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Author Topic:   Descent with Modification v. Larval Hybridization
Dr Jack
Member (Idle past 448 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 16 of 23 (479319)
08-26-2008 12:32 PM
Reply to: Message 15 by Blue Jay
08-26-2008 8:57 AM


Re: Trochophore larvae
Actually, that brings up an interesting point - if this genetic transfer is occuring why aren't we seeing evidence of it on cladistic trees reconstructed from genetic data?

This message is a reply to:
 Message 15 by Blue Jay, posted 08-26-2008 8:57 AM Blue Jay has responded

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Fosdick 
Suspended Member (Idle past 3843 days)
Posts: 1793
From: Upper Slobovia
Joined: 12-11-2006


Message 17 of 23 (479340)
08-26-2008 3:19 PM
Reply to: Message 15 by Blue Jay
08-26-2008 8:57 AM


Re: Trochophore larvae
Bluejay writes:

I have always read that all the phyla in that diagram (Sipuncula, Mollusca, Annelida and Rotifera) are grouped in the clade Lophotrochozoa, whose common ancestor was proposed to have had a trochophore larva.


But, so far as the lophotrochozoans are concerned, they are protostomes, not deuterostomes. Yet the trochophore larvae can be found in both protostomes phyla (e.g. annelids) and deuterostomes phyla (e.g., echinoderms)—see this chart. This suggests that larval hybridization may have occurred across the protostomes-deuterostomes boundary, which is a huge leap on any cladogram.

—HM


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 Message 15 by Blue Jay, posted 08-26-2008 8:57 AM Blue Jay has responded

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Fosdick 
Suspended Member (Idle past 3843 days)
Posts: 1793
From: Upper Slobovia
Joined: 12-11-2006


Message 18 of 23 (479347)
08-26-2008 3:32 PM
Reply to: Message 14 by Dr Jack
08-25-2008 7:11 PM


Re: Punc Eq is wrong; this compounds it.
Mr Jack writes:

There is no "punc eq"; it doesn't need explaining.


So, do you think all evolutionary prcosses can be explained by descent with modification?

—HM


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Dr Jack
Member (Idle past 448 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 19 of 23 (479351)
08-26-2008 3:46 PM
Reply to: Message 18 by Fosdick
08-26-2008 3:32 PM


Re: Punc Eq is wrong; this compounds it.
It depends what you mean by that; there is horizontal gene transfer between organisms, and certain apparently deeply significant events in evolutionary history appear to have occurred by advanced symbiosis - most obviously the history of mitochondria and other organelles in Eukaryotic cells.

But the extent to which these events have influenced evolution is not clear, particularly among the "higher" organisms. Also, it is not clear to me that these are not considered most productively as special forms of individual heritable variation (of which mutation and sexual recombination form the two most important examples) upon which the normal processes of natural selection then operate rather than as distinct processes of evolution.

Finally, various non-adaptive effects certainly do occur (genetic drift and the founder effect to name just two) but, again, these are processes that operate with, rather than instead of, descent with modification.

Even if larval hybridization does turn out to be correct; it will represent a new means of generating genetic variety rather than a strictly alternative means of evolving.


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 Message 18 by Fosdick, posted 08-26-2008 3:32 PM Fosdick has responded

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Blue Jay
Member (Idle past 1041 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 20 of 23 (479385)
08-26-2008 6:19 PM
Reply to: Message 16 by Dr Jack
08-26-2008 12:32 PM


Re: Trochophore larvae
Hi, Mr Jack.

Mr Jack writes:

if this genetic transfer is occuring why aren't we seeing evidence of it on cladistic trees reconstructed from genetic data?

I would think it's for multiple reasons:

  1. Most cladograms are based on just one or two genes, which are not chosen for their roles in development.
  2. Cladists use the same handful of genes for all cladograms they make.
  3. There is less funding for research into invertebrate taxonomy than for, say, human cancer research or grizzly bear monitoring.
  4. The majority of people don't give a wet slap about worms and slugs.

Now, I can't, for certain, say whether these are all in effect over this particular issue, but it seems likely to me. Genes used in cladograms are selected for their estimated mutation rate, not for their activity level at different periods of development. And, since larval development is often quite ephemeral and larvae are often smaller and harder to find and process, scientists probably try to stick with adult-active genes.


