Meeting Abstract

122.3  Tuesday, Jan. 7 14:00  Developmental plasticity of locomotor morphology in an animal model for the quadrupedal-to-bipedal transition FOSTER, AD; University of Arizona adfoster@email.arizona.edu

The evolution of bipedalism in the human lineage involved significant changes in musculoskeletal morphology to accommodate the locomotor shift from quadrupedalism to upright walking. However, the evolutionary mechanisms that underpin this shift remain unclear. This study seeks to better understand how this transition might have occurred by taking advantage of the inherent plasticity of musculoskeletal tissues. Because bone adapts to the predominant forces placed upon it, this study explores the relationship between bipedal loading patterns and skeletal morphology during growth and development. A novel method was used to experimentally induce a locomotor shift during ontogeny in an animal model for the quadrupedal-to-bipedal transition. Rats (n=10) were placed in a custom harness system mounted on a treadmill which allowed for bipedal locomotion over 60 minute periods, 5 days a week, for three months. The harness imparts an adjustable upward force on the torso which alters the load experienced by the hindlimbs. A quadrupedal control group (n=10) was exercised for the same period. Micro-CT scans were taken every third week to track skeletal changes. At the end of the experiment, bipedal rats had significantly greater growth in relative hindlimb length (p<0.05) and significantly larger distal and proximal joint dimensions (p<0.05). These findings suggest that initial changes consistent with the evolution of bipedal traits in the human lineage can occur through developmental plasticity in response to bipedal walking and may provide a blueprint for which traits may have occurred first in the earliest hominins. Funding was provided by: NSF (BCS-1153863), Force & Motion Foundation, and the University of Arizona.