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Why go bipedal? Locomotion and morphology in Australian agamid lizards
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Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S74–S92
streamlined technical bodies, with augmentation vanishing at about 3 body diameters below the surface. Drag “inverted” is approximately 15% less than that “dorsal side up” near the surface. Consistent with this, at any given velocity, tailbeat frequency and stride length are lower and higher respectively for inverted swimming in surface proximity (P b 0.05). Deeply submerged, there are no significant differences in drag and kinematics between postures (P N 0.05). In steady swimming bouts, carangiform motions (associated with high hydrodynamic efficiency) minimize “self generated” dispersive waves relative to the anguilliform and subcarangiform modes. At the critical Froude number of 0.45, speeds in surface proximity correspond to prolonged swimming that ends in fatigue. To exceed these speeds, the fish must swim deeply submerged and this behaviour is observed. Inverted swimming facilitates efficient airbreathing. Drag dorsal side up during aquatic surface respiration is ×1.5 that for the inverted posture. Fast-starts are rectilinear, directly away from the stimulus. Average and maximum velocity and acceleration decrease in surface proximity (P b 0.05) and are higher inverted (maximum acceleration: 2030 m s− 2; P b 0.05) and comparable to locomotor generalists (e.g. trout). Mechanical energy losses due to wave generation are about 20% and 40% for inverted and dorsal side up respectively and lower than trout fast-starting in shallow water (70% losses); bottom effects and large amplitude C-starts (c.f. relatively low amplitude rectilinear motions in S. nigriventris) enhance resistance in trout. S. nigriventris probably evolved from a diurnal or crepuscular “Chiloglanis like” benthic ancestor. Nocturnality and reverse countershading likely coevolved with the inverted habit. Presumably, the increased energy cost of surface swimming is off-set by exploiting the air/water interface for food and/or air breathing. doi:10.1016/j.cbpa.2008.04.151
A3.46 3D Kinematics of the walk of the quail A. Abourachid (Museum National d'Histoire Naturelle); R. Hackert (Museum National d'Histoire Naturelle); H. Gioanni (Université Paris 5); V. Hugel (Université de Versailles Saint Quentin) Using non-synchronous 2D cineradiography views, we reconstructed the 3D movements of trunk, head and limbs during locomotor cycles of quails (Coturnix coturnix) walking symmetrically at moderate speed. The trunk made small but significant phasic medio-lateral motion and biphasic sagittal pitch during one locomotor cycle. The trunk was medially translated during double support and showed rightward roll and yaw movements during the right stance until the left touch down at the middle of the cycle. Then, the trunk moved leftward during the left stance until the next right touch down. The trunk was moving downward at the touch down of the right foot, and reached the most downward pitched position during the right single support phase. It was then pitched upward and reached the more erected position soon before the touch down of the left foot. The trunk finally moved down again. The limb kinematics was affected by the motion of the trunk, but the motion of the proximal joints, hip and knee, was mainly synchronized with the feet lift off and touch down. The distal intertarsal and metatarsophalangal joints motion was mostly synchronized with the trunk motion. The headbobbing was also synchronized with the trunk motion. These data indicate that the study of one single limb is not enough to explain the kinematics of locomotion in birds. Moreover, the redundancy brought about by the large number of joints involved in the locomotion may explain the functional versatility of bird pelvic limbs, walking, but also landing and taking off. doi:10.1016/j.cbpa.2008.04.153
A3.45 Coordination of hindlimb joints to control speed in swimming frogs C. Richards, B. Joo, A. Biewener (Harvard University) Prior research has shown differences in anuran hindlimb muscle function across locomotor modes (e.g. hopping vs. swimming). Far less is understood about the control of performance within a locomotor mode, particularly within swimming. To address this, we recorded high speed video and electromyography (EMG) from four hindlimb muscles of the right leg of Xenopus laevis frogs: semimebranosus (a hip extensor), cruralis and gluteus magnus (knee extensors), and the plantaris (an ankle extensor). Frogs were stimulated to swim across peak stroke speeds ranging from 0.11 to 0.94 m/s. All swimming strokes analyzed showed symmetrical kinematics between both legs. Preliminary data suggest that the plantaris muscle is active at all swimming speeds. Activity from the semimembranosus was recorded in all but the slowest 20% of swimming strokes. The gluteus magnus was active in strokes reaching at least ~ 50% maximum speed, and the cruralis was only recruited for the fastest 16% of swimming strokes. As expected, EMG intensity was positively correlated with peak swimming speed for all muscles. Moreover, as swimming speed increased from stroke to stroke, the variance of EMG onset time among the four muscles decreased (r2 = 0.33), suggesting that faster speeds require more synchronous activation of the extensor muscles. Further analysis may illuminate how anurans actively control the coordination of hindlimb joints to modulate swimming performance.
