Meeting Abstract
Muscle is responsible for an immense array of tasks essential to the function of all animals and integral to permitting vertebrate life to expand and diversify into virtually every niche. One of the most spectacular examples of niche expansion was the water-to-land transition, during which the evolution of terrestrial locomotion placed extraordinary demands on muscles accustomed to powering swimming. Recent work on Polypterus, basal ray-finned fishes that share many traits with stem tetrapods, has shown the importance of morphological changes to musculoskeletal structures for dealing with the locomotor challenges of terrestrialization. However, it is unclear how the neuromuscular control and coordination of their muscles differ during swimming and walking. We assessed muscle activity patterns of both the pectoral fin and body during walking and swimming in Polypterus senegalus using synchronized electromyography and three-dimensional high-speed video. Not only is motor unit recruitment greater during walking than swimming, but the timing of activity of the body muscles is shifted such that peak activity occurs closer to the time of peak body bending. Further, despite an increase in the absolute duration of muscle activity during walking compared to swimming, the proportion of the stroke during which muscle activity is present is smaller in walking than in swimming. Together these data suggest that there is a shift in the relationship between muscle activity and kinematics in walking versus swimming and that the muscles generate forces via more rapid, high-intensity bursts of activity to power walking compared to swimming. These data will significantly advance our understanding of how muscle function can be modulated to perform novel behaviours in the face of changes in demand.
