A biomechanical description of the anuran tadpole startle response and some implications of anatomical diversity.

Abstract

Differential survival of predation partially determines which species exist in communities of aquatic organisms. One factor affecting anuran tadpole survival is variation in performance of the startle response. This dissertation explores how variation in tadpole morphology affects startle response performance. I began by describing the interactions between tadpoles and a common predator, an aquatic dragonfly naiad. From these behavioral interactions, I determined that the tadpole head/body cavity and the intersection between the head/body and tail were common and deadly targets during dragonfly strikes. Thus, I focused biomechanical analyses on acceleration performance of these anterior sections of the tadpole. I described the acceleration performance of three species: bullfrog (<italic>Rana catesbeiana</italic>), wood frog (<italic>Rana sylvatica</italic>), and American toad (<italic>Bufo americanus </italic>). Bullfrogs had the highest acceleration performance, and there was no difference between wood frog and American toad performance. I examined possible anatomical causes of differential startle response performance via two approaches for predicting acceleration performance. First, I hypothesized that various tail shapes produce different amounts of translational force and torque during motions of the startle response. I explored this using a quantitative, hydrodynamic model that calculated the force and torque of the tail during a startle response. This analysis suggested that the variation among tail shapes did not lead to substantial differences in translational force and torque production and, thus, would not lead to differences in acceleration performance. Second, I hypothesized that the potential of tadpoles to accelerate could be ranked according to the ratio between the force production capability of the tail muscle and inertial resistance to acceleration. To evaluate this hypothesis, I ranked tadpoles both in terms of acceleration performance and also with respect to anatomical estimates for maximum muscle force production and inertial resistance. The anatomical estimate of acceleration potential accurately predicted the interspecific rankings of acceleration performance. However, the anatomical estimates of acceleration potential did not coincide with the rankings of the acceleration performance of individuals within the species. All the metrics used in these analyses showed very high variance, which may explain the lack of intraspecific concordance of individual anatomical estimates and performance rankings.