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Session Schedule & Abstracts

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Sunday 3rd July, 2016

Locomotion 6

Room: Salon F   11:30 am–1:00 pm

Moderator(s): Shapiro D, Vereecke EE
LOC6-1  11:30 am  The biological role of carpal sinus hair sensing on the body posture during locomotion of rats (Rattus norvegicus, Rodentia). Niederschuh S.*, Institute of Systematic Zoology and Evolutionary Biology, FSU Jena; Thomas H., Department of Biomechatronics, Ilmenau University of Technology; Danja V., Department of Biomechatronics, Ilmenau University of Technology; Witte H., Department of Biomechatronics, Ilmenau University of Technology; Schmidt M., Institute of Systematic Zoology and Evolutionary Biology, FSU Jena
Abstract: While the facial (mystacial) sinus hairs are intensively studied regarding their structure, follicle anatomy and biological role in various mammals, less is known about the tactile hairs found on the palmar side of the rat’s forelimbs near the wrist. These carpal sinus hairs are assumed to play an important role during locomotion in dark or narrow environments as well as for animals possessing a poor vision. In these cases, sensing substrate properties and diameters before touchdown of the forelimbs would facilitate the adjustment of body posture to maintain the dynamic stability of the trunk. So, a coupled sensorimotor control mechanism between the sinus hairs’ sensory system as well as the proprioceptors of the body should exist. To explore the biological role of the carpal sinus hairs and their function during substrate contact, spatiotemporal speed-dependent and kinematic parameters of the limbs and spine were quantified. Measuring was done by x-ray fluoroscopy and normal-light high-speed cameras. A continuous and a discontinuous substrate in the form of a treadmill were used. Data were collected under the presence and absence of the sinus hairs during the preferred animals’ speed. Our investigation shows a time window of approx. 30 ms from carpal sinus hairs’ contact to the substrate until forelimb touchdown. Within this time, adjusting the body posture due to a changing surface takes place. While the sensory input of the carpal sinus hairs does not affect the failure rate on a perforated substrate, it affects the mystacial sinus hairs’ motion (whisking) pattern and has a stabilizing effect on the trajectory of the center of mass, pointing to a connected sensorimotor control loop. Further the carpal sensors act as speedometer by influencing the speed dependence or speed-dependent adaptations of the limb and body kinematics.

LOC6-2  11:45 am  3D dynamics of burrowing in pocket gophers . Moore Crisp AL*, UNLV; Lee DV, UNLV
Abstract: Using a self-designed force-sensitive tunnel tube inside an X-Ray, we have been able to measure burrowing in realistic and natural substrates. Here, we present the first full 3-D dynamic analysis of burrowing biomechanics in a vertebrate. The Tunnel-Tube 3.0 is comprised of two tubes arranged in series, with each half mounted on an ATI nano-17 6-axis load cell. The animal enters the first tube and begins digging at the second tube, which is filled with the substrate material. The substrate-filled tubes are uniformly packed and can be exchanged between trials, allowing for a more consistent substrate over time. The dual-tube design allows us to independently measure forces produced by the animal’s fore- and hindlimbs. We tested our design in a representative digger: the Botta’s pocket gopher (Thomomys bottae), which spend most of their lives underground. Pocket gophers burrowed through the Tunnel-Tube in four substrate conditions: Soft radiolucent substrate, hard radiolucent substrate, soft natural soil, and hard natural soil. In soft substrates, pocket gophers exhibited scratch-digging, using the forelimbs to loosen and remove the substrate. In harder substrates, pocket gophers exhibited both chisel-tooth and scratch-digging, typically using the teeth to penetrate the hard substrate and the forelimbs to remove loosened substrate. As substrate hardness increased, the pocket gophers produced more force in order to penetrate the substrate. During scratch digging, gophers produced a minimum mean force of 0.08±0.03 body weights in soft radiolucent substrate and a maximum of 2.0±0.81 BW force during chisel-tooth digging in the hardest substrate. The fact that force profiles spanned nearly two orders of magnitude between treatment conditions indicates that gophers are able to effectively modulate force production during digging in response to soil conditions.

LOC6-3  12:00 pm  The kinematics of grooming: How mammals clean their coat. Schmidt M.*, Friedrich Schiller University Jena; van Beesel J., Friedrich Schiller University Jena; Dargel L., Friedrich Schiller University Jena; Fischer M.S., Friedrich Schiller University Jena
Abstract: Non-locomotory movements in the behavioural context of grooming, social interaction or food acquisition, in sum referred to as idiomotion, play a major role in the daily activities of mammals. We are interested in their significance for the functional morphology of the motion system in order to better understand the evolutionary role of idiomotion in mammals. So far, studies into grooming, reaching, grasping and other idiomotory activities are mainly initiated by neurobiological questions. Our present studies focus on grooming and we studied the kinematics of grooming-associated movements of limbs and trunk in species with different locomotor adaptations (rats, rabbits, dogs and squirrels) using biplanar X-ray fluoroscopy. Our observations so far support the notion that idiomotion rather than locomotion explains the form and mobility of ball-and-socket joints. Idiomotion also involves repetitive and stereotypic motion cycles (e.g., during scratching or face washing), likely controlled by central rhythm-generating networks. However, grooming movements are less symmetrical than locomotory movements. Differences across species appear to be related to the mobility of the trunk. Rats are able to groom almost all of their body regions using mouth, tongue and teeth, and make use of a plenty of assisting and stabilising postures. Rabbits and dogs have in common a rather limited overall flexibility; they predominantly scratch their fur using the hindlimbs. For the future, we hope to further expand the base for interspecific comparison with respect to the biomechanics of idiomotion as the prerequisite for linking variations in structure and behaviour. This research project is funded by the budget of the institute.

