Evolution of Host Associations in Symbiotic Zoanthidea

Symbioses are pervasive in life and confer novel adaptive capabilities that enable ecological expansion into unexplored niches. Evolutionary transitions in symbiosis (terminations, origins, host shifts, or changes in relationship outcomes) can therefore have dramatic effects on the fitness, life history, and distribution of organisms. Because symbiotic interactions require coordination among traits that control recognition, colonization, and maintenance of symbiosis, transitions in symbiosis should generally be rare and conserved across evolutionary time. Cnidarians in the order Zoanthidea (class Anthozoa) are symbionts of taxa representing at least five invertebrate phyla and occur in most major benthic habitats from the intertidal to the deep sea. The Zoanthidea exhibit a startling array of evolutionary transitions in symbioses, and host associations and relationship outcomes appear to be highly homoplasious. To better understand these transitions and the effects of symbioses on Zoanthidea, I use a multifaceted approach that combines molecular phylogenetics and morphology with manipulative field experiments and surveys to clarify species delimitations, diversity and specificity of host associations, context-dependent relationship outcomes, and the evolution of symbioses. The results of this research indicate that our current understanding of symbiosis evolution in Zoanthidea is confounded by incomplete data on associations and relationships, and systematics that do not reflect evolutionary relationships; the data presented here indicate that host associations are largely conserved across evolutionary time.