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Author Topic:   Interesting development at the base of the animal tree (Re: comb jellies)
Dr Jack
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Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
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Message 2 of 13 (463439)
04-17-2008 6:47 AM
Reply to: Message 1 by Chiroptera
04-16-2008 7:08 PM


A quote from the paper (which by the way, interesting stuff):
quote:
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. Independent analyses of ribosomal and non-ribosomal proteins (Supplementary Information and Supplementary Fig. 10) indicate that support for this hypothesis (and for others presented for the first time here, such as Clade A and Clade B) is much greater in the combined analyses than in partitioned analyses with fewer genes. This may explain why these novel clades have not been recovered before, because support requires very broad gene sampling
Emphasis mine.

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 8 of 13 (463787)
04-20-2008 7:42 AM
Reply to: Message 6 by Chiroptera
04-18-2008 4:53 PM


you'll see something interesting. Sponges and true jellyfish compose a single taxon. Now that is something that surprises me (perhaps for no greater reason than I don't know much about the early branchings of the animal tree).
Hmm... if I understand the way this tree was constructed correctly, that's not a necessary interpretation, what it actually shows is that the Bilatera are most closely related to each other than they are to either sponges and true jellyfish, and that sponges and true jellyfish are more closely related to Bilatera that they are to Ctenophora.
This is not particularly surprising as Bilatera has long been recognised as a grouping (a subregnum, in some classifications).

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 10 of 13 (463806)
04-20-2008 5:26 PM
Reply to: Message 9 by Chiroptera
04-20-2008 4:34 PM


Well, no, I don't think so.
In your graphics you have shown essentially equal genetic differences between the branch points. As I understand it the method used in the paper (which I have read - one of the great joys of doing on Open University course is I get free online access to pretty much every journal out there - but cannot claim to have understood all of) cannot distinguish between your scenario 2, and a situation like scenario 1 but where the common ancestor of Cnidaria and Bilatera is close to the common ancestor of all three and the Common ancestor of Bilatera is more distant.
This is particularly true as there are many Bilatera analysed and only one representative for Cnidaria and Porifera.

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Dr Jack
Member
Posts: 3514
From: Immigrant in the land of Deutsch
Joined: 07-14-2003
Member Rating: 8.7


Message 13 of 13 (463831)
04-21-2008 8:36 AM
Reply to: Message 11 by Chiroptera
04-20-2008 6:44 PM


Hmm... yes, I was wrong to assume you'd intended to imply relative differences from the spacing in the graph; while I have seen such, it's not the usual standard. My bad, not yours.
However, leaving that aside, do you think my conclusion regarding the implications of their data is correct? That they cannot distinguish between two seperations close together, a seperation followed by a fork?

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