-Bluejay

Darwin loves you.


This message is a reply to:
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Blue Jay
Member (Idle past 1041 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 21 of 23 (479386)
08-26-2008 6:25 PM
Reply to: Message 17 by Fosdick
08-26-2008 3:19 PM


Re: Trochophore larvae
Hi, Hoot Mon.

Hoot Mon writes:

the trochophore larvae can be found in both protostomes phyla (e.g. annelids) and deuterostomes phyla (e.g., echinoderms)

Really? Are you sure it's in echinoderms? I've never heard that before. Williamson and Vickers say it's in echiurans, but those are lophotrochozoan worms.

Can you find me a source for this? If you're right, it would lend at least a little credence to this concept, I think. However, I'm still not sure how it would compare to convergent evolution in terms of parsimony and evidence.

You'll still have to do the cladistics test I proposed before I'm fully convinced.


-Bluejay

Darwin loves you.


This message is a reply to:
 Message 17 by Fosdick, posted 08-26-2008 3:19 PM Fosdick has responded

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Fosdick 
Suspended Member (Idle past 3843 days)
Posts: 1793
From: Upper Slobovia
Joined: 12-11-2006


Message 22 of 23 (479393)
08-26-2008 7:38 PM
Reply to: Message 21 by Blue Jay
08-26-2008 6:25 PM


Re: Trochophore larvae
Bluejay writes:

Bluejay writes:

the trochophore larvae can be found in both protostomes phyla (e.g. annelids) and deuterostomes phyla (e.g., echinoderms)


Really? Are you sure it's in echinoderms? I've never heard that before. Williamson and Vickers say it's in echiurans, but those are lophotrochozoan worms.

I'm wrong! Thanks for the biology lesson. Echinoderms do not have trochophore larvae; they have bipinnaria larvae. They do look a little like trochophores, but they don't have the midrift fringe of cilia. Also, trochophore larvae appear to be much more ontogenetically advanced than the bispinnaria larvae of the starfish, for example, which are modified gastrula.

I'm afraid I can't support the idea that larval hybridization occurred between Protostomes and Deuterostomes.
But as you say to Mr Jack in Message 20:

The majority of people don't give a wet slap about worms and slugs.

Probably true, but I like 'em.

—HM


This message is a reply to:
 Message 21 by Blue Jay, posted 08-26-2008 6:25 PM Blue Jay has not yet responded

  
Fosdick 
Suspended Member (Idle past 3843 days)
Posts: 1793
From: Upper Slobovia
Joined: 12-11-2006


Message 23 of 23 (479403)
08-26-2008 8:20 PM
Reply to: Message 19 by Dr Jack
08-26-2008 3:46 PM


Re: Punc Eq is wrong; this compounds it.
Mr Jack writes:


It depends what you mean by that; there is horizontal gene transfer between organisms, and certain apparently deeply significant events in evolutionary history appear to have occurred by advanced symbiosis - most obviously the history of mitochondria and other organelles in Eukaryotic cells...But the extent to which these events have influenced evolution is not clear, particularly among the "higher" organisms.


HGT between nuclear genomes of a "higher" organisms, so that it makes a difference to their natural history, is probably a stretch. (I haven't yet gotten over "The Fly.")

But the extent to which these events have influenced evolution is not clear, particularly among the "higher" organisms. Also, it is not clear to me that these are not considered most productively as special forms of individual heritable variation (of which mutation and sexual recombination form the two most important examples) upon which the normal processes of natural selection then operate rather than as distinct processes of evolution.

Finally, various non-adaptive effects certainly do occur (genetic drift and the founder effect to name just two) but, again, these are processes that operate with, rather than instead of, descent with modification.


Well said. I have to agree.

Even if larval hybridization does turn out to be correct; it will represent a new means of generating genetic variety rather than a strictly alternative means of evolving.

I suppose one could say that genetic engineering and its use of HGT is a new way of evolving without the need for descent with modification (as discussed in Digital Life Design—What a concept!).

—HM


This message is a reply to:
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