Three-gene based phylogeny of the Urostyloidea (Protista, Ciliophora, Hypotricha), with notes on classification of some core taxa.

ABSTRACT

Classifications of the Urostyloidea were mainly based on morphology and morphogenesis. Since molecular phylogeny largely focused on limited sampling using mostly the one-gene information, the incongruence between morphological data and gene sequences have risen. In this work, the three-gene data (SSU-rDNA, ITS1-5.8S-ITS2 and LSU-rDNA) comprising 12 genera in the "core urostyloids" are sequenced, and the phylogenies based on these different markers are compared using maximum-likelihood and Bayesian algorithms and tested by unconstrained and constrained analyses. The molecular phylogeny supports the following conclusions: (1) the monophyly of the core group of Urostyloidea is well supported while the whole Urostyloidea is not monophyletic; (2) Thigmokeronopsis and Apokeronopsis are clearly separated from the pseudokeronopsids in analyses of all three gene markers, supporting their exclusion from the Pseudokeronopsidae and the inclusion in the Urostylidae; (3) Diaxonella and Apobakuella should be assigned to the Urostylidae; (4) Bergeriella, Monocoronella and Neourostylopsis flavicana share a most recent common ancestor; (5) all molecular trees support the transfer of Metaurostylopsis flavicana to the recently proposed genus Neourostylopsis; (6) all molecular phylogenies fail to separate the morphologically well-defined genera Uroleptopsis and Pseudokeronopsis; and (7) Arcuseries gen. nov. containing three distinctly deviating Anteholosticha species is established.