The microtubular cytoskeleton of most single-celled eukaryotes radiates from an organizing center called
the flagellar apparatus, which is essential for locomotion, feeding and reproduction. The structure of the
flagellar apparatus tends to be conserved within diverse clades of eukaryotes, and modifications of this
overall structure distinguish different clades from each other. Understanding the unity and diversity of
the flagellar apparatus provides important insights into the evolutionary history of the eukaryotic cell.
Diversification of the flagellar apparatus is particularly apparent during the multiple independent transitions
to parasitic lifestyles from free-living ancestors. However, our understanding of these evolutionary
transitions is hampered by the lack of detailed comparisons of the microtubular root systems in different
lineages of parasitic microbial eukaryotes and those of their closest free-living relatives. Here we help
to establish this comparative context by examining the unity and diversity of the flagellar apparatus in
six major clades containing both free-living lineages and endobiotic (parasitic and symbiotic) microbial
eukaryotes: stramenopiles (e.g., Phytophthora), fornicates (e.g., Giardia), parabasalids (e.g., Trichomonas),
preaxostylids (e.g.,Monocercomonoides), kinetoplastids (e.g., Trypanosoma), andapicomplexans (e.g., Plasmodium).
These comparisons enabled us to address some broader patterns associated with the evolution
of parasitism, including a general trend toward a more streamlined flagellar apparatus