Eastern/Canadian Tiger Swallowtails

Pavulaan at aol.com Pavulaan at aol.com
Sun Oct 12 14:05:03 EDT 1997


In a message dated 97-10-11 14:20:53 EDT, "Dave" (evoluhol at magnum.wpe.com)
writes of the Eastern/Canadian Tiger Swallowtail "controversy".

I thought that was finally resolved with the Hagen, Lederhouse, Bossart &
Scriber paper.  Some comments on Dave's comments:

<< Species from one end of cline lost viability in breeding with indivisuals
from the other end of the cline but would breed with ones next door all down
the cline. >> 

This has been proven out in some breeding studies, but with canadensis and
glaucus, we are not talking about a cline.  The southern end of the glaucus
cline is in Florida, where they achieve their largest size, and the black
form is rare.  The northern end of the glaucus cline ends roughly where the
range of canadensis begins, and achieves another distinct form at the
northern end of the cline, approaching adult canadensis in physical
appearance.  The black form is also rare.  

No doubt, the two may have been part of a cline at one time in their
evolution, but were separated into two populations, evolved differences, and
have made secondary contact.  After secondary contact, they generally
maintained their specificity, though there does APPEAR to be some sort of
hybridization going on in some areas.  Or perhaps this is not hybridization,
but a remnant gene pool of glaucus (at the northern end of the glaucus cline)
that still have some characteristics of the ancient cline to canadensis.
 (Note: There is still some debate over whether Mexican P. alexiares is a
subspecies of glaucus, and no doubt we may not know for a very long time,
thanks to rediculous Mexican wildlife export regulations.)  
 
<< I have studied...tigers from Atlantic to Pacific and Canada to the
Carolinas,
and they will vary from environment to environment (where there are  pipevine
swallowtails there will be black tiger females). >>  

The geographical range of Dave's study covers several entities, all of which
are found in a broad variety of environments.  Generally, Tigers west of the
Rockies are P. rutulus.  Canada and the northern U.S. border states have
canadensis.  Glaucus is primarily east of the Rockies, and mainly in the U.S.
 The range of glaucus east of the Rockies closely approximates the range of
B. philenor (Pipevine Swallowtail), precisely where the black female of
glaucus occurs.  Black females do not occur in rutulus, despite the fact that
rutulus' range overlaps broadly with that of philenor.  Black females rarely
occur in canadensis, where they are considered abberrants.

<< Originally, the determination of "species" was left to the butterfly -- if
it bred and had viable male and female offspring -- it was a species.  If
there was no offspring or only males, it was not a species. >>  

This is still true.  Only problem is, now we are finding out that the concept
of "species" is a bit more complex than originally thought (the Linnaean
concept). 
 
<< One "claim" of different species is that foodplants are different.  If a
 tiger oviposits on aspen here at my house, and wild cherry in the valley,
 it does not make it a separate species.  Viceroys here oviposit on aspen, in
the valley on willow -- those are not two seperate species.  If cecropia
oviposit on wild cherries on my mountain, and on maple in Green County (NY)
-- it does not make them separate species. >>

One has to be careful when comparing apples to oranges.  Sure, the Viceroy
uses a variety of hosts, and sure, also the Cecropia.  Glaucus and canadensis
also each use a variety of hosts.  However, Dave's assertion that just
because they use different hosts on the mountain and in the valley does not
make them different species, is easily supported when you are well within the
range of a butterfly (or moth), but when we are talking about an area at the
EDGE of the range of two sibling species like canadensis and glaucus, it is
entirely possible that the cherry-feeders in the valley ARE glaucus, and the
aspen-feeders on the mountain are canadensis.  Canadensis, being a northern
species, would naturally inhabit mountaintops in the northeast, where the
habitat and hosts are similar to those in Canada.  Glaucus, on the other
hand, being a southern species, would naturally inhabit the warmer valleys
which contain more southerly habitats and hosts.

