ORCID Profile
0000-0001-8174-3890
Current Organisation
University of the Sunshine Coast
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Publisher: Wiley
Date: 03-05-2019
Publisher: American Physiological Society
Date: 06-2023
DOI: 10.1152/JAPPLPHYSIOL.00080.2023
Abstract: Here, we measured internal muscle properties in vivo to determine their influence on the varying shape change and gearing behaviors in the synergistic gastrocnemii muscles. These relationships have previously only been hypothesized or examined within isolated muscles during supramaximal contractions. Our results contribute to a more comprehensive understanding of the factors that influence a muscle’s mechanical response to force with implications for preventing or treating muscle deficits associated with aging, disease, and disuse.
Publisher: The Company of Biologists
Date: 2015
DOI: 10.1242/JEB.113803
Abstract: Burrowing is an important form of locomotion in reptiles, but no study has examined the energetic cost of burrowing for reptiles. This is significant since burrowing is the most energetically expensive mode of locomotion undertaken by animals, and many burrowing species therefore show specialisations for their subterranean lifestyle. We examined the effect of temperature and substrate characteristics (coarse sand or fine sand) on the net energetic cost of burrowing (NCOB) and burrowing rate in two species of the Egernia group of skinks (Liopholis striata and Liopholis inornata) and compared it with those of other burrowing animals. We further tested for morphological specialisations among burrowing species by comparing the relationship between body shape and retreat preference in Egernia skinks. For L. striata and L. inornata, NCOB is 350 times more expensive than the predicted cost of pedestrian terrestrial locomotion. Temperature had a positive effect on burrowing rate for both species, and a negative effect on NCOB for L. striata but not L. inornata. Both NCOB and burrowing rate were independent of substrate type. Burrows constructed by skinks had smaller cross-sectional area than those constructed by mammals of comparable mass, and NCOB of skinks was lower than that of mammals of similar mass. After accounting for body size, retreat preference was significantly correlated with body shape in Egernia group skinks. Species of Egernia group skinks that use burrows for retreats have narrower bodies and shorter front limbs than other species. We conclude that the morphological specialisations of burrowing skinks allow them to construct relatively narrow burrows, thereby reducing NCOB and the total cost of constructing their burrow retreats.
Publisher: MDPI AG
Date: 06-08-2017
Publisher: The Royal Society
Date: 02-2021
Abstract: Geometric scaling predicts a major challenge for legged, terrestrial locomotion. Locomotor support requirements scale identically with body mass ( α M 1 ), while force-generation capacity should scale α M 2/3 as it depends on muscle cross-sectional area. Mammals compensate with more upright limb postures at larger sizes, but it remains unknown how sprawling tetrapods deal with this challenge. Varanid lizards are an ideal group to address this question because they cover an enormous body size range while maintaining a similar bent-limb posture and body proportions. This study reports the scaling of ground reaction forces and duty factor for varanid lizards ranging from 7 g to 37 kg. Impulses (force×time) ( α M 0.99−1.34 ) and peak forces ( α M 0.73−1.00 ) scaled higher than expected. Duty factor scaled α M 0.04 and was higher for the hindlimb than the forelimb. The proportion of vertical impulse to total impulse increased with body size, and impulses decreased while peak forces increased with speed.
Publisher: The Royal Society
Date: 10-03-2008
Abstract: Adhesive organs on the legs of arthropods and vertebrates are strongly direction dependent, making contact only when pulled towards the body but detaching when pushed away from it. Here we show that the two types of attachment pads found in cockroaches ( Nauphoeta cinerea ), tarsal euplantulae and pretarsal arolium, serve fundamentally different functions. Video recordings of vertical climbing revealed that euplantulae are almost exclusively engaged with the substrate when legs are pushing, whereas arolia make contact when pulling. Thus, upward-climbing cockroaches used front leg arolia and hind leg euplantulae, whereas hind leg arolia and front leg euplantulae were engaged during downward climbing. Single-leg friction force measurements showed that the arolium and euplantulae have an opposite direction dependence. Euplantulae achieved maximum friction when pushed distally, whereas arolium forces were maximal during proximal pulls. This direction dependence was not explained by the variation of shear stress but by different contact areas during pushing or pulling. The changes in contact area result from the arrangement of the flexible tarsal chain, tending to detach the arolium when pushing and to peel off euplantulae when in tension. Our results suggest that the euplantulae in cockroaches are not adhesive organs but ‘ friction pads’, mainly providing the necessary traction during locomotion.
Publisher: IOP Publishing
Date: 16-02-2012
DOI: 10.1088/1748-3182/7/1/016010
Abstract: To explore the interplay between muscle function and propulsor shape in swimming animals, we built a robotic foot to mimic the morphology and hind limb kinematics of Xenopus laevis frogs. Four foot shapes ranging from low aspect ratio (AR = 0.74) to high (AR = 5) were compared to test whether low-AR feet produce higher propulsive drag force resulting in faster swimming. Using feedback loops, two complementary control modes were used to rotate the foot: force was transmitted to the foot either from (1) a living plantaris longus (PL) muscle stimulated in vitro or (2) an in silico mathematical model of the PL. To mimic forward swimming, foot translation was calculated in real time from fluid force measured at the foot. Therefore, bio-robot swimming emerged from muscle-fluid interactions via the feedback loop. Among in vitro-robotic trials, muscle impulse ranged from 0.12 ± 0.002 to 0.18 ± 0.007 N s and swimming velocities from 0.41 ± 0.01 to 0.43 ± 0.00 m s(-1), similar to in vivo values from prior studies. Trends in in silico-robotic data mirrored in vitro-robotic observations. Increasing AR caused a small (∼10%) increase in peak bio-robot swimming velocity. In contrast, muscle force-velocity effects were strongly dependent on foot shape. Between low- and high-AR feet, muscle impulse increased ∼50%, while peak shortening velocity decreased ∼50% resulting in a ∼20% increase in net work. However, muscle-propulsion efficiency (body center of mass work/muscle work) remained independent of AR. Thus, we demonstrate how our experimental technique is useful for quantifying the complex interplay among limb morphology, muscle mechanics and hydrodynamics.
Publisher: Cold Spring Harbor Laboratory
Date: 14-01-2021
DOI: 10.1101/2021.01.12.426469
Abstract: The life and death of an organism often depends on its ability to perform well at some ecologically relevant task. Yet despite this significance we have little idea how well species are optimised for competing locomotor tasks. Most scientists generally accept that the ability for natural systems to become optimised for a specific task is limited by structural, historic or functional constraints. Climbing lizards provide a good ex le of constraint where climbing ability requires the optimization of conflicting tasks such as speed, stability, or efficiency. Here we reconstruct multiple performance landscapes of climbing locomotion using a 10-DOF robot based upon the lizard bauplan, including an actuated spine, shoulders, and feet, the latter which interlock with the surface via claws. This design allows us to independently vary speed, foot angles, and range of motion, while simultaneously collecting data on climbed distance, stability and efficiency. We first demonstrate a trade-off between speed and stability with high speeds resulting in decreased stability and low speeds an increased cost of transport. By varying foot orientation of fore and hindfeet independently, we found geckos converge on a narrow optimum for both speed and stability, but avoid a secondary wider optimum highlighting a possible constraint. Modifying the spine and limb range of movement revealed a gradient in performance. Evolutionary modifications in movement among extant species appear to follow this gradient towards areas which promote speed and efficiency. This approach can give us a better understanding about locomotor optimization, and provide inspiration for industrial and search-and-rescue robots. Climbing requires the optimization of conflicting tasks such as speed, stability, or efficiency, but understanding the relative importance of these competing performance traits is difficult. We used a highly modular bio-inspired climbing robot to reconstruct performance landscapes for climbing lizards. We then compared the performance of extant species onto these and show strong congruence with lizard phenotypes and robotic optima. Using this method we can show why certain phenotypes are not present among extant species, illustrating why these would be potentially mal-adaptive. These principles may be useful to compare with relative rates of evolution along differing evolutionary histories. It also highlights the importance of biological inspiration towards the optimization of industrial climbing robots, which like lizards, must negotiate complex environments.
Publisher: Oxford University Press (OUP)
Date: 05-2021
DOI: 10.1093/ICB/ICAB037
Abstract: Tail movement is an important component of vertebrate locomotion and likely contributes to dynamic stability during steady-state locomotion. Previous results suggest that the tail plays a significant role in lizard locomotion, but little data are available on tail motion during locomotion and how it differs with morphological, ecological, and phylogenetic parameters. We collected high-speed vertical climbing and horizontal locomotion video data from 43 lizard species from four taxonomic groups (Agamidae, Gekkota, Scincidae, and Varanidae) across four habitats. We introduce a new semi-automated and generalizable analysis pipeline for tail and spine motion analysis including markerless pose-estimation, semi-automated kinematic recognition, and muti-species data analysis. We found that step length relative to snout-vent length (SVL) increased with tail length relative to SVL. Examining spine cycles agnostic to limb stride phase, we found that ranges of inter-tail bending compared with inter-spine bending increased with relative tail length, while ranges of tail deflection relative to spine deflection increased with relative speed. Considering stepwise strides, we found the angular velocity and acceleration of the tail center of mass increased with relative speed. These results will provide general insights into the biomechanics of tails in sprawling locomotion enabling biomimetic applications in robotics, and a better understanding of vertebrate form and function. We look forward to adding more species, behaviors, and locomotor speeds to our analysis pipeline through collaboration with other research groups.