LOC6-4  12:15 pm  Out on a limb: effects of substrate compliance on the gait mechanics of common marmosets (Primates: Callithrix jacchus). Chadwell BA*, Northeast Ohio Medical University (NEOMED); Stricklen BM, Kent State University; Young JW, Northeast Ohio Medical University (NEOMED)
Abstract: The arboreal “fine-branch niche” - the zone at the edge of canopies where supports are narrow and compliant - has been cited as fundamental in adaptive scenarios of primate locomotor evolution. However, though previous studies have evaluated the influence of substrate breadth on primate locomotor performance, the influence of substrate compliance has been mostly unexamined. We investigated how substrate compliance affects the gait kinematics of marmosets (Callithrix jacchus; n = 2 males) moving over simulated arboreal substrates. As small-bodied quadrupeds with limited grasping abilities, marmosets are a reasonable analogue for ancestral stem primates, and a good model for testing the performance demands of fine-branch locomotion. We used 3D-calibrated video to quantify marmoset locomotion over a 4m long trackway constructed of differently-sized poles (5, 2.5 and 1.25cm), analyzing a total of 120 strides. Depending on experimental condition, the central 0.6m of the trackway was either immobile or mounted on compliant foam blocks. Marmosets predominantly used asymmetrical gaits (i.e., gallops and half-bounds), using symmetrical gaits in only 8% and 15% of strides on the stable and compliant substrates, respectively. Marmosets responded to substrate compliance by increasing contact durations (i.e., greater forelimb and hindlimb duty factors) and more evenly distributing hindlimb contacts (i.e., relatively longer lead durations). Together, variation in duty factor and hindlimb lead spacing explained nearly 60% of the variation in compliant substrate displacement over a stride, suggesting a direct performance advantage to these kinematic changes. Overall, our results show that compliant substrates can exert a significant influence on primate arboreal locomotor performance. Substrate compliance, and not just substrate breadth, should be considered a critical environmental variable in models of primate locomotor evolution. Supported by NSF BCS-1126790 and NEOMED.

LOC6-5  12:30 pm  Quantifying trabecular bone density and anisotropy in the primate lower ilium with implications for reconstructing locomotor loading. Shapiro D*, Rutgers, The State University of New Jersey
Abstract: Understanding the relationship between bony pelvic morphology and locomotor behavior has long been of interest to evolutionary anthropologists seeking to use the fossil record to reconstruct our lineage's transition to bipedalism. While early work focused on morphological variation in the external anatomy of the innominate, recent technological advances have permitted the examination and quantification of the internal trabecular architecture of this skeletal element. As trabecular bone is understood to change during life in response to mechanical loading, it is first crucial to characterize the cancellous architecture of extant primates of known locomotor mode in order to build a comparative sample for later work on fossil primates. One of the issues here is that pelvic loading (particularly in non-human primates) is not well understood. Recent experimental work has suggested potential loading regimes for the primate lower ilium (e.g., axial compression, bending, and torsion), which may serve as hypotheses to be tested via trabecular bone analyses (i.e., each should produce different, predictable patterns of trabeculae). The aims of this study were to quantify bone volume fraction and degree of anisotropy (which together explain greater than 80% of mechanical properties of bone) in the lower ilium of 31 extant primates (six species) using high-resolution X-ray CT scans, and to test hypotheses about relationships between loading regime/locomotor mode and these trabecular variables. These results will be novel, as primate iliac trabecular architecture has not previously been quantified at such a fine-grained resolution, and will have important implications for future work using cancellous bone in reconstructing locomotor behavior in fossil primates. This project was funded by a Wenner-Gren Foundation Dissertation Fieldwork Grant, a Bigel Endowment Grant, a Zelnick Research Award, and the Center for Human Evolutionary Studies at Rutgers University.

LOC6-6  12:45 pm  The stability-mobility conflict in the primate thumb. Vereecke EE*, University of Leuven; Vanhoof M, University of Leuven; Szu-Ching L, University of Kent; Kerkhof F, University of Leuven
Abstract: Primates use their thumb both in manipulation and locomotion leading to conflicting mechanical demands. High thumb mobility is required for manipulative skills while stability and strength are important in locomotion. In this study, we want to investigate how the anatomy of the primate thumb is adapted to this stability-mobility conflict. We focus on two highly dexterous catarrhines, the bonobo (Pan paniscus) and the olive baboon (Papio anubis), with a distinct locomotor, postural and prehensile behavior leading to a different thumb use and load. We obtained fresh-frozen cadaveric hand and forearm specimens via collaboration with the Royal Zoological Society of Antwerp (RZSA), Belgium (5 bonobos; Bonobo Morphology Initiative) and the CNRS, France (3 baboons). A detailed dissection was performed of each specimen with quantification of soft-tissue parameters (e.g. muscle mass and length, fascicle length, ligament dimensions). Each specimen was CT scanned and 3D surface models were created for the trapezium and first metacarpal (MC1) using Mimics software to assess the geometry of the trapeziometacarpal (TMC) joint. Bonobos and olive baboons have a fully opposable thumb, which is reflected in the well-developed thumb musculature. Bonobos have a saddle-shaped TMC joint allowing a wide range of motion, while the prominent volar beak and high joint curvature provide stability. In addition, five ligaments surround the TMC joint, acting as passive stabilizers. We believe that this anatomical configuration offers the required stability for forceful gripping during climbing and suspensory locomotion. Thumb loading is relatively low in baboons, being restricted to occasional climbing and palmigrady. Despite the cylindrical-shaped TMC joint, opposability is maintained by the relatively long length of the thumb. We want to thank Drs. Nauwelaerts, Stevens, Pereboom (RZSA), and Berillon (CNRS) for giving us access to the primate specimens.

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