Effects of ingesting large prey on the kinematics of rectilinear locomotion in Boa constrictor.

Large and stout snakes commonly consume large prey and use rectilinear crawling; yet, whether body wall distention after feeding impairs rectilinear locomotion is poorly understood. After eating large prey (30-37% body mass), all Boa constrictor tested could perform rectilinear locomotion in the region with the food bolus despite a greatly increased distance between the ribs and the ventral skin that likely lengthens muscles relevant to propulsion. Unexpectedly, out of 11 kinematic variables, only two changed significantly (P<0.05) after feeding: cyclic changes in snake height increased by more than 1.5 times and the longitudinal movements of the ventral skin relative to the skeleton decreased by more than 25%. Additionally, cyclic changes in snake width suggest that the ribs are active and mobile during rectilinear locomotion, particularly in fed snakes, but also in unfed snakes. These kinematic changes suggest that rectilinear actuators reorient more vertically and undergo smaller longitudinal excursions following large prey ingestion, both of which likely act to reduce elongation of these muscles that may otherwise experience substantial strain.

Evidence for multi-scale power amplification in skeletal muscle.

Many animals use a combination of skeletal muscle and elastic structures to amplify power output for fast motions. Among vertebrates, tendons in series with skeletal muscle are often implicated as the primary power-amplifying spring, but muscles contain elastic structures at all levels of organization, from the muscle tendon to the extracellular matrix to elastic proteins within sarcomeres. The present study used ex vivo muscle preparations in combination with high-speed video to quantify power output, as the product of force and velocity, at several levels of muscle organization to determine where power amplification occurs. Dynamic ramp-shortening contractions in isolated frog flexor digitorum superficialis brevis were compared with isotonic power output to identify power amplification within muscle fibers, the muscle belly, free tendon and elements external to the muscle tendon. Energy accounting revealed that artifacts from compliant structures outside of the muscle-tendon unit contributed significant peak instantaneous power. This compliance included deflection of clamped bone that stored and released energy contributing 195.22±33.19 W kg-1 (mean±s.e.m.) to the peak power output. In addition, we found that power detected from within the muscle fascicles for dynamic shortening ramps was 338.78±16.03 W kg-1, or approximately 1.75 times the maximum isotonic power output of 195.23±8.82 W kg-1. Measurements of muscle belly and muscle-tendon unit also demonstrated significant power amplification. These data suggest that intramuscular tissues, as well as bone, have the capacity to store and release energy to amplify whole-muscle power output.

Walking on chains: the morphology and mechanics behind the fin ray derived limbs of sea-robins.

Fish fin rays (lepidotrichia) are typically composed of paired and segmented flexible structures (hemitrichia) that help support and change the shape of the fins to affect water flow. Yet, marine ray-finned fish that are members of the family Priontinae (sea-robins) have specialized pectoral fin rays that are separated from the fin and used as limbs to walk along the seafloor. While previous kinematic studies have demonstrated the use of these specialized fin rays as walking appendages, there is little information on how the morphology of the 'walking rays' and associated musculature facilitate underwater walking. Here, we examine the musculoskeletal anatomy of the walking and pectoral fin rays in the striped sea-robin Prionotus evolans and compare the mechanical properties of the rays with those of the smaller northern sea-robin Prionotus carolinus We aimed to determine what structural modifications in the walking rays allow them to function as a supportive limb. We found enlarged processes for muscle attachment, bone extensions that brace the hemitrich articulations, and reduced flexibility and increased second moment of area along the rostro-caudal bending axis in the rays used for walking. This novel limb design may have promoted the benthic foraging behavior exhibited by these species by uncoupling locomotion and feeding.