Publisher: The Company of Biologists
Date: 2019
DOI: 10.1242/JEB.189654
Abstract: Characterisation of an organism's performance in different habitats provides insight into the conditions that allow it to survive and reproduce. In recent years, Northern quolls (Dasyurus hallucatus)—a medium-sized semi-arboreal marsupial native to northern Australia—have undergone significant population declines within open forest, woodland and riparian habitats, but less so in rocky areas. To help understand this decline, we quantified the biomechanical performance of wild Northern quolls as they ran up inclined narrow (13 mm pole) and inclined wide (90 mm platform) substrates. We predicted that quolls may possess biomechanical adaptations to increase stability on narrow surfaces, which are more common in rocky habitats. Our results display that quolls have some biomechanical characteristics consistent with a stability advantage on narrow surfaces. This includes the coupled use of limb pairs, as indicated via a decrease in footfall time, and an ability to produce corrective torques to counteract the toppling moments commonly encountered during gait on narrow surfaces. However, speed was constrained on narrow surfaces, and quolls did not adopt diagonal sequence gaits unlike true arboreal specialists such as primates. In comparison with key predators, such as cats and dogs, Northern quolls appear inferior in terrestrial environments but have a stability advantage at higher speeds on narrow supports. This may partially explain the heterogenous declines in Northern quoll populations among various habitats on mainland Australia.
Publisher: The Company of Biologists
Date: 11-2022
DOI: 10.1242/JEB.244435
Abstract: Manoeuvrability, the ability to make rapid changes in direction, is central to animal locomotion. Turning performance may depend on the ability to successfully complete key challenges including: withstanding additional lateral forces, maintaining sufficient friction, lateral leaning during a turn and rotating the body to align with the new heading. We filmed high-speed turning in domestic dogs (Canis lupus familiaris) to quantify turning performance and explore how performance varies with body size and shape. Maximal speed decreased with higher angular velocity, greater centripetal acceleration and smaller turning radii, supporting a force limit for wider turns and a friction limit for sharp turns. Variation in turning ability with size was complex: medium sized dogs produced greater centripetal forces, had relatively higher friction coefficients, and generally aligned the body better with the heading compared with smaller and larger bodied dogs. Body shape also had a complex pattern, with longer forelimbs but shorter hindlimbs being associated with better turning ability. Further, although more crouched forelimbs were associated with an increased ability to realign the body in the direction of movement, more upright hindlimbs were related to greater centripetal and tangential accelerations. Thus, we demonstrate that these biomechanical challenges to turning can vary not only with changes in speed or turning radius, but also with changes in morphology. These results will have significant implications for understanding the link between form and function in locomotory studies, but also in predicting the outcome of predator–prey encounters.
Publisher: The Company of Biologists
Date: 15-10-2016
DOI: 10.1242/JEB.143867
Abstract: The short-beaked echidna (Tachyglossus aculeatus) is a monotreme and therefore provides a unique combination of phylogenetic history, morphological differentiation and ecological specialisation for a mammal. The echidna has a unique appendicular skeleton, a highly specialised myrmecophagous lifestyle and a mode of locomotion that is neither typically mammalian nor reptilian, but has aspects of both lineages. We therefore were interested in the interactions of locomotor biomechanics, ecology and movements for wild, free-living short-beaked echidnas. To assess locomotion in its complex natural environment, we attached both GPS and accelerometer loggers to the back of echidnas in both spring and summer. We found that the locomotor biomechanics of echidnas is unique, with lower stride length and stride frequency than reported for similar-sized mammals. Speed modulation is primarily accomplished through changes in stride frequency, with a mean of 1.39 Hz and a maximum of 2.31 Hz. Daily activity period was linked to ambient air temperature, which restricted daytime activity during the hotter summer months. Echidnas had longer activity periods and longer digging bouts in spring compared with summer. In summer, echidnas had higher walking speeds than in spring, perhaps because of the shorter time suitable for activity. Echidnas spent, on average, 12% of their time digging, which indicates their potential to excavate up to 204 m3 of soil a year. This information highlights the important contribution towards ecosystem health, via bioturbation, of this widespread Australian monotreme.
Publisher: The Company of Biologists
Date: 2018
DOI: 10.1242/JEB.172544
Abstract: Movement speed can underpin an animal's probability of success in ecological tasks. Prey often use agility to outmanoeuvre predators, however faster speeds increase inertia and reduce agility. Agility is also constrained by grip, as the foot must have sufficient friction with the ground to apply the forces required for turning. Consequently, ground surface should affect optimum turning speed. We tested the speed-agility trade-off in buff-footed antechinus (Antechinus mysticus) on two different surfaces. Antechinus used slower turning speeds over smaller turning radii on both surfaces, as predicted by the speed-agility trade-off. Slipping was 64% more likely on the low-friction surface, and had a higher probability of occurring the faster the antechinus were running before the turn. However, antechinus compensated for differences in surface friction by using slower pre-turn speeds as their amount of experience on the low-friction surface increased, which consequently reduced their probability of slipping. Conversely, on the high-friction surface, antechinus used faster pre-turn speeds in later trials, which had no effect on their probability of slipping. Overall, antechinus used larger turning radii (0.733 ± 0.062 vs 0.576 ± 0.051 m) and slower pre-turn (1.595 ± 0.058 vs 2.174 ± 0.050 ms-1) and turning speeds (1.649 ± 0.061 vs 2.01 ± 0.054 ms-1) on the low-friction surface. Our results demonstrate the interactive effect of surface friction and the speed-agility trade-off on speed choice. To predict wild animals’ movement speeds, future studies should examine the interactions between biomechanical trade-offs and terrain, and quantify the costs of motor mistakes in different ecological activities.
Publisher: American Arachnological Society
Date: 12-2010
DOI: 10.1636/B09-96.1
Publisher: Public Library of Science (PLoS)
Date: 21-02-2018
Publisher: Springer International Publishing
Date: 2018
Publisher: The Royal Society
Date: 31-03-2021
Abstract: Locomotion is a key aspect associated with ecologically relevant tasks for many organisms, therefore, survival often depends on their ability to perform well at these tasks. Despite this significance, we have little idea how different performance tasks are weighted when increased performance in one task comes at the cost of decreased performance in another. Additionally, the ability for natural systems to become optimized to perform a specific task can be limited by structural, historic or functional constraints. Climbing lizards provide a good ex le of these constraints as climbing ability likely requires the optimization of tasks which may conflict with one another such as increasing speed, avoiding falls and reducing the cost of transport (COT). Understanding how modifications to the lizard bauplan can influence these tasks may allow us to understand the relative weighting of different performance objectives among species. Here, we reconstruct multiple performance landscapes of climbing locomotion using a 10 d.f. robot based upon the lizard bauplan, including an actuated spine, shoulders and feet, the latter which interlock with the surface via claws. This design allows us to independently vary speed, foot angles and range of motion (ROM), while simultaneously collecting data on climbed distance, stability and efficiency. We first demonstrate a trade-off between speed and stability, with high speeds resulting in decreased stability and low speeds an increased COT. By varying foot orientation of fore- and hindfeet independently, we found geckos converge on a narrow optimum of foot angles (fore 20°, hind 100°) for both speed and stability, but avoid a secondary wider optimum (fore −20°, hind −50°) highlighting a possible constraint. Modifying the spine and limb ROM revealed a gradient in performance. Evolutionary modifications in movement among extant species over time appear to follow this gradient towards areas which promote speed and efficiency.
Publisher: Elsevier BV
Date: 10-2018
DOI: 10.1016/J.ENVPOL.2018.03.087
Abstract: Neuromotor deficits are an important sign of manganese (Mn) toxicity in humans and laboratory animals. However, the impacts of Mn exposure on the motor function of wild animals remains largely unknown. Here, we assessed the impact of chronic exposure to Mn from active mining operations on Groote Eylandt, Australia on the motor function of the semi-arboreal northern quoll (Dasyurus hallucatus), an endangered species. The three motor tests conducted-maximum sprint speed on a straight run, manoeuvrability around a corner, and motor control on a balance beam-showed that elevated Mn body burden did not diminish performance of these traits. However, quolls with higher Mn body burden approached a corner at a significantly narrower range of speeds, due to a significantly lower maximum approach speed. Slower speeds approaching a turn may reduce success at catching prey and avoiding predators. Given that maximum sprint speed on a straight run was not affected by Mn body burden, but maximum speed entering a corner was, slower speeds approaching a turn may reflect compensation for otherwise impaired performance in the turn.
