Molecular phylogenetic hypotheses of Zoanthus species (Anthozoa:Hexacorallia) using RNA secondary structure of the internal transcribed spacer 2 (ITS2)
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- Aguilar, C. & Reimer, J.D. Mar Biodiv (2010) 40: 195. doi:10.1007/s12526-010-0043-2
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Previously, it has been found that species of the zoanthid genus Zoanthus (Cnidaria: Hexacorallia) possess high levels of intrageneric ITS-rDNA sequence variation both between congeners and also within one species, Zoanthus sansibaricus, resulting in an uncertain internal transcribed spacer of ribosomal DNA (ITS-rDNA) phylogeny for this group. For the first time, the secondary structures of the internal transcribed spacer 2 (ITS 2) sequences were analyzed in an attempt to further clarify and solve relationships within Zoanthus, and also with the closely related genera Acrozoanthus and Isaurus (all in family Zoanthidae). Results show that most species’ ITS2 secondary structures follow the basic four-helix-ring model proposed for most eukaryotes including anthozoans. However, not all structures had the conserved motifs present in scleractinian corals, and Z. sansibaricus had two different structural conformations from the two different ITS2 types present. The ITS2 secondary structures of Zoanthus in this study, present a well resolved and supported phylogeny that makes it an appropriate tool for solving phylogenies in this taxonomic group. Based on ITS2 secondary structure results here, we theorize that: (1) Acrozoanthus is a valid monophyly separate from Zoanthus; (2) Z. gigantus, Z. sansibaricus, and Z. praelongus do not have any compensatory base changes (CBCs) between them and form a related clade distinct from the more divergent Z. kuroshio/Z. vietnamensis clade. The results furthermore suggest that the presence of CBCs may exist only at much lower ratios between different species in zoanthids than in other investigated organism lineages.