[Taxacom] microRNAs and Brachiopoda relatives (correction)

[Ken Kinman]

Dear All,
      Just wanted to correct one thing in my posting yesterday.  
Conway-Morris' idea was actually that halkieriids folded up to evolve into 
*brachiopods*.  Others relate them to molluscs instead.  In any case, I 
still strongly believe that bivalved molluscs, bivalved arthropods, and 
brachiopods are relatively primitive forms which sometimes *unfold* to 
evolve into wormlike forms (whether they retain shells or not).  This is 
clear for some forms (shipworms for instance), but not so clear for others 
(gastropods, annelids, nemerteans, platyhelminths, etc.).  Unfolding and 
shell loss is far more common than people realize, but the transformations 
are often so radical that it isn't going to be easy to prove.  I don't know 
why all these "folding up" hypotheses are so popular.  Seems backwards to 
me.
     -----Ken Kinman
********************************
>From: "Ken Kinman" <kinman at hotmail.com>
>To: TAXACOM at mailman.nhm.ku.edu
>Subject: [Taxacom] microRNAs and Brachiopoda relatives
>Date: Mon, 08 Oct 2007 02:45:47 +0000
>
>Dear All,
>      Using the sequences of microRNAs to study the phylogeny of Metazoa 
>and Metaphyta is a relatively recent science.  I was just reading an 
>abstract to this month's GSA Conference that claims Brachiopoda and 
>Phoronida are members of Lophotrochosa (not Deuterostomia) based on the 
>presence of two microRNA sequences (which are lacking in deuterostomes and 
>ecdysozoans).
>
>     They base this on the assumption (which I question) that microRNAs are 
>"almost never secondarily lost" once acquired.  Is such an assumption 
>really warranted?  Granted, a clear majority of microRNAs seem to persist 
>once acquired, but is that statement "almost never secondarily lost" 
>actually warranted?  From what I have read, I believe this statement is a 
>real stretch (extrapolation) from limited data, if not just wishful 
>thinking.  Anyone else have any opinion on this subject?  Here is the link 
>to the abstract of their conference paper:
>
>http://gsa.confex.com/gsa/2007AM/finalprogram/abstract_128502.htm
>
>   -----Ken Kinman
>P.S.  They also mention some unspecified nuclear "housekeeping genes" as 
>well.  But if their strongest evidence consists of just two microRNAs 
>(which they assume are "almost never" lost and which they presumably also 
>assume appear in most, if not all, Lophotrochozoa), then I can't say it is 
>terribly impressive given the morphological data connecting brachiopods and 
>phoronids with deuterostomes.  Since Briggs is one of the authors, they are 
>probably partially influenced by the ideas of Simon Conway-Morris that 
>halkieriid worms somehow "folded up" and evolved into bivalved molluscs 
>(which I also found very unconvincing).  Conway-Morris has done a lot of 
>fine work, but that particular hypothesis never made any sense to me.
>

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