Burt Guttman wrote:

I'm coming to this debate late -- haven't caught up with Tweeters
mail yet -- but I want to express a viewpoint similar to those that I
think a couple of other folks (?Michael Hobbs, Doug Canning?) have at
least implied in their responses. I think DNA is great stuff; as a
molecular biologist, I've worked with it in some way all of my
professional life. It makes us what we are, obviously. But I think
biology has taken a seriously wrongheaded turn if the question of
delimiting species has been turned into a question of the similarity
or difference in DNA sequences. The link between DNA sequences and
the final whole organism, especially one as complicated as a bird or
mammal, is just too long and complicated and tenuous. The only
species definition that makes any sense is one based on the question
of interbreeding. (Irregular or complicated interbreeding, or
interbreeding between groups that aren't sister species, just means
that evolution is still in process and that nat!
ure doesn't always allow us humans to have neat, orderly
classifications for everything.) Whether two organisms will mate
depends on complicated matters of appearance and behavior, which
can't be read off a DNA sequence. I believe DNA sequences, or DNA
hybridization, can be used to make cladograms and to sort out
phylogenies, but I sure as hell hope ornithologists aren't going to
let themselves be bullied by champions of DNA For Everything into
making their judgements about species limits just on the basis of
sequence similarity.
-----------------

I agree with much of what Burt says here, but on the contrary, I
think there is much need for the use of DNA to establish species
relationships, not only phylogenies of groups but even status of
individual species.

I grew up in southern Florida and visited the West Indies quite
often. I can see why Darwin was stimulated, even though it took a
while for the significance of what he was seeing to soak in. It was
always very impressive to me to go from one island group to another
and not only see different species, often filling the same niche, but
different versions of the same species. Whether bird, bat, or lizard,
geographic variation was flamboyantly obvious as we made our way from
island to island in the Bahamas, Greater Antilles, or Lesser
Antilles. You can see the same thing in any major archipelago.

So for a long time the biological species concept has been used to
define species. This concept considers two species to be separate if
they cannot interbreed. It works great when judging SYMPATRIC
species, those that occur together. A Downy and a Hairy Woodpecker
don't seem to interbreed, even though they are very similar. Tree and
Violet-green Swallows don't seem to interbreed, even though they are
very similar. Etc. On the other hand, we've already discussed the
rampant interbreeding between Townsend's and Hermit Warblers, Blue-
winged and Golden-winged Warblers, and our own Western and Glaucous-
winged Gulls as dramatic exceptions to this. Are those species not
distinct species? This does not even take into account all the ducks
and other birds that hybridize regularly enough that they are often
reported by birders. No one who I know doubts that any of these are
full species.

But what to do about assessing species status of all those species
that are ALLOPATRIC: they DO NOT occur together. My West Indian
experience made me very curious about those species. As a birder, it
has been fun to see my life list increase as these island "species"
were split again and again, but it was much more of interest to me as
a biologist, as I had long held the opinion that those populations,
easily distinguished visually, seemed to deserve species status as
much as all those similar species of, for example, warblers on the
mainland (Nashville vs Virginia's, Mourning vs McGillivray's, Common
vs Belding's Yellowthroat, Northern vs Louisiana Waterthrush,
Northern vs Tropical Parula, etc.).

Decisions about species distinctness for species that don't occur
together and thus could never interbreed were long left in abeyance,
because of the primacy of the biological species concept. It has been
rare for humans to actually bring some of the geographically isolated
species together to see if they were also reproductively isolated.
This has happened so seldom that a list of avian examples might be
confined to waterfowl, chickens, parrots and a few other groups that
have long been popular in captivity. In some cases breeders have
attempted to hybridize species just to get something new and
commercially valuable - one of my all-time pet peeves, I have to add.
But researchers seem to have spent little effort to toss a few birds
from different islands in a cage together to see what might happen.
More recently, this has been done at a distance by playing songs and
calls from one population to another to assess reactions.

But in most cases we just didn't know. Now along comes our ability to
sequence DNA, and people can look at parts of the genome of two
Spindalis tanagers on Cuba and Hispaniola, or a House Wren on the
Mexican mainland and one on Cozumel, or an obscure greenish
honeycreeper on two Hawaiian islands, and compare the differences
between their DNA with the differences between a series of mainland
species that all would recognize as distinct (they don't interbreed,
after all). I see every benefit from using this technique. We are
using the DNA as at least a measurable and objective way of saying
either "A and B have divereged genetically sufficiently for us to
consider them separate species in the grand tapestry of life," or "no
they haven't." What's wrong with this picture?

Obviously other features such as morphology, ecology, and behavior
come into play when making these judgments, but I think degree of
genetic difference is quite another valid character to add to
judgments about species distinctness, especially when clues from
those other areas may be confusing and especially when reproductive
isolation cannot be judged.

Having said all that, i agree with those who have suggested that
there's a certain amount of hype and PR involved in these recent
announcements. But more power to their analyses, which, like
specimens in a museum, remain to be interpreted again and again as we
learn more ways to interpret them.

-----
Dennis Paulson
1724 NE 98 St.
Seattle, WA 98115
206-528-1382
dennispaulson at comcast.net



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