Multigene-based phylogeny analyses of the controversial family Condylostomatidae (Ciliophora,Heterotrichea)

Condylostoma, the type genus of the family Condylostomatidae, is a well-known and taxonomically confusing genus with more than 30 nominal species. The phylogenetic relationships among congeners and related genera remain obscure despite the continuous discovery of new species and detailed redescription of known species over the past decades. Based on a total of 24 new sequences obtained from nine Condylostoma isolates, we conducted phylogenetic analyses by combining multiple marker genes. The molecular phylogenetic trees indicate that: (a) the monophyly of the family Condylostomatidae is supported by the rDNA locus and SSU rDNA sequences with high support value but is no longer sustained by both the ITS1-5.8S-ITS2 and LSU rDNA sequences; (b) Condylostoma is very likely a paraphyletic genus, and the possibility that it is a polyphyletic group cannot be denied, and (c) the genera Condylostentor and Chattonidium are suggested to evolve from a radiation of Condylostoma species. Furthermore, in an effort to provide better resolutions for understanding the evolutionary relationships of condylostomatids, the secondary structures of the variable regions 2 and 4 (V2 and V4) of SSU rDNA and ITS2 transcripts are predicted. The results revealed that the V2 and V4 structures are rather conserved at the genus level, while the ITS2 structures are much more variable.