1Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, 2Department of Biomedical Engineering, Stony Brook University, 3Department of Biomedical Engineering, Stony Brook University, 4Department of Biology, University of California Riverside, 5Department of Anatomical Sciences, Stony Brook University
Saturday Morning, Alexander's
To reconstruct the activity levels of hominins living in the past, anthropologists infer functional loading history from the morphology of limb bone remains. It is assumed that, during life, loading had a positive (anabolic) effect on bone structure that largely overruled other influences such as genetic background. In this study, we investigate the relative influence of genetic background and functional loading on limb bones using four genetically distinct lines of mice that had been selectively bred for high levels of voluntary wheel running. Growing males from each line were either allowed or denied access to wheels for two months. At the end of the experiment, femoral morphology was assessed using micro-CT at two cortical sites (mid-diaphysis, distal metaphysis) and one trabecular site (distal metaphysis). We found that genetic background (line) had a highly significant effect on all cortical morphological indices analyzed and most trabecular indices. Voluntary wheel running had only a minor influence on bone morphology, and the functional response did not result in enhanced structure. In the mid-diaphysis, running caused significant endocortical expansion and thinning of the cortical walls, and an almost significant reduction in bone area. Thinner cortices were also observed in the metaphyses of runners. Trabecular morphology was unaffected by running. These results underscore the strong influence of genetic background on limb bone structure and the complexity by which mechanical stimuli may cause alterations in it. This study suggests that prudence is necessary when limb bone remains are used to glean information about ancient hominin activity.
Grant sponsors: LSB Leakey Foundation, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Science Foundation.