At 06:55 AM 1/4/99 -0800, Deborah Wisti-Peterson wrote:
>
>Michelle <MBlanchrd at aol.com> said;
>
>"Has anyone done DNA testing on American and Northwestern Crows? I'm
willing to
>bet that's the only way we'll really be able to tell if they are truly two
>different species."
>
> the problem with the method of speciating crows (or anything else,
> for that matter) using DNA analyses is defining exactly how similar
> or different two species must be before they are classified as
> separate species.
>
> Deborah Wisti-Peterson

Deborah is essentially correct: species are not usually defined by an
agreed-upon number of differences in DNA sequence, but by morphological
differences and the ability (or inability) to interbreed.
There are ways in which DNA differences could be used as evidence for
distinct species. Here are a couple of simplified examples. The most
obvious is if the "genuine" NW crows were found to be more closely related
in DNA sequence to another accepted Corvus species than to AM crows. (This
would leave open the question of whether NW crows belong to the other
Corvus species.)
A more likely scenario would be if "genuine" NW crows were found to have a
distinct set of DNA markers that were absent in all AM crows, and vice
versa. If Puget Sound crows were found to have the markers of one type of
crow but not the other (or neither), the result could be interpreted to
mean that NW and AM crows do not interbreed and are distinct species.
Conversely, if the Puget Sound crows had a mixture of the two sets of
markers, it could be interpreted as evidence of interbreeding. However, if
people accept interbreeding populations like Glaucus-Winged and Western
Gulls as "good species" (which seems bizarre to me, but no ornithologists
have asked for my opinion), then establishing that Puget Sound crows
interbreed with populations of NW and AM crows will not in any way resolve
how many species there are.

Paul Talbert
Seattle
tuisto at oz.net