Publisher: The Company of Biologists
Date: 07-2008
DOI: 10.1242/JEB.018044
Abstract: Bipedal locomotion by lizards has previously been considered to provide a locomotory advantage. We examined this premise for a group of quadrupedal Australian agamid lizards, which vary in the extent to which they will become bipedal. The percentage of strides that each species ran bipedally, recorded using high speed video cameras, was positively related to body size and the proximity of the body centre of mass to the hip, and negatively related to running endurance. Speed was not higher for bipedal strides, compared with quadrupedal strides, in any of the four species, but acceleration during bipedal strides was significantly higher in three of four species. Furthermore, a distinct threshold between quadrupedal and bipedal strides, was more evident for acceleration than speed, with a threshold in acceleration above which strides became bipedal. We calculated these thresholds using probit analysis, and compared these to the predicted threshold based on the model of Aerts et al. Although there was a general agreement in order, the acceleration thresholds for lizards were often lower than that predicted by the model. We suggest that bipedalism, in Australian agamid lizards, may have evolved as a simple consequence of acceleration, and does not confer any locomotory advantage for increasing speed or endurance. However, both behavioural and threshold data suggest that some lizards actively attempt to run bipedally, implying some unknown advantage to bipedal locomotion.
Publisher: The Company of Biologists
Date: 15-02-2010
DOI: 10.1242/JEB.038232
Abstract: Insects possess adhesive organs that allow attachment to erse surfaces. Efficient adhesion must be retained throughout their lifetime even when pads are exposed to contamination. Many insects groom their adhesive structures, but it is possible that self-cleaning properties also play an important role. We measured attachment forces of insect pads on glass after contamination with microspheres and found that both smooth pads (stick insects: Carausius morosus) and hairy pads (dock beetles: Gastrophysa viridula) exhibit self-cleaning. Contaminated pads recovered high levels of adhesion after only eight simulated steps this was accompanied by the deposition of spheres. Self-cleaning was strongly enhanced by shear movements, and only beetle pads showed the ability to self-clean during purely perpendicular pull-offs. Hairy pads also self-cleaned more efficiently than smooth pads for both large (45 μm) and small (1 μm) particle sizes. However, the beetles' self-cleaning was not superior to smooth pads when contaminated with 10-μm beads. This limitation of self-cleaning is explained by the coincidence of bead diameter and inter-seta distance, which caused beads to remain trapped in between setae.
Publisher: The Company of Biologists
Date: 15-12-2019
DOI: 10.1242/JEB.207506
Abstract: The morphology and locomotor performance of a species can determine their inherent fitness within a habitat type. Koalas have an unusual morphology for marsupials, with several key adaptations suggested to increase stability in arboreal environments. We quantified the kinematics of their movement over ground and along narrow arboreal trackways to determine the extent to which their locomotion resembled that of primates, occupying similar niches, or basal marsupials from which they evolved. On the ground, the locomotion of koalas resembled a combination of marsupial behaviours and primate-like mechanics. For ex le, their fastest strides were bounding type gaits with a top speed of 2.78 m s−1 (mean 1.20 m s−1), resembling marsupials, while the relatively longer stride length was reflective of primate locomotion. Speed was increased using equal modification of stride length and frequency. On narrow substrates, koalas took longer but slower strides (mean 0.42 m s−1), adopting diagonally coupled gaits including both lateral and diagonal sequence gaits, the latter being a strategy distinctive among arboreal primates. The use of diagonally coupled gaits in the arboreal environment is likely only possible because of the unique gripping hand morphology of both the fore and hind feet of koalas. These results suggest that during ground locomotion, they use marsupial-like strategies but alternate to primate-like strategies when moving amongst branches, maximising stability in these environments. The locomotion strategies of koalas provide key insights into an independent evolutionary branch for an arboreal specialist, highlighting how locomotor strategies can convergently evolve between distant lineages.
Publisher: The Royal Society
Date: 17-03-2021
Abstract: In our everyday lives, we negotiate complex and unpredictable environments. Yet, much of our knowledge regarding locomotion has come from studies conducted under steady-state conditions. We have previously shown that humans rely on the ankle joint to absorb energy and recover from perturbations however, the muscle–tendon unit (MTU) behaviour and motor control strategies that accompany these joint-level responses are not yet understood. In this study, we determined how neuromuscular control and plantar flexor MTU dynamics are modulated to maintain stability during unexpected vertical perturbations. Participants performed steady-state hopping and, at an unknown time, we elicited an unexpected perturbation via rapid removal of a platform. In addition to kinematics and kinetics, we measured gastrocnemius and soleus muscle activations using electromyography and in vivo fascicle dynamics using B-mode ultrasound. Here, we show that an unexpected drop in ground height introduces an automatic phase shift in the timing of plantar flexor muscle activity relative to MTU length changes. This altered timing initiates a cascade of responses including increased MTU and fascicle length changes and increased muscle forces which, when taken together, enables the plantar flexors to effectively dissipate energy. Our results also show another mechanism, whereby increased co-activation of the plantar- and dorsiflexors enables shortening of the plantar flexor fascicles prior to ground contact. This co-activation improves the capacity of the plantar flexors to rapidly absorb energy upon ground contact, and may also aid in the avoidance of potentially damaging muscle strains. Our study provides novel insight into how humans alter their neural control to modulate in vivo muscle–tendon interaction dynamics in response to unexpected perturbations. These data provide essential insight to help guide design of lower-limb assistive devices that can perform within varied and unpredictable environments.
Publisher: The Company of Biologists
Date: 2013
DOI: 10.1242/JEB.089060
Abstract: Adaptations promoting greater performance in one habitat are thought to reduce performance in others. However, there are many ex les of where, despite habitat differences, such predicted differences in performance do not occur. One such ex le is the relationship between locomotory performance to habitat for varanid lizards. To explain the lack of difference in locomotor performance we examined detailed observation of the kinematics of each lizard's stride. Differences in kinematics were greatest between climbing and non-climbing species. For terrestrial lizards, the kinematics indicated that increased femur adduction, femur rotation and ankle angle all contributed positively to changes in stride length, but they were constrained for climbing species, probably due to biomechanical restrictions on the centre of mass height (to increase stability on vertical surfaces). Despite climbing species having restricted stride length, no differences have been previously reported in sprint speed between climbing and non-climbing varanids. This is best explained by climbing varanids using an alternative speed modulation strategy of varying stride frequency to avoid the potential trade-off of speed vs stability on vertical surfaces. Thus, by measuring the relevant biomechanics for lizard strides, we have shown how kinematic differences among species can mask performance differences typically associated with habitat variation.
Publisher: Oxford University Press (OUP)
Date: 31-07-2016
Publisher: Proceedings of the National Academy of Sciences
Date: 02-06-2009
Abstract: The predatory ecology of Varanus komodoensis (Komodo Dragon) has been a subject of long-standing interest and considerable conjecture. Here, we investigate the roles and potential interplay between cranial mechanics, toxic bacteria, and venom. Our analyses point to the presence of a sophisticated combined-arsenal killing apparatus. We find that the lightweight skull is relatively poorly adapted to generate high bite forces but better adapted to resist high pulling loads. We reject the popular notion regarding toxic bacteria utilization. Instead, we demonstrate that the effects of deep wounds inflicted are potentiated through venom with toxic activities including anticoagulation and shock induction. Anatomical comparisons of V. komodoensis with V. ( Megalania ) priscus fossils suggest that the closely related extinct giant was the largest venomous animal to have ever lived.
Publisher: Wiley
Date: 06-03-2017
DOI: 10.1111/MEC.14042
Abstract: Some of the best evidence for rapid evolutionary change comes from studies of archipelagos and oceanic islands. City parks are analogous systems as they create geographically isolated green spaces that differ in size, structure and complexity. Very little, however, is known about whether city parks within a single urban centre drive selection and result in the ersification of native species. Here, we provide evidence for the rapid genetic and morphological differentiation of a native lizard (Intellagama lesueurii) at four geographically close yet unconnected parks within one city. Year of establishment of each city park varied from 1855 (oldest) to 2001 (youngest) equating to a generation time range of 32 to three generations. Genetic ergence among city park populations was large despite the small pairwise geographic distances (<5 km) and found to be two to three times higher for microsatellites and three to 33 times higher for mtDNA relative to nonurban populations. Patterns of morphological differentiation were also found to be most extensive among the four city park populations. In contrast to nonurban populations, city park populations showed significant differentiation in relative body size, relative head and limb morphology and relative forelimb and hindlimb length. Crucially, we show that these patterns of differentiation are unlikely to have been caused by founder events and/or drift alone. Our results suggest that city park 'archipelagos' could represent theatres for rapid evolution that may, in time, favour adaptive ersification.