doi:10.1016/j.cbpa.2008.04.152
A3.47 Why go bipedal? Locomotion and morphology in Australian agamid lizards C. Clemente (Cambridge); P. Withers (University of Western Australia); G. Thompson (University of Western Australia); G. Thompson (Edith Cowan University) 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 bipedaly, 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. (2003). While 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
Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S74–S92
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.
S87
stride length, while the time variables have already reached their limit. doi:10.1016/j.cbpa.2008.04.156
doi:10.1016/j.cbpa.2008.04.154
A3.48 Biomimetic analysis of locomotion in tortoise, Geochelone graeca
A3.50 Pushing and pulling: Direction dependence of insect attachment structures W. Federle, C. Clemente, T. Endlein (University of Cambridge)
H. EL Daou, (ISIR, Universite Pierre et Marie Curie); P. Libourel (Muséum National d'Histoire Naturelle); S. Renous (Muséum National d'Histoire Naturelle); V. Bels (Muséum National d'Histoire Naturelle); J. Guinot (ISIR, Universite Pierre et Marie Curie); Terrestrial locomotion of turtles has been poorly studied and modelized. In this paper, we studied locomotor behavior in the terrestrial tortoise, Geochelone graeca to present a biomimetic approach for modeling and controlling a virtual model of tortoise like robot. Experiments in vivo and in vitro were performed on adult specimens in order to measure the inertial proprieties of body limbs, the variations of joint angles between bones and the ground reactions forces on each leg. A virtual model of tortoise was developed using the MSC.ADAMS mechanical simulation software. This model has similar kinematics and inertial proprieties than the studied animals. It was controlled using real recording from walking animals. The ground reaction forces generated on the virtual model and the real animal were compared in order to find similarities and/ or invariant criteria. doi:10.1016/j.cbpa.2008.04.155
A3.49 The variations of temporal and spatial limb coordination in dogs as a function of speed and gaits
Many climbing animals cling to smooth surfaces using adhesive pads on their feet. Pads with strong adhesion would make walking and running very difficult, if they were not direction-dependent. Typically, claws or adhesive pads make contact when pulled towards the body but detach easily when pushed. Direction-dependence in smooth pads could be based on simple tape-like behaviour or could arise if pads unfold when pulled proximally. Force measurements in ants revealed an abrupt decline of adhesion for pull-off angles greater than ca. 35°, which was neither explained by peeling theory nor by the unfolding of pads. Normal climbing and level running, however, require not only pulling but also pushing. We found that cockroaches solve this problem by using different parts of their foot. When climbing upward, they engaged the distal pad (arolium) of the front legs and the tarsal pads (euplantulae) of the hind legs, whereas the reverse held true during downward climbing. Single-pad friction force measurements showed that arolium and euplantulae have an opposite direction-dependence that helps their specific role during locomotion. This direction-dependence was explained by different contact areas during pushing or pulling, resulting from the arrangement of the flexible tarsal chain. Our findings suggest that the tarsal pads in cockroaches are not ‘adhesive’ organs but ‘friction pads’, mainly providing the necessary traction during locomotion. We show that a similar division of labour between attachment structures on the proximal and distal tarsus is present in other insects with different pad designs. doi:10.1016/j.cbpa.2008.04.157
