Message 2000-09-0002: Nathan Wilson's question

Tue, 26 Sep 2000 17:04:35 -0400

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Date: Tue, 26 Sep 2000 17:04:35 -0400
From: Philip Cantino <>
Subject: Nathan Wilson's question


Since no one else has responded to Nathan Wilson's question, I will
make a stab at it.  I discussed this with Kevin over lunch today, so
the ideas are partially his (I'll leave it to him to correct me if I
misrepresent any of them).

Nathan is concerned about the effect of interclade genetic transfer
on clade nomenclature.  I don't think this is a problem if one
accepts that a species may belong to two non-nested clades.  For
example, if clades A and B are non-nested, and members of species 1
(in clade A) and species 2 (in clade B) hybridize to produce an
offspring that gives rise to species 3, species 3 is a member of both
clade A and clade B.  This must be the case because species 3 is
simultaneously a descendant of both the immediate common ancestor of
clade A and the immediate common ancestor of clade B.

Similarly, if genetic material is transferred by some other means
from species 1 to species 2, then one might argue that species 2 (but
not species 1) is a member of both clades A and B.  It is debatable
whether it is worth treating species 2 nomenclaturally as belonging
to two non-nested clades if only a small percentage of its genetic
material came from clade A, but the principle is the same.

There is nothing in the PhyloCode that prohibits naming a clade, some
species of which belong to another non-nested clade, so I don't think
that the issue that Nathan raised requires that the wording of clade
definitions be modified, as he suggests.  However, the taxonomic
issue of species belonging to non-nested clades is an interesting one
that I don't think has been addressed in the literature.  It is a
significant departure from the traditional rank-based system, in
which a species may belong to only one genus, one family etc.  (I am
comparing ranks to clades here by way of analogy, not suggesting that
they are the same thing.)


Philip D. Cantino
Professor and Chair
Department of Environmental and Plant Biology
Ohio University
Athens, OH 45701-2979

Phone: (740) 593-1128; 593-1126
Fax: (740) 593-1130


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