Dunn et al Nature 2008

Dunn et al Nature 2008 - Vol 452 | 10 April 2008 |...

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LETTERS Broad phylogenomic sampling improves resolution of the animal tree of life Casey W. Dunn 1 { , Andreas Hejnol 1 , David Q. Matus 1 , Kevin Pang 1 , William E. Browne 1 , Stephen A. Smith 2 , Elaine Seaver 1 , Greg W. Rouse 3 , Matthias Obst 4 , Gregory D. Edgecombe 5 , Martin V. Sørensen 6 , Steven H. D. Haddock 7 , Andreas Schmidt-Rhaesa 8 , Akiko Okusu 9 , Reinhardt Møbjerg Kristensen 10 , Ward C. Wheeler 11 , Mark Q. Martindale 1 12,13 Long-held ideas regarding the evolutionary relationships among animals have recently been upended by sometimes controversial hypotheses based largely on insights from molecular data 1,2 . These new hypotheses include a clade of moulting animals (Ecdysozoa) 3 and the close relationship of the lophophorates to molluscs and annelids (Lophotrochozoa) 4 . Many relationships remain disputed, including those that are required to polarize key features of character evolution, and support for deep nodes is often low. Phylogenomic approaches, which use data from many genes, have shown promise for resolving deep animal relationships, but are hindered by a lack of data from many important groups. Here we report a total of 39.9 Mb of expressed sequence tags from 29 ani- mals belonging to 21 phyla, including 11 phyla previously lacking genomic or expressed-sequence-tag data. Analysed in combina- tion with existing sequences, our data reinforce several previously identified clades that split deeply in the animal tree (including Protostomia, Ecdysozoa and Lophotrochozoa), unambiguously resolve multiple long-standing issues for which there was strong conflicting support in earlier studies with less data (such as velvet worms rather than tardigrades as the sister group of arthropods 5 ), and provide molecular support for the monophyly of molluscs, a group long recognized by morphologists. In addition, we find strong support for several new hypotheses. These include a clade that unites annelids (including sipunculans and echiurans) with nemerteans, phoronids and brachiopods, molluscs as sister to that assemblage, and the placement of ctenophores as the earliest diverging extant multicellular animals. A single origin of spiral cleavage (with subsequent losses) is inferred from well-supported nodes. Many relationships between a stable subset of taxa find strong support, and a diminishing number of lineages remain recalcitrant to placement on the tree. Expressed sequence tags (ESTs) provide opportunities to sample diverse genes from a large number of taxa 6 . Several recent phyloge- nomic studies, based largely on EST data, analysed matrices contain- ing more than 140 genes from up to 34 metazoans (multicellular animals) 7–9 . However, the included species were not well sampled across extant metazoan diversity. These analyses also relied on either ribosomal proteins or a list of target genes identified from a small (1,152 ESTs) choanoflagellate data set 10 , limiting the possibilities of EST studies to inform gene selection and homology assignment. Rather than look for predefined sets of genes in our data, we present
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Dunn et al Nature 2008 - Vol 452 | 10 April 2008 |...

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