<< the main argument seems to be the chromosome and gene differences under a
microscope.  "Canadensis" is clamed to be different from "glaucus" because of
the number of genes that are different -- which is backed up by  comparison
with other species. >>  

This was only part of the study.  Decades of genetic work was backed up
decades of hostplant research.  I have been told that humans and chimpanzees
have a similar number of genes or chromosomes, and we are supposedly
something like 99% similar, though we appear different.
 
<<Ultimately -- what is happening here is a researchers attempt to overturn
the concept of species and propose a BRAND NEW CONCEPT OF SPECIES based on
the microscope quite apart from the butterfly's behavior.>>  

This is nothing new, Dave.  It is called the Biological Species Concept, and
has been around for a long time.  It is also not the creation of a single
researcher or a few.  This is a concept that has been developed by the work
of hundreds of researchers in the field of genetics.  It is gaining
acceptance now because geneticists finally have new technologies to prove it
(electron microscopes, electrophoresis, chromosome analysis, etc. etc. etc.).
 

Just because we used the old Linnaean system to the present, does not mean it
was correct.  The way I understand it, is Linnaeus categorized everything
based on physical appearance of adults.  Thus, a proliferation of available
names in literature.  One quick look at Miller and Brown's
Catalogue/Checklist of the Butterflies of America North of Mexico will show
precisely how many names were devised for various butterflies.
 Interestingly, many of these were found to be mere forms or varieties of
butterflies.  Some forms or varieties turned out to be full species.  

Modern evolutionary and genetic research has shown that evolution is
happening literally before our eyes, and the old concept of the black and
white distinctness of species is no longer sufficient to explain the
incredible genetic diversity of plant and animal populations all across the
planet.  What is being found out is that some populations of a species are
slightly different, genetically, from the main population gene pool.  In
others, they are more different, in others yet more.  Some of these
more-different populations show minor differences in appearance and overall
biology, and though they are not CLEARLY different species, they are unique
in small ways.
Linnaean systematics gives you two choices: separate species, or the same
species.  Black or white.  No in-betweens.  We have gotten around this with
the concepts of subspecies and "hybrid zones" which are really catch-all
categories that cover a broad range of possibilities.

The biological species concept allows us to separate organisms down to their
level of evolutionary development, though nobody has yet come out with a
refined systematic/taxonomic replacement to the Linnaean system.  Do we call
these ecotypes, biotypes, sibling species, races, or a variety of other
designations?  Do we name these organisms?

<< There seems to be in this concept that there is a point where after
counting a number of gene differences, just one more different gene
constitutes a different
species. >> 

No.  It takes a lot more genes.  But biological differences make a difference
too.
 
<< Meanwhile, my tigers are exempt from the controversy, they carry on their
life in spite of a labratory paper that says they shouldn't.  My tigers I get
50 miles away that have distinct yellow spots on the under front  wings, mate
with those I have here at 1,200 feet higher which have a yellow "band".  The
caterpillars variably will eat populus, prunus, or crategus. >>

Dave:  It sounds like you have a lot of work ahead of you.  You no doubt,
have an interesting local situation that requires a lot of study.  I hope you
make careful notes, keep statistics, and compare your finds to those of
others.  Who knows, you may find something new in the field of evolution that
researchers like Hagen, Lederhouse, Bossart and Scriber missed, or you may
refine their concepts.  

Please do post or publish your finds, and maybe it will help me explain why
in Rhode Island, we have at least two entities (canadensis and glaucus),
which fly together, look similar, and yet have different responses to
environmental influences in the same habitats, with the same available hosts.
 Note: the "southern" R.I. summer glaucus which I reared, "breeds true" by
producing typical "southern" glaucus spring adults (FW underside spotband),
and not individuals like canadensis (FW underside solid band) the next year.
 The late-spring, giant canadensis-like R.I. individuals bred true to produce
identical adults the next summer(!), not spring forms.  I was never able to
get canadensis pupae to eclose adults the following year.  However, unlike
you, I have not yet tried mating adults from different populations, to see
what they produce.

Best of luck,
Harry Pavulaan
 



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