How rapid changes in body mass affect the locomotion of terrestrial vertebrates: ecology, evolution and biomechanics of a natural perturbation

Abstract

Animals rarely move through their natural habitat without experiencing an environmental perturbation, such as an obstacle or drop in height. However, rapid perturbations due to mass changes are little studied, and these can have significant impacts on the ecology and evolution of animal locomotion due to associated changes in relative muscle mass, altered body shape, shifts in the position of the centre of mass and changes in the overall load on the animal. These ecologically important situations arise during gravidity, parturition/oviposition, feeding, load bearing and autotomy. How these ubiquitous changes shape the function of animals in their natural habitat will have profound impacts on survival, and are thus crucial for understanding the functional ecology of locomotion. We first discuss locomotor perturbations, with an emphasis on the duration associated with them. We then address how commonly studied modes of rapid mass changes (e.g. parturition, autotomy, feeding) perturb locomotion by examining the effects of natural and artificial changes in mass on locomotor performance, kinematics, kinetics and muscle function in terrestrial animals, with an emphasis on non-human vertebrates. After a detailed discussion of the functional ecology of rapid mass changes, we generate a framework for future studies, including predictions for why some animals are more robust to changes in mass.