Ctenophores and O’Leary jumping the gun
Predictably, Denyse O’Leary is getting all excited about a paper in this week’s Nature that finds Ctenophora (comb jellies) to be the first multicellular branch off the Tree of Life, a divergence that precedes that of the relatively simpler sponges. Apparently only accessing a LiveScience article, O’Leary breathlessly declares:
All this shock and awe comes from not taking the Avalon explosion and the Cambrian explosion of life forms seriously for what they can tell us about the real history of life, rather than the Darwinian fantasy.
Problem is, if one reads the original article, one gets a somewhat more hesitant view of things:
The placement of ctenophores (comb jellies) as the sister group to all other sampled metazoans is strongly supported in all our analyses. This result, which has not been postulated before, should be viewed as provisional until more data are considered from placozoans and additional sponges. If corroborated by further analyses, it would have major implications for early animal evolution, indicating either that sponges have been greatly simplified or that the complex morphology of ctenophores has arisen independently from that of other metazoans. [emphasis mine]
The gun. It is being jumped. Only two species of sponge (Oscarella carmella and Suberites dormuncula) were analyzed and, as the authors themselves note, Suberites has poor gene sampling which may simply provide too few informative characters for phylogenetic reconstruction. In addition, no Placozoans were analyzed. These factors – as the authors themselves note – weakens the reliability of the claim that ctenophores diverged first. Simply put, further work is required.
Here’s a suggestion, Denyse. Read the article before you pontificate, m’kay? I’m guessing they taught you something in journalism school about that.
Ref: CW Dunn et al. (2008) "Broad phylogenomic sampling improves resolution of the animal tree of life." Nature 452: 745-749. doi:10.1038/nature06614