Interesting question.  Of course Art is using the information from
     his black box sequencer as a piece of data (albeit probably the most
     important) along with other information derived from his research.  It
     is hard to say without knowing if the snails were found in the same
     niche, the same molluscan provenance, or the same ocean.  I would say
     that if all three were found in geographically different areas, then
     Art has DNA evidence to support convergent and divergent evolution.
     The two snails that look different, but have similar DNA have diverged
     from a common ancestor, perhaps by geographic separation, to the point
     that they look very different, but their isolation has not been so
     long as to have caused a significantly different DNA profile (except
     maybe that gene or genes responsible for it's shell morphology).  The
     two that are very similar phenotypicly, but not genotypicly could have
     evolved independently from two totally different looking ancestors.
     Perhaps the ecological niche in which they were found requires a
     morphological adaptation for survival such as large stout spines and a
     heavy shell to remain anchored in a high energy environment.  Is
     morphology still a valuable tool?  I would say very much so.  My
     experience is mostly in the field of bacterial genetics were many
     times bacteria look the same but are very different.  In all cases,
     biochemical/metabolic/physiological parameters are determined in the
     identification of a potentially new strain or species.  Never is DNA
     data used as the sole determination of identification.  So are these
     different species or subspecies?  That depends on whether Art is a
     lumper or a splitter.  If it was me, and the snails looked
     significantly different, I might call them different species and at a
     minimum different subspecies (perhaps Artopsis weilensis and A.
     weilensis weilensis) whereas the two similar looking, but genotypicly
     dissimilar species would definitely be different species.
 
        What is a paleontologist to do?  I do not know, but at least he
     does not have DNA evidence to question his interpretations.  However
     in regards to soft parts, I have found the soft tegumen (I hope that
     is the correct term) that holds the two shells of bivalves together
     preserved in several locations (Miocene Choptank fm. in Maryland and
     Chipola Fm. in Florida as well as on large Lower Eocene Venericardia
     at Hatchetigbee Bluff in Alabama).  Would anyone know if DNA could be
     retained in these tissues?  I have always wondered.
 
 
     Michael Reagin
     Cleveland Heights, OH
 
 
______________________________ Reply Separator _________________________________
Subject: Re: DNA question
Author:  Conchologists of America List <[log in to unmask]> at
Internet-APBiotech-America
Date:    10/20/98 9:17 AM
 
 
Art Weil's question and the various lively answers have made an interesting
thread. The latest message, by Michael Reagin, supports some of Art Weil's
"wild" speculation. Yes, DNA sequencing is getting cheaper as time goes by,
and he even suggests that rapid DNA sequencing would be done using
mitochondrial DNA rather than whole-organism DNA. I doubt if Art would mind!
Art Weil's "black box" may be simplistic, but Michael Reagin shows that the
"Question Man" has indeed asked a reasonable question. (Of course, anyone
who saw the recent movie "Gattaca" has been wondering along similar lines.)
 
My question has to do with the results. Suppose that Art has his black box
that rapidly and inexpensively sequences DNA. He finds that some snails
look almost alike but have very different DNA. Very well, DNA is the code
of life itself, so obviously these are different taxa
(species/genera/etc.), and he is inspired to search for the morphologic
details that might distinguish them in the field. More work is needed, but
no change in principles.
 
Then Art tests two snails that look very different but have almost
identical DNA. He tests many more snails and finds that these results are
consistent, not due to a mistake or to a single pathological individual. My
questions for Michael Reagin and other interested conchologists are: Are
these also separate taxa? Would the DNA specialist prefer to call them
different subspecies rather than different species or genera? Is the DNA
criterion the only one to be considered, or is morphology still considered
to be a valuable tool in taxonomy?
 
And what is a paleontologist supposed to do about it? Fossils usually don't
retain soft parts, much less DNA.
 
Andrew K. Rindsberg
Geological Survey of Alabama