THE DIETARY EVOLUTION AND REGENERATION PHYSIOLOGY OF FRESHWATER ANNELIDS

Abstract

All organisms must acquire materials to build their bodies and generate energy to fuel essential functions. Animals are especially reliant on the consumption of organic matter, ranging from detritus to other animals, to fuel processes that build, maintain, repair, and replicate their bodies. Without the ingestion, absorption, and metabolism of nutrients, most organismal functions are impossible. To understand organismal function and adaptation, it is important to understand how organisms acquire and use resources. In this dissertation, I investigated both how new diets evolve and the physiological mechanisms that power regeneration, using a family of meiofaunal annelids as models. In the first part of my thesis, I explored dietary evolution by investigating how carnivory evolved in an unusually predatory annelid genus. Recent transitions to carnivory are rare among animals, limiting our understanding of how and why non-carnivorous lineages become predatory. In my first two chapters, I employed a molecular phylogeny and metabarcoding gut content analysis to demonstrate that carnivory evolved twice in the genus, likely mediated by intermediate diets of ciliates and by mollusc symbiosis. These data suggest thatcarnivory can evolve from non-carnivorous ancestors through distinct evolutionary pathways, even among closely related lineages. In the second part of my thesis, I explored the metabolic pathways that fuel regeneration. Much is known about the developmental mechanisms that initiate and shape regeneration, but relatively little research has explored the physiological mechanisms that fuel regeneration. For my third chapter, I employed comparative respirometry, qPCR, and pharmacological experiments to demonstrate that anaerobic metabolism, but not aerobic metabolism, is required to fuel regeneration in annelids. These data add to accumulating evidence that regeneration, cancer, and development are regulated by similar metabolic mechanisms. I expand on regeneration physiology for my fourth and final chapter, where I synthesize literature exploring the significance of nutrition, metabolism, and the environment to regeneration across invertebrates. Ultimately, my investigations of dietary evolution and regeneration physiology deepen our understanding of the ways that animals obtain energy and allocate it to essential functions.