Plastic and evolved morphological responses of the hind limb skeleton to mechanical loading in mice

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Skeletal morphology is determined by a combination of genetic background and phenotypic plasticity induced by mechanical loading. The changes in limb bone morphology associated with locomotor activity through ontogeny and over evolutionary time can provide insight into the mechanisms of adaptation in locomotor systems. Here, a mouse model is used to explore the effects of mechanical loading and locomotor selection on skeletal morphology and phenotypic plasticity. The source of loading (muscular, ground reaction, or combined forces) was found to differentially affect the pattern and rate of mineral apposition at the mid-diaphysis of the femur, and the femoral cross-sectional morphology produced by running locomotion appears to be most influenced by muscular forces. Loading environment also differentially altered the gross shapes of the hind limb bones, and a blending of the influence of ground reaction and muscular forces was observed in the bones of running mice. Finally, artificial selection for increased voluntary running distance resulted in evolved changes in skeletal morphology and the plastic response of bone to mechanical loading. The results suggest regional sensitivity of skeleton to morphological change and inform our understanding of the plastic and evolutionary lability of the skeleton.