Investigating the function of the caudofemoralis longus muscle and musculoskeletal plasticity in American alligators (Alligator mississippiensis) (919.9)

The CFL ‐ a major retractor/medial rotator of the thigh ‐ is substantial in reptiles with a sprawling gait and long tail. The CFL originates on the transverse processes and chevrons of the caudal vertebrae and inserts on the fourth trochanter of the femur. Evolutionary changes to the hindlimb/tail module in archosaurs have been ascribed to a reduced role of the CFL in terrestrial locomotion, but no alteration of CFL function has been attempted. To discern its role in locomotion, and investigate muscular plasticity, we used bilateral tenotomy to deactivate the CFL in juvenile alligators (Mb=180±30g, SVL=213±28mm). After surgery, we found no significant differences between experimental animals and sham‐operated controls (n=6 each) in average speed, stride length or hip height during walking, when filmed on a level grid trackway. Eight months post‐surgery, CFL wet mass and fiber length were significantly reduced, by 23% and 13% respectively, in experimental animals compared to controls (n=12 per group). This suggests that the contribution of the CFL to hindlimb stance/movement is limited, or compensatory mechanisms are present in the hip during slow and steady locomotion. Further study of muscle fiber phenotype and bone growth/remodeling following tenotomy will provide insight into the nature of plasticity associated with disuse atrophy, and help elucidate the role of musculoskeletal strain in evolutionary transformations of the hindlimb and tail locomotor modules in archosaurs. Grant Funding Source : Supported by: Research Initiative for Scientific Enhancement (RISE), National Institutes of Health