Meeting Abstract

93.5  Monday, Jan. 6 14:30  Stability of cockroaches running rapidly on rigid rods HUNT, N/H*; MOON, H/S; HAMMOND, A; BURNETT, N/P; PRITCHARD-BERMAN, M; FULL, R/J; University of California, Berkeley; University of California, Berkeley; University of California, Berkeley; University of California, Berkeley; University of California, Berkeley; University of California, Berkeley nathaniel.hunt@berkeley.edu

Running on branches or rods represents a challenge relative to flat surfaces because stance width and stability can be limited. Cockroaches (Periplaneta americana) are highly adept arboreal locomotors, capable of fast running speeds on large branches to small stems. We investigated rapid running on horizontal rods ranging in diameter from 3.2-38.1mm. Cockroaches ran using both an upright orientation on top and an inverted orientation underneath the rods. They exhibited a gait transition from upright to inverted running as rod diameter was decreased with both modes being present at intermediate diameters. We defined gait transition frequency as the proportion of trials that animals transitioned from upright to inverted running. Gait transition frequency did not change abruptly over rod sizes, but gradated with a transition frequency inversely proportional to rod diameter. Surprisingly, animals ran nearly equally fast upside down on the smallest rod (39.0±12.2cm/s) as they did upright on the largest rod (32.9±11.6cm/s). As rod diameter was decreased below 12.7mm, sprawl angle became constrained, eventually violating conditions for passive mechanical stability and leading to a fixed point destabilization of upright running. With the presence of a transition deterrent below small rods, animals used sensory feedback to consistently maintain an upright orientation, indicating that the transition was a choice, not a necessity.