title: Monoplacophoran mitochondrial genomes: convergent gene arrangements and little phylogenetic signal.
abstract: Although recent studies have greatly advanced understanding of deep molluscan phylogeny, placement of some taxa remains uncertain as different datasets support competing class-relationships. Traditionally, morphologists have placed Monoplacophora, a group of morphologically simple, limpet-like molluscs as sister group to all other conchiferans (shelled molluscs other than Polyplacophora), a grouping that is supported by the latest large-scale phylogenomic study that includes Laevipilina. However, molecular datasets dominated by nuclear ribosomal genes support Monoplacophora + Polyplacophora (Serialia). Here, we evaluate the potential of mitochondrial genome data for resolving placement of Monoplacophora.
  
  
  
  Two complete (Laevipilina antarctica and Vema ewingi) and one partial (Laevipilina hyalina) mitochondrial genomes were sequenced, assembled, and compared. All three genomes show a highly similar architecture including an unusually high number of non-coding regions. Comparison of monoplacophoran gene order shows a gene arrangement pattern not previously reported; there is an inversion of one large gene cluster. Our reanalyses of recently published polyplacophoran mitogenomes show, however, that this feature is also present in some chiton species. Maximum Likelihood and Bayesian Inference analyses of 13 mitochondrial protein-coding genes failed to robustly place Monoplacophora and hypothesis testing could not reject any of the evaluated placements of Monoplacophora.
  
  
  
  Under both serialian or aculiferan-conchiferan scenarios, the observed gene cluster inversion appears to be a convergent evolution of gene arrangements in molluscs. Our phylogenetic results are inconclusive and sensitive to taxon sampling. Aculifera (Polyplacophora + Aplacophora) and Conchifera were never recovered. However, some analyses recovered Serialia (Monoplacophora + Polyplacophora), Diasoma (Bivalvia + Scaphopoda) or Pleistomollusca (Bivalvia + Gastropoda). Although we could not shed light on deep evolutionary traits of Mollusca we found unique patterns of gene arrangements that are common to monoplacophoran and chitonine polyplacophoran species but not to acanthochitonine Polyplacophora. Complete mitochondrial genome of Laevipilina antarctica.
authors.affiliation: SNSB-Bavarian State Collection of Zoology, Muenchhausenstrasse 21, 81247, Munich, Germany. Isabella.Stoeger@zsm.mwn.de.
authors.forename: I
authors.initials: I
authors.lastname: Stöger
authors.affiliation: Department of Biological Sciences, University of Alabama, Box 870344, Tuscaloosa, AL, 35487, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Kocot
authors.affiliation: Max-Planck Institut fuer Molekulare Genetik, Evolution and Development Group, Ihnestrasse 73, 14195, Berlin, Germany.|Dahlem Center for Genome Research and Medical Systems Biology, Environmental and Phylogenomics Group, Fabeckstraße 60-62, 14195, Berlin, Germany.|Alacris Theranostics GmbH, Fabeckstr. 60-62, 14195, Berlin, Germany.
authors.forename: A J
authors.initials: AJ
authors.lastname: Poustka
authors.affiliation: Western Australian Museum, Aquatic Zoology/Molecular Systematics Unit, 49 Kew Street, Welshpool, WA, 6106, Australia.
authors.forename: N G
authors.initials: NG
authors.lastname: Wilson
authors.affiliation: Zoological Museum, Moscow State University, Bolshaya Nikitskaya Str. 6, 225009, Moscow, Russia.
authors.forename: D
authors.initials: D
authors.lastname: Ivanov
authors.affiliation: Biological Sciences Department, Auburn University, Life Sciences Bld. 101, Auburn, AL, 36849, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Halanych
authors.affiliation: SNSB-Bavarian State Collection of Zoology, Muenchhausenstrasse 21, 81247, Munich, Germany.|Faculty of Biology, Department II, Ludwig-Maximilians-Universitaet Muenchen, Großhaderner Strasse 2-4, 82152, Planegg-Martinsried, Germany.|GeoBio-Center at LMU, Richard-Wagner-Strasse 10, 80333, Munich, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Schrödl
mesh_terms: D000818:Animals; D001499:Bayes Theorem; D005075:Biological Evolution; D049872:Bivalvia / Q000235:genetics; D049851:Gastropoda / Q000235:genetics; D023061:Gene Order; D054629:Genome, Mitochondrial; D008974:Mollusca / Q000235:genetics*; D005810:Multigene Family; D010802:Phylogeny
keywords: Aculifera; Conchifera; Evolution; Gene arrangement; Mitogenome; Mollusca; Monoplacophora; Phylogeny; Serialia