Meeting Abstract
Cockroaches are excellent at traversing dense obstacles in complex terrain. For example, to traverse grass-like beam obstacles, the discoid cockroach often transitions from a pitch mode, in which its body pitches up against the beams, to a roll mode, in which its body rolls to align with the gaps between beams. A recent study in our group found that passive body vibration from oscillatory leg propulsion helped discoid cockroaches and robots traverse grass-like beam obstacles, because the kinetic energy fluctuation helps the body overcome a potential energy barrier to transition from the pitch to the roll mode. Here, we further study the neuromechanics of traversal by measuring active adjustments of head and legs (N = 8 individuals, n = 64 trials). We attached BEEtags to the animal body and head and small markers to the abdomen and legs and used automatic marker and DeepLabCut tracking to obtain ~200,000 digitized points to reconstruct detailed 3-D kinematics. When the animal pitched up against the beams (body pitch angle = 33° ± 15°), its head flexed repeatedly (standard deviation of bending angle = 8.8°). Then, the animal used its two hind legs differentially, extending one while flexing the other (difference in toe distance from body coronal plane between left and right legs = 10 ± 3 mm). These adjustments helped the animal transition to the roll mode into the gap, after which the hind legs pushed to propel forward while the abdomen flexed (standard deviation of flexion angle = 8.5°) to reduce terrain resistance (P < 0.05, ANOVA). A potential energy landscape model with a bendable head suggested that head bending lowered the potential energy barrier to transition from the pitch to the roll mode. Our study showed that active adjustments complement passive mechanics to help animals traverse complex terrain.
