Message 2000-10-0007: RE: RE: Nathan Wilson's question

Tue, 10 Oct 2000 12:48:14 -0400

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Date: Tue, 10 Oct 2000 12:48:14 -0400
From: "Moore, Gerry" <gerrymoore@bbg.org>
To: 'Philip Cantino' <cantino@ohiou.edu>
Cc: PhyloCode@ouvaxa.cats.ohiou.edu
Subject: RE: RE: Nathan Wilson's question




PC: I am confused by Gerry Moore's position, as presented 
in his first message on this subject and referred to subsequently.

GM: For example, let's say Clade Z is defined as the least inclusive clade
containing species 3 and species 4. Species 3 is then shown to have
originated through the hybridization between species in Clade A and Clade B.
When the definition was originally formulated it was believed that species 3
was a member of only Clade A (not B) and the circumscription of Clade Z was
exclusive of Clade B.  Doesn't the circumscription of Clade Z have to
include all nonnested clades to which each specifier (see Art. 11.1) is a
member (i.e.,  the circumscription of Clade Z will have to be expanded to
include Clade B to accommodate specifier Species 3 being a member of the
nonnested Clades A and B)?


In this example, Species 3 was originally thought to have a single origin in
clade A.  It was later shown that it was of hybrid origin with one parental
species from Clade A and the other from Clade B.  The problem is then how
does one (re)circumscribe Z (in above example) in light of this new
information regarding the specifier species 3? 

PC: I don't understand why Gerry thinks that the circumscription of Clade Z
must include all nonnested clades to which each specifier belongs....
Clearly, the named clade can't include all nested clades to which each
specifier belongs (if it did, every name would refer to the clade comprising
all of life).  Why should it include all non-nested clades to which each
specifier belongs?

  That's not what I meant. I meant all nonnested clades in the context of
the definition. The original definition of Z: "The least inclusive clade
that contains species 3 and species 4". Thus, I don't mean all nested clades
(which would refer to the clade of life) ... but rather I  raise the
question as to what clades must be included in the circumscription of Z in
order to properly apply the definition of Z?  In light of the new
information on species 3 (i.e., its hybrid status) does the circumscription
of Clade Z change (i.e., expand to include clade B since species 3 has now
been shown to be a member of clade A and clade B due to its hybrid origin)?
More broadly the question here is how are definitions to be applied when one
or more of their specifier species belong to multiple nonnested clades (also
refer to Michel Laurin's post)?
  Looking at it another way, each specifier species serves as a point of
reference in the definition of a taxon name.  In the context of an accepted
phylogeny one uses these reference points to apply the definition of a taxon
name (i.e., circumscribe the taxon).  However, when a specifier species
belongs to multiple nonnested clades it has multiple points of reference and
which of these are to be used when applying the definition of the taxon
name? In my earlier posts I advocated that all points of reference are to be
used by advocating the expansion of Z's circumscription to include Clade B
(to which species 3 also belongs).
  Phil, I think this issue (example) might best be dealt with reviewing the
example using cladograms.  I will put one together and send it to you.   

Cheers,
Gerry Moore   





  

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