An Investigation of the Evolution of Autotrophic Endosymbioses in Bivalves By Comparative Molecular Phylogenetic Analysis of Host and Symbiont rRNA Sequences

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9420051 DISTEL Symbiotic associations between animals and bacteria are extremely diverse and commonplace in nature. In fact, it is difficult to find examples of animal species whose existence is not profoundly influenced by symbiotic associations with bacteria. For example, mitochondria (the structures within human cells that generate the energy for metabolic processes) are thought to have arisen from ancient bacteria that long ago formed a symbiotic association with the ancestor of all living animals. The support provided for this project will allow investigation of a type of symbiosis commonly found in clams and worms from deep-sea hydrothermal vents (marine hot springs) that can be used as a model system for studying the questions of how bacterial symbioses become established and what role they may play in the creation of new animal and bacterial species. This will be accomplished by comparing the primary DNA sequence (genetic code) of genes which are found in both symbionts and hosts. Computer analysis will be used to generate family trees demonstrating the relationships among symbionts and hosts. Comparison of the branching patterns of host and symbiont trees should reveal the point(s) in the lineages these hosts and symbionts first became associated and what impact their association has had on the diversification of the partner species. This understanding will lay the historical and conceptual foundation upon which future studies of the physiology and ecology of animal bacterial associations will be built. %%% Symbiotic associations ranging from enteric bacteria in the human gut to nitrogen fixing bacteria associated with plant roots or luminous light organs in deep-sea fish provide a broad range of benefits to their hosts. Consequently, symbioses between bacteria and animals are critically important to our ecosystems, agriculture and health. This study will provide an experimental model system to address major questions about how bacterial/host symbioses came to exist and wha t role they have played in the history of life on earth. ***