AN ATTEMPT AT RECONSTRUCTING A PHYLOGENETIC TREE OF THE CILIOPHORA USING PARSIMONY METHODS

Phylogenetic trees were constructed for the Ciliophora using a parsimo ny analysis that applies the Camin-Sokal method to characters of known polarity and the Wagner method (which requires no knowledge of the an cestral state) to the other characters. The data covered 56 species an d 23 morphological, nuclear and ultrastructural multistate characters. Since no real-world outgroup can be assumed with certainity to root t he ciliophoran tree, we used three hypothetical ancestor hypotheses; o nly one of them (hypothesis 3: somatic kinetosomes in pairs considered ancestral; no character transformation series assumed for the positio n of the buccal area or for the organization of the buccal infraciliat ure) produced interesting trees. Two trees, called A and D, have been retained because they were shorter than the others and were equally op timal for different codings of the hypothetical ancestor. In tree A, t here is an early separation in two main branches. The first one contai ns two groups: the Karyorelictea-Heterotrichea (Postciliodesmatophora) and the Hypotrichea-Oligotrichea (Spirotricha) on the one hand, and t he colpodids (Transversala) on the other. The second branch leads to 3 groups containing all other ciliates. In tree D, the Postciliodesmato phora and Spirotricha are first separated from all other ciliates; thi s is in agreement with molecular phylogenies. Despite these difference s, the same five major groups appear in both trees; the main differenc e is in the position of the colpodid group. Class Karyorelictea appear s to be polyphyletic, with (a) a Loxodia-Trachelocercia line whose gen era share the same type of somatic cortex and nuclear organization, an d (b) a Protoheterotrichia-Protocruziidia line which is closer to the Heterotrichia. Nyctotherus is closer to the hypotrichs than to the het erotrichs. As in the molecular trees, the heterotrichs are closer to s ome of the Karyorelictea, with which they share the same main type of cortical cytoskeleton (postciliary ribbons), than to the hypotrichs an d oligotrichs, where the cortical microtubules are not postciliary fib ers. So, there are two competing types of reinforcement of the cell co rtex by microtubules, and these were selected as early as the first (i n tree D) or the second branching (in tree A); this is justification e nough to consider the subphylum Tubulicorticata as totally artificial. The validity of the subphylum Filocorticata is also discussed, consid ering the cortical cytoskeleton of some of the Vestibuliferea (Blephar ocorythida and Entodiniomorphida). The Litostomatea, Vestibuliferea an d Phyllopharyngea emerge as a sister-group of the Oligohymenophorea. I n the phyllopharyngids, macronuclear DNA is gene-sized, as in the hypo trichs; this means that DNA fragmentation occurs independently in diff erent lineages. Macronuclear characters concerning chromatin organizat ion that depend on the size of the DNA molecules have become diversifi ed into paraphyletic lines such as the phyllopharyngids, oligotrichs a nd hypotrichs for the character ''DNA duplication in replication bands ''. Nassula is separated from the Furgasonia-Pseudomicrothorax group, which is close to the scuticociliates. Nassula is close to Coleps. The peniculids branch away markedly from the tetrahymenids and are closer to the scuticociliates and peritrichs. The results are discussed with reference to some other new data, phylogenetic reconstructions and mo lecular trees.