Subject: Re: VCR Fox Sparrows (was Cascadian Fox Sparrows)
Date: Jun 16 09:22:29 1995
From: Christopher Hill - cehill at u.washington.edu




On Fri, 16 Jun 1995, Dennis Paulson wrote:

[about breeding fox sparrows on Vancouver Island:]

> Much the more interesting question, to me, is to try to figure out their
> origin--that is, which subspecies are they. This could only be solved by a
> specimen or, at the very least, netting, capture and close-up photography.
> If they are "pure" individuals of one of the subspecies, probably just good
> photos in the field would tell us that, but it sounds as if there were some
> thought that they might be intermediate. As I wrote, if this is indeed a
> hybrid population, it may have some bearing on the question of whether the
> coastal and mountain breeders are distinct species. I'm not sure whether
> mitochondrial DNA, which could be checked, can be extracted from blood
> samples or not.
>

I am fairly certain that R. M. Zink would argue that the existence
of some hybrids on Vancouver Island has about zilch to do with whether or
not the coastal and mountain breeders are distinct species. In fact I
heard him argue exactly that point when he visited the U. of Washington
this past winter. His position is that ability to hybridize is a an
ancestral trait, and that the retention of that ability by two genetically
divergent populations is not, in and of itself, particularly important
(consider polar bears and grizzlies, whose hybrids offspring are fertile
to the nth generation, as a somewhat trivial example). Two species may
long ago have diverged irreversibly, but still the members of those
species may occasionally hybridize in the wild. As long as the level of
interbreeding is not enough to mix the two gene pools appreciably, the
hybridization is pretty irrelevant. You can determine how different the
two gene pools are with molecular techniques such as mitochondrial DNA
sequencing.

I am well aware, and of course, so is Zink, that the "do they
hybridize in the wild?" criterion has been an important part of the
definition of a species in ornithology for a long time, although it is
not given such weight in botany, for one example. Hybridization may
or or may not be important, but why focus so much attention on the process
(hybridization)? Why not instead look directly at the results (degree of
genetic mixing across populations)?

Chris Hill
Seattle, WA
cehill at u.washington.edu


> The recent reference that I mentioned yesterday is: Zink, R. M. 1994.
> The geography of mitochondrial DNA variation, population structure,
> hybridization, and species limits in the Fox Sparrow (_Passerella iliaca_).
> Evolution 48: 96-111. Sorry, it wasn't in Systematic Zoology after all.
>
> Dennis Paulson, Director phone: (206) 756-3798
> Slater Museum of Natural History fax: (206) 756-3352
> University of Puget Sound e-mail: dpaulson at ups.edu
> Tacoma, WA 98416
>
>
>