Behaviour 2019
Tardigaits: Coordination and neuromodulation of locomotive gait in tardigrade
Steven Munoz1, Zainab Tanvir1, Andrew Spence2, Simon Wilshin3, Daphne Soares1, Gal Haspel1. 1New Jersey Institute of Technology, Newark, New Jersey, United States; 2Temple university, Philadelphia , Pennsylvania, United States; 3The Royal Veterinary College, Hertfordshire, , United Kingdom

Animals move deliberately through their environment, and much of their body plan and physiology are dedicated to locomotion. The 3mm long tardigrades use eight short and clawed legs for locomotion. Although they are known for centuries and famous for their hardiness, their locomotive leg coordination is unknown. We quantified the locomotive patterns of two species while swimming and walking. We determined the gaits of H. exemplaris (semi-terrestrial) and D. dispar (aquatic) by video microscopy and kinematic analysis to compare them to known eight-legged gaits. In both species, walking is more coordinated with clean alternation of all eight limbs, and in swimming the hind pair of limbs are not involved. We also tested whether, as in other animals, gait selection is mediated by monoaminergic neuromodulators. Bath application of serotonin induces swimming, while dopamine induces crawling in tardigrades. We describe, for the first time, the unique eight-legged gait of tardigrades and its neuromodulatory control. These insights could be used to inspire stable multi-legged robots and prompt further research on tardigrades to determine the neural basis of their locomotion.