The genomics of the gelatinous: Genomic insights into major evolutionary transitions within the Cnidaria

Abstract

Cnidaria is a marine phylum of over 13,000 species that possess an astounding diversity of habitats, body plans and life cycles. As early-diverging animals that are sister to all of the Bilateria, the study of cnidarians can help us reconstruct the evolutionary histories of traits in common to all bilaterians. The extreme diversity of cnidarian life histories, as well as their important phylogenetic position, makes Cnidaria an excellent group for the study of the drivers of diversity and the evolution of complexity and novelty. In my dissertation, I use phylogenetic, genomic, and population genetic approaches to study genome-scale and population-level changes associated with the evolution of major life history transitions. Chapter 1 is a brief introduction to cnidarian evolutionary genomics. In Chapter 2, I investigate the cnidarian transition to endoparasitism by contributing to phylogenomic analyses to place these parasites within the cnidaria, and characterizing major genome-scale changes, such as gene loss and genome size change, as compared with other non-parasitic cnidarians. In Chapter 3, I assess the population genetic consequences of the re-evolution of coloniality from a solitary ancestor in the hydrozoan Ectopleura larynx, which creates colonies by fusion of offspring rather than budding. My research tests whether or not these colonies are genetically chimeric, and therefore may be subject to evolutionary conflict between polyps. In Chapter 4, I gain insight into the cnidarian transition to freshwater by studying the euryhaline, invasive hydrozoan Cordylophora. I use phylogenomic and population genomic techniques in order to study the relationship between salinity level and population structure, reconstruct the evolution of salinity tolerance within Cordylophora, and to clarify some taxonomic uncertainty within the genus. My work contributes to the important and growing field of cnidarian evolutionary genomics and hopefully paves the way for future evolutionary genomic work on these and other intriguing cnidarian systems.