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New Insight Into the Phylogeny of Mesozoa: Evidence from the 18S and 28S Rrna Genes N

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New Insight Into the Phylogeny of Mesozoa: Evidence from the 18S and 28S Rrna Genes N ISSN 00963925, Moscow University Biological Sciences Bulletin, 2010, Vol. 65, No. 4, pp. 167–169. © Allerton Press, Inc., 2010. Original Russian Text © N.B. Petrov, V.V. Aleshin, A.N. Pegova, M.V. Ofitserov, G.S. Slyusarev, 2010, published in Vestnik Moskovskogo Universiteta. Biologiya, 2010, No. 4, pp. 42–45. New Insight into the Phylogeny of Mesozoa: Evidence from the 18S and 28S rRNA Genes N. B. Petrova, V. V. Aleshina, A. N. Pegovab, M. V. Ofitserovc, and G. S. Slyusarevd a Research Institute of Physical and Chemical Biology, Moscow State University, Moscow, Russia b International Biotechnology Center, Moscow State University, Moscow, Russia c State Scientific Center, Russian Research Institute of Irrigative Pisciculture, Russian Academy of Agricultural Sciences d Invertebrate Zoology Department, St. Petersburg State University, St. Petersburg, Russia Received April 15, 2010 Abstract—The phylogenetic relationships of two Mesozoa groups were studied by the comparative analysis of complete sequences of 18S and 28S rRNA. Two groups of Mesozoa were found to form a statistically sup ported clade in phylogenetic trees. The results of the analysis placed Mesozoa in the Spiralia group of Lophotrochozoa and showed the tendency of Mesozoa to converge with one of the Annelida groups. Keywords: 18S and 28S rRNA genes, Mesozoa, Orthonectida, Dicyemida, phylogeny. DOI: 10.3103/S0096392510040127 Two small groups of simply organized inverte obtained sequences were aligned with sequences of brates: Dicyemida (Rhombozoa) and Orthonectida, representatives of main phyla of multicellular animals, are included in Mesozoa. Animals of both groups con including an extended sequence set of 82 Annelida sist of a small number of cells that form an outer ciliary species. Initial alignment with length of 4564 nucle layer and inner reproductive mono (Dicyemida) or otides included sequences of 101 bilaterally symmetri multilayer (Orthonectida). They do not have the tis cal species. sues, organs, or organ systems that are common to Bayes analysis was performed using the general other animals, which could be evidence that these ani time reversed model of nucleotide sequence evolution mals are an intermediate between unicellular eukary taking the heterogeneity of evolution rates and per otes and multicellular animals, as their name indi centage of invariant positions (GTR + H + I) into cates. All representatives of this group are endopara account. The parameters of evolution were calculated sites of invertebrates and are characterized by a by the mrbayes program [9]. During four independent complicated and not completely understood life cycle analyses, from 2 to 6 million generations by four to with a change of asexual and sexual generations but eight Markov chains were made. 10000 generated without change of host. trees were chosen, and then 6000 of them were consid The phylogenetic relationships between Mesozoa ered as chains that did not reach stationary state and and other groups of invertebrates are not clear yet due cast out; and the remaining 4000 were used for making to their scarcity of morphological features. The analy a consensus tree. sis of 18S rRNA and Hox genes [1, 2, 3] and recently The schematic representation of a tree constructed obtained molecular [4] and morphological data [5] from the initial alignment is shown in Figure 1. On this have not completely solved this problem and the ques tree the Ecdysozoa group is represented by Cephalo tion of the close relationship of the two Mesozoa rhyncha (Priapulida + Kinorhyncha), Nematoda, groups. For a better understanding of phylogenetic Nematomorpha, and Arthropoda phyla. Spiralia relations of Mesozoa, a comprehensive analysis of an includes a large group of trochophore animals united extended set of joint 18S and 28S rRNA gene into Lophotrochozoa clade (Mollusca, Nemertea and sequences of main animal phyla was performed. Annelida, Brachiopoda, Echiura and Sipuncula) and Almost complete nucleotide sequences of the 28S also the Syndermata subgroup (Rotifera + Acantho rRNA genes of two Orthonectida species (Rhopalura cephala) and flatworms (Platyhelminthes). Three litorali and Intoshia linei) and one Dicyemida species Mesozoa species (two Orthonectida and one (Dicyema sp.), as well as the 18S rRNA gene of Dicyemida species) form a well supported clade, Intoshia linei were obtained by PCR [6] with appropri which is placed in the group of lophotrochophore ani ate primer kits [7, 8] followed by direct sequencing of mals (Mollusca, Brachiopoda, Annelida, Sipuncula amplification products in an automatic analyzer in the and Echiura). Considering the tendency of Mesozoa Genom collective