Phylogeny of Lichen- and Non-Lichen-Forming Omphalinoid Mushrooms and the Utility of Testing for Combinability among Multiple Data Sets

As an initial step toward developing a model system to study requirements for and consequences of transitions to mutualism, the phylogeny of a group of closely related lichenized and nonlichenized basidiomycetes (Omphalina) was reconstructed. The phylogenetic analyses are based on four data sets representing different regions of the nuclear ribosomal repeat unit (ITS1, 5.8S, ITS2, and 25S) obtained from 30 species of Omphalina and related genera. The resulting phylogenetic trees from each of these four data sets, when analyzed separately, were not identical. Testing for the combinability of these four data sets suggested that they could not be combined in their entirety. The removal of ambiguous alignments and saturated sites was sufficient, after reapplying the combinability test on the pruned data sets, to explain the topological discrepancies. In this process, the first of two complementary tests developed by Rodrigo et al. (1993, N.Z. J. Bot. 31:257--268) to assess whether two data ...