Eastern/Canadian Tiger Swallowtails

James J. Kruse kruse at nature.berkeley.edu
Mon Oct 13 12:41:33 EDT 1997


Hello,

I tried to read all of the responses to this message thus far before
replying:

On 11 Oct 1997 evoluhol at magnum.wpe.com wrote:

> I have studied (not under electron microscope -- but neither does the

molecular systematics/genetics is not done via microscope. For more
questions about that, write to me off line and either I will be able to
answer or I can ask someone here who can. I am underway in my research on
Tortricid moths and I am starting work in both the molecular and classical
systematic methods. Because Tortricids are small, and I must make
genitalia preparation, I use a microscope constantly for the classical
work.

> and they will vary from environment to environment (where there are
> pipevine swallowtails there will be black tiger females).

Quick aside: The black form ranges well north of the pipevine
swallowtail's range (especially Wisconsin), though the supposed mimic
benefits are still working to the north, and so the approximate overlap
is considered reason enough for black forms (though I observed a blue jay 
in Maryland consuming great quantities of yellow and black form tiger
swallowtails unabated).

> 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.

Biological species concept definition.

> 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.

Different food plants is one valid line of evidence for different species,
not just a "claim". One thing you have to remember is that some plants are
more closely related than others. This requires the insect to posess
different, general, or specialized digestive and metabolic chemicals and
traits. Poplars (aspen included) and willows both belong to the 
Salicaceae.  The fact that many insects feed on both poplar and willow is
not surprising to anyone. However, if one feeds only on Rosaceae and
another only on Salicaceae, that is decent evidence that some
differentiation is going on with the herbivore. Comparing specialists to
generalists in the context that you have, especially something as
omnivorous as H. cecropia, is not appropriate. Also be careful about
oviposition.  H. cecropia and many other moths will oviposit in paper
bags, but that doesn't mean they eat them.

> However, in my reading of the papers that claim different species, 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.

I'm not convinced it was the "main" argument, just the latest
"straw" that made them decide to separate the glaucus subspecies
into two separate ones.  Generally you want to explain new methods
or discoveries fully in a paper, and so it may have sounded like
they were not weighting other evidence equally.  Again, in this case, we
have "just another line of evidence". If there was no other difference
between two suspected species than a food plant or a gene, chances are
that no splitting would be done at that time. In the case of P.
glaucus/canadensis however, there was lots of other evidence before the
molecular came along. Food plant and genes aside, there is also: double vs
single brooded, lack of a black morph in canadensis (a sex-linked
character), wing markings (band on underside of forewing in canadensis vs
spots on the underside in glaucus) plus differing black markings on the
hindwing, and the clinal nature of the hybrid zone from one form to the
other.

> 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.  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. (??)

Read Doug's passage about some of this (and the microscope is only a
tool to help us see what is already there). The biological species concept
is quickly becoming inadequate due to many cases of naturally occuring
hybrid fertility (and the behavior of the butterflies).  I think in the
long run, moderation will prevail. I don't foresee the counting of single
base pair differences becoming the sole reason for naming species catching
on with most groups, particularly animals and plants (though in single
cell organisms where there are few other characters there is/will be
more).

> 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.

Using those "classic" field markings, I'd say you have P. canadensis in
the higher elevations and the spotted ones 50 miles away are P. glaucus.
The fact that they mate is not surprising, as they do so in nature as
well as the laboratory. Your hybrid larvae variably feeding on food plants
of both parents is also is not surprising.  

Hate to say it, but virtually all of the "basic" work has been done on
North American Papilio.  As you probably already know, before you begin
your research in earnest, you will be required to read most if not all of
what has been done already so that you can define your research 
questions. There are two wonderfully MONSTEROUS books on North American
Papilio, one by Scriber, Lederhouse and others which covers just about
everything you ever wanted to know about the "Pterourus" group, including
extensive hybridization studies.  Check it out!

Cheers!
Jim Kruse
University of California at Berkeley
Dept. of Environ Sci, Policy and Mgmt.
Div. of Insect Biology
Sperling Lab
201 Wellman Hall
Berkeley, California, 94720-3113
(510) 642-5114/7410
http://www.CNR.Berkeley.EDU/sperlinglab/sperlinglab.html



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