| The diet choices of animals can directly affect growth, survivorship, and reproduction. Understanding diet selection and nutrition in an animal can therefore provide valuable insight into the evolution of its life history characteristics and behavior. Various factors influence diet selection, including diet chemistry, digestive physiology and anatomy of the consumer, and associative effects (interactions) between simultaneously ingested diet items. The purpose of this dissertation was to examine how these factors influence diet selection in yellow-bellied slider turtles, Trachemys scripta. As juveniles, these turtles are carnivores that feed on aquatic invertebrates, but as they mature, they become opportunistic omnivores that feed primarily on aquatic plants. Although adult turtles are primarily herbivorous, they will supplement their diet with animal material when it is readily available. Therefore, associative effects between plant and animal diet items could be important.;In feeding trials, I fed juvenile and adult turtles plant, animal, and mixed diets. During these trials, I measured various digestive parameters including intake, digestibility, and daily gain of nutrients and energy. I also measured short-chain fatty acid concentrations in the gastrointestinal tract. The results of this work allowed me to address a number of questions related to T. scripta diet selection. First, I examined the role digestive physiology plays in the ontogenetic diet shift and found that juveniles were unable to meet their nutritional demands on the plant diet because of limits imposed on intake. Second, I observed a negative associative effect between plant and animal diet items in both juveniles and adults; this effect varied with different ratios of plant to animal material. Third, I described the gastrointestinal tract morphology of juveniles and adults and found that both age classes harbor microbial fermentations in their hindguts and that gastrointestinal tract morphology does not vary with age. Finally, I found that gross gastrointestinal tract morphology is not flexible in response to plant and animal diets. |
