Abstracts

The evolutionary relationships amongst excavates: a concatenated protein analysis.

Morphological studies and phylogenies of ribosomal RNA, taken together, suggest that excavate protists may be related to

each other, but many of the deepest level relationships amongst these organisms remain poorly understood. We have assembled a data set of six slowly evolving nuclear-encoded protein genes that include nine of the 10 recognized excavate groups. Maximum likelihood analyses demonstrate that diplomonads and Carpediemonas than parabasalids are related to each other. They also confirm that Trimastix is specifically related to oxymonads, forming the taxon Preaxostyla. There is strong support for a clade of Euglenozoa, Heterolobsea and jakobids, but, unexpectedly, jakobids and Heterolobosea are robustly recovered as sister taxa. Malawimonas is placed either as sister to Preaxostyla or as sister to the (Euglenozoa, Heterolobosea, jakobid) clade. The original data set strongly supports an association between the (diplomonad, Carpediemonas, parabasalid) clade and Opisthokonts. However, this grouping is not recovered when α-tubulin is excluded from the analysis, suggesting that the signal for this relationship lies within this one protein and might be suspect. All other important nodes in the tree are, by contrast, robust to the removal of any one gene. With a-tubulin excluded, excavates tend to form just two clades, with no strong nodes separating them. Jakobids, with their apparently ancestral bacterial-type mitrochondrial RNA polymerase are nonetheless nested within a clade with normal phage-type RNA polymerases, complicating any understanding of deep-level mitochondrial evolution The position of jakobids also seriously challenges the now well-accepted concept of a taxon Discicristata.