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Author Topic:   Interesting development at the base of the animal tree (Re: comb jellies)
Chiroptera
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Posts: 6638
From: Oklahoma
Joined: 09-28-2003
Member Rating: 4.9


Message 1 of 13 (463433)
04-16-2008 7:08 PM


A recent genetic study seems to show that the comb jellies (a phylum which look like a simpler version of jelly fish) was the first taxon to split from the main animal tree.

This is surprising in a way; since sponges are the simplest extant animals, it was assumed that Porifera was the first to branch off, the complexity of the rest of the animal kingdom being assumed to be due to the complexity of the common ancestor.

But if Ctenophora did branch off first, there are a couple of intriguing possibilities: either the last common ancestor of extant animals was already relatively complex and sponges then evolved to be simpler, or Ctenophora and the non-sponge animals represent two branches that evolved complexity independently.

Fascinating stuff. I got this from Theology Web, where there has already been a bit of a discussion.

Edited by Adminnemooseus, : Added the "(Re: comb jellies)" to the topic title.


Speaking personally, I find few things more awesome than contemplating this vast and majestic process of evolution, the ebb and flow of successive biotas through geological time. Creationists and others who cannot for ideological or religious reasons accept the fact of evolution miss out a great deal, and are left with a claustrophobic little universe in which nothing happens and nothing changes.
-- M. Alan Kazlev
Replies to this message:
 Message 2 by Dr Jack, posted 04-17-2008 6:47 AM Chiroptera has not yet responded
 Message 3 by Blue Jay, posted 04-17-2008 4:27 PM Chiroptera has responded
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Dr Jack
Member (Idle past 275 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


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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Blue Jay
Member (Idle past 868 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 3 of 13 (463480)
04-17-2008 4:27 PM
Reply to: Message 1 by Chiroptera
04-16-2008 7:08 PM


This is the title of the Theology Web article:

quote:
Shock: First Animal on Earth Was Surprisingly Complex

And, from then on, they intepret everything as two-faced pandering for the great religion of evolutionism.

It's frustrating to hear this sort of nonsense. Anybody who knows the slightest thing about the ToE should realize that the complexity of a modern animal does not necessitate its ancestor to be complex.

quote:
The first is that the comb jelly evolved its complexity
independent of other animals
after branching off to forge its own path. (emphasis mine)

It didn't start as complex, it evolved into complexity just like all other complex animals, but it did so separately.

Sorry, I had to make sure there was an answer to that: I couldn't just like sit.


I'm Thylacosmilus.

Darwin loves you.


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Adminnemooseus
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Message 4 of 13 (463526)
04-17-2008 9:40 PM


Thread moved here from the Links and Information forum.
    
randman 
Suspended Member (Idle past 3069 days)
Posts: 6367
Joined: 05-26-2005


Message 5 of 13 (463535)
04-17-2008 11:20 PM
Reply to: Message 3 by Blue Jay
04-17-2008 4:27 PM


Actually, the evidence (assuming evo assumptions) is surprisingly that the theoritical common metazoan ancestor had about the same number of genes as we do, and in fact, "many animal lineages" evolved through "a massive loss of genes" according to one paper (I'd link but the article isn't allowed here).

So there really is no support for the idea:

It didn't start as complex, it evolved into complexity

at least genetically.

Edited by randman, : No reason given.


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Chiroptera
Member
Posts: 6638
From: Oklahoma
Joined: 09-28-2003
Member Rating: 4.9


Message 6 of 13 (463599)
04-18-2008 4:53 PM
Reply to: Message 3 by Blue Jay
04-17-2008 4:27 PM


It didn't start as complex, it evolved into complexity just like all other complex animals, but it did so separately.

It is possible that the last common ancestor of the animal kingdom did have a degree of complexity, and that the sponges did evolve to become simpler. Such things have happened -- look at the tunicates, which are essentially simplified chordates.

Either two branches evolved to be complex independently, or the clade started relatively complex and one branch evolved to become less complex. Both scenarios have two events, so I think that (just looking at relative complexity) both are equally parsimonius.

If you look at the tree developed by this group:


Click to enlarge

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).


Speaking personally, I find few things more awesome than contemplating this vast and majestic process of evolution, the ebb and flow of successive biotas through geological time. Creationists and others who cannot for ideological or religious reasons accept the fact of evolution miss out a great deal, and are left with a claustrophobic little universe in which nothing happens and nothing changes.
-- M. Alan Kazlev
This message is a reply to:
 Message 3 by Blue Jay, posted 04-17-2008 4:27 PM Blue Jay has not yet responded

Replies to this message:
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LucyTheApe
Inactive Member


Message 7 of 13 (463601)
04-18-2008 5:22 PM
Reply to: Message 1 by Chiroptera
04-16-2008 7:08 PM


Upside down tree of life
A recent genetic study seems to show that the comb jellies (a phylum which look like a simpler version of jelly fish) was the first taxon to split from the main animal tree.

Does this mean that I can head back up the trees?


