Broad phylogenomic sampling improves resolution of the animal tree of life.
Long-held ideas regarding the evolutionary relationships among animals have recently been upended by sometimes controversial hypotheses based largely on insights from molecular data. These new hypotheses include a clade of moulting animals (Ecdysozoa) and the close relationship of the lophophorates to molluscs and annelids (Lophotrochozoa). 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), 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.
Dunn
Casey W
CW
Kewalo Marine Laboratory, PBRC, University of Hawaii, 41 Ahui Street, Honolulu, Hawaii 96813, USA. casey_dunn@brown.edu
Hejnol
Andreas
A
Matus
David Q
DQ
Pang
Kevin
K
Browne
William E
WE
Smith
Stephen A
SA
Seaver
Elaine
E
Rouse
Greg W
GW
Obst
Matthias
M
Edgecombe
Gregory D
GD
Sørensen
Martin V
MV
Haddock
Steven H D
SH
Schmidt-Rhaesa
Andreas
A
Okusu
Akiko
A
Kristensen
Reinhardt Møbjerg
RM
Wheeler
Ward C
WC
Martindale
Mark Q
MQ
Giribet
Gonzalo
G
D000818:Animals; D001499:Bayes Theorem; D002965:Classification / Q000379:methods*; D019295:Computational Biology; D030541:Databases, Genetic; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D015723:Gene Library; D006801:Humans; D008390:Markov Chains; D010802:Phylogeny; D015203:Reproducibility of Results; D018401:Sample Size; D012680:Sensitivity and Specificity