Exploring contradictory phylogenetic relationships in yeasts.

Phylogenetic trees underlie our understanding of yeast evolution and are also proving instrumental in the development of a more robust yeast classification system based upon natural (i.e. evolutionary) relationships. In an effort to refine/improve taxonomic resolution, recent studies have focused on the use of multigene rather than single gene sequencing. Nevertheless, searches to determine 'the tree' remain problematic, as they can often overlook conflicts in the dataset. In such instances, phylogenetic networks such as neighbor-nets and consensus networks can provide a more useful and indeed more informative alternative means of analysis. In this study, we have used the latter two phylogenetic network techniques to reanalyze the multigene sequence dataset of Kurtzman & Robnett, which was used to redefine the taxonomy of the family Saccharomycetaceae. Results from our analyses show that, in general, established clades are robust. However, they also reveal conflict between mitochondrial- and nuclear-encoded genes and indicate the existence of complex patterns of hybridization and introgression not detected in the original study. These patterns are discussed in relation to how they may impact upon the current classification of this group of yeasts.