Genetic and Physiological Bases of Wheel-Running Behavior

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Animals frequently respond to changes in environmental conditions by altering their behavior. This common observation has led to the hypothesis that behavior evolves first, prior to changes in underlying aspects of morphology, physiology, or biochemistry. Artificial selection experiments will be used to test this hypothesis with respect to voluntary wheel-running behavior of randombred laboratory mice. Replicated within-family selection on amount of wheel-running during the 5th and 6th days of exposure to activity wheels will be used to produce two high- and two low-selected lines, while maintaining two unselected control lines, each of 10-12 breeding pairs. As lines diverge genetically in wheel-running behavior, they will be compared with regard to a series of possibly correlated locomotor behaviors as well as physiological characteristics that are hypothesized to partly determine capacities for sustained locomotor activity. Possibly correlated behaviors to be tested include several components of open-field activity, maximal sprint running speed, and swimming endurance. Physiological traits to be measured include maximal (VO2max) and basal (BMR) rates of oxygen consumption, hematocrit and blood hemoglobin content, thyroid hormone levels, heart, gastrocnemius muscle, and liver masses, and key indicator enzymes for both aerobic (oxidative) and anaerobic glycolytic capacities at the cellular level. Correlated responses to selection will allow quantification of genetic correlations between behaviors and between behavior and physiology. Results will have significance for the understanding of animal and human behavior, genetics, evolution, and physiology, including the interrelationships of health and well- being, voluntary activity patterns, and innate exercise capacities.