Deciphering phylogenetic relationships of and delimiting species boundaries within the controversial ciliate genus Conchophthirus using an integrative morpho-evo approach

• Published in: Molecular phylogenetics and evolution 2024-01, Vol.190, p.107931-107931, Article 107931
• Main Authors: Zhang, Tengyue, Vďačný, Peter
• Format: Article
• Language: English
• Subjects: freshwater bivalves; host specificity; nuclear and mitochondrial rRNA genes; Scuticociliatia; secondary structure
• ISSN: 1055-7903; 1095-9513
• DOI: 10.1016/j.ympev.2023.107931

[Display omitted] •As many as 144 new Conchophthirus sequences.•First nuclear ITS1-5.8S-ITS2-28S and mitochondrial 16S sequences of Conchophthirus.•First 2D models of 18S, ITS2, 28S and 16S molecules of Conchophthirus.•Conchophthirus, Dexiotricha and Haptophrya represent an orphan scuticociliate clade.•Host species and plate tectonics could govern the diversification of Conchophthirus. The phylum Ciliophora (ciliates) comprises about 2600 symbiotic and over 5500 free-living species. The inclusion of symbiotic ciliates in phylogenetic analyses often challenges traditional classification frameworks due to their morphological adaptions to the symbiotic lifestyle. Conchophthirus is such a controversial obligate endocommensal genus whose affinities to other symbiotic and free-living scuticociliates are still poorly understood. Using uni- and multivariate morphometrics as well as 2D-based molecular and phylogenetic analyses, we attempted to test for the monophyly of Conchophthirus, study the boundaries of Conchophthirus species isolated from various bivalves at mesoscale, and reveal the phylogenetic relationships of Conchophthirus to other scuticociliates. Multidimensional analyses of morphometric and cell geometric data generated the same homogenous clusters, as did phylogenetic analyses based on 144 new sequences of two mitochondrial and five nuclear molecular markers. Conchophthirus is not closely related to ‘core’ scuticociliates represented by the orders Pleuronematida and Philasterida, as assumed in the past using morphological data. Nuclear and mitochondrial markers consistently showed the free-living Dexiotricha and the mouthless endosymbiotic Haptophrya to be the nearest relatives of Conchophthirus. These three highly morphologically and ecologically dissimilar genera represent an orphan clade from the early radiation of scuticociliates in molecular phylogenies.