Meeting Abstract
Fast movements in articulated animals (e.g., locust jumps), use levers, latches, or locks to pre-load a skeletal structure slowly and then release mechanical energy quickly. But soft animals lack such stiff elastic structures necessary for rapid movements. Some, like cuttlefish or squids, are highly pressurized and deform constant-volume tissues. However, caterpillars, despite being pressure-limited and non-hydrostatic, can perform rapid strikes, jumps, and ballistic rolls. Manduca sexta caterpillars strike defensively at noxious stimuli by whipping their head backwards. We characterized this behavior by using infra-red lasers to provide highly localized and repeatable heat stimuli. The latency between stimulation and beginning of strike suggests that strike movements are coordinated by central neural processing rather than local reflexes. In support of this, latency decreased with repeated stimulation and generalized to other locations consistent with centrally-mediated sensitization. Strikes could be evoked with two successive sub-threshold stimuli at different locations. When stimulated on both sides, strikes were generally towards the first side and rarely reversed direction. The tendency to strike decreased with increasing time intervals between the stimuli revealing a decay in sensitization with a time constant of 0.5 s (general only) to 1.1 s (local and general). High speed movement tracking revealed that strikes followed a broad general trajectory with course correction towards the end for targeting. During a strike the ipsilateral length of the segments decreased monotonically, but the contralateral length changed little initially then expanded suddenly suggesting a store-and-release mechanism. Neural control of these movements is being examined by recording the activity of identified muscles.
