UC Riverside

Physical performance inextricably ties variation in physiology, morphology, and behavior to fitness. By studying how morphology is linked to performance, and the consequences of performance ability on survival and reproduction, evolutionary biologists can understand the selection pressures driving the evolution of particular morphological characteristics. However, many studies of performance are conducted in the lab in order to control external factors, allowing for detailed analyses of a few potentially influential variables but reducing the overall ecological realism of the results. The capacity for field studies to capture natural levels of variability helps to elucidate important ecological factors that influence locomotor performance and therefore drive individual fitness. This dissertation explores the evolution of bipedalism in rodents and the factors that affect their jump performance using a field-based approach. To do this, I investigated (1) the natural jump performance of kangaroo rats (Dipodomys) by filming their escapes from rattlesnake strikes, (2) the conditions under which they utilize these impressive jump escapes, (3) the relationship between hindlimb morphology and jump performance, and (4) how jump performance compares between bipedal and quadrupedal rodents. From these studies, I was able to determine their natural levels of performance, the ecological contexts that place selective pressure on jump performance, how those pressures on performance have shaped the evolution of their hindlimb morphology, and whether bipedality indeed confers improved jump performance when compared to quadrupedal rodents.