Abstract
In order to clarify the phylogeny and relationships of the most confused hypotrichous ciliates,
Holosticha
-complex, four closely related holostichids (five populations),
Holosticha bradburyae, H. diademata, Anteholosticha
sp., and
A. manca
, were compared and analyzed using ITS2 secondary structures, ITS1-5.8S-ITS2 region and SSrRNA gene sequences. The ITS1-5.8S-ITS2 region sequences of these four species were first sequenced, and they shared sequence identities ranging from 68.0% to 90.1%, while two populations of
Anteholosticha
sp. differed in three nucleotides (sequence identity 99.8%). There were several minor differences among ITS2 secondary structures of these species, while two populations of
Anteholosticha
sp. had the identical secondary structure. Phylogenetic trees inferred from the ITS1-5.8S-ITS2 region sequences of stichotrichs using multiple algorithms (Neighbor-Joining, Maximum Parsimony and Bayesian) revealed similar topologies. The results show that: (1)
Holosticha bradburyae
and
H. diademata
firmly clustered together with strong bootstrap supports, forming a sister clade with
Anteholosticha
sp., (2)
Anteholosticha
appeared to be a paraphyletic assemblage, in which the morphotype
A. manca
was more closely related to
Diaxonella trimarginata
than to its congener
Anteholosticha
sp. Phylogenetic analyses based on the SSrRNA gene and the combined sequences of SSrRNA gene and ITS1-5.8S-ITS2 region revealed the similar relationships between
Holosticha
and
Anteholosticha
, nevertheless their positions within the subclass Stichotrichia differed from each other inferred from different genes.