KIRKTON, S.D.*; HARRISON, J.F.: Effects of Body Size Changes on Jumping Performance in the American Locust
Allometric changes in body size during development can cause dramatic ecological and physiological consequences. In the American locust (Schistocerca americana) body mass increases continually during development, while the femur mass changes discontinuously — increasing only between instars. We investigated how this growth might affect locomotory performance both between instars and within an instar. Individuals of known ages within second, fourth, sixth instars and adults were jumped for 20 minutes or until exhaustion. We measured jump frequency and distance and calculated power output. Within an instar, older animals fatigued more rapidly. The reduced jumping performance for animals later in the instar was not due to muscle loading (as the ratios of femur mass to body mass were constant through each instar) or increased power output by the muscle of older animals (mass specific power outputs were lower in older animals). The reduced performance may be due to increased femoral muscle growth compressing trachea and hence reducing oxygen delivery. Across instars, older/larger animals fatigued more rapidly during jumping. The reduced endurance across instars was again not due to muscle loading (older animals have greater femur to body mass ratios) or increased power output of the muscle (smaller juveniles have greater power outputs). We further investigated if older animals fatigued more rapidly because of poor oxygen delivery by jumping animals in artificial atmospheres ranging from 5 kPa to 60 kPa PO2. Older/larger juveniles had reduced endurance in hypoxic atmospheres compared to younger/smaller juveniles suggesting that increases in body size may reduce oxygen delivery. In adults, the first minute jump rate increased in hyperoxic atmospheres, but endurance was not affected by hyperoxia.