L. Maes, M. Herbin, R. Hackert, A. Abourachid (Muséum National d'Histoire Naturelle de Paris) Mammals increase their velocity by adjusting their interlimb coordination, in time as well as in space. These modifications may result in simple variations in gaits or a real change of gaits. We explored the relationship between the temporal or the spatial interlimb coordination and speed, through the entire gait repertoire of dogs, from low to high speeds (from 0.4 m s− 1 to 10.0 m s− 1). In symmetrical gaits, the maintainance of a perfect alternation between the limbs of the same pair is due to a similar increase of lags and gaps within the pairs with an increase in speed. On the contrary, asymmetrical gaits show a relative consistency in the temporal and spatial coordination of the limbs of the same pair whatever the speed. The temporal coordination between pairs of limbs depends more on the gait than on the speed, whereas the spatial coordination between the pairs is strongly related to speed. Trunk length explains this difference for lateral walk, pace and transverse gallop. Lateral and sagittal flexions of the vertebral axis, during trot and rotary gallop respectively, explain the residual difference between temporal and spatial coordination between pairs of limbs, after a rectification by trunk length. Thus, in addition to the increasing occurrences of one or two suspension phases, trunk length variations due to a vertebral flexion, especially at the highest speeds, is responsible for the increase of the
A3.51 Effect of morphological variation on single seta force in eight gecko species A. Peattie (University of Cambridge) The adhesive structures on gecko feet exhibit extensive morphological variation. To test the effect of this variation on their adhesive performance, we measured single-seta force in eight species with varying setal morphology and broad phylogenetic distribution. We attached setae to a silicon surface fixed to a wire functioning as a cantilever force gauge, then collected high-speed video of each trial to determine the shear and normal adhesives forces, as well as critical detachment angle during normal pulloffs. The van der Waals hypothesis of gecko adhesion predicts that an increased number of spatulae should lead to an increased adhesive force. Shear and normal forces both increased with the number of spatulae. Since number of spatulae per seta was correlated with seta width, there was a corresponding increase in shear force with width. Seta width also had a significant effect on pulloff force, but to a lesser degree. Due to a strong correlation between seta width and length, we expected similar correlations between seta length and adhesive force. We found no
Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S74–S92
streamlined technical bodies, with augmentation vanishing at about 3 body diameters below the surface. Drag “inverted” is approximately 15% less than that “dorsal side up” near the surface. Consistent with this, at any given velocity, tailbeat frequency and stride length are lower and higher respectively for inverted swimming in surface proximity (P b 0.05). Deeply submerged, there are no significant differences in drag and kinematics between postures (P N 0.05). In steady swimming bouts, carangiform motions (associated with high hydrodynamic efficiency) minimize “self generated” dispersive waves relative to the anguilliform and subcarangiform modes. At the critical Froude number of 0.45, speeds in surface proximity correspond to prolonged swimming that ends in fatigue. To exceed these speeds, the fish must swim deeply submerged and this behaviour is observed. Inverted swimming facilitates efficient airbreathing. Drag dorsal side up during aquatic surface respiration is ×1.5 that for the inverted posture. Fast-starts are rectilinear, directly away from the stimulus. Average and maximum velocity and acceleration decrease in surface proximity (P b 0.05) and are higher inverted (maximum acceleration: 2030 m s− 2; P b 0.05) and comparable to locomotor generalists (e.g. trout). Mechanical energy losses due to wave generation are about 20% and 40% for inverted and dorsal side up respectively and lower than trout fast-starting in shallow water (70% losses); bottom effects and large amplitude C-starts (c.f. relatively low amplitude rectilinear motions in S. nigriventris) enhance resistance in trout. S. nigriventris probably evolved from a diurnal or crepuscular “Chiloglanis like” benthic ancestor. Nocturnality and reverse countershading likely coevolved with the inverted habit. Presumably, the increased energy cost of surface swimming is off-set by exploiting the air/water interface for food and/or air breathing. doi:10.1016/j.cbpa.2008.04.151