use center (Institute of Molecular to converge with Annelida and its allied groups Biology of Russian Academy of Sciences). The (Echiura and Pogonophora) and particularly with the 167 168 PETROV et al. 54 Annelida2 (33) 64 Annelida1 (38) 100 Mesozoa (3) 70 Mollusca (2) 99 Lophotrochozoa Nemertea (3) Spiralia Protostomia 100 Platyhelminthes (5) 100 Syndermata (2) 100 Ecdysozoa (9) Deuterostomia (4) Acoelomorpha (1) +Nemertodermatida (1) Fig. 1. A schematic representation of Bayes phylogenetic tree of main groups of bilaterally symmetrical animals. The analyzed set included 101 sequences of 18 + 28S rRNA genes (4564 nucleotide positions), 71 of them belonged to Annelida groups and related species (Sipuncula, Echiura, and Pogonophora). The numbers on the branches represent the statistical support, % of posterior probability. The parenthetical numbers indicate the number of sequences. (a) (b) Annelida1 Annelida2 69 94 69 Mesozoa 93 Mollusca 54 Mollusca 87 Nemertea 80 Nemertea Mesozoa 100 81 100 Platyhelminthes Platyhelminthes Ecdysozoa Ecdysozoa Deuterostomia Deuterostomia (c) (d) Annelida1 Annelida2 95 66 95 Orthonectida 68 Orthonectida 80 Mollusca 72 Mollusca 97 Nemertea 75 Nemertea 100 Platyhelminthes 100 Platyhelminthes 100 Ecdysozoa 100 Ecdysozoa Deuterostomia Deuterostomia Acoelomorpha+ Acoelomorpha+ Nemertodermatida Nemertodermatida Fig. 2. Schematic representation of the Bayes phylogenetic tree of main groups of bilaterally symmetrical animals. The analyzed set included various numbers of 18 + 28S rRNA gene sequences (4564 nucleotide positions). In the (a) and (b) panels Mesozoa are represented by two groups (Orthonectida and Dicyemida); in (c) and (d) Mesozoa are represented only by Orthonectida. Numbers on branches represent the statistical support, % of posterior probability. group that includes Capitellida, Echiura, Sipuncula, Sipuncula, and Oligochaeta inter alia, the second and Oligochaeta, we tried to define the Mesozoa place group (Annelida2) included the remaining Annelida in the scheme more accurately by dividing Annelida groups in our analysis. and related species sequences into two groups. The The results of the analysis of Annelida1 groups are first group (Annelida1) included Capitellida, Echiura, shown in Figure 2a. The monophyly of Mesozoa had MOSCOW UNIVERSITY BIOLOGICAL SCIENCES BULLETIN Vol. 65 No. 4 2010 NEW INSIGHT INTO THE PHYLOGENY OF MESOZOA 169 100% support and it was also supported by eight 090401150a. Calculations were performed on the molecular synapomorphies; Mesozoa directly bor SKIF MSU Chebyshev supercomputer. dered with Annelida1 group with 69% support. Although such support is considered moderate for Bayes trees [10], it exceeds the support of groups REFERENCES within the Annelida1 clade (35–60%). The position of 1. Pawlowski, J. et al., Origin of the Mesozoa Inferred Mesozoa on the tree obtained by analysis of the second from 18S rRNA Gene Sequences, Mol. Biol. Evol., set of sequences, which included the Annelida2 group, 1996, vol. 13, no. 8, pp. 1128–1132. is shown in Figure 2b. On this tree Mesozoa does not 2. Hanelt, B. et al., The Phylogenetic Position of Rho border with the Annelida2 group and takes a more palura ophiocomae (Orthonectida) Based on 18S Ribo basal position bordering with flatworms (Platyhelm somal DNA Sequence Analysis, Mol. Biol. Evol., 1996, intes); however in this case a Mesozoan position in the vol. 13, no. 9, pp. 1187–1191. Spiralia group is 87% supported. 3. Kobayashi, M. et al., Dicyemids Are Higher Animals, Nature, 1999, vol. 401, p. 762. Mesozoa (especially Dicyemida) branches on all 4. Petrov, N.B. et al., Combined 18S and 28S rRNA Gene trees were much longer then other branches, which is Sequences Show That Gastrotricha and Dicyemida are the evidence of high rate of evolution of their rRNA Related to Flatworms Whereas Orthonectida Are genes. Apparently the Mesozoan position was influ Related to Annelids, in Vychislitel’naya filogenetika i enced by the longbranch attraction effect [11], which genosistematika “VFGS 2007” (Computational Phylo shifted this group towards the base of the tree. To genetics and Genosystematics “VFGS 2007”), Mos check this observation, Orthonectida and Dicyemida cow, 2007, pp. 245–248. were analyzed separately in sets that included 5. Slyusarev, G.S., Type Orthonectida: Structure, Biology, Annelida1 and Annelida2. A single sequence of and Taxonomic Position among Metazoans, Zh. Dicyemida (trees are not shown) was united with flat Obshch. Biol., 2008, vol. 69, no. 6, pp. 403–427. worm sequences, at that Annelida1 and Annelida2 sets 6. Saiki, R.K., Gelfand, D.H., Stoffel, S., Scharf, S.J., provided this united group with different support, 89% Higuch, R., Horn, G.T., Mullis, K.B., and Erlich, H.A., PrimerDirected Enzymatic Amplification of DNA and 80%, respectively. Inclusion of only Orthonectida with a Thermostable DNA Polymerase,
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