Effect of Thoracic Connective Lesion on Inter-Leg Coordination in Freely Walking Stick Insects

Multi-legged locomotion requires appropriate coordination of all legs with coincident ground contact. Whereas behaviourally derived coordination rules can adequately describe many aspects of inter-leg coordination, the neural mechanisms underlying these rules are still not entirely clear. The fact that inter-leg coordination is strongly affected by cut thoracic connectives in tethered walking insects, shows that neural information exchange among legs is important. As yet, recent studies have shown that load transfer among legs can contribute to inter-leg coordination through mechanical coupling alone, i.e., without neural information exchange among legs. Since naturalistic load transfer among legs works only in freely walking animals but not in tethered animals, we tested the hypothesis that connective lesions have less strong effects if mechanical coupling through load transfer among legs is possible. To do so, we recorded protraction/retraction angles of all legs in unrestrained walking stick insects that either had one thoracic connective cut or had undergone a corresponding sham operation. In lesioned animals, either a pro-to-mesothorax or a meso-to-metathorax connective was cut. Overall, our results on temporal coordination were similar to published reports on tethered walking animals, in that the phase relationship of the legs immediately adjacent to the lesion was much less precise, although the effect on mean phase was relatively weak or absent. Lesioned animals could walk at the same speed as the control group, though with a significant sideward bias toward the intact side. Detailed comparison of lesion effects in free-walking and supported animals reveal that the strongest differences concern the spatial coordination among legs. In free walking, lesioned animals, touch-down and lift-off positions shifted significantly in almost all legs, including legs of the intact body side. We conclude that insects with disrupted neural information transfer through one connective adjust to this disruption differently if they experience naturalistic load distribution. While mechanical load transfer cannot compensate for lesion-induced effects on temporal inter-leg coordination, several compensatory changes in spatial coordination occur only if animals carry their own weight.

Tardigrades exhibit robust inter-limb coordination across walking speeds

Tardigrades must negotiate heterogeneous, fluctuating environments, and accordingly utilize locomotive strategies capable of dealing with variable terrain. We analyze the kinematics and inter-leg coordination of freely walking tardigrades (species: Hypsibius dujardini). We find that tardigrade walking replicates several key features of walking in insects despite disparities in size, skeleton, and habitat. To test the effect of environmental changes on tardigrade locomotor control circuits, we measure kinematics and inter-leg coordination during walking on two substrates of different stiffnesses. We find that the phase offset between contralateral leg pairs is flexible, while ipsilateral coordination is preserved across environmental conditions. This mirrors similar results in insects and crustaceans. We propose that these functional similarities in walking co-ordination between tardigrades and arthropods is either due to a generalized locomotor control circuit common to panarthropods, or to independent convergence onto an optimal strategy for robust multi-legged control in small animals with simple circuitry. Our results highlight the value of tardigrades as a comparative system towards understanding the mechanisms – neural and/or mechanical – underlying coordination in panarthropod locomotion.

Author Correction: Rules for the Leg Coordination of Dung Beetle Ball Rolling Behaviour

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Analysis of Motor Intervention Program on the Development of Gross Motor Skills in Preschoolers

This study aimed to investigate the influence of a structured movement activity program on the motor development of children aged three to five years attending preschool. Participants were 136 preschool students with normative development at three to four years old who lived in the Region of Murcia (Spain). The McCarthy Children’s Psychomotricity and Aptitude Scales (MSCA) battery of psychomotor tests was used to evaluate the motor development profiles of preschoolers before and after the intervention. The sample was divided into two groups: an intervention group (28 students) and a comparison group (108 students). A structured 24 week physical education program was used in the intervention group. An experiential program based on free play was used in the comparison group during the same period. Preschoolers in both groups got a significant improvement in the contrast of pre-intervention with post-intervention in limb coordination. Statistically significant differences in the post-intervention measurements between the comparison group and the intervention group on arm and leg coordination were observed, whereby the intervention group presented higher arm coordination values (F1,134 = 14,389, p = 0.000, η2 = 0.097) and higher leg coordination values (F1,134 = 19,281, p = 0.000, η2 = 0.126) than the comparison group. It was pointed out that structured physical activity education is better educational methodology than free play to achieve adequate motor development in preschool children.

Rules for the Leg Coordination of Dung Beetle Ball Rolling Behaviour

Dung beetles can perform a number of versatile behaviours, including walking and dung ball rolling. While different walking and running gaits of dung beetles have been described in previous literature, little is known about their ball rolling gaits. From behavioural experiments and video recordings of the beetle Scarabaeus (Kheper) lamarcki, we analysed and identified four underlying rules for leg coordination during ball rolling. The rules describe the alternation of the front legs and protraction waves of the middle and hind legs. We found that while rolling a ball backwards, the front legs are decoupled or loosely coupled from the other legs, resulting in a non-standard gait, in contrast to previously described tripod and gallop walking gaits in dung beetles. This provides insight into the principles of leg coordination in dung beetle ball rolling behaviour and its underlying rules. The proposed rules can be used as a basis for further investigation into ball rolling behaviours on more complex terrain (e.g., uneven terrain and slopes). Additionally, the rules can also be used to guide the development of control mechanisms for bio-inspired ball rolling robots.