were outcomes that might influence the magnitude of the effect. Results: The implementation of a strength-training mesocycle in running, cycling, cross-country skiing, and swimming was associated with moderate improvements in middle- and long-distance performance (net SMD [95%CI] = 0.52 [0.33–0.70]). These results were associated with improvements in the energy cost of locomotion (0.65 [0.32–0.98]), maximal force (0.99 [0.80–1.18]), and maximal power (0.50 [0.34–0.67]). Maximal-force training led to greater improvements than other intensities. Subgroup analyses also revealed that beneficial effects on performance were consistent irrespective of the athletes’ level. Conclusion: Taken together, these results provide a framework that supports the implementation of strength training in addition to traditional sport-specific training to improve middle- and long-distance performance, mainly through improvements in the energy cost of locomotion, maximal power, and maximal strength.