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Dr Jack
Member (Idle past 275 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


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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Chiroptera
Member
Posts: 6638
From: Oklahoma
Joined: 09-28-2003
Member Rating: 4.9


Message 9 of 13 (463803)
04-20-2008 4:34 PM
Reply to: Message 8 by Dr Jack
04-20-2008 7:42 AM


Hi, Mr. Jack.

Actually, a little bit more can be said. I have composed a graphicthat shows two scenarios, both of which imply that the members of Bilateria are more closely related to each other than they are to any other group, and that sponges (Porifera) and jellyfish (Cnidaria) are both more closely related to Bilateria than either are to comb jellies (Ctenophora):


Click to enlarge

Thanks to ImageShack for Free Image Hosting

However, there is a subtle difference: in scenario 1, jellyfish are more closely related to Bilateria than to sponges, while in scenario 2 jellyfish and sponges are more closely related to each other than either are to Bilateria.

According to the graphic that I have already posted, the authors of the paper chose scenario 2 as their preferred scenario; you'll see that members of Porifera and Cnidaria share a common node that is not shared with the other groups.

Now, I haven't read the paper yet (I haven't yet made it to the library -- I'm also going to see whether I can scam a copy of the paper for free before I resign myself to paying for it), so it is possible that in the paper the authors caution that their data doesn't rule out scenario 1 (or a third scenario where Porifera is more closely related to Bilateria than they are to Cnidaria). I'm just going by the graphic.

So, according to this scenario, there was a hypothetical ancestor, A, to all extant animals. A then split into two reproductively isolated populations, one of which evolved into the comb jellies, and the other which evolved into B'. B' then split into two isolated populations, one of which evolved into the ancestor of the Bilateria, and the other which evolved into D. Finally, D was the ancestor of sponges and jellyfish.


Speaking personally, I find few things more awesome than contemplating this vast and majestic process of evolution, the ebb and flow of successive biotas through geological time. Creationists and others who cannot for ideological or religious reasons accept the fact of evolution miss out a great deal, and are left with a claustrophobic little universe in which nothing happens and nothing changes.
-- M. Alan Kazlev
This message is a reply to:
 Message 8 by Dr Jack, posted 04-20-2008 7:42 AM Dr Jack has responded

Replies to this message:
 Message 10 by Dr Jack, posted 04-20-2008 5:26 PM Chiroptera has responded

  
Dr Jack
Member (Idle past 275 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


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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 Message 9 by Chiroptera, posted 04-20-2008 4:34 PM Chiroptera has responded

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 Message 11 by Chiroptera, posted 04-20-2008 6:44 PM Dr Jack has responded

  
Chiroptera
Member
Posts: 6638
From: Oklahoma
Joined: 09-28-2003
Member Rating: 4.9


Message 11 of 13 (463807)
04-20-2008 6:44 PM
Reply to: Message 10 by Dr Jack
04-20-2008 5:26 PM


In your graphics you have shown essentially equal genetic differences between the branch points.

Actually, my graphics show no information whatsoever about the absolute genetic differences, and were intended to show only the relative timing of the splits. I didn't realize that the convention in molecular biology is to include information about genetic differences visually in the cladogram. Evidently, I was misled by cladograms prepared by paleontologists (and molecular biologists preparing materials for popular consumption), which seem to use more or less regularly spaced nodes. Next time I prepare a simplified cladogram I will explicitly state that no implications about absolute differences or absolute dates are intended.

Thanks for the clarification.

Edited by Chiroptera, : No reason given.


Speaking personally, I find few things more awesome than contemplating this vast and majestic process of evolution, the ebb and flow of successive biotas through geological time. Creationists and others who cannot for ideological or religious reasons accept the fact of evolution miss out a great deal, and are left with a claustrophobic little universe in which nothing happens and nothing changes.
-- M. Alan Kazlev
This message is a reply to:
 Message 10 by Dr Jack, posted 04-20-2008 5:26 PM Dr Jack has responded

Replies to this message:
 Message 13 by Dr Jack, posted 04-21-2008 8:36 AM Chiroptera has not yet responded

  
platypus
Member (Idle past 3924 days)
Posts: 139
Joined: 11-12-2006


Message 12 of 13 (463818)
04-20-2008 10:01 PM
Reply to: Message 5 by randman
04-17-2008 11:20 PM


quote:
Actually, the evidence (assuming evo assumptions) is surprisingly that the theoritical common metazoan ancestor had about the same number of genes as we do, and in fact, "many animal lineages" evolved through "a massive loss of genes" according to one paper (I'd link but the article isn't allowed here).

So there really is no support for the idea:

quote:
It didn't start as complex, it evolved into complexity

at least genetically.


Actually, the complexity refered to in the article is visual complexity, posessing a nervous system, mouth, and anus in particular. It is general unknown how genetic complexity relates to visual complexity. A longer genome does not necessarily mean you get something that looks more complex. Even thoush Ctenophores (comb jellies) have a nervous system like higher animals, that nervous system could have evolved from a different set of genes, after the split from the main animal line. So as the paper says, there is not enough evidnce one way or another (yet).


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Dr Jack
Member (Idle past 275 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


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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