A3.46 3D Kinematics of the walk of the quail A. Abourachid (Museum National d'Histoire Naturelle); R. Hackert (Museum National d'Histoire Naturelle); H. Gioanni (Université Paris 5); V. Hugel (Université de Versailles Saint Quentin) Using non-synchronous 2D cineradiography views, we reconstructed the 3D movements of trunk, head and limbs during locomotor cycles of quails (Coturnix coturnix) walking symmetrically at moderate speed. The trunk made small but significant phasic medio-lateral motion and biphasic sagittal pitch during one locomotor cycle. The trunk was medially translated during double support and showed rightward roll and yaw movements during the right stance until the left touch down at the middle of the cycle. Then, the trunk moved leftward during the left stance until the next right touch down. The trunk was moving downward at the touch down of the right foot, and reached the most downward pitched position during the right single support phase. It was then pitched upward and reached the more erected position soon before the touch down of the left foot. The trunk finally moved down again. The limb kinematics was affected by the motion of the trunk, but the motion of the proximal joints, hip and knee, was mainly synchronized with the feet lift off and touch down. The distal intertarsal and metatarsophalangal joints motion was mostly synchronized with the trunk motion. The headbobbing was also synchronized with the trunk motion. These data indicate that the study of one single limb is not enough to explain the kinematics of locomotion in birds. Moreover, the redundancy brought about by the large number of joints involved in the locomotion may explain the functional versatility of bird pelvic limbs, walking, but also landing and taking off. doi:10.1016/j.cbpa.2008.04.153
A3.45 Coordination of hindlimb joints to control speed in swimming frogs C. Richards, B. Joo, A. Biewener (Harvard University) Prior research has shown differences in anuran hindlimb muscle function across locomotor modes (e.g. hopping vs. swimming). Far less is understood about the control of performance within a locomotor mode, particularly within swimming. To address this, we recorded high speed video and electromyography (EMG) from four hindlimb muscles of the right leg of Xenopus laevis frogs: semimebranosus (a hip extensor), cruralis and gluteus magnus (knee extensors), and the plantaris (an ankle extensor). Frogs were stimulated to swim across peak stroke speeds ranging from 0.11 to 0.94 m/s. All swimming strokes analyzed showed symmetrical kinematics between both legs. Preliminary data suggest that the plantaris muscle is active at all swimming speeds. Activity from the semimembranosus was recorded in all but the slowest 20% of swimming strokes. The gluteus magnus was active in strokes reaching at least ~ 50% maximum speed, and the cruralis was only recruited for the fastest 16% of swimming strokes. As expected, EMG intensity was positively correlated with peak swimming speed for all muscles. Moreover, as swimming speed increased from stroke to stroke, the variance of EMG onset time among the four muscles decreased (r2 = 0.33), suggesting that faster speeds require more synchronous activation of the extensor muscles. Further analysis may illuminate how anurans actively control the coordination of hindlimb joints to modulate swimming performance.
doi:10.1016/j.cbpa.2008.04.152
A3.47 Why go bipedal? Locomotion and morphology in Australian agamid lizards C. Clemente (Cambridge); P. Withers (University of Western Australia); G. Thompson (University of Western Australia); G. Thompson (Edith Cowan University) 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 bipedaly, 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. (2003). While 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
Abstracts / Comparative Biochemistry and Physiology, Part A 150 (2008) S74–S92
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.
