Date of Award

12-2017

Document Type

Thesis

Degree Name

Master of Science in Biology

Department

Biology

First Reader/Committee Chair

Horner, Angela

Abstract

Variations in skeletal morphology have often been used to interpret an organism’s overall activity level when direct observation is not possible. Although skeletal change in response to exercise is well documented, the skeleton’s response to mechanical loading is modulated by several factors (e.g. age, hormones, sex). Additionally, variation in skeletal morphology is partially a result of genetic variation, which is rarely accounted for in inferences of locomotor activity from skeletal remains. However, blood flow to long bones serves as a proxy for bone metabolic activity, which can be used to infer locomotor activity. Long bones receive blood from three sources, with the nutrient artery supplying the bulk of total blood volume in mammals (50-70%). The size of the nutrient artery can be estimated from the dimensions of the nutrient canal, which is present long after the vascular tissue has degenerated. The literature on nutrient canals is sparse, with most studies consisting of anatomical descriptions from surgical proceedings, and only a few studies investigating the links between nutrient canals and physiology or behavior. Moreover, no study to date has accurately modelled the size and shape of the nutrient canal. For this study, mice from an artificial selection experiment for high voluntary wheel-running behavior were used. High Runner mice from the experiment are known to differ in both metabolic and locomotor activity, with mice from HR lines having increased VO2max and increased voluntary wheel-running behavior when compared to controls. 137 femora from mice of the 11th generation of this selection experiment were µCT scanned. Three-dimensional reconstructions of nutrient canals were measured for minimum cross-sectional area (an index of blood flow). Nutrient canals varied far more in number and shape than prior descriptions would indicate. Canals adopted non-linear shape and pathing as they traversed from the periosteum to the medullary cavity, occasionally even branching within the cortical bone. Additionally, mice from both HR and control lines had more than four nutrient canals per femur. Mice from HR lines had significantly larger nutrient canal area than controls, which was not the result of an increase in the number of nutrient canals, but rather an increase in their average size. This study demonstrates that mice with an evolutionary history of increased locomotor activity and metabolic rate have a concomitant increase in the size of their nutrient canals.

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