Meeting Abstract
After losing legs, cockroaches can still run, showing phenomenal fault tolerance. We hypothesized that this remarkable robustness is likely to increase the metabolic cost of locomotion. We tested this hypothesis for cockroaches, Blaberus discoidalis, running on a treadmill. We used open-flow respirometry to measure steady-state oxygen consumption at a range of speeds (2.5-12.5 cm/s) and video cameras to determine stride frequency and ground contact time. We compared cost for individuals missing one and two middle legs with intact controls. Animals maintained steady-state locomotion for at least 5 min. For all conditions, oxygen consumption and stride frequency increased with speed, whereas contact time decreased. Losing one leg increased cost by 8-30%, whereas the loss of two legs increased cost by 27-76% relative to the 6-legged condition. Middle leg loss showed no gait change, but resulted in an increase in stride frequency and a decrease in leg contact compared to intact controls. Middle leg loss destabilized animals in roll and caused animals to take more, smaller steps than intact animals to maintain the same speed. Correcting for the faster rate of force generation in animals with reduced leg number by calculating the cost per stride resulted in no significant differences, but animals with two middle legs missing did show significantly greater ground contact costs. Cockroaches exhibit fault tolerance, but at a metabolic cost.