Publisher: The Royal Society
Date: 02-2023
DOI: 10.1098/RSOS.221180
Abstract: Semelparity is a breeding strategy whereby an in idual invests large amounts of resources into a single breeding season, leading to the death of the in idual. Male northern quolls ( Dasyurus hallucatus ) are the largest known mammal to experience a post-breeding die-off however, the cause of their death is unknown, dissimilar from causes in other semelparous dasyurids. To identify potential differences between male northern quolls that breed once, and females that can breed for up to four seasons, the behaviours, activity budgets, speeds and distances travelled were examined. Northern quolls were captured on Groote Eylandt off the coast of the Northern Territory, Australia, and were fitted with accelerometers. A machine learning algorithm (Self-organizing Map) was trained on more than 76 h of recorded footage of quoll behaviours and used to predict behaviours in 42 days of data from wild roaming quolls (7M : 6F). Male northern quolls were more active (male 1.27 g , s.d. = 0.41 female 1.18 g, s.d. = 0.36), spent more time walking (13.09% male: 8.93% female) and engaged in less lying/resting behaviour than female northern quolls (7.67% male: 23.65% female). Reduced resting behaviour among males could explain the post-breeding death as the deterioration in appearance reflects that reported for sleep-deprived rodents.
Publisher: CSIRO Publishing
Date: 2008
DOI: 10.1071/ZO08030
Abstract: In our earlier analysis of Varanus body shape, size was a dominating factor with some qualitative phylogenetic patterns and grouping of species into ecological categories. With a phylogeny and an improved capacity to account for the effects of size, we have reanalysed our morphometric data for male Australian goannas (Varanus spp.) using an increased number of specimens and species to examine whether variations in body shape can be accounted for by retreat choice, as it can for Western Australian Ctenophorus dragon lizards. After accounting for body size in the current analysis, four ecotypes based on retreat choice (i.e. those that retreat to oblique crevices between large rocks or rock faces, those that retreat to burrows dug into the ground, those that retreat to spaces under rocks or in tree hollows, and those that retreat to trees but not tree hollows) accounted for much of the variation in body shape. There is a phylogenetic pattern to the ecotypes, but accounting for phylogenetic effects did not weaken the link between body shape and ecotype based on retreat choice. This suggests that there are large differences in body shape among ecotypes, and shape is relatively independent of phylogeny. The strong link between shape and choice of retreat site in Varanus spp. is consistent with that for Ctenophorus spp. We speculate on why there might be a strong link between retreat choice and body shape for both Varanus and Ctenophorus.
Publisher: Wiley
Date: 25-10-2012
DOI: 10.1111/J.1420-9101.2011.02406.X
Abstract: Carnivorous plants of the genus Nepenthes have evolved a striking ersity of pitcher traps that rely on specialized slippery surfaces for prey capture. With a comparative study of trap morphology, we show that Nepenthes pitcher plants have evolved specific adaptations for the use of either one of two distinct trapping mechanisms: slippery wax crystals on the inner pitcher wall and 'insect aquaplaning' on the wet upper rim (peristome). Species without wax crystals had wider peristomes with a longer inward slope. Ancestral state reconstructions identified wax crystal layers and narrow, symmetrical peristomes as ancestral, indicating that wax crystals have been reduced or lost multiple times independently. Our results complement recent reports of nutrient source specializations in Nepenthes and suggest that these specializations may have driven speciation and rapid ersification in this genus.
Publisher: Oxford University Press (OUP)
Date: 02-09-2015
DOI: 10.1093/ICB/ICV103
Abstract: The ability for prey to escape a pursuing predator is dependent both on the prey's speed away from the threat and on their ability to rapidly change directions, or maneuverability. Given that the biomechanical trade-off between speed and maneuverability limits the simultaneous maximization of both performance traits, animals should not select their fastest possible speeds when running away from a pursuing predator but rather a speed that maximizes the probability of successful escape. We explored how variation in the relationship between speed and maneuverability-or the shape of the trade-off-affects the optimal choice of speed for escaping predators. We used tablet-based games that simulated interactions between predators and prey (human subjects acting as predators attempting to capture "prey" moving across a screen). By defining a specific relationship between speed and maneuverability, we could test the survival of each of the possible behavioral choices available to this phenotype, i.e., the best combination of speed and maneuverability for prey fitness, based on their ability to escape. We found that the shape of the trade-off function affected the prey's optimal speed for success in escaping, the prey's maximum performance in escaping, and the breadth of speeds over which the prey's performance was high. The optimal speed for escape varied only when the trade-off between speed and maneuverability was non-linear. Phenotypes possessing trade-off functions for which maneuverability was only compromised at high speeds exhibited lower optimal speeds. Phenotypes that exhibited greater increases in maneuverability for any decrease in speed were more likely to have broader ranges of performance, meaning that in iduals could attain their maximum performance across a broader range of speeds. We also found that there was a differential response of the subject's learning to these different components of locomotion. With increased experience through repeated trials, subjects were able to successfully catch faster and faster dots. However, no improvement was observed in the subject's ability to capture more maneuverable prey. Our work highlights the costs of high-speed movement on other traits, including maneuverability, which make the use of an animal's fastest speeds unlikely, even when attempting to escape predators. By investigating the shape of the trade-off functions between speed and maneuverability and the way the environment and morphology mediates this trade-off, we can begin to understand why animals choose to move at the speeds they do when they are running away from predators or attempting to capture prey.
Publisher: Springer Science and Business Media LLC
Date: 17-07-2017
Publisher: Springer Science and Business Media LLC
Date: 30-06-2021
DOI: 10.1038/S41598-021-92896-4
Abstract: Collecting quantitative information on animal behaviours is difficult, especially from cryptic species or species that alter natural behaviours under observation. Using harness-mounted tri-axial accelerometers free-roaming domestic cats ( Felis Catus ) we developed a methodology that can precisely classify finer-scale behaviours. We further tested the effect of a prey–protector device designed to reduce prey capture. We aligned accelerometer traces collected at 50 Hz with video files (60 fps) and labelled 12 in idual behaviours, then trained a supervised machine-learning algorithm using Kohonen super self-organising maps (SOM). The SOM was able to predict in idual behaviours with a ~ 99.6% overall accuracy, which was slightly better than for random forest estimates using the same dataset (98.9%). There was a significant effect of s le size, with precision and sensitivity decreasing rapidly below 2000 1-s observations. We were also able to detect a behaviour specific reduction in the predictability when cats were fitted with the prey–protector device indicating it altered biomechanical gait. Our results can be applied in movement ecology, zoology and conservation, where habitat specific movement performance between predators or prey may be critical to managing species of conservation significance, or in veterinary and agricultural fields, where early detection of movement pathologies can improve animal welfare.
Publisher: Springer Science and Business Media LLC
Date: 10-2013
Publisher: The Royal Society
Date: 04-2023
Abstract: Many climbing animals use direction-dependent adhesives to attach to vertical or inclined surfaces. These structures adhere when activated via a pull but detach when pushed. Therefore, a challenge arises when a change in climbing direction causes external forces such as gravity to change its acting orientation upon the lizard. To investigate how specialized climbers adjust, we studied kinematics and dynamics of six Hemidactylus frenatus geckos climbing head-up and head-down a vertical racetrack. We found that limbs functionally swap their adhesive role: feet above the centre of mass (COM) generated adhesive forces, feet below the COM compressive forces, both equal in magnitude across directions. To investigate how lizards perform this swap, despite the constraint of their direction-dependent adhesives, we analysed kinematic adjustments across multiple smaller levels of hierarchy: limbs, feet and toes. All levels contributed: the hindfoot angle was reoriented realigning the adhesive structure, the hindlimb centre range of motion was further protracted and the hindfoot toe spreading was reduced. Notably, all three variables were adjustments of hindlimbs, suggesting that they make a more flexible contribution in upward versus downward climbing, while forelimbs may be anatomically or functionally constrained. The relevance of multilevel dynamic adjustments might inform the development of performant gaits for legged climbing robots.
Publisher: Oxford University Press (OUP)
Date: 22-10-2015
DOI: 10.1093/ICB/ICV106
Abstract: An animal's movement speed affects all behaviors and underlies the intensity of an activity, the time it takes to complete it, and the probability of successfully completing it, but which factors determine how fast or slow an animal chooses to move? Despite the critical importance of an animal's choice of speed (hereafter designated as "speed-choice"), we still lack a framework for understanding and predicting how fast animals should move in nature. In this article, we develop a framework for predicting speed that is applicable to any animal-including humans-performing any behavior where choice of speed occurs. To inspire new research in this area, we (1) detail the main factors likely to affect speed-choice, including organismal constraints (i.e., energetic, physiological, and biomechanical) and environmental constraints (i.e., predation intensity and abiotic factors) (2) discuss the value of optimal foraging theory in developing models of speed-choice and (3) describe how optimality models might be integrated with the range of potential organismal and environmental constraints to predict speed. We show that by utilizing optimality theory it is possible to provide quantitative predictions of optimal speeds across different ecological contexts. However, the usefulness of any predictive models is still entirely dependent on being able to provide relevant mathematical functions to insert into such models. We still lack basic knowledge about how an animal's speed affects its motor control, maneuverability, observational skills, and vulnerability to predators. Studies exploring these gaps in knowledge will help facilitate the field of optimal performance and allow us to adequately parameterize models predicting the speed-choice of animals, which represents one of the most basic of all behavioral decisions.
