Field and Experimental Approaches to the Study of Locomotor Ontogeny in Propithecus verreauxi

Abstract

In this chapter, we use field-behavioral, morphometric, and laboratory-based data to demonstrate complex links among morphology, performance, and fitness. Although Propithecus verreauxi become “ecological adults” at a very young age, skeletal growth of Propithecus is slow. This incongruity creates a challenge for a small, developing animal to move efficiently when traveling along the same pathways with larger adults. To explore the effects of this disparity, we quantified the relationships among postcranial morphology, behavior, and fitness in an ontogenetic sample of wild Propithecus and subsequently tested functional relationships in the laboratory. Juvenile Propithecus exhibit growth allometries and functional changes in locomotion related to decreasing emphasis on pedal grasping and increasing emphasis on thigh-powered leaping. Whereas adult Propithecus use their long, muscular thigh and leg segments to increase leaping distance and reduce collisional costs during galloping on the ground, juvenile Propithecus increase angular excursions and acceleration and use a hopping gait on the ground that reduces the number of collisions. We show how this juvenile locomotor strategy and other aspects of the “locomotor phenotype” are associated with fitness. Understanding how variation in morphology influences variation in performance throughout ontogeny and the consequences of these associations on fitness should be a major focus of both field and laboratory studies.