Whole-body kinematics and 3D targeting of foot contacts in unrestrained climbing stick insects (Carausius morosus)

Theunissen L, Dürr V (2011)
In: Proc. Göttingen Neurobiol. Conf. T21-12C.

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Keywords
Stick insects appropriately coordinate their legs when moving in a complex environment. The six legs are coordinated not only temporally ; but also spatially. Appropriate touch-down of each foot is crucial for stable climbing in the canopy. Cruse (1979) found that stick insects adjust the touch-down position of a hind leg according to the current position of the ipsilateral middle leg. This "targeting mechanism" was also found for the middle legs that touch-down in close vicinity to the front legs. As yet ; these findings concern coordination on a horizontal platform ; whereas in their natural environment ; stick insects need to coordinate their legs in a three-dimensionally structured canopy.Here ; we analysed three-dimensional targeting of unrestrained climbing stick insects on a parcours with steps of different height. Three step heights and an additional flat walkway (as control) were used to reveal differences between normal walking and different levels of climbing complexity. The walking behaviour of stick insects across the low step (8 mm) was close to normal walking. A step height of 24 mm could be climbed by means of a single higher foot step. In the highest condition (48 mm) stick insects typically required several foot contacts on the vertical aspect of the step. Apart from their legs ; stick insects adjusted their body posture also by use of thoracic joints. A motion capture system yielded three-dimensional positions of retro-reflective markers attached to the stick insect legs ; thorax and head. The movement of each body segment and each one of the six legs ; was reconstructed by means of kinematic calculations based on marker positions and anatomical measurements. The measured touch-down positions of hind and middle legs were expressed relative to the positions of the corresponding anterior legs. For this ; both external ; world-centred coordinates and relative ; body-centred coordinates were used. The touch-down positions of the middle legs were located posteriorly and medially to the concurrent front leg position. The median Euclidian distance for steps during horizontal walking is 10.1mm (SD ±7.1mm). Euclidean distances of foot contacts on vertical surfaces of the setup were in a similar range (11.3 ±7.5mm). Detailed analysis of the x- ; y- and z-coordinates revealed a similar "targeting mechanism" during climbing as proposed by Cruse(1979) for level walking. In comparison ; targeting in hind legs was more precise ; exhibiting a median Euclidian distance of 4.5mm (SD ±7.3mm) to the concurrent position of the ipsilateral middle leg. On vertical surfaces ; the Euclidian distances were slightly larger than during level walking (vertical: 6.2 ±6.9mm ; horizontal: 4.2 ±6.7mm). In both middle and hind legs ; the likelihood distributions of relative touch-down positions were more widespread for contacts onto vertical surfaces than for contacts onto horizontal surfaces. Finally ; the x- ; y- and z-coordinates of the body-centred touch-down positions of hind legs were similar during horizontal walking and climbing. This suggests that ; indeed ; targeting takes place in three-dimensional space.
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Proc. Göttingen Neurobiol. Conf.
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Göttingen
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Theunissen L, Dürr V. Whole-body kinematics and 3D targeting of foot contacts in unrestrained climbing stick insects (Carausius morosus). In: Proc. Göttingen Neurobiol. Conf. 2011: T21-12C.
Theunissen, L., & Dürr, V. (2011). Whole-body kinematics and 3D targeting of foot contacts in unrestrained climbing stick insects (Carausius morosus). Proc. Göttingen Neurobiol. Conf., T21-12C.
Theunissen, L., and Dürr, V. (2011). “Whole-body kinematics and 3D targeting of foot contacts in unrestrained climbing stick insects (Carausius morosus)” in Proc. Göttingen Neurobiol. Conf. T21-12C.
Theunissen, L., & Dürr, V., 2011. Whole-body kinematics and 3D targeting of foot contacts in unrestrained climbing stick insects (Carausius morosus). In Proc. Göttingen Neurobiol. Conf. pp. T21-12C.
L. Theunissen and V. Dürr, “Whole-body kinematics and 3D targeting of foot contacts in unrestrained climbing stick insects (Carausius morosus)”, Proc. Göttingen Neurobiol. Conf., 2011, pp.T21-12C.
Theunissen, L., Dürr, V.: Whole-body kinematics and 3D targeting of foot contacts in unrestrained climbing stick insects (Carausius morosus). Proc. Göttingen Neurobiol. Conf. p. T21-12C. (2011).
Theunissen, Leslie, and Dürr, Volker. “Whole-body kinematics and 3D targeting of foot contacts in unrestrained climbing stick insects (Carausius morosus)”. Proc. Göttingen Neurobiol. Conf. 2011. T21-12C.
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