On Tue, 20 Jun 1995, Dennis Paulson wrote:
> [snip]
> I wonder if it is worth questioning the molecular data. I'm afraid I'm n=
ot
> convinced, Scott Freeman's dissertation notwithstanding, that Baltimore i=
s
> more closely related to Altamira and Bullock's to Streak-backed. In
> addition to the fact that Baltimore and Bullock's hybridize fairly readil=
y
> where in contact (but not entirely freely, apparently some selection
> against hybrids), they seem more similar to one another in just about eve=
ry
> way than either is to their putative closest relatives.

Scott Freeman'=92s mtDNA analysis is the only phylogenetic wor=20
on orioles I am aware of, and it cannot be dismissed simply=20
because Baltimore and Bullock'=92s hybridize. This fact is
irrelevant to evaluation of phylogenetic/genealogic=20
relationships among organisms. It indicates that the=20
organisms in question share a common ancestor, but it does=20
*not* indicate that they are each other'=92s closest relatives. =20
Quite simply, the ability of descendants of a common ancestor=20
to reproduce with one another is not automatically lost when=20
descendant populations diverge from one another. This ability can=20
be lost at different times in different descendant populations. =20
Whenever it is present, it is a retained ancestral character=20
(a "symplesiomorphy" in the nomenclature of cladistics). (As an=20
example of how persistent this trait can be, White-lipped and=20
Collared Peccaries can still hybridize after being members of=20
distinct clades for at least *7 million* years.). =20

You can question the molecular data, but doing so in a=20
meaningful way requires getting a dataset with a number of=20
morphological characters (or behavioral, or other molecular,=20
or...) and analyzing it *cladistically*. Simply observing that=20
because Baltimore and Bullock'=92s are more like each other than
either is like Altamira or Streak-backed (i.e. gross phenotypic=20
similarity) and concluding that they are more closely related to one=20
another is not an appeal to parsimony. The application of parsimony=20
to character data requires distinguishing apomorphic (novel or "derived")=
=20
characters from plesiomorphic (ancestral or "primitive") characters. =20
Degree of similarity does not equal degree of relationship. What=20
exactly are the characters shared by Baltimore and Bullock'=92s=20
that require so much convergence? Are you perhaps referring=20
to Bullock'=92s and Baltimore both being sexually dichromatic s
well as migratory? If so, I agree that this is very=20
interesting, but I believe that this association occurs in=20
several other groups as well (tanagers, for example). Why=20
couldn'=92t it occur multiple times in orioles as well? And=20
there are solid theoretical reasons to expect the evolution of=20
sexually selected characters such as bright plumage to proceed=20
from expression in both sexes to expression in males only, and=20
the "loss" of the male character in females will more likely than=20
not happen at different times in different lineages. This does not=20
mean that sexual dichromatism can be dismissed as a potential=20
synapomorphy (shared-derived character) linking Baltimore and=20
Bullock'=92s, but it does mean that we need to include many other=20
characters in the analysis. (And incidentally, finding that=20
Altamira is the sister group of Baltimore does not imply that=20
Altamira was the ancestor of Baltimore.)

Hey, at least we're talking about birds. =20

David Wright
dwright at u.washington.edu