Eastern/Canadian Tiger Swallowtails

[Daniel Glaeske]

Semjase wrote:
> 
> Harry:
> 
> The thought strikes me as these Giant Canadensis Swallowtails may actually be
> another undescribed species or at least a race.
> 
> Best
> 
> S.

There may be some gene transfer between the populations all along the
contact zone.  I've noted some glaucus-like creatures flying in July and
early August here in Northwestern North Dakota, long after the usual
canadensis flight.  Haven't actually collected or photographed any of
them, however.  I have never seen typical glaucus this far north.  Ron
Royer may have more to add about this - he knows this area far better
than I.  What may be happening is not widespread hybridization, but
occasional hybridization which allows some glaucus genes into the
canadensis population.  I think it is more likely we are seeing aberrant
canadensis rather than true hybrids or a new race or species. 
Conversely, the small, spring phenotype of glaucus in some areas may
have originated with introgression of canadensis genes from the border
areas.  

Pure speculation at this point, but I believe that canadensis and
glaucus diverged relatively recently, probably from the last
glaciation.  During the last glaciation about 18,000 years ago, there
was a relatively narrow open Parkland/Transitional region along the
glacier edge except for the northwest (where it was much broader) and
the southeast, where it merged with the deciduous forest refugia.  My
theory is that canandensis evolved primarly in the northwest while
typical glaucus remained in the deciduous refugia.  They were largely
separated by a vast, dry desert in the middle of the continent and only
with the retreat of the glaciers and expansion of both their habitats
did they come into contact again.

Well, it's not worth three cents, just my two cents.
-- 


It's easy to find something worth dying for.
Do you have anything worth living
for?" 

- Lorien to Captain Sheridan in the chasm on Z'Ha'Dum