Is What You Eat More Important than What's Eating You? Top-Down Versus Bottom-up Effects on Body Shape of Utah Chub (Gila atraria)

Geometric morphometrics was used to characterize body shape and determine how top-down and bottom-up effects influence the morphology of Utah chub (Gila atraria). Diet (bottom-up influences), indicated by relative intestinal length, has a significant effect on morphology. Fish with longer intestines had deep, protruding bellies, while fish with short intestines had a more streamlined shape. Differences in body shape between predation environments and non-predation environments (top-down influences) were also significant. Fish in predatory environments displayed thinner, streamlined bodies and longer caudal peduncle regions than those in non-predatory environments. Body shape in Utah chub reflects both bottom-up and top-down effects, and bottom-up effects account for more variation in body shape.