Mitochondrial Genome of Savalia savaglia (Cnidaria, Hexacorallia) and Early Metazoan Phylogeny

Mitochondrial genomes have recently become widely used in animal phylogeny, mainly to infer the relationships between vertebrates and other bilaterians. However, only 11 of 723 complete mitochondrial genomes available in the public databases are of early metazoans, including cnidarians (Anthozoa, mainly Scleractinia) and sponges. Although some cnidarians (Medusozoa) are known to possess atypical linear mitochondrial DNA, the anthozoan mitochondrial genome is circular and its organization is similar to that of other metazoans. Because the phylogenetic relationships among Anthozoa as well as their relation to other early metazoans still need to be clarified, we tested whether sequencing the complete mitochondrial genome of Savalia savaglia, an anthozoan belonging to the order Zoantharia (=Zoanthidea), could be useful to infer such relationships. Compared to other anthozoans, S. savaglia's genome is unusually long (20,766 bp) due to the presence of several noncoding intergenic regions (3691 bp). The genome contains all 13 protein coding genes commonly found in metazoans, but like other Anthozoa it lacks most of the tRNAs. Phylogenetic analyses of S. savaglia mitochondrial sequences show Zoantharia branching closely to other Hexacorallia, either as a sister group to Actiniaria or as a sister group to Actiniaria and Scleractinia. The close relationships suggested between Zoantharia and Actiniaria are reinforced by strong similarities in their gene order and the presence of similar introns in the COI and ND5 genes. Our study suggests that mitochondrial genomes can be a source of potentially valuable information on the phylogeny of Hexacorallia and may provide new insights into the evolution of early metazoan

Phylogeny of the order Zoantharia (Anthozoa, Hexacorallia) based on the mitochondrial ribosomal genes

Zoantharia (or Zoanthidea) is the third largest order of Hexacorallia, characterised by two rows of tentacles, one siphonoglyph and a colonial way of life. Current systematics of Zoantharia is based exclusively on morphology and follows the traditional division of the group into the two suborders Brachycnemina and Macrocnemina, each comprising several poorly defined genera and species. To resolve the phylogenetic relationships among Zoantharia, we have analysed the sequences of mitochondrial 16S and 12S rRNA genes obtained from 24 specimens, representing two suborders and eight genera. In view of our data, Brachycnemina appears as a monophyletic group diverging within the paraphyletic Macrocnemina. The macrocnemic genus Epizoanthus branches as the sister group to all other Zoantharia that are sampled. All examined genera are monophyletic, except Parazoanthus, which comprises several independently branching clades and individual sequences. Among Parazoanthus, some groups of species can be defined by particular insertion/deletion patterns in the DNA sequences. All these clades show specificity to a particular type of substrate such as sponges or hydrozoans. Substrate specificity is also observed in zoantharians living on gorgonians or anthipatharians, as in the genus Savalia (Gerardia). If confirmed by further studies, the substrate specificity could be used as reliable character for taxonomic identification of some Macrocnemin

Mitochondrial genome of Savalia savaglia (Cnidaria, Hexacorallia) and early metazoan phylogeny. Journal of Molecular Evolution

Mitochondrial genomes have recently become widely used in animal phylogeny, mainly to infer the relationships between vertebrates and other bilaterians. However, only 11 of 723 complete mitochondrial genomes available in the public databases are of early metazoans, including cnidarians (Anthozoa, mainly Scleractinia) and sponges. Although some cnidarians (Medusozoa) are known to possess atypical linear mitochondrial DNA, the anthozoan mitochondrial genome is circular and its organization is similar to that of other metazoans. Because the phylogenetic relationships among Anthozoa as well as their relation to other early metazoans still need to be clarified, we tested whether sequencing the complete mitochondrial genome of Savalia savaglia, an anthozoan belonging to the order Zoantharia (=Zoanthidea), could be useful to infer such relationships. Compared to other anthozoans, S. savaglia's genome is unusually long (20,766 bp) due to the presence of several noncoding intergenic regions (3691 bp). The genome contains all 13 protein coding genes commonly found in metazoans, but like other Anthozoa it lacks most of the tRNAs. Phylogenetic analyses of S. savaglia mitochondrial sequences show Zoantharia branching closely to other Hexacorallia, either as a sister group to Actiniaria or as a sister group to Actiniaria and Scleractinia. The close relationships suggested between Zoantharia and Actiniaria are reinforced by strong similarities in their gene order and the presence of similar introns in the COI and ND5 genes. Our study suggests that mitochondrial genomes can be a source of potentially valuable information on the phylogeny of Hexacorallia and may provide new insights into the evolution of early metazoans

Phylogeny of the order Zoantharia (Anthozoa, Hexacorallia) based on the mitochondrial ribosomal genes.

Zoantharia (or Zoanthidea) is the third largest order of Hexacorallia, characterised by two rows of tentacles, one siphonoglyph and a colonial way of life. Current systematics of Zoantharia is based exclusively on morphology and follows the traditional division of the group into the two suborders Brachycnemina and Macrocnemina, each comprising several poorly defined genera and species. To resolve the phylogenetic relationships among Zoantharia, we have analysed the sequences of mitochondrial 16S and 12S rRNA genes obtained from 24 specimens, representing two suborders and eight genera. In view of our data, Brachycnemina appears as a monophyletic group diverging within the paraphyletic Macrocnemina. The macrocnemic genus Epizoanthus branches as the sister group to all other Zoantharia that are sampled. All examined genera are monophyletic, except Parazoanthus, which comprises several independently branching clades and individual sequences. Among Parazoanthus, some groups of species can be defined by particular insertion/deletion patterns in the DNA sequences. All these clades show specificity to a particular type of substrate such as sponges or hydrozoans. Substrate specificity is also observed in zoantharians living on gorgonians or anthipatharians, as in the genus Savalia (Gerardia). If confirmed by further studies, the substrate specificity could be used as reliable character for taxonomic identification of some Macrocnemina