Phylogenetic reconstruction of hypotrichous ciliates (protozoa, ciliophora, hypotrichida)

Abstract

To assess the phylogenetic relationships of hypotrichous ciliates and related ciliates, the complete sequences of small subunit ribosomal RNA (ssu-rRNA) genes of ciliates were analyzed using several phylogenetic analysis packages. For this purpose, nine species of hypotrichous ciliates, Paraurostyla weissei, Uroleptus pisci, Eschaneustyla sp., Euplotes aediculatus, Tachysoma pellionellum, Gonostomum sp., Holosticha sp., H. multistylata, and Stylonychia mytilus were isolated and cultured and their ssu-rRNA genes were sequenced using standard molecular techniques. The sequences of ssu-rRNA gene of the other ciliates were retrieved from worldwide databases. Two of the nonciliate species, Labyrinthuloides minuta and Prorocentrum minimum were used as outgroups for the phylogenetic analysis. The reconstructed tree demonstrated that the hypotrichous ciliates formed a monophyletic group within the global ciliate tree, and the members of this group composed of all hypotrichs and one oligotrichous ciliate. This monophyletic group (Hypotrichida) was divided into five main lineages or clades: Phacodinium line, Euplotidium-Diophrys line, Euplotes-Aspidisca line, Oxytricha-Stylonychia-Onychodromu line and Holosticha-Urostyla-Eschaneustyla line. The Hateria (considered as a member of oligotrichs previously) allied more closely with a clade (Oxytricha-Stylonychia-Holosticha-Urostyla) than with other clades.