EIDIETIS, L; Univ. of Michigan: Scaling of escape response performance over ontogeny for Rana sylvatica tadpoles

Rana sylvatica tadpoles escape from sit-and-wait predators via tearing from a predator grasp, accelerating so that the predator cannot gain a grasp, or some combination of these. Thus, escape success depends on tail force production. Force production depends on tail muscle mass and on tail size, shape, and kinematics. Morphology was analyzed over ontogeny to estimate relative force production potentials. The proportion of muscle mass to total mass increased with size. Using a simple inviscid model, the added mass contribution to the tail�s force-generating effectiveness is affected by tail size, tail depth, and depth distribution, and this contribution increased with size. Tail kinematics were recorded for escape responses induced by poking. For the first stage of motion, curvature of the tail increased with mass, as did tail motion amplitudes. For a given tail shape, these kinematics would result in increased tail force with increasing size. Therefore, the morphological and kinematic factors combined increased tail force production capability with increased size. If motion is uninhibited by a predator grasp, acceleration performance depends on the ratio between force and resistance, which is mainly inertial. This ratio increased with size. Therefore, based on a force balance, acceleration was also expected to increase with size. As predicted, maximum acceleration and velocity for the first two tail motions of the escape response increased with growth. Thus, with growth, allometric morphological changes and differences in tail motion kinematics increased the amount of force produced by tail motions relative to mass. This analysis indicates that larger tadpoles should be better able to reduce the ability of a predator to both initiate and set its grasp, and it contributes proximate causes for lower predation mortality of larger tadpoles.