LETTERS TO THE EDITOR A Mitochondrial Intron in a Verongid Sponge Dirk Erpenbeck • Ratih Aryasari • John N. A. Hooper • Gert Wo ¨rheide Received: 12 September 2014 / Accepted: 5 November 2014 Ó Springer Science+Business Media New York 2014 Abstract We discovered for the first time a mitochon- drial intron in a non-tetillid demosponge, which sheds new light on the interpretation of mitochondrial intron evolution among non-bilaterian animals and has consequences for phylogenetic and DNA barcoding studies. The newly dis- covered class 1 intron of Aplysinella rhax (Verongida) CO1 has an ORF for a putative LAGLIDADG-type and resem- bles other sponge and cnidarian mitochondrial introns. Our analysis of the Aplysinella rhax intron underlines that the patchy distribution of introns in sponges is caused by a combination of horizontal and vertical transmission. Fur- ther implications for CO1 phylogenetic and barcoding projects are discussed. Keywords Porifera Á Mitochondrial intron Á LAGLIDADG Á Homing endonuclease Á Sponges Á Verongida Introduction A decade since the publication of the first complete mito- chondrial (mt) poriferan genomes (Lavrov et al. 2005), our understanding of animal mtDNA evolution is still incom- plete. These genomes revealed major structural differences to their bilaterian counterparts. Subsequently, published mt-genomes of placozoans (Dellaporta et al. 2006), cte- nophores (Pett et al. 2011), and calcareous sponges (Lavrov et al. 2013) displayed even more dramatic differences to the relatively homogeneous bilaterian mt-genomes. Several differences can directly be attributed to ancestral traits, successively lost in Bilateria. Additionally, there are sev- eral mt-intragenic elements only present in sponges and other non-bilaterian mtDNA, such as repetitive hairpin elements (see e.g., Erpenbeck et al. 2009). Likewise mitochondrial introns, frequently self-splicing and mobile elements, are known from choanoflagellates, ichthyospo- reans, and other close relatives of Metazoa (Burger et al. 2003; Burt and Koufopanou 2004), furthermore in Porifera, Cnidaria, and Placozoa (e.g., Beagley et al. 1996; Della- porta et al. 2006; Rot et al. 2006). Bilateria, however, (mostly) lack mitochondrial introns (see Valle `s et al. 2008). Mitochondrial introns in sponges are rare. Only three different types are known, all in the cytochrome oxidase subunit 1 (CO1) gene of tetillid Demospongiae (Cinachy- rella and Tetilla), but also in plakinid Homoscleromorpha (Plakina and Plakinastrella) (Gazave et al. 2010; Rot et al. 2006; Szitenberg et al. 2010) (Fig. 1). All these introns harbor an ORF for a putative LAGLIDADG-type homing D. Erpenbeck (&) Á R. Aryasari Á G. Wo ¨rheide Department of Earth and Environmental Sciences & GeoBio- Center, Ludwig-Maximilians-Universita ¨t Mu ¨nchen (LMU), Richard-Wagner Str. 10, 80333 Munich, Germany e-mail: erpenbeck@lmu.de D. Erpenbeck Á G. Wo ¨rheide GeoBio-Center, Ludwig-Maximilians-Universita ¨t Mu ¨nchen (LMU), Munich, Germany D. Erpenbeck Á J. N. A. Hooper Biodiversity Program, Queensland Museum, PO Box 3300, South Brisbane, QLD 4101, Australia R. Aryasari Faculty of Biology, Gadjah Mada University, Yogyakarta, Indonesia J. N. A. Hooper Eskitis Institute, Griffith University, Nathan, QLD, Australia G. Wo ¨rheide SNSB – Bavarian State Collections of Palaeontology and Geology, Richard-Wagner Str. 10, 80333 Munich, Germany 123 J Mol Evol DOI 10.1007/s00239-014-9653-9