Phylogenomics Revives Traditional Views on Deep Animal Relationships

Abstract

The origin of many of the defining features of animal body plans, such as symmetry, nervous system, and the mesoderm, remains shrouded in mystery because of major uncertainty regarding the emergence order of the early branching taxa: the sponge groups, ctenophores, placozoans, cnidarians, and bilaterians. The "phylogenomic" approach [1] has recently provided a robust picture for intrabilaterian relationships [2, 3] but not yet for more early branching metazoan clades. We have assembled a comprehensive 128 gene data set including newly generated sequence data from ctenophores, cnidarians, and all four main sponge groups. The resulting phylogeny yields two significant conclusions reviving old views that have been challenged in the molecular era: (1) that the sponges (Porifera) are monophyletic and not paraphyletic as repeatedly proposed [4-9], thus undermining the idea that ancestral metazoans had a sponge-like body plan; (2) that the most likely position for the ctenophores is together with the cnidarians in a "coelenterate" clade. The Porifera and the Placozoa branch basally with respect to a moderately supported "eumetazoan" clade containing the three taxa with nervous system and muscle cells (Cnidaria, Ctenophora, and Bilateria). This new phylogeny provides a stimulating framework for exploring the important changes that shaped the body plans of the early diverging phyla.

Evolutionary history of the mammalian synaptonemal complex

“…These, however, show an exceptionally large evolutionary distance as it is indicated by their long branches. Apart from this, the proteins cluster together in the phylogenetic tree which roughly recovers metazoan phylogeny (Philippe et al 2009; see also reference tree in Figure 6-1). This points to their potential common origin.…”

“…A comparison with the phylogeny of Metazoa (Philippe et al 2009; see also reference tree in Figure 6-1) reveals that the two respective sequences of the vertebrate species separate into two distinct clusters in this tree (green and red in Figure 9-2). Both are further separated from the invertebrate sequences (blue in Figure 9-2).…”

Entre homéostasie et développement, quelles stratégies pour régénérer ?

“…En conséquence, il apparaît impérieux d'identifier des modèles expérimentaux qui offrent la possibilité de (Trembley, 1744). L'Hydre est un hydrozoaire qui appartient au phylum des cnidaires, phylum qui, avec celui des cténophores, forme un groupe frère de celui des bilatériens (Philippe et al, 2009). Cependant l'Hydre a un cycle de vie différent de celui de la plupart des hydrozoaires qui prennent la forme de méduse à l'âge adulte.…”

Gènes anciens et gènes nouveaux dans la boîte à outils moléculaire de la cellule souche ancestrale des animaux

“…Dès lors, comprendre les bases génétiques de l'acquisition des cellules souches peut nous aider à comprendre celles de l'émergence et de l'évolution des animaux. Les éponges forment le groupe frère de tous les autres métazoaires (appelés eumétazoaires) [2,3] et occupent à ce titre une position clé pour comprendre les premières étapes évolutives des animaux [15] (➜). Depuis 2010, le s é q u e n ç a g e d u génome de trois espèces d'éponges et des transcriptomes d'une dizaine d'autres a révélé la présence de la plupart des familles et sous-familles de gènes de développement connus chez l'homme ou la drosophile [4].…”