Meeting Abstract

45.7  Tuesday, Jan. 5  Anticipation of obstacles in soft bodied terrestrial locomotion VAN GRIETHUIJSEN, L.I*; TRIMMER, B.A.; Tufts University; Tufts University linnea.van_griethuijsen@tufts.edu

Animals moving in complex environments must identify objects in their path and know the relative position of the object to their limbs. For soft bodied locomotion this is a particularly difficult problem because tissues can deform and proprioceptive information may not predict body position. In the absence of remote sensing such as vision or sonar, objects must be detected by touch. Object avoidance could be achieved by gathering mechanosensory information in leading parts of the body and then using it to adjust movements in the following limbs. Another strategy is to respond directly to local touch without any need for anticipation. Manduca sexta caterpillars can negotiate small objects in their path by stepping on top of them. During such a step, the maximum upward velocity of the approaching leg in the first quartile of the swing phase was much higher than that of a normal step (45 trials from 5 animals. Max. y velocity: obstacle: 0.25 cm/s, step: 0.12 cm/s, p<0.0001), indicating that information about the upcoming obstacle was present. In some cases, when the proleg was further away from the obstacle at lift off, there was a second velocity peak during the later part of the swing phase. The distance from the obstacle at which this adjustment occurred was significantly reduced when the sensory hairs on the prolegs were experimentally cut short (0.21 cm in intact animals (45 trials), 0.18 cm short-hair animals (58 trials), p=0.043). In this subset of the data, the first peak of upward velocity was still significantly higher than in a normal step both in intact (p=0.001) and short-hair animals (p<0.0001). These results suggest that Manduca can use intersegmental information to anticipate objects and that it also fine-tunes movements using local touch sensors.