Comparative Musculoskeletal Adaptive Plasticity

Ectothermic reptiles have relatively more robust limb bones than mammals and birds, which result in higher skeletal safety factors in ectotherms. We hypothesize that the relative gracility of mammalian and avian limb bones is enabled by a more sensitive mechanobiological response to changes in habitual mechanical loading – increasing bone mass when needed instead of the ectothermic approach of carrying around extra bone tissue all the time. Current dogma in skeletal mechanobiology emphasizes the role of bone matrix-embedded osteocytes in forming a mechanosensitive syncytium that influences osteoblastic bone formation in response to changes in habitual loading. Do different amniote taxa (non-avian reptiles, birds, marsupials & eutherians) vary in their skeletal response to changes in skeletal loading? Are differences in the sensitivity of this response related to inherent differences in osteocyte network organization, the potential for the osteoblast cell population to form bone, or systemic physiological factors? 

We address these questions through biomechanical measures to determine in vivo bone strains in the skeleton during both locomotion and applied axial compression loading. We conduct applied loading studies to induce controlled loads on the tibia that are physiological in orientation, but greater in magnitude than those encountered in vivo. We measure the skeleton’s response to these loads in the different taxa through transcriptomic measures (qRT-PCR, RNA-Seq), changes in cell behavior (histology) and bone structure (computed tomography).