Peter Vďačný ist stellvertretender Leiter des Fachbereichs Zoologie an der Comenius Universität in Bratislava.
Abstract:
The very diverse and comparatively complex morphology of ciliates has given rise to numerous taxonomic concepts. However, robust testing of morphological homology statements and the apomorphic nature of diagnostic characters of ciliate taxa is rarely carried out. Likewise, the information content of the utilized molecular markers has seldom been explored prior to phylogenetic analyses and taxonomic decisions. Standard tree-building methods assume independent evolution at each site and occurrence of neutral (stochastic) evolutionary processes, a priori conditions that are also rarely explored in taxonomic studies.
Five phylogenetic techniques that may help address these issues will be presented: split spectrum analysis, network approaches, quartet likelihood mapping, reconstruction of ancestral traits, and neutrality tests. (1) Split spectrum analysis serves to determine the exact number and quality of nucleotide positions supporting individual nodes in phylogenetic trees and to discern long-branch artefacts that cause spurious phylogenies. (2) Network analysis can depict all possible evolutionary trajectories inferable from the dataset and locate and measure the conflict between them. (3) A priori likelihood mapping tests the suitability of data for reconstruction of a well resolved tree, visualizes the tree-likeness of quartets, and assesses the support of an internal branch of a given tree topology. (4) Reconstruction of ancestral morphologies can be applied for analyzing homology and apomorphy statements without circular reasoning. (5) And finally neutrality tests can help to recognize which codon positions in protein-coding genes are under positive or negative selection pressures and hence inappropriate for phylogenetic inferences. Principles and interpretation of results obtained with these phylogenetic tools will be introduced and exemplified using various groups of ciliates.