ABSTRACT
Previous studies using the nuclear SSU rDNA and partial LSU rDNA have demonstrated that the euglenoid loricate taxa form a monophyletic clade within the photosynthetic euglenoid lineage. It was unclear, however, whether the loricate genera Trachelomonas and Strombomonas were monophyletic. In order to determine the relationships among the loricate taxa, SSU and LSU nuclear rDNA sequences were obtained for eight Strombomonas and 25 Trachelomonas strains and combined in a multigene phylogenetic analysis. Conserved regions of the aligned data set were used to generate maximum-likelihood (ML) and Bayesian phylogenies. Both methods recovered a strongly supported monophyletic loricate clade with Strombomonas and Trachelomonas species separated into two sister clades. Taxa in the genus Strombomonas sorted into three subclades. Within the genus Trachelomonas, five strongly supported subclades were recovered in all analyses. Key morphological features could be attributed to each of the subclades, with the major separation being that all of the spine-bearing taxa were located in two sister subclades, while the more rounded, spineless taxa formed the remaining three subclades. The separation of genera and subclades was supported by 42 distinct molecular signatures (33 in Trachelomonas and nine in Strombomonas). The morphological and molecular data supported the retention of Trachelomonas and Strombomonas as separate loricate genera.
ABSTRACT
Previous studies using the nuclear SSU rDNA have indicated that the photosynthetic euglenoids are a monophyletic group; however, some of the genera within the photosynthetic lineage are not monophyletic. To test these results further, evolutionary relationships among the photosynthetic genera were investigated by obtaining partial LSU nuclear rDNA sequences. Taxa from each of the external clades of the SSU rDNA-based phylogeny were chosen to create a combined dataset and to compare the individual LSU and SSU rDNA datasets. Conserved areas of the aligned sequences for both the LSU and SSU rDNA were used to generate parsimony, log-det, maximum-likelihood and Bayesian trees. The SSU and LSU rDNA consistently generated the same seven terminal clades; however, the relationship among those clades varied depending on the type of analysis and the dataset used. The combined dataset generated a more robust phylogeny, but the relationships among clades still varied. The addition of the LSU rDNA dataset to the euglenophyte phylogeny supports the view that the genera Euglena, Lepocinclis and Phacus are not monophyletic and substantiates the existence of several well-supported clades. A secondary structural model for the D2 region of the LSU rDNA was proposed on the basis of compensatory base changes found in the alignment.
