Assessing the usefulness of histone H3, U2 snRNA and 28S rDNA in analyses of polychaete relationships

Abstract

DNA sequence data from for histone H3 (34 species), U2 snRNA (34 species) and two segments (D1 and D9–10 expansion regions) of 28S rDNA (28 and 26 species, respectively) have been collected to investigate the relationships of polychaetes. Representatives of all of the major morphologically identified clades were used, as well as members of the Sipuncula, Echiura, Turbellaria, Clitellata and Siboglinidae (formerly the phyla Pogonophora and Vestimentifera). Maximum parsimony analyses of the separate data sets gave conflicting results and none conformed closely to previous results based on morphology. Instead each data set provided corroboration of a few of the morphological groupings, usually pairing, though inconsistently, members of the same family. Higher groupings proposed on morphological grounds were rarely recovered. Maximum parsimony analysis of the combined data, excluding areas of uncertain alignment, recovered some morphological groupings such as Cirratulidae, Terebellidae, scale worms and eunicimorphs, and did not significantly contradict others. However, some expected groupings were not recovered. Surprisingly, the fanworms (Sabellidae and Serpulidae) were not shown as sister taxa, and monophyly of Phyllodocida, a morphologically well corroborated clade, required four more steps than most parsimonious trees. Aciculata was not seen in our analyses, although it was the most strongly supported large clade in Rouse and Fauchald (1997, Cladistics and polychaetes. Zoologica Scripta 26, 138–204). Trees constrained to show Aciculata as monophyletic were 18 steps longer than the most parsimonious trees. If trees are rooted on sipunculans rather than the nematode, Aciculata is nearly recovered, being rendered paraphyletic by the inclusion of the sister-pair of Oweniidae and Chaetopteridae. As suggested by some recent morphological and molecular analyses, Siboglinidae and Clitellata may well have sister groups among polychaetes. The morphologically aberrant Sternaspidae are closest to members of Terebellida in the present analyses, supporting the placement of Rouse and Fauchald. Interesting results deserving further assessment concern the placement of Chaetopteridae, Oweniidae and Sipuncula.

On the origin of the Hirudinea and the demise of the Oligochaeta

“…No less than ¢ve genes have been studied so far with this aim in view, but none of them has convincingly recovered groupings (McHugh 1997;Giribet & Ribera 1998;Kojima 1998;Brown et al 1999;Erse¨us et al 2000). If the lack of resolution among polychaetes was initially interpreted to result from poor taxonomic sampling (Brown et al 1999), the careful study of Brown et al based on three di¡erent genes did not signi¢cantly improve the resolution, despite a broad sampling of polychaete diversity, including clitellates. The biological reality of these polytomies thus appears corroborated by independent evidence supporting the hypothesis of an ancient radiation of polychaetes and emergence of clitellates.…”

“…To date, only two of them has identi¢ed a supported although contradictory polychaete sister group to the Clitellata. In the analyses of Brown et al (1999), the pairing of the Siboglinidae with the Clitellata had notable Bremer and some bootstrap support. However, it is signi¢cant that this support was only obtained when the three genes studied (histone H3, U2 snRNA and 28S rDNA) were combined together; each gene taken separately yielded a di¡erent and unsupported sister group to the clitellates.…”

Phylogeny of sipunculan worms: A combined analysis of four gene regions and morphology

“…Several recent publications focusing on systematics of annelids based on DNA sequence data included sipunculans and unanimously placed them in the annelid ingroup, although the number of outgroups was sometimes limited (Brown et al, 1999) and the branch support was generally low for deep nodes in the tree (Bleidorn et al, 2003a,b;Hall et al, 2004). Better resolution and support for deep relationships was achieved by Telford et al (2005) who presented a phylogeny of the Bilateria, based on 72 complete 18S ribosomal RNA sequences.…”

Molecular phylogenetic evidence of a haplosporidian parasite infecting the polychaete Syllis nipponica (Imajima, 1966)

“…Molecular characterization of annelids for the purpose of phylogenetic analysis is experiencing a surge of activity (e.g., Brown et al 1999;Bleidorn et al 2003;Siddall et al 2004). Moreover, the edicts of DNA bar coding are such (DeSalle et al 2005) that for it to be at all useful, many individuals across a taxon's range need to be sequenced.…”