Application of spectral analysis to examine phylogenetic signal among euglenid SSU rDNA data sets (Euglenozoa)

Euglenid flagellates as a common and widespread group of protists display a broad morphological variety. Against the background of pronounced genetic diversity and varying sequence characteristics of SSU rDNA sequences among different euglenid subgroups we analyzed the content and distribution of phylogenetic signal and noise within different euglenozoan data sets. Two statistical approaches, PTP-test and RASA, were employed to achieve a measure of overall signal content. Spectral analyses were used to evaluate support and conflict for given bi-partitions of the data sets. These investigations revealed a large amount of phylogenetic information present in the molecular data. Convincing support could be found for primary osmotrophic euglenids and corresponding subgroups, a taxon mainly based on molecular data. On the other hand, in agreement with weak corroboration from morphological data, euglenid monophyly and interrelationships of phagotrophs, phototrophs and osmotrophs were not supported. Focusing on the primary osmotrophic subclade Rhabdomonadina spectral analysis revealed only few well supported splits. Generally, the application of sequence evolution models in maximum likelihood and spectral analyses of euglenid SSU rDNA data sets did not lead to significant amplification of split supporting signal. Phylogenetic hypotheses are discussed in regard to the evolution of morphological and ultrastructural characters.