Symbiotic dinoflagellates are single-celled organisms that inhabit a variety of invertebratre hosts (e.g., coelenterates). Dinoflagellates belong to a diverse and poorly understood assemblage of unicellular organisms known as protists. They are also important indicators of water quality, which makes them important to ecologists and physiologists. Dr. Robert Trench is a leading researcher on the life cycles and ecology of dinoflagellates, and he proposes to widen his research by learning to analyze the RNA sequences of symbiotic dinoflagellates in order to reconstruct their evolutionary relationships. Dr. Trench will learn these techniques in the lab of Dr. Clifford Brunk of the University of California, Los Angeles, who uses molecular techniques to study other protists. The proposed research will equip Dr. Trench to pursue an unexplored aspect of dinoflagellate evolution. The results of his studies will address the ways in which symbiotic organisms come to inhabit their hosts, a question of wide interest to biologists. The collaboration between Drs. Trench and Brunk will energize the current efforts to understand the evolution of protists, among which the ancestors to multicellular life will be found.