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Re: SPEC-setosa/hookeri

>The idea that hookeri came from setosa or vis-versa is a somewhat
>simplistic view of the probable origin of the two species.  It seems
>most likely that there was one species that was spread around the
>northern parts of North America.  When the ice age came, the ice
>penetrated sufficiently far south in Central Canada that it killed off
>this species in the middle and the two populations on either side simple
>grew to be different.  Although it would be difficult to prove, the
>setosa is probably as different, today, from the parent species as
>hookeri.  We must also consider tridentata in the area of Florida,
>Tennessee and the Carolinas, which is closely related to the other two
>species and is now separated by much of the east coast area. This
>species seems to have evolved into a semi-tropical cousin of the two
>Arctic or semi-Arctic species.
>Ian, in Ottawa where it is quite mild - around 0C

Yes, but you have to consider also the Asian populations of setosa.  If the
setosa complex originated in Asia and migrated to North America, then it
seems likely that the original species was indeed very close to what we
call setosa today, or that the Asian setosa and North American setosa
evolved entirely in parallel from the hypothetical parental species.  The
latter hypothesis is more ad hoc and thus less likely to be true.

It's also possible (and perhaps marginally more likely) that the Asian
populations of setosa represent a colonisation event that took place AFTER
the hypothetical ancestor had split into setosa and hookeri.  If that is
true, then both setosa and hookeri are much older than the last glacial
maximum, having speciated during some earlier GM.

The biogeographic connections between east Asia and North America can be
quite ancient.  I've studied a number of species of soil animals (daddy
longlegs, millipeds) which have seemingly identical species, or very
closely related ones, in the Appalachians and in Japan.  Species pairs tend
to be from eastern North America and southern Japan, or from western North
America and northern Japan.  Sometimes you get a complex of closely related
species from the Appalachians, the Cascades, Japan, and the Mexican or
Central American Highlands.  In at least one case, the distribution also
includes Chile/Argentina, South Africa, and Tasmania.  Glacial events can't
cover this.  If you try to use continental drift, you wind up pushing
events back literally hundreds of millions of years.  I've been trying to
figure this out for 20 years and seem no closer to reconstruction the
history than at the beginning...anyhow, enough of my hobbyhorse.

Back to setosa/hookeri.  As I understand it, the differences between the
two species are not great, but are consistant.  So it seems reasonable to
assume that whatever the precursor population might have been, it was not
that different from the two descending species.  I'm puzzled, too, by
tridentata.  Perhaps it is not at all related to setosa/hookeri, the loss
of the standards being just a case of convergent evolution.  The plants
certainly look different, with narrower, tougher foliage, and the bloom
season is way later.  This would be a nice problem to look at using
biochemical or DNA methods.

Iris-l is sure a great list.  It has 10 times the traffic of the scientific
lists to which I still subscribe, and the level of discussion is much
higher! Keep those cards and letters coming.

Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
FAX (804)223-6374

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