Publisher: The Company of Biologists
Date: 04-2023
DOI: 10.1242/JEB.245310
Abstract: Among terrestrial mammals, the largest, the 3 tonne African elephant, is one-million times heavier than the smallest, the 3 g pygmy shrew. Body mass is the most obvious and arguably the most fundamental characteristic of an animal, impacting many important attributes of its life history and biology. Although evolution may guide animals to different sizes, shapes, energetic profiles or ecological niches, it is the laws of physics that limit biological processes and, in turn, affect how animals interact with their environment. Consideration of scaling helps us to understand why elephants are not merely scaled-up shrews, but rather have modified body proportions, posture and locomotor style to mitigate the consequences of their large size. Scaling offers a quantitative lens into how biological features vary compared with predictions based on physical laws. In this Review, we provide an introduction to scaling and its historical context, focusing on two fields that are strongly represented in experimental biology: physiology and biomechanics. We show how scaling has been used to explore metabolic energy use with changes in body size. We discuss the musculoskeletal and biomechanical adaptations that animals use to mitigate the consequences of size, and provide insights into the scaling of mechanical and energetic demands of animal locomotion. For each field, we discuss empirical measurements, fundamental scaling theories and the importance of considering phylogenetic relationships when performing scaling analyses. Finally, we provide forward-looking perspectives focused on improving our understanding of the ersity of form and function in relation to size.
Publisher: Wiley
Date: 21-11-2018
DOI: 10.1111/JZO.12521
Publisher: Oxford University Press (OUP)
Date: 20-03-2021
DOI: 10.1093/BIOLINNEAN/BLAB002
Abstract: The Galápagos marine iguana (Amblyrhynchus cristatus), the world’s only extant marine lizard, may have had one of the most unique and challenging transitions to aquatic life. Curiously, previous studies have identified relatively few physiological adaptations in the marine iguana however, little is known about the extent of morphological specialization and performance trade-offs associated with the marine environment. By examining the morphology and locomotory performance of the marine iguana in comparison to their closely related mainland ancestors, the black spiny-tailed iguana (Ctenosaura similis) and green iguana (Iguana iguana), we found variation reflected specialization to ecological niches. However, variation was more pronounced among subspecies of marine iguana, suggesting that little morphological or performance modification is required for iguanids to successfully invade aquatic environments, thus raising the question why there are so few extant aquatic reptilian lineages. Our findings indicate that specialization for the marine environment likely resulted in a trade-off in sprint speed in a terrestrial environment, which may explain why other lizards have not undergone transitions to the marine environment. Additionally, we found that the magnitude of morphological and performance variation was more pronounced between subspecies of marine iguana than between iguanid species. This illustrates that the form-function relationship is more complex than previously thought and sheds light on the ecomorphological mysteries of the marine iguana.
Publisher: The Royal Society
Date: 10-2016
DOI: 10.1098/RSOS.160203
Abstract: Elephants, the largest living land mammals, have evolved a specialized foot morphology to help reduce locomotor pressures while supporting their large body mass. Peak pressures that could cause tissue damage are mitigated passively by the anatomy of elephants' feet, yet this mechanism does not seem to work well for some captive animals. This study tests how foot pressures vary among African and Asian elephants from habitats where natural substrates predominate but where foot care protocols differ. Variations in pressure patterns might be related to differences in husbandry, including but not limited to trimming and the substrates that elephants typically stand and move on. Both species' s les exhibited the highest concentration of peak pressures on the lateral digits of their feet (which tend to develop more disease in elephants) and lower pressures around the heel. The trajectories of the foot's centre of pressure were also similar, confirming that when walking at similar speeds, both species load their feet laterally at impact and then shift their weight medially throughout the step until toe-off. Overall, we found evidence of variations in foot pressure patterns that might be attributable to husbandry and other causes, deserving further examination using broader, more comparable s les.
Publisher: Proceedings of the National Academy of Sciences
Date: 19-01-2016
Abstract: How adhesive forces can be scaled up from microscopic to macroscopic levels is a central problem for biological and bio-inspired adhesives. Here, we elucidate how animals with sticky footpads cope with large body sizes. We find an extreme positive allometry of footpad area across all 225 species studied, implying a 200-fold increase of relative pad area from mites to geckos. Within groups, however, pads were almost isometric, but their adhesive strength increased with size, inconsistent with existing models. Extrapolating the observed scaling, we show that to support a human’s body weight, an unrealistic 40% of the body surface would have to be covered with adhesive pads, suggesting that anatomical constraints may prohibit the evolution of adhesion-based climbers larger than geckos.
Publisher: CSIRO Publishing
Date: 2004
DOI: 10.1071/ZO04026
Abstract: Metabolic physiology, morphology, activity patterns, performance traits and movement kinematics are thought to have coevolved in lizards. We examined links between these parameters for the thorny devil (Moloch horridus), a morphologically and ecologically specialised agamid lizard (body mass ~30 g). It has a maximum sustainable metabolic rate (VO2max) of 0.99 mL O2 g–1 h–1 while running at a velocity of 0.11�m�sec–1 at 35°C. This VO2 is typical of that for other lizards (except varanids), but its burst speed (1.21�m�sec–1) is slower than for a typical agamid (e.g. Ctenophorus ornatus at 3.59 m sec–1) and its endurance is appreciably higher. The kinematic pattern of hind-limb movement for M. horridus is different to that of a 'typical' similar-sized agamid, Ctenophorus ornatus, which is a fast-moving lizard that shelters in rock crevices. It is also different to the ecologically equivalent Phrynosoma platyrhinos. The slow and erratic ventilation of M. horridus (2.3 breaths min–1) at its maximum sustainable aerobic running speed occurs when it stops running. This might be a consequence of the hypaxial muscles being used for both lung ventilation and locomotion, which might be impairing pulmonary ventilation when running, but might also contribute to its high endurance. M. horridus is metabolically typical of agamids, but its body shape, movement patterns and locomotory performance traits are different, and might have coevolved with its specialisation for eating ants.
Publisher: The Royal Society
Date: 05-2017
Abstract: Many hemipteran bugs can jump explosively from plant substrates, which can be very smooth. We therefore analysed the jumping performance of froghoppers ( Philaenus spumarius, Aphrophoridae) and leafhoppers ( Aphrodes bicinctus/makarovi, Cicadellidae) taking off from smooth (glass) and rough (sandpaper, 30 µm asperity size) surfaces. On glass, the propulsive hind legs of Philaenus froghoppers slipped, resulting in uncontrolled jumps with a fast forward spin, a steeper angle and only a quarter of the velocity compared with jumps from rough surfaces. By contrast, Aphrodes leafhoppers took off without their propulsive hind legs slipping, and reached low take-off angles and high velocities on both substrates. This difference in jumping ability from smooth surfaces can be explained not only by the lower acceleration of the long-legged leafhoppers, but also by the presence of 2–9 soft pad-like structures (platellae) on their hind tarsi, which are absent in froghoppers. High-speed videos of jumping showed that platellae contact the surface briefly (approx. 3 ms) during the acceleration phase. Friction force measurements on in idual hind tarsi on glass revealed that at low sliding speeds, both pushing and pulling forces were small, and insufficient to explain the recorded jumps. Only when the tarsi were pushed with higher velocities did the contact area of the platellae increase markedly, and high friction forces were produced, consistent with the observed jumps. Our findings show that leafhoppers have special adhesive footpads for jumping from smooth surfaces, which achieve firm grip and rapid control of attachment/detachment by combining anisotropic friction with velocity dependence.
Publisher: Wiley
Date: 09-05-2018
Publisher: Springer Science and Business Media LLC
Date: 11-2013
DOI: 10.1038/NCOMMS3737
Abstract: Studies of the muscle force-velocity relationship and its derived n-shaped power-velocity curve offer important insights into muscular limits of performance. Given the power is maximal at 1/3 V(max), geometric scaling of muscle force coupled with fluid drag force implies that this optimal muscle-shortening velocity for power cannot be maintained across the natural body-size range. Instead, muscle velocity may decrease with increasing body size, conferring a similar n-shaped power curve with body size. Here we examine swimming speed and muscle function in the aquatic frog Xenopus laevis. Swimming speed shows an n-shaped scaling relationship, peaking at 47.35 g. Further, in vitro muscle function of the ankle extensor plantaris longus also shows an optimal body mass for muscle power output (47.27 g), reflecting that of swimming speed. These findings suggest that in drag-based aquatic systems, muscle-environment interactions vary with body size, limiting both the muscle's potential to produce power and the swimming speed.
Publisher: CSIRO Publishing
Date: 21-11-2022
DOI: 10.1071/ZO22011
Abstract: Australia was isolated for approximately 40 million years from the presence of eutherian predation until the introduction of the dingo (Canis familiaris 4000 years ago), foxes (Vulpes vulpes 1871) and feral cats (Felis catus post-1788). The arrival of these invasive species coincides with the decline and extinction of many native mammals, specifically within the critical weight range (35–5500 g). These extinctions are likely a result of competition and predation, where locomotor performance and the associated behaviours contribute largely to overall fitness. We used the population responses of native fauna in the presence of introduced predators to establish a research framework. Introduction/extinction timelines, predator diets, and prey occurrence were used to identify invasive/native relationships where predation may define the population outcome. We then examined the locomotor performance of these species using current data (maximum speeds). Consumption of prey items does not seem to be associated with the probability of the predator encountering the prey. Dingoes had the most variable mammalian prey of all invasive predators, likely due to higher maximal speeds. Feral cats favour Dasyuridae and smaller species, preying upon these prey groups more than dingoes and foxes. The role of locomotor performance in invasive ecology is not well understood we identified relationships for further exploration.
