Journal Article

Broad phylogenomic sampling improves resolution of the animal tree of life

Okusu, Akiko, Haddock, Steven H. D., Martindale, Mark Q., Matus, David Q., Edgecombe, Gregory D., Rouse, Greg W., Pang, Kevin, Sørensen, Martin V., Seaver, Elaine, Giribet, Gonzalo, Hejnol, Andreas, Dunn, Casey W., Browne, William E., Wheeler, Ward C., Smith, Stephen A., Schmidt-Rhaesa, Andreas, Obst, Matthias, Kristensen, Reinhardt Møbjerg

2008

Overview

Improved relations The accumulation of molecular data is reshaping our understanding of the evolutionary relationships between the major groups of animals. Early work in the field relied upon data from a small number of genes, but the availability of fully sequenced genomes and expressed sequence tags (ESTs, short sub-sequences obtained from large numbers of complementary DNA clones), means that huge swathes of the animal kingdom can now be subjected to such analysis. A new study describes and discusses almost 40 megabases-worth of ESTs from animals of 21 phyla, including 11 animals for which no genomic or EST data were previously available. The conclusions confirm ideas long established by anatomy, including the monophyletic nature of the molluscs, deriving from a common ancestor despite their remarkable variety. New and interesting evolutionary relationships are also uncovered, including a single origin for spiral cleavage of the early embryo. The cover illustrates animal diversity, including acorn, ribbon, arrow and velvet worms, jellyfish and sea spider. This paper describes and discusses almost 40 megabases of expressed sequence tags (EST) clones from the DNA of animals from 21 phyla, including 11 animals for which genomic or EST data were previously lacking. The conclusions confirm ideas long established by anatomy, but raise new and interesting evolutionary relationships. 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 animals belonging to 21 phyla, including 11 phyla previously lacking genomic or expressed-sequence-tag data. Analysed in combination 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.

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: Animals / Annelida / Arthropoda / Bayes Theorem / Biologi / Biological and medical sciences / Biological evolution / Biological Sciences / Brachiopoda / Classification / Classification - methods / Computational Biology / Databases, Genetic / Ecdysozoa / Evolution / Evolution, Molecular / Evolutionary biology / Expressed Sequence Tags / Fundamental and applied biological sciences. Psychology / Gene Library / Genetic / Genetics of eukaryotes. Biological and molecular evolution / Genomics / Humanities and Social Sciences / Humans / Hypotheses / letter / Lophotrochozoa / Marine / Markov Chains / methods / Molecular / Molecular biology / Mollusca / Mollusks / multidisciplinary / Phylogeny / Protostomia / Reproducibility of Results / Sample Size / Science / Science (multidisciplinary) / Sensitivity and Specificity / Taxonomy