[Taxacom] microRNAs and Brachiopoda relatives

[Ken Kinman]

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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