The morphologic features of many protozoans can vary significantly with environmental conditions, and therefore are unreliable indicators of ancestor-descendant relationships. A molecular approach to the parasitic trypanosomes will be pursued, using slowly evolving ribosomal RNA to reveal distant relationships, a particular DNA sequence with intermediate evolutionary rates for less distant relationships, and rapidly evolving nuclear DNA restriction patterns for more recent divergences. Protist phylogeny would be compared with phylogeny of vertebrate hosts to test the degree to which host evolution controls evolution among parasitises. The proposed research will illuminate the evolutionary history of a pivotal group of protists, and will set the stage for a better understanding of host-parasite coevolution. A better understanding of the trypanosome's ancestry can lead to important medical advances.
