RUI: Phylogeny of the Terebellida and Sabellida (Annelida),and Evolution of Larval Developmental Modes

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9806848 McHugh The goal of this research project is to decipher the evolutionary relationships among the polychaete annelid orders Terebellida and Sabellida, so that historical patterns of change in larval development can be examined in this group. The orders Terebellida and Sabellida together form one of the most diverse and best known groups of polychaete annelid worms for which larval developmental modes have been well-characterized. They provide an excellent opportunity to address some fundamental questions regarding the evolution of larval development in marine invertebrates, because both feeding (planktotrophic) and non-feeding (lecithotrophic) larvae occur in this group of worms. I will use nuclear (elongation factor-1a and RNA polymerase II) and mitochondrial (cytochrome oxidase I) DNA sequence data to analyze the phylogenetic relationships of the Terebellida and Sabellida. Drawing on the results of the phylogenetic analyses, the ancestral mode of larval development will be inferred, and the frequency and direction of changes among lecithotrophy, opposed-band planktotrophy, and non-metatrochal planktotrophy throughout the history of the group will be examined. The results of the phylogenetic analysis will provide the basis for a re-classification of the Terebellida and Sabellida. Character optimization on the phylogeny will provide insights into the evolution of larval developmental modes. If it is shown that the opposed-band trochophore of serpulids has been derived from an ancestor for which non-feeding larval development is inferred, then homology of the trochophore among spiralian phyla, a character upon which theories of early animal evolution hinge, must be re-evaluated; if derived planktotrophy has arisen more than once in the Terebellida and Sabellida, then arguments that functional constraints on larval feeding have led to multiple parallelism may be supported.