From ciliary patterns to molecular characterization: new insights into the evolutionary phylogeny of tintinnid ciliates (Ciliophora: Tintinnida), with new data on one novel and three poorly known species

Abstract

As dominant components of microzooplankton, tintinnid ciliates act as a vital link between the microbial food web and the traditional planktonic food chain in marine ecosystems. However, polymorphism of the lorica and the lack of ciliature information and gene sequence data have significantly complicated taxonomic analysis and restricted the development of tintinnid-related research fields such as ecology and physiology. In the present study, the morphological and molecular characterization of three poorly described species—Tintinnopsis estuariensis, T. angusta, and Leprotintinnus nordqvisti—and one novel species, Metacylis parajorgensenii sp. nov., were revealed, and the evolutionary relationships of tintinnids were discussed based on all currently known information on lorica morphology, ciliary pattern, and molecular phylogeny. The ciliary patterns of this group of ciliates were grouped into eight types—VO-type, S-type, A-type, N-type, E-type, F-type, M-type, and C-type—from which an evolutionary hypothesis was proposed. In combination with the SSU rRNA gene phylogeny tree, six types (corresponding gene sequence data were unavailable for species of VO-type and N-type), from simple to complex, were found to be consistent with the evolutionary direction of the order Tintinnida. However, the lorica type did not agree with the topology, suggesting that the ciliary pattern can be more reliable than the lorica morphology for classifying tintinnids. The interspecific comparison of known ciliary patterns demonstrated that the numbers of somatic kineties and kinetids could distinguish these species well. In addition, the population distributions of the genera Metacylis, Tintinnopsis, and Leprotintinnus, based on reliable data, revealed large differences in lorica opening diameters between inshore species, suggesting niche differentiation caused by competition for food resources.

Keywords

Ciliary pattern / Distribution / Evolutionary direction / Phylogeny / Tintinnids

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