title: A transcriptomic-phylogenomic analysis of the evolutionary relationships of flatworms.
abstract: The interrelationships of the flatworms (phylum Platyhelminthes) are poorly resolved despite decades of morphological and molecular phylogenetic studies. The earliest-branching clades (Catenulida, Macrostomorpha, and Polycladida) share spiral cleavage and entolecithal eggs with other lophotrochozoans. Lecithoepitheliata have primitive spiral cleavage but derived ectolecithal eggs. Other orders (Rhabdocoela, Proseriata, Tricladida and relatives, and Bothrioplanida) all have derived ectolecithal eggs but have uncertain affinities to one another. The orders of parasitic Neodermata emerge from an uncertain position from within these ectolecithal classes. To tackle these problems, we have sequenced transcriptomes from 18 flatworms and 5 other metazoan groups. The addition of published data produces an alignment of >107,000 amino acids with less than 28% missing data from 27 flatworm taxa in 11 orders covering all major clades. Our phylogenetic analyses show that Platyhelminthes consist of the two clades Catenulida and Rhabditophora. Within Rhabditophora, we show the earliest-emerging branch is Macrostomorpha, not Polycladida. We show Lecithoepitheliata are not members of Neoophora but are sister group of Polycladida, implying independent origins of the ectolecithal eggs found in Lecithoepitheliata and Neoophora. We resolve Rhabdocoela as the most basally branching euneoophoran taxon. Tricladida, Bothrioplanida, and Neodermata constitute a group that appears to have lost both spiral cleavage and centrosomes. We identify Bothrioplanida as the long-sought closest free-living sister group of the parasitic Neodermata. Among parasitic orders, we show that Cestoda are closer to Trematoda than to Monogenea, rejecting the concept of the Cercomeromorpha. Our results have important implications for understanding the evolution of this major phylum.
authors: Department Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK; Institute of Zoology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria.
authors: Bernhard
authors: B
authors: Egger
authors: Department Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK.
authors: François
authors: F
authors: Lapraz
authors: Department Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK.
authors: Bartłomiej
authors: B
authors: Tomiczek
authors: Department Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK.
authors: Steven
authors: S
authors: Müller
authors: Department Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK; Department of Computer Science, University College London, Gower Street, London WC1E 6BT, UK.
authors: Christophe
authors: C
authors: Dessimoz
authors: Department Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK.
authors: Johannes
authors: J
authors: Girstmair
authors: ETH Zurich, Department of Computer Science, Universitätsstrasse 19, 8092 Zurich, Switzerland.
authors: Nives
authors: N
authors: Škunca
authors: Department Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK.
authors: Kate A
authors: KA
authors: Rawlinson
authors: Université de Montréal, Département de Sciences Biologiques, Pavillon Marie-Victorin, CP 6128, Succ. Centre-ville, Montréal, QC H3C 3J7, Canada.
authors: Christopher B
authors: CB
authors: Cameron
authors: Université de Montréal, Département de Sciences Biologiques, Pavillon Marie-Victorin, CP 6128, Succ. Centre-ville, Montréal, QC H3C 3J7, Canada; Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università del Salento, 73100 Lecce, Italy.
authors: Elena
authors: E
authors: Beli
authors: Università degli Studi di Modena e Reggio Emilia, Via Campi 213/d, 41100 Modena, Italy.
authors: M Antonio
authors: MA
authors: Todaro
authors: Université Tunis El-Manar Campus Universitaire, 2092 Tunis, Tunisia.
authors: Mehrez
authors: M
authors: Gammoudi
authors: Museo Nacional de Ciencias Naturales (CSIC), José Gutiérrez Abascal 2, 28006 Madrid, Spain.
authors: Carolina
authors: C
authors: Noreña
authors: Department Genetics, Evolution and Environment, University College London, Gower Street, London WC1E 6BT, UK. Electronic address: m.telford@ucl.ac.uk.
authors: Maximilian J
authors: MJ
authors: Telford
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002503:Centromere / Q000235:genetics; D005260:Female; D020869:Gene Expression Profiling; D008297:Male; D010063:Ovum / Q000502:physiology; D010802:Phylogeny; D010932:Planarians / Q000235:genetics; D010986:Platyhelminths / Q000235:genetics* / Q000502:physiology; D013094:Spermatozoa / Q000502:physiology; D009626:Terminology as Topic