Energy cost of wheel running in house mice: Implications for coadaptation of locomotion and energy budgets

Laboratory house mice (Mus domesticus) that had experienced 10 generations of artificial selection for high levels of voluntary wheel running ran abou t 70% more total revolutions per day than did mice from random-bred control lines. The difference resulted primarily from increased average velocities rather than from increased time spent running. Within all eight lines (fou r selected, four control), females ran more than males. Average daily runni ng distances ranged from 4,4 km in control males to 11.6 km in selected fem ales, Whole-animal food consumption was statistically indistinguishable in the selected and control lines. However, mice from selected lines averaged approximately 10% smaller in body mass, and mass-adjusted food consumption was 4% higher in selected lines than in controls. The incremental cost of l ocomotion (grams food/revolution), computed as the partial regression slope of food consumption on revolutions run per day, did not differ between sel ected and control mice. On a 24-h basis, the total incremental cost of runn ing (covering a distance) amounted to only 4.4% of food consumption in the control lines and 7.5% in the selected ones. However, the daily incremental cost of time active is higher (15.4% and 13.1% of total food consumption i n selected and control lines, respectively). If wheel running in the select ed lines continues to increase mainly by increases in velocity, then constr aints related to energy acquisition are unlikely to be an important factor limiting further selective gain. Mon generally, our results suggest that, i n small mammals, a substantial evolutionary increase in daily movement dist ances can be achieved by increasing running speed, without remarkable incre ases in total energy expenditure.