Experimental determination of the impact of ambient temperatures on leg coordination, force distribution and body dynamics of fast locomotion in arthropods and 3D numerical modelling of polypedal locomotion.

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Owing to their abundance, practical ubiquity as well as their morphological, behavioural and ecological diversity, arthropods are among the most important ecological actors. However, surprisingly little is known about their terrestrial locomotion, particularly on higher running speeds. Most available studies focus on a few laboratory species, which hardly cover the immense diversity of arthropod body plans. The arthropods’ bodies vary in a multitude of parameters. With regard to locomotion physiology, important parameters are the number of propulsive legs, body size, posture and dynamics, leg design and length, timing and coordination as well as the way leg forces are generated and transferred to the ground. Force generation depends on leg muscle function and limitations thereof. Many of these parameters are limited by ambient temperatures, i.e. a constraint that has hardly been examined so far in the context of locomotion. In previous experiments, I was able to demonstrate the enormous influence of temperatures on all possible kinematic parameters for cockroaches. However, a much larger database on arthropod locomotion is needed. Therefore, I plan to investigate the locomotion of ecologically differently adapted arthropods, like faster and slower runners, with different numbers of propulsive legs, like insects and arachnids, and different body sizes, like juveniles and adults of hemimetabolous species. 3D Kinematics shall be examined for three different temperatures each. The forces transmitted by the legs to the ground and the interactions of these forces with each other determine locomotion dynamics, stability and energetics. I plan to examine ground reaction forces particularly at high running speeds in order to reveal interactions between the legs and passive contributions such as elasticity and damping for many legged designs. To complete the picture, the properties of the legs’ drives, i.e. the muscles, will be mapped using histological methods to determine myosin-ATPase activity and sarcomere lengths, which provide information on contraction speed and maximum muscle stress. For key species, the contraction properties, like the force-length relation and the force-velocity relation of functionally important leg muscles will be investigated directly. The data obtained on kinematics, dynamics and ground reaction forces of arthropod locomotion as well as on muscle contraction properties will be used for the development of a multimodal scalable 3D model. This multifaceted approach combining the examination of locomotion dynamics in fast arthropod species covering a range of locomotor apparatuses and temperature regimes, the examination of muscle properties, and the development of improved numerical models has a high potential to further integrate morphological and functional knowledge, connects function and ecology and may lead to knowledge transfer into technical implementations.