S87
stride length, while the time variables have already reached their limit. doi:10.1016/j.cbpa.2008.04.156
doi:10.1016/j.cbpa.2008.04.154
A3.48 Biomimetic analysis of locomotion in tortoise, Geochelone graeca
A3.50 Pushing and pulling: Direction dependence of insect attachment structures W. Federle, C. Clemente, T. Endlein (University of Cambridge)
H. EL Daou, (ISIR, Universite Pierre et Marie Curie); P. Libourel (Muséum National d'Histoire Naturelle); S. Renous (Muséum National d'Histoire Naturelle); V. Bels (Muséum National d'Histoire Naturelle); J. Guinot (ISIR, Universite Pierre et Marie Curie); Terrestrial locomotion of turtles has been poorly studied and modelized. In this paper, we studied locomotor behavior in the terrestrial tortoise, Geochelone graeca to present a biomimetic approach for modeling and controlling a virtual model of tortoise like robot. Experiments in vivo and in vitro were performed on adult specimens in order to measure the inertial proprieties of body limbs, the variations of joint angles between bones and the ground reactions forces on each leg. A virtual model of tortoise was developed using the MSC.ADAMS mechanical simulation software. This model has similar kinematics and inertial proprieties than the studied animals. It was controlled using real recording from walking animals. The ground reaction forces generated on the virtual model and the real animal were compared in order to find similarities and/ or invariant criteria. doi:10.1016/j.cbpa.2008.04.155
A3.49 The variations of temporal and spatial limb coordination in dogs as a function of speed and gaits
Many climbing animals cling to smooth surfaces using adhesive pads on their feet. Pads with strong adhesion would make walking and running very difficult, if they were not direction-dependent. Typically, claws or adhesive pads make contact when pulled towards the body but detach easily when pushed. Direction-dependence in smooth pads could be based on simple tape-like behaviour or could arise if pads unfold when pulled proximally. Force measurements in ants revealed an abrupt decline of adhesion for pull-off angles greater than ca. 35°, which was neither explained by peeling theory nor by the unfolding of pads. Normal climbing and level running, however, require not only pulling but also pushing. We found that cockroaches solve this problem by using different parts of their foot. When climbing upward, they engaged the distal pad (arolium) of the front legs and the tarsal pads (euplantulae) of the hind legs, whereas the reverse held true during downward climbing. Single-pad friction force measurements showed that arolium and euplantulae have an opposite direction-dependence that helps their specific role during locomotion. This direction-dependence was explained by different contact areas during pushing or pulling, resulting from the arrangement of the flexible tarsal chain. Our findings suggest that the tarsal pads in cockroaches are not ‘adhesive’ organs but ‘friction pads’, mainly providing the necessary traction during locomotion. We show that a similar division of labour between attachment structures on the proximal and distal tarsus is present in other insects with different pad designs. doi:10.1016/j.cbpa.2008.04.157
L. Maes, M. Herbin, R. Hackert, A. Abourachid (Muséum National d'Histoire Naturelle de Paris) Mammals increase their velocity by adjusting their interlimb coordination, in time as well as in space. These modifications may result in simple variations in gaits or a real change of gaits. We explored the relationship between the temporal or the spatial interlimb coordination and speed, through the entire gait repertoire of dogs, from low to high speeds (from 0.4 m s− 1 to 10.0 m s− 1). In symmetrical gaits, the maintainance of a perfect alternation between the limbs of the same pair is due to a similar increase of lags and gaps within the pairs with an increase in speed. On the contrary, asymmetrical gaits show a relative consistency in the temporal and spatial coordination of the limbs of the same pair whatever the speed. The temporal coordination between pairs of limbs depends more on the gait than on the speed, whereas the spatial coordination between the pairs is strongly related to speed. Trunk length explains this difference for lateral walk, pace and transverse gallop. Lateral and sagittal flexions of the vertebral axis, during trot and rotary gallop respectively, explain the residual difference between temporal and spatial coordination between pairs of limbs, after a rectification by trunk length. Thus, in addition to the increasing occurrences of one or two suspension phases, trunk length variations due to a vertebral flexion, especially at the highest speeds, is responsible for the increase of the
A3.51 Effect of morphological variation on single seta force in eight gecko species A. Peattie (University of Cambridge) The adhesive structures on gecko feet exhibit extensive morphological variation. To test the effect of this variation on their adhesive performance, we measured single-seta force in eight species with varying setal morphology and broad phylogenetic distribution. We attached setae to a silicon surface fixed to a wire functioning as a cantilever force gauge, then collected high-speed video of each trial to determine the shear and normal adhesives forces, as well as critical detachment angle during normal pulloffs. The van der Waals hypothesis of gecko adhesion predicts that an increased number of spatulae should lead to an increased adhesive force. Shear and normal forces both increased with the number of spatulae. Since number of spatulae per seta was correlated with seta width, there was a corresponding increase in shear force with width. Seta width also had a significant effect on pulloff force, but to a lesser degree. Due to a strong correlation between seta width and length, we expected similar correlations between seta length and adhesive force. We found no