The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Differentiation of bone functional adaptations in the forelimb and hind limb


1Institute for Human Evolution, University of the Witwatersrand, 2Department of Anthropology, Indiana University, 3Department of Anatomical Sciences, Stony Brook University, 4Department of Biomedical Engineering, Stony Brook University

Saturday 1:45-2:00, Ballroom C Add to calendar

Documented links between specific locomotor behaviors and bone functional adaptations are rare, but are often assumed when reconstructing activity patterns of extinct primates. Turning, or changing direction, is a major component of locomotor repertoires, and may ultimately reflect habitat complexity. Here we study bone functional adaptations of forelimb and hind limb diaphyses in response to turning. We ask whether turning elicits a reponse in both the humerus and femur, whether one bone exhibits a greater response than the other, and whether responses support predictions based on external forces and kinematics associated with turning.

At 4 weeks postnatal, female C57BL/6J mice (n = 35) were introduced to one of three living conditions for a continuous 4 month period: custom-designed cages accentuating either turning (condition 1) or linear locomotion (condition 2), or standard cages permitting normal activity (control group). Instantaneous focal sampling was used to collect daily behavior frequencies throughout this period. After 4 months, mice were euthanized, limb bones extracted, and diaphyseal structure quantified using microfocus CT scanning. Analysis of standard cross-sectional geometric properties was performed, and interpreted with respect to activity profiles.

Both experimental groups exhibited lower activity levels than the control group. Despite their comparatively depressed activity levels, experimental groups exhibited predicted responses (e.g., higher turning frequencies were associated with more mediolaterally elliptical cross sections). Linear and control mice differed less often in many properties, while turning mice were often most distinctive. These data suggest terrestrial habitat complexity may not be trivial in importance compared to arboreal habitat complexity.

Financial support for the experiment was provided by the NYCOM Office of Research.

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