title: Phylogeny of Syndermata (syn. Rotifera): Mitochondrial gene order verifies epizoic Seisonidea as sister to endoparasitic Acanthocephala within monophyletic Hemirotifera.
abstract: A monophyletic origin of endoparasitic thorny-headed worms (Acanthocephala) and wheel-animals (Rotifera) is widely accepted. However, the phylogeny inside the clade, be it called Syndermata or Rotifera, has lacked validation by mitochondrial (mt) data. Herein, we present the first mt genome of the key taxon Seison and report conflicting results of phylogenetic analyses: while mt sequence-based topologies showed monophyletic Lemniscea (Bdelloidea+Acanthocephala), gene order analyses supported monophyly of Pararotatoria (Seisonidea+Acanthocephala) and Hemirotifera (Bdelloidea+Pararotatoria). Sequence-based analyses obviously suffered from substitution saturation, compositional bias, and branch length heterogeneity; however, we observed no compromising effects in gene order analyses. Moreover, gene order-based topologies were robust to changes in coding (genes vs. gene pairs, two-state vs. multistate, aligned vs. non-aligned), tree reconstruction methods, and the treatment of the two monogonont mt genomes. Thus, mt gene order verifies seisonids as sister to acanthocephalans within monophyletic Hemirotifera, while deviating results of sequence-based analyses reflect artificial signal. This conclusion implies that the complex life cycle of extant acanthocephalans evolved from a free-living state, as retained by most monogononts and bdelloids, via an epizoic state with a simple life cycle, as shown by seisonids. Hence, Acanthocephala represent a rare example where ancestral transitional stages have counterparts amongst the closest relatives.
authors.affiliation: Institute of Molecular Genetics, Johannes Gutenberg-University Mainz, J.J. Becher-Weg 30a, D-55099 Mainz, Germany.
authors.forename: Malte
authors.initials: M
authors.lastname: Sielaff
authors.affiliation: Institute of Molecular Genetics, Johannes Gutenberg-University Mainz, J.J. Becher-Weg 30a, D-55099 Mainz, Germany.
authors.forename: Hanno
authors.initials: H
authors.lastname: Schmidt
authors.affiliation: National Centre for Biosystematics, Natural History Museum, University of Oslo, P.O. Box 1172, Blindern, NO-0318 Oslo, Norway.
authors.forename: Torsten H
authors.initials: TH
authors.lastname: Struck
authors.affiliation: Institute of Anthropology, Johannes Gutenberg-University Mainz, Anselm-Franz-von-Bentzel-Weg 7, D-55099 Mainz, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Rosenkranz
authors.affiliation: Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA, United States.
authors.forename: David B
authors.initials: DB
authors.lastname: Mark Welch
authors.affiliation: Institute of Molecular Genetics, Johannes Gutenberg-University Mainz, J.J. Becher-Weg 30a, D-55099 Mainz, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hankeln
authors.affiliation: Institute of Anthropology, Johannes Gutenberg-University Mainz, Anselm-Franz-von-Bentzel-Weg 7, D-55099 Mainz, Germany. Electronic address: herlyn@uni-mainz.de.
authors.forename: Holger
authors.initials: H
authors.lastname: Herlyn
mesh_terms: D000049:Acanthocephala / Q000145:classification* / Q000235:genetics*; D000818:Animals; D023061:Gene Order / Q000235:genetics*; D050259:Genes, Mitochondrial / Q000235:genetics*; D054629:Genome, Mitochondrial / Q000235:genetics; D008018:Life Cycle Stages; D010802:Phylogeny; D012403:Rotifera / Q000145:classification* / Q000235:genetics*
keywords: Adjacencies; Eurotatoria; Gene order; Gene rearrangements; Life cycle; Parasitism