S1-3.1 Jan. 5 Active Tail Stabilizes Rapid Vertical Running in Geckos JUSUFI, A.**; GOLDMAN, D.I.; FULL, R.J.; Univ. of California, Berkeley firstname.lastname@example.org
Animals running vertically must respond rapidly to gaps, obstacles and slippery surfaces to negotiate complex scansorial terrains. We challenged geckos (Cosymbotus platyurus; n=7) with three vertical surfaces that produced different degrees of foot slippage. Vertically running geckos held their tails off the wall when footholds on the high traction surface were secure. We induced foot slippage by placing a low traction horizontal patch in the vertical track. Foot slippage initiated a tail reflex that prevented catastrophic pitch-back. C. platyurus, running on a vertical high traction surface, began to move their tail tip towards the wall approximately 28±6 ms after fore foot contact with the low traction patch. Tail tip wall impact occurred within 47±11 ms after slip initiation. Geckos running up a bead-covered force platform that continuously resulted in moderate foot slippage always kept their tails in contact with the wall. Tail tip force on the beaded substrate of intermediate traction increased further 17±5 ms after the fore foot contacted the low traction patch. The tail reflex induced a stabilizing impulse moment (0.007±0.004 mN-m-s) that counterbalanced the natural pitch-back moment (0.012±0.007 mN-m-s). Geckos confronted with large, repeated slips tolerated pitch-back by placing their tail in a posture where the last 2/3 of the tail pressed against the wall similar to that of a bicycle’s kickstand. Even during these extreme perturbations tailed animals never fell off the wall. In contrast, catastrophic pitch-back resulting in falling was observed in nearly 20% of animals that had naturally lost their tails. In over 60% of the trials, tailless animals failed to cross the slippery patch, whereas less than 15% of the tailed animal trials were unsuccessful.