Publisher: Springer Science and Business Media LLC
Date: 07-2009
DOI: 10.1007/S00359-009-0457-0
Abstract: The contact of adhesive structures to rough surfaces has been difficult to investigate as rough surfaces are usually irregular and opaque. Here we use transparent, microstructured surfaces to investigate the performance of tarsal euplantulae in cockroaches (Nauphoeta cinerea). These pads are mainly used for generating pushing forces away from the body. Despite this biological function, shear stress (force per unit area) measurements in immobilized pads showed no significant difference between pushing and pulling on smooth surfaces and on 1-microm high microstructured substrates, where pads made full contact. In contrast, on 4-mum high microstructured substrates, where pads made contact only to the top of the microstructures, shear stress was maximal during a push. This specific direction dependence is explained by the interlocking of the microstructures with nanometre-sized "friction ridges" on the euplantulae. Scanning electron microscopy and atomic force microscopy revealed that these ridges are anisotropic, with steep slopes facing distally and shallow slopes proximally. The absence of a significant direction dependence on smooth and 1-microm high microstructured surfaces suggests the effect of interlocking is masked by the stronger influence of adhesion on friction, which acts equally in both directions. Our findings show that cockroach euplantulae generate friction using both interlocking and adhesion.
Publisher: Springer Science and Business Media LLC
Date: 03-2021
DOI: 10.1007/S00359-021-01468-4
Abstract: Among invertebrates, spiders (order Araneae) may be unique in their relationship between speed and mass as they use a combination of direct muscular contractions to flex their appendages, and internally controlled hydraulic pressure to extend them. To explore this, we measured maximal running speeds in 128 in idual lycosids and sparassids, which varied in mass between 0.0054 and 3.01 g. We show maximum speed scaled with M
Publisher: The Royal Society
Date: 15-09-2010
Abstract: Many insects cling to vertical and inverted surfaces with pads that adhere by nanometre-thin films of liquid secretion. This fluid is an emulsion, consisting of watery droplets in an oily continuous phase. The detailed function of its two-phasic nature has remained unclear. Here we show that the pad emulsion provides a mechanism that prevents insects from slipping on smooth substrates. We discovered that it is possible to manipulate the adhesive secretion in vivo using smooth polyimide substrates that selectively absorb its watery component. While thick layers of polyimide spin-coated onto glass removed all visible hydrophilic droplets, thin coatings left the emulsion in its typical form. Force measurements of stick insect pads sliding on these substrates demonstrated that the reduction of the watery phase resulted in a significant decrease in friction forces. Artificial control pads made of polydimethylsiloxane showed no difference when tested on the same substrates, confirming that the effect is caused by the insects’ fluid-based adhesive system. Our findings suggest that insect adhesive pads use emulsions with non-Newtonian properties, which may have been optimized by natural selection. Emulsions as adhesive secretions combine the benefits of ‘wet’ adhesion and resistance against shear forces.
Publisher: CSIRO Publishing
Date: 13-05-2022
DOI: 10.1071/ZO21048
Abstract: Kangaroos and other macropodoids stand out among mammals for their unusual hopping locomotion and body shape. This review examines the scaling of hind- and forelimb bones, and the primary ankle extensor muscles and tendons. We find that the scaling of the musculoskeletal system is sensitive to the phylogenetic context. Tibia length increases with positive allometry among most macropodoids, but negative allometry in eastern grey kangaroos and isometry in red kangaroos. Femur length decreases with stronger negative allometry in eastern grey and red kangaroos than among other macropodoids. Muscle masses scale with negative allometry in western grey kangaroos and with isometry in red kangaroos, compared to positive allometry in other macropodoids. We further summarise the work on the hopping gait, energetics in macropodoids, and stresses in the musculoskeletal system in an evolutionary context, to determine what trade-offs may limit locomotor performance in macropodoids. When large kangaroos hop, they do not increase oxygen consumption with speed, unlike most mammals, including small hopping species. We conclude that there is not enough information to isolate the biomechanical factors that make large kangaroos so energy efficient. We identify key areas for further research to fill these gaps.
Publisher: The Royal Society
Date: 09-2018
Abstract: Certain lizards are known to run bipedally. Modelling studies suggest bipedalism in lizards may be a consequence of a caudal shift in the body centre of mass, combined with quick bursts of acceleration, causing a torque moment at the hip lifting the front of the body. However, some lizards appear to run bipedally sooner and for longer than expected from these models, suggesting positive selection for bipedal locomotion. While differences in morphology may contribute to bipedal locomotion, changes in kinematic variables may also contribute to extended bipedal sequences, such as changes to the body orientation, tail lifting and changes to the ground reaction force profile. We examined these mechanisms among eight Australian agamid lizards. Our analysis revealed that angular acceleration of the trunk about the hip, and of the tail about the hip were both important predictors of extended bipedal running, along with increased temporal asymmetry of the ground reaction force profile. These results highlight important dynamic movements during locomotion, which may not only stabilize bipedal strides, but also to de-stabilize quadrupedal strides in agamid lizards, in order to temporarily switch to, and extend a bipedal sequence.
Publisher: The Royal Society
Date: 06-07-2013
Abstract: Rowing is demanding, in part, because drag on the oars increases as the square of their speed. Hence, as muscles shorten faster, their force capacity falls, whereas drag rises. How do frogs resolve this dilemma to swim rapidly? We predicted that shortening velocity cannot exceed a terminal velocity where muscle and fluid torques balance. This terminal velocity, which is below V max , depends on gear ratio (GR = outlever/inlever) and webbed foot area. Perhaps such properties of swimmers are ‘tuned’, enabling shortening speeds of approximately 0.3 V max for maximal power. Predictions were tested using a ‘musculo-robotic’ Xenopus laevis foot driven either by a living in vitro or computational in silico plantaris longus muscle. Experiments verified predictions. Our principle finding is that GR ranges from 11.5 to 20 near the predicted optimum for rowing (GR ≈ 11). However, gearing influences muscle power more strongly than foot area. No single morphology is optimal for producing muscle power. Rather, the ‘optimal’ GR decreases with foot size, implying that rowing ability need not compromise jumping (and vice versa ). Thus, despite our neglect of additional forces (e.g. added mass), our model predicts pairings of physiological and morphological properties to confer effective rowing. Beyond frogs, the model may apply across a range of size and complexity from aquatic insects to human-powered rowing.
Publisher: Wiley
Date: 13-06-2017
Publisher: Elsevier BV
Date: 12-2021
DOI: 10.1016/J.JBIOMECH.2021.110823
Abstract: When muscles contract and change length, they also bulge in thickness and/or width. These shape changes extend the functional range of skeletal muscle by allowing in idual muscle fibres to shorten at different velocities than the whole muscle. Age-related differences in muscle architecture and tissue properties influence how older muscles change shape and architecture during contractions, yet this remains unexplored in active older adults. The aim of this study was to quantify and compare in vivo muscle architecture and shape changes in the medial (MG) and lateral (LG) gastrocnemii of active younger and older adults during isometric plantarflexion contractions. Fifteen younger (21 ± 2y) and 15 older (70 ± 3y) participants performed contractions at 20%, 40%, 60%, 80%, and 100% of maximum voluntary contraction (MVC). B-mode ultrasound was used to measure fascicle length, pennation angle and muscle thickness in MG and LG. We found no influence of age on changes in normalized fascicle length and thickness, or absolute change in pennation angle during contractions. With increasing contraction level, MG and LG fascicle shortening (P < 0.001) and rotation (P < 0.001) increased. However, the change in muscle thickness increased at higher contraction levels in LG, and not MG. Similarly, increased changes in pennation angle were associated with increased muscle thickness in LG, but not MG at 80% and 100% MVC. These results suggest that (1) gastrocnemii shape changes are similar in active older and younger adults at matched levels of effort, and (2) the relationship between pennation angle and muscle thickness can differ between synergistics (LG and MG) and across contraction levels.
Publisher: Wiley
Date: 29-11-2017
DOI: 10.1111/JOA.12569
Publisher: Wiley
Date: 21-01-2020
DOI: 10.1002/EAP.2055
Abstract: Urbanization significantly impacts the health and viability of wildlife populations yet it is not well understood how urban landscapes differ from non-urban landscapes with regard to their effects on wildlife. This study investigated the physiological response of eastern grey kangaroos (Macropus giganteus) to land use at a landscape scale. Using fecal glucocorticoid metabolites (FGM) we compared stress levels of kangaroo populations in urban and non-urban environments. We modeled FGM concentrations from 24 kangaroo populations against land use (urban or non-urban) and other anthropogenic and environmental factors, using a linear modeling approach. We found that land use was a significant predictor of FGM concentrations in eastern grey kangaroos with significant differences in concentrations between urban and non-urban populations. However, the direction of the relationship differed between northern and southern regions of Australia. In the northern study sites, kangaroos in urban areas had significantly higher FGM levels than their non-urban counterparts. In contrast, in southern sites, where kangaroos occur in high densities in many urban areas, urban kangaroos had lower FGM concentrations than non-urban kangaroos. Rainfall and temperature were also significant predictors of FGM and the direction of the relationship was consistent across both regions. These results are consistent with the contrasting abundance and persistence of kangaroo populations within the urban matrix between the two study regions. In the northern region many populations have declined over the last two decades and are fragmented, also occurring at lower densities than in southern sites. Our study indicates that it is the characteristics of urban environments, rather than the urban environment per se, which determines the extent of impacts of urbanization on kangaroos. This research provides insights into how the design of urban landscapes can influence large mammal populations.
