Tetrahymena australis (Protozoa, Ciliophora): A Well-Known But "Non-Existing" Taxon - Consideration of Its Identification, Definition and Systematic Position.
A cryptic species of the Tetrahymena pyriformis complex, Tetrahymena australis, has been known for a long time but never properly diagnosed based on taxonomic methods. The species name is thus invalid according to the International Code of Zoological Nomenclature. Recently, a population isolated from a freshwater lake in Wuhan, China was investigated using live observations, silver staining methods and gene sequence data. This organism can be separated from other described species of the T. pyriformis complex by its relatively small body size, the number of somatic kineties and differences in sequences of two genes, namely the small subunit ribosomal RNA (SSU rRNA) and the mitochondrial cytochrome c oxidase subunit I (cox1). We compared the SSU rRNA gene sequences of all available Tetrahymena species to reveal the nucleotide differences within this genus. The sequence of the Wuhan population is identical to two sequences of a previously isolated strain of T. australis (ATCC #30831). Phylogenetic analyses indicate that these three sequences (X56167, M98015, KT334373) cluster with Tetrahymena shanghaiensis (EF070256) in a polytomy. However, sequence divergence of the cox1 gene between the Wuhan population and another strain of T. australis (ATCC #30271) is 1.4%, suggesting that these may represent different subspecies.
Key Laboratory of Aquatic Biodiversity and Conservation of Chinese Academy of Sciences, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.|Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003, China.
Mingjian
M
Liu
School of Life Sciences, East China Normal University, Shanghai, 200241, China.
Xinpeng
X
Fan
Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003, China.
Feng
F
Gao
Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao, 266003, China.
Shan
S
Gao
Key Laboratory of Aquatic Biodiversity and Conservation of Chinese Academy of Sciences, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
Yuhe
Y
Yu
Department of Life Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom.
Alan
A
Warren
Key Laboratory of Aquatic Biodiversity and Conservation of Chinese Academy of Sciences, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China. jhuang@ihb.ac.cn.
Jie
J
Huang
D001483:Base Sequence; D004272:DNA, Mitochondrial / Q000235:genetics; D016054:DNA, Protozoan / Q000235:genetics; D005618:Fresh Water / Q000469:parasitology; D008928:Mitochondria / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013768:Tetrahymena / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*
D004272:DNA, Mitochondrial; D016054:DNA, Protozoan
SSU rRNA gene; Tetrahymena pyriformis complex; cox1 gene; cryptic species