[Taxacom] Underlying synapomorphies

[Kenneth Kinman]

Hi Bob,
       In example one, I think it would probably be unparsimonious to
call state 1 an underlying synapomorphy.  Given the numbers, I would say
it is either a synapomorphy for the two species (as a clade), or if it
is a rather simple character, more likely a parallelism.        
      The second example is slightly more complicated.  The two species
that have the plesiomorphic state could be: (1) displaying a reversal
(together or separately); (2) simply not part of this genus at all; or
perhaps the most interesting possibility (3) they are at the base of the
genus (as stem-species) before the synapomorphy developed.  If other
characters also show them at the base (as stem-species), they might even
best be regarded as one or two separate subgenera.  Again, it depends on
how complex the characters are (more complex characters are probably
less subject (more "resistant", if you will) to homoplasies like
reversals and parallelisms).        
        In either example, underlying synapomorphy is an hypothesis used
"a posteriori" (after the analysis is done) to perhaps help explain
cases where some characters are at odds with a more prominent
phylogenetic pattern.  In my opinion, I highly doubt it would be helpful
in the first example, and possibly helpful in the second example
(depending on whether other characters show the same pattern).  Like you
said, you will have a lot better idea after you look at a lot of other
characters.  In a perfect world (for taxonomists), synapomorphies would
never be reversed or arise in parallel (after lying genetically
unexpressed).  However, it would also be a lot more boring and less
challenging. 
           -----------Ken Kinman
      
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Bob Mesibov wrote:
I am now thoroughly confused.  Can I ask you to think about two
examples? 
(1) I have 50 species in a genus that I want to 'cladify'. I also have
one outgroup. For a character of interest, the state is 0 for 48 species
and the outgroup and 1 for two species. 
So 1 is a synapomorphy for the two species. It could be evidence of
close common ancestry, or parallel evolution. I'll have a better idea
after I look at a lot more characters. 
The other 48 species might have the *potential* to exhibit state 1.
Should I call 1 an underlying synapomorphy for the whole genus? 
(2) Same 50 species and same outgroup. This time 48 species are state 1,
two species and the outgroup are state '0'. 
Looks like '1' is a good synapomorphy for the genus. The two '0' species
might have had character reversals, or maybe they don't belong in this
genus. I'll have a better idea after I look at a lot more characters. 
The two '0' species might have the *potential* to exhibit state 1.
Should I call 1 an underlying synapomorphy for the whole genus as
currently circumscribed? 
My problem here is that I don't understand how the idea of 'underlying
synapomorphies' can help me in a cladistic analysis. It might help me
interpret the results of an analysis after it's done, but even then
there would be other possibilities. How exactly is the idea useful?