Meeting Abstract
The skeleton is phenotypically plastic and remodels in response to changes in the mechanical demands placed upon it. Natural selection acts upon the genetic bases for basic skeletal form and the sensitivity of these adaptive mechanisms to load. Here, we take preliminary steps toward comparing functional adaptive plasticity in the limb skeleton of different tetrapod taxa, using the chukar partridge and lab mouse as tractable starting points. We first assessed bone strains in the tibotarsus (TBT) and tibia during treadmill running. Based upon a hind limb loading technique for rodents, we assessed the strains induced in the TBT/tibia during axial compression. Loading studies were conducted in which both taxa received cyclic compression hind limb loading (216 cycles/day, 5 days/wk) to induce strains on the medial bone surface 2.5x the peak treadmill strains. The skeletal response to load was assessed by micro-computed tomography and histomorphometry. The loaded mouse tibia (n=6) was greater in cortical area (+4%) and second moments of area (+6-8 %) than the non-loaded, contralateral tibia. Following loading in the chukar (n=4), the maximum second moment of area was greater in the loaded TBT (+2%) and there were trends for decreased cortical area and increased marrow area in the loaded TBT. The relatively small changes in bone geometry in both taxa did not result in measurable effects by histomorphometry, except that applied load suppressed endosteal bone deposition in the loaded chukar TBTs. The results of these studies preliminarily suggest that different mechanisms may regulate the long bone response to increased mechanical load in these taxa. While the loaded bones of both taxa likely become stiffer in response to load, the murine tibia increases overall bone volume following load, while the chukar TBT becomes stiffer without increasing bone mass.
