Congruence between nuclear and mitochondrial genes in Demospongiae: A new hypothesis for relationships within the G4 clade (Porifera: Demospongiae) C.C. Morrow a,⇑ , B.E. Picton b , D. Erpenbeck c , N. Boury-Esnault d , C.A. Maggs a , A.L. Allcock e a School of Biological Sciences, MBC, 97 Lisburn Road, Queen’s University, Belfast BT9 7BL, UK b National Museums Northern Ireland, 153 Bangor Road, Holywood BT18 0EU, Northern Ireland, UK c Dept. of Earth- and Environmental Sciences and GeoBio-CenterLMU, Ludwig-Maximilians Universität, Richard-Wagner-Str. 10, 80333 München, Germany d Aix-Marseille Université, CNRS UMR-6540 DIMAR, Centre d’Océanologie de Marseille, Station Marine d’Endoume, Rue Batterie des Lions, 13007 Marseille, France e Dept. of Zoology, Ryan Institute, National University of Ireland Galway, University Road, Galway, Ireland article info Article history: Received 25 April 2011 Revised 22 September 2011 Accepted 23 September 2011 Available online 7 October 2011 Keywords: Demospongiae Porifera Sponges Molecular systematics Taxonomy Phylogeny Evolution abstract The current morphological classification of the Demospongiae G4 clade was tested using large subunit ribosomal RNA (LSU rRNA) sequences from 119 taxa. Fifty-three mitochondrial cytochrome oxidase 1 (CO1) barcoding sequences were also analysed to test whether the 28S phylogeny could be recovered using an independent gene. This is the largest and most comprehensive study of the Demospongiae G4 clade. The 28S and CO1 genetrees result in congruent clades but conflict with the current morphological classification. The results confirm the polyphyly of Halichondrida, Hadromerida, Dictyonellidae, Axinel- lidae and Poecilosclerida and show that several of the characters used in morphological classifications are homoplasious. Robust clades are clearly shown and a new hypothesis for relationships of taxa allo- cated to G4 is proposed. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Sponges are a very diverse and successful group with more than 8000 valid species (World Porifera Database, van Soest et al., 2011), and potentially a similar number of undescribed and undiscovered taxa (Hooper and Lévi, 1994). They occur in all aquatic habitats, from temporary fresh water ponds to the abyssal plains. Sponges also have economic potential e.g. the commercial ‘bath sponge’ and more recently as a source of novel compounds for the pharma- ceutical industry (e.g. Faulkner, 2000). They are also of interest from a phylogenetics perspective as they are assumed to be one of the earliest diverging metazoans (Philippe et al., 2009). This re- cent interest in the group has sparked a new wave of research in sponge systematics. By far the largest group of sponges is the class Demospongiae which represents almost 80% of all known sponges. The classifica- tion of Demospongiae has been difficult to resolve. Minchin (1900) stated ‘‘The subdivisions of the class Demospongiae is a mat- ter of great difficulty, and one upon which little agreement is to be found amongst authorities.’’ Lévi (1957) pointed out that Demo- spongiae was one of the last groups where the classification at the levels of subclasses, orders and families was still unresolved. Due to the paucity of characters available to sponge taxonomists the classification has mostly been based on spicule morphology and skeletal architecture, yet both of these types of characters can be subject to secondary loss and reversion as well as parallel evolu- tion and convergence. The difficulty of distinguishing between homoplasy and homology in these circumstances has meant that the characters have been interpreted differently by sponge taxono- mists. The most recent attempt to produce a stable classification was based (almost entirely) on morphology (Systema Porifera, Hoo- per and van Soest, 2002). Since the early 1990s a number of molec- ular studies have suggested that several of the orders and families defined in Systema Porifera are not monophyletic; this was recently reviewed by Boury-Esnault (2006) and by Erpenbeck and Wörheide (2007). Borchiellini et al. (2004) obtained full length sequences of 18S rRNA and the C1–D1 region of 28S rRNA for a range of demosponge species to test whether the order-level classification was congru- ent with molecular data. On the basis of combined 28S and 18S sequence data they showed that the class Demospongiae is mono- phyletic as long as homoscleromorpha is excluded. Homo- scleromorph sponges possess a basal membrane of collagen IV distinguishing them from other sponges. Recent phylogenomic data suggest their sister group relationship with calcareous 1055-7903/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.ympev.2011.09.016 ⇑ Corresponding author. E-mail address: christinemorrow@gmail.com (C.C. Morrow). Molecular Phylogenetics and Evolution 62 (2012) 174–190 Contents lists available at SciVerse ScienceDirect Molecular Phylogenetics and Evolution journal homepage: www.elsevier.com/locate/ympev