Molecular phylogeny of Demospongiae: implications for classification and scenarios of character evolution.
An analysis of the phylogenetic relationships of the 13 orders of Demospongiae, based on 18S and C1, D1 and C2 domains of 28S rRNA (for, respectively, 26 and 32 taxa) has been performed. The class Demospongiae as traditionally defined is not found to be monophyletic. Instead, a clade comprising all demosponges except Homoscleromorpha is well-supported, and we define phylogenetically the name Demospongiae in this more restricted sense to preclude the possibility of drastic alterations of the meaning of Demospongiae in the future, depending on the position of Homoscleromorpha. Within this clade Demospongiae s.s., ceractinomorphs and tetractinomorphs are polyphyletic, implying homoplastic evolution of characters such as reproductive strategies (viviparity vs. oviparity) and skeleton architecture (reticulate vs. radiate). The topology derived from our molecular data provides a basis for proposing a new classification of Demospongiae s.s., and suggests a reverse polarity of some characters, with respect to traditional conceptions: viviparity, presence of monaxon spicules and of spongin appear to be ancestral, whereas oviparity, and presence of tetraxon spicules appear as derived characters.
Centre d'Océanologie de Marseille, Université de la Méditerranée, UMR-CNRS 6540, Station marine d'Endoume, rue de la Batterie des Lions, 13007 Marseille, France. borchiellini@com.univ-mrs.fr
Carole
C
Borchiellini
Catherine
C
Chombard
Michaël
M
Manuel
Eliane
E
Alivon
Jean
J
Vacelet
Nicole
N
Boury-Esnault
D000818:Animals; D001483:Base Sequence; D016000:Cluster Analysis; D017931:DNA Primers; D016013:Likelihood Functions; D008522:Mediterranean Sea; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D011161:Porifera / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics*; D012339:RNA, Ribosomal, 28S / Q000235:genetics; D012098:Reproduction / Q000235:genetics; D017422:Sequence Analysis, DNA
D017931:DNA Primers; D012339:RNA, Ribosomal, 28S