Systematic studies on ciliates (Alveolata, Ciliophora) in China: Progress and achievements based on molecular information

Abstract

Due to complex morphological and convergent morphogenetic characters, the systematics of ciliates has long been ambiguous. Since 1990, the Laboratory of Protozoology, Ocean University of China, in collaboration with other research groups worldwide, has carried out a series of integrative investigations on ciliate systematics. To date, genomic DNA has been extracted from about 1700 ciliate strains, and phylogenetic analyses have been performed for two-thirds of orders. Main findings are: (1) Classifications of about 50 hypotrichous species have been resolved, although the monophylies of three hypotrichous orders remain unconfirmed; (2) Euplotia and two orders and all seven families within them are monophyletic assemblages; (3) Lynnella represents an order-level taxon, and is separated from two sister monophyletic subclasses Oligotrichia and Choreotrichia; (4) the peritrich families Zoothamniidae and Vorticellidae are separated from each other, and Zoothamnium exhibits a high genetic diversity; (5) the scuticociliate order Philasterida is monophyletic and separated from loxocephalids, and the thigmotrichids is a suborder within Pleuronematida; (6) 14 classes were recovered including one new class Protocruziea, and Mesodiniea is basal to subphyla Intramacronucleata and Postciliodesmatophora; (7) mitochondrial cytochrome c oxidase subunit I heteroplasmy was reported in ciliates for the first time, and candidate barcoding genes for Frontonia species identification were identified.