Publisher: Public Library of Science (PLoS)
Date: 11-01-2017
Publisher: Oxford University Press (OUP)
Date: 23-06-2009
Publisher: PeerJ
Date: 31-10-2018
DOI: 10.7717/PEERJ.5779
Abstract: This paper is the second of a three-part series that investigates the architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and therefore has the potential to provide insight into locomotor biomechanics in extinct tetrapod vertebrates such as dinosaurs. Here in Part II, a new biomechanical modelling approach is outlined, one which mechanistically links cancellous bone architectural patterns with three-dimensional musculoskeletal and finite element modelling of the hindlimb. In particular, the architecture of cancellous bone is used to derive a single ‘characteristic posture’ for a given species—one in which bone continuum-level principal stresses best align with cancellous bone fabric—and thereby clarify hindlimb locomotor biomechanics. The quasi-static approach was validated for an extant theropod, the chicken, and is shown to provide a good estimate of limb posture at around mid-stance. It also provides reasonable predictions of bone loading mechanics, especially for the proximal hindlimb, and also provides a broadly accurate assessment of muscle recruitment insofar as limb stabilization is concerned. In addition to being useful for better understanding locomotor biomechanics in extant species, the approach hence provides a new avenue by which to analyse, test and refine palaeobiomechanical hypotheses, not just for extinct theropods, but potentially many other extinct tetrapod groups as well.
Publisher: Elsevier BV
Date: 03-2019
Publisher: Cold Spring Harbor Laboratory
Date: 16-05-2020
DOI: 10.1101/2020.05.16.099184
Abstract: Reptiles have repeatedly invaded and thrived in aquatic environments throughout history, however fewer than 8% of the 6000 extant species are primarily aquatic. The Galápagos Marine Iguana ( Amblyrhynchus cristatus ), the world’s only marine lizard, may have had one of the most unique and challenging transitions to aquatic life. Curiously, previous studies have identified relatively few physiological adaptations in Marine Iguanas, however, little is known about the extent of morphological specialisation and performance trade-offs associated with the marine environment. By examining the morphology and locomotory performance of the Marine Iguana in comparison to their closely related mainland ancestors, the Black Spiny-tailed iguana ( Ctenosaura similis ) and Green Iguana ( Iguana iguana ), we found variation reflected specialisation to ecological niches. However, variation was more pronounced among subspecies of Marine Iguana, suggesting that little morphological or performance modification is required for iguanids to successfully invade aquatic environments, thus raising the question why there are so few extant aquatic reptilian lineages. We found that specialisation for the marine environment resulted in a trade-off in sprint speed in a terrestrial environment, similar to that seen in extant crocodilians. Reduced performance in a terrestrial environment likely poses little risk to large-bodied apex predators, whereas in iguanids, a performance trade-off would likely incur increased predation. As such, we suggest that this may explain why iguanids and other ancestral lineages have not undergone transitions to aquatic life. Additionally, we found that the magnitude of morphological and performance variation was more pronounced between subspecies of Marine Iguana than between iguanid species. The Marine Iguana has undergone a unique evolutionary transition to aquatic behaviour, we explore the extent of morphological and performance specialisation required and why there are so few extant marine reptiles.
Publisher: PeerJ
Date: 31-10-2018
DOI: 10.7717/PEERJ.5777
Abstract: This paper is the last of a three-part series that investigates the architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is highly sensitive to its prevailing mechanical environment, and may therefore help further understanding of locomotor biomechanics in extinct tetrapod vertebrates such as dinosaurs. Here in Part III, the biomechanical modelling approach derived previously was applied to two species of extinct, non-avian theropods, Daspletosaurus torosus and Troodon formosus . Observed cancellous bone architectural patterns were linked with quasi-static, three-dimensional musculoskeletal and finite element models of the hindlimb of both species, and used to derive characteristic postures that best aligned continuum-level principal stresses with cancellous bone fabric. The posture identified for Daspletosaurus was largely upright, with a subvertical femoral orientation, whilst that identified for Troodon was more crouched, but not to the degree observed in extant birds. In addition to providing new insight on posture and limb articulation, this study also tested previous hypotheses of limb bone loading mechanics and muscular control strategies in non-avian theropods, and how these aspects evolved on the line to birds. The results support the hypothesis that an upright femoral posture is correlated with bending-dominant bone loading and abduction-based muscular support of the hip, whereas a crouched femoral posture is correlated with torsion-dominant bone loading and long-axis rotation-based muscular support. Moreover, the results of this study also support the inference that hindlimb posture, bone loading mechanics and muscular support strategies evolved in a gradual fashion along the line to extant birds.
Publisher: PeerJ
Date: 31-10-2018
DOI: 10.7717/PEERJ.5778
Abstract: This paper is the first of a three-part series that investigates the architecture of cancellous (‘spongy’) bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and has previously been used to infer locomotor biomechanics in extinct tetrapod vertebrates, especially primates. Despite great promise, cancellous bone architecture has remained little utilized for investigating locomotion in many other extinct vertebrate groups, such as dinosaurs. Documentation and quantification of architectural patterns across a whole bone, and across multiple bones, can provide much information on cancellous bone architectural patterns and variation across species. Additionally, this also lends itself to analysis of the musculoskeletal biomechanical factors involved in a direct, mechanistic fashion. On this premise, computed tomographic and image analysis techniques were used to describe and analyse the three-dimensional architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs for the first time. A comprehensive survey across many extant and extinct species is produced, identifying several patterns of similarity and contrast between groups. For instance, more stemward non-avian theropods (e.g. ceratosaurs and tyrannosaurids) exhibit cancellous bone architectures more comparable to that present in humans, whereas species more closely related to birds (e.g. paravians) exhibit architectural patterns bearing greater similarity to those of extant birds. Many of the observed patterns may be linked to particular aspects of locomotor biomechanics, such as the degree of hip or knee flexion during stance and gait. A further important observation is the abundance of markedly oblique trabeculae in the diaphyses of the femur and tibia of birds, which in large species produces spiralling patterns along the endosteal surface. Not only do these observations provide new insight into theropod anatomy and behaviour, they also provide the foundation for mechanistic testing of locomotor hypotheses via musculoskeletal biomechanical modelling.
Publisher: IOP Publishing
Date: 16-12-2021
Abstract: Robotic systems for complex tasks, such as search and rescue or exploration, are limited for wheeled designs, thus the study of legged locomotion for robotic applications has become increasingly important. To successfully navigate in regions with rough terrain, a robot must not only be able to negotiate obstacles, but also climb steep inclines. Following the principles of biomimetics, we developed a modular bio-inspired climbing robot, named X4, which mimics the lizard’s bauplan including an actuated spine, shoulders, and feet which interlock with the surface via claws. We included the ability to modify gait and hardware parameters and simultaneously collect data with the robot’s sensors on climbed distance, slip occurrence and efficiency. We first explored the speed-stability trade-off and its interaction with limb swing phase dynamics, finding a sigmoidal pattern of limb movement resulted in the greatest distance travelled. By modifying foot orientation, we found two optima for both speed and stability, suggesting multiple stable configurations. We varied spine and limb range of motion, again showing two possible optimum configurations, and finally varied the centre of pro- and retraction on climbing performance, showing an advantage for protracted limbs during the stride. We then stacked optimal regions of performance and show that combining optimal dynamic patterns with either foot angles or ROM configurations have the greatest performance, but further optima stacking resulted in a decrease in performance, suggesting complex interactions between kinematic parameters. The search of optimal parameter configurations might not only be beneficial to improve robotic in-field operations but may also further the study of the locomotive evolution of climbing of animals, like lizards or insects.
Publisher: IOP Publishing
Date: 03-07-2012
DOI: 10.1088/1748-3182/7/4/046001
Abstract: Pressure-sensitive adhesives such as tapes become easily contaminated by dust particles. By contrast, animal adhesive pads are able to self-clean and can be reused millions of times over a lifetime with little reduction in adhesion. However, the detailed mechanisms underlying this ability are still unclear. Here we test in adhesive pads of stick insects (Carausius morosus) (1) whether self-cleaning is enhanced by the liquid pad secretion, and (2) whether alternating push-pull movements aid the removal of particles. We measured attachment forces of insect pads on glass after contamination with 10 µm polystyrene beads. While the amount of fluid present on the pad showed no effect on the pads' susceptibility to contamination, the recovery of adhesive forces after contamination was faster when higher fluid levels were present. However, this effect does not appear to be based on a faster rate of self-cleaning since the number of spheres deposited with each step did not increase with fluid level. Instead, the fluid may aid the recovery of adhesive forces by filling in the gaps between contaminating particles, similar to the fluid's function on rough surfaces. Further, we found no evidence that an alternation of pushing and pulling movements, as found in natural steps, leads to a more efficient recovery of adhesion than repeated pulling slides.
