HARTY, T.H.*; ROBERTS, T.J.: Mighty Mice: Amazing Jumping Power from the Pacific Jumping Mouse

Previous studies have revealed unique morphological and physiological specializations that enable frogs and insects to power spectacular jumps. To determine whether jumping mammals can achieve similar levels of performance, we examined the jumping ability of a small rodent, the Pacific jumping mouse (Zapus trinotatus). Observations from 20th-century naturalists report that Z. trinotatus are incredible jumpers for their size (approx. 25g), achieving heights up to 1 meter and distances of 2 meters. We trapped Z. trinotatus locally and maintained them in the lab. To calculate power outputs, we filmed the mice with high-speed video during standing jumps. The maximal jump distances elicited in the lab were 0.46m vertically and 0.80m horizontally. Peak takeoff velocities measured from high-speed video were in excess of 3.0 m/s. Using takeoff velocity, takeoff angle, and center-of-mass measurements, we calculated peak power outputs of 75 W/kg body mass. We assumed this power was developed primarily by hindlimb muscles; video observations indicate that forelimbs do not contribute significantly to jumping. Using measurements of the total mass of dissected hindlimb musculature, we estimated peak power outputs during jumping in excess of 1300 W/kg total hindlimb muscle mass. This remarkably high power output exceeds all published values for isolated rodent hindlimb muscle, which are no higher than 400 W/kg hindlimb muscle. Future work will explore three possible explanations for the high power output during jumping in Z. trinotatus: (1) there is a significant contribution from elastic mechanisms, (2) back and trunk muscles are transferring power to assist the jump, and/or (3) the hindlimb muscles have exceptional contractile properties.