Meeting Abstract

LBS2.6  Thursday, Jan. 3  Bone to run: Selective breeding and skeletal response to high voluntary activity in mice MIDDLETON, K.M.*; KELLY, S.A.; GARLAND, JR., T.; Cal. State Univ. San Bernardino; Univ. California Riverside; Univ. California Riverside kmm@csusb.edu

The development of mammalian skeletal models has excellent potential as a way to study the mechanisms that underlie morphological evolution. Here we summarize changes in bone size and shape that have resulted from long-term selective breeding for high levels of voluntary wheel-running behavior in house mice. Beginning with a population of outbred, genetically variable Hsd:ICR mice, eight closed lines were established: four non-selected control lines, and four lines up-selected for voluntary running (total revolutions on days 5 + 6 of a 6-day exposure to wheels). A variety of traits have changed in correlation with selection for high wheel running, including nesting behavior, predatory aggression, maximal oxygen consumption, heart mass, muscle mass, and circulating hormone levels (corticosterone, leptin, adiponectin). Several aspects of the appendicular skeleton have also evolved. We have found greater symmetry of hind limb bone lengths in the selected compared to the control lines. We have also found larger femoral heads and wider distal femora, traits that have been suggested in other vertebrates as adaptations for larger load-distributing articular areas at joints. When coupled with experiments involving chronic exercise (long-term access to wheels), these same mice can be used to explore the relative effects of exercise and selective breeding on bone morphological and mechanical properties. We have found significant phenotypic plasticity in mouse hind limb skeletons over relatively short time periods (8 weeks), but diminishing differences between active and sedentary mice at later ages (20 months), which suggests that mechanical benefits of increased anteroposterior and mediolateral diameters present in the younger population may be lost as the animals age. Supported by NSF grant IOB-0543429 to T.G. and NIH grant 1 F32 AR053008 to K.M.M.