Publisher: The Company of Biologists
Date: 02-2015
DOI: 10.1242/JEB.111682
Abstract: Movement speed is fundamental to all animal behaviour, yet no general framework exists for understanding why animals move at the speeds they do. Even during fitness-defining behaviours like running away from predators, an animal should select a speed that balances the benefits of high speed against the increased probability of mistakes. In this study, we explored this idea by quantifying trade-offs between speed, manoeuvrability and motor control in wild northern quolls (Dasyurus hallucatus) – a medium-sized carnivorous marsupial native to northern Australia. First, we quantified how running speed affected the probability of crashes when rounding corners of 45, 90 and 135 deg. We found that the faster an in idual approached a turn, the higher the probability that they would crash, and these risks were greater when negotiating tighter turns. To avoid crashes, quolls modulated their running speed when they moved through turns of varying angles. Average speed for quolls when sprinting along a straight path was around 4.5 m s−1 but this decreased linearly to speeds of around 1.5 m s−1 when running through 135 deg turns. Finally, we explored how an in idual's morphology affects their manoeuvrability. We found that in iduals with larger relative foot sizes were more manoeuvrable than in iduals with smaller relative foot sizes. Thus, movement speed, even during extreme situations like escaping predation, should be based on a compromise between high speed, manoeuvrability and motor control. We advocate that optimal – rather than maximal – performance capabilities underlie fitness-defining behaviours such as escaping predators and capturing prey.
Publisher: Wiley
Date: 24-07-2020
DOI: 10.1111/JOA.13273
Publisher: The Royal Society
Date: 07-2017
Abstract: How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width—the mediolateral (transverse) distance between successive footfalls—was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods ( p 0.001), as well as the five tallest bird species studied ( p 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk–run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history.
Publisher: Wiley
Date: 06-2014
DOI: 10.1111/EVO.12447
Abstract: The origin of bipedal locomotion in lizards is unclear. Modeling studies have suggested that bipedalism may be an exaptation, a byproduct of features originally designed to increase maneuverability, which were only later exploited. Measurement of the body center of mass (BCOM) in 124 species of lizards confirms a significant rearward shift among bipedal lineages. Further racetrack trials showed a significant acceleration threshold between bipedal and quadrupedal runs. These suggest good general support for a passive bipedal model, in which the combination of these features lead to passive lifting of the front of the body. However, variation in morphology could only account for 56% of the variation in acceleration thresholds, suggesting that dynamics have a significant influence on bipedalism. Deviation from the passive bipedal model was compared with node age, supporting an increase in the influence of dynamics over time. Together, these results show that bipedalism may have first arisen as a consequence of acceleration and a rearward shift in the BCOM, but subsequent linages have exploited this consequence to become bipedal more often, suggesting that bipedalism in lizards may convey some advantage. Exploitation of bipedalism was also associated with increased rates of phenotypic ersity, suggesting exploiting bipedalism may promote adaptive radiation.
Publisher: IOP Publishing
Date: 08-06-2012
DOI: 10.1088/1748-3182/7/3/036018
Abstract: Frogs are capable of impressive feats of jumping and swimming. Recent work has shown that anuran hind limb muscles can operate at lengths longer than the 'optimal length'. To address the implications of muscle operating length on muscle power output and swimming mechanics, we built a robotic frog hind limb model based upon Xenopus laevis. The model simulated the force-length and force-velocity properties of vertebrate muscle, within the skeletal environment. We tested three muscle starting lengths, representing long, optimal and short starting lengths. Increasing starting length increased maximum muscle power output by 27% from 98.1 W kg(-1) when muscle begins shortening from the optimal length, to 125.1 W kg(-1) when the muscle begins at longer initial lengths. Therefore, longer starting lengths generated greater hydrodynamic force for extended durations, enabling faster swimming speeds of the robotic frog. These swimming speeds increased from 0.15 m s(-1) at short initial muscle lengths, to 0.39 m s(-1) for the longest initial lengths. Longer starting lengths were able to increase power as the muscle's force-length curve was better synchronized with the muscle's activation profile. We further dissected the underlying components of muscle force, separating force-length versus force-velocity effects, showing a transition from force-length limitations to force-velocity limitations as starting length increased.
Publisher: Springer Science and Business Media LLC
Date: 02-03-2020
DOI: 10.1038/S41598-020-60795-9
Abstract: From the camel’s toes to the horse’s hooves, the ersity in foot morphology among mammals is striking. One distinguishing feature is the presence of fat pads, which may play a role in reducing foot pressures, or may be related to habitat specialization. The camelid family provides a useful paradigm to explore this as within this phylogenetically constrained group we see prominent (camels) and greatly reduced (alpacas) fat pads. We found similar scaling of vertical ground reaction force with body mass, but camels had larger foot contact areas, which increased with velocity, unlike alpacas, meaning camels had relatively lower foot pressures. Further, variation between specific regions under the foot was greater in alpacas than camels. Together, these results provide strong evidence for the role of fat pads in reducing relative peak locomotor foot pressures, suggesting that the fat pad role in habitat specialization remains difficult to disentangle.
Publisher: University of Chicago Press
Date: 05-2012
DOI: 10.1086/665275
Abstract: Studies of locomotor performance often link variation in morphology with ecology. While maximum sprint speed is a commonly used performance variable, the absolute limits for this performance trait are not completely understood. Absolute maximal speed has often been shown to increase linearly with body size, but several comparative studies covering a large range of body sizes suggest that maximal speed does not increase indefinitely with body mass but rather reaches an optimum after which speed declines. Because of the comparative nature of these studies, it is difficult to determine whether this decrease is due to biomechanical constraints on maximal speed or is a consequence of phylogenetic inertia or perhaps relaxed selection for lower maximal speed at large body size. To explore this issue, we have examined intraspecific variations in morphology, maximal sprint speed, and kinematics for the yellow-spotted monitor lizard Varanus panoptes, which varied in body mass from 0.09 to 5.75 kg. We show a curvilinear relationship between body size and absolute maximal sprint speed with an optimal body mass with respect to speed of 1.245 kg. This excludes the phylogenetic inertia hypothesis, because this effect should be absent intraspecifically, while supporting the biomechanical constraints hypothesis. The relaxed selection hypothesis cannot be excluded if there is a size-based behavioral shift intraspecifically, but the biomechanical constraints hypothesis is better supported from kinematic analyses. Kinematic measurements of hind limb movement suggest that the distance moved by the body during the stance phase may limit maximum speed. This limit is thought to be imposed by a decreased ability of the bones and muscles to support body mass for larger lizards.
Publisher: Wiley
Date: 21-07-2009
Publisher: Springer Science and Business Media LLC
Date: 18-02-2016
Publisher: The Company of Biologists
Date: 15-09-2011
DOI: 10.1242/JEB.059345
Abstract: Geometric scaling predicts that stresses on limb bones and muscles should increase with body size. Mammals counter this size-related increase in stress partially through changes in bone geometry, but largely through changes in posture, with larger species having a more erect stance. However, the ability to counter size-related stresses in this fashion may be limited to those taxa that have a parasagittal gait (such as mammals), where legs are swung underneath the body. We examined locomotor kinematics for 11 species of varanid lizards (from 0.04 to 8 kg body mass) that have a sprawling gait, to determine how they moderate size-related stresses. Posture, as indicated by femur adduction and hip heights, did not change significantly with body size, beyond that expected from geometrical scaling. Instead, lizards mitigated size-related increases in stress by increasing duty factor and possibly reducing femur rotation. Incorporating these factors in biomechanical models predicted that both bending (∝M0.016, where M is mass) and torsional (∝M–0.049) stresses should be nearly independent of body size over the size range examined. However, increasing duty factor and reducing femur rotation probably have deleterious effects on speed, and this difference in kinematics with size may explain why speed scales lower for sprawling lizards than for parasagittal mammals (∝M0.17 and ∝M0.24, respectively). Further, paralleling conclusions for the synapsid lineage, these findings suggest that evolution from sprawling to upright posture did not occur in archosaurs as a response to larger size rather, these archosaurs likely became upright first and larger later.
Publisher: American Arachnological Society
Date: 12-2005
DOI: 10.1636/S04-35.1
Location: Australia
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2018
End Date: 2020
Funder: Australian Research Council
View Funded ActivityStart Date: 2018
End Date: 2020
Funder: Australian Research Council
View Funded ActivityStart Date: 2012
End Date: 2014
Funder: Australian Research Council
View Funded ActivityStart Date: 2014
End Date: 2015
Funder: University of Queensland
View Funded Activity