Papilio joanae

Fri Jan 26 20:45:58 EST 2001

Well, I'm glad to see that systematics is getting some serious
discussion, and Papilio systematics at that.

My name was mentioned by Ron Gatrelle a couple of days ago in the
context of Papilio name changes, while Norbert Kondla and Mark Walker
followed it up with intimations about the dark motives and jealously/
arrogance/ unresponsiveness of the "Powers That Be" who change names.
I suppose that it might be helpful to mention that I have a job that
takes 12-16 hours per day of my time, including preparing lectures to
450 very demanding Intro Bio students, sitting in committees to help
along graduate students, planning biodiversity networks, and new
museums, and otherwise being run ragged in the normal course of one
day of the life of a professor. So if the slowness of my response
seems due to the motives above, then I should remind you that I am a
lepidopterist just like the rest of you - and that there are much
less nasty explanations for what happens in taxonomy.

Onward to Papilio:

1. What did my research on Papilio joanae show? In a 1994 paper in
Evolution, I showed that Papilio joanae and Papilio brevicauda have
virtually identical mitochondrial (mt) DNA, and that their mtDNA is
very similar to that of Papilio machaon populations. These mtDNA
lineages were very different from those of Papilio polyxenes, even
for P. polyxenes collected near P. joanae in Missouri. This says that
one  part of the total genome of P. joanae is a lot more like that of
P. machaon than P. polyxenes. This is particularly interesting
because another part of the genome of P. joanae, which is the genes
for the black color pattern, is a lot more like P. polyxenes than
most populations of P. machaon.

2. What does this mean? Some other Papilio populations have very
similar mtDNA to that of P. joanae, including P. brevicauda and some
peripheral populations that I have interpreted as hybrids with P.
machaon. All these populations are found in an east-west band across
the center of North America. One reasonable explanation is that their
mtDNA is a genetic remnant of formerly more widespread populations of
P. machaon that lived south of the continental ice sheets during
glacial times. Assuming that the black color genes of P. joanae did
come from P. polyxenes, these genes could have been acquired later -
sometime after the ice receded, and both P. machaon and P. polyxenes
populations moved northward. P. machaon populations left behind in
the Missouri Ozark highlands could plausibly have hybridized with
invading P. polyxenes.

3. Does this mean that P. joanae is the same species as P. machaon?
Not necessarily. The phylogeny (= family tree relationships) of one
gene is not necessarily the same as that of the other genes contained
by a species. MtDNA is just one small set of totally linked genes and
the P. joanae mtDNA may be the *only* remnant of the genome of P.
machaon, while the remainder of the genome of P. joanae is comprised
of P. polyxenes genes that have introgressed (= swamped out) the rest
of the old machaon-type genes. Or maybe the black color genes are the
only genes that have introgressed into P. joanae populations. Or
maybe the situation is even more complicated. This suggests a rather
obvious test - look at the relationships of a selection of other
genes to see what the "average" gene is doing. We've already been
hard at work on this in my lab, but the work is unpublished and in
fact the results are still quite ambiguous because we have not found
enough variation in other genes to get a clear answer. So we are now
trying other methods and if we are very lucky then I may be able to
report something interesting in a year or two or three.

4. What about the name Papilio joanae - should it be sunk? In my
opinion, it is premature to sink P. joanae on the basis of one just
one linked gene set, even though those results are very interesting
and clearly show that there is at least some genetic difference
between P. joanae and P. polyxenes. Just because the mtDNA of P.
joanae is so much like that of P. machaon does not mean that it is a
P. machaon. In another study in Heredity in 1993, I showed that
Papilio rutulus and P. eurymedon have almost the same mtDNA, yet here
there is abundant evidence that these two species maintain their
integrity when they contact each other over a large geographic range.
This is not to say that I strongly feel that P. joanae is one thing
or another, only that I prefer to keep the same names that people
have gotten used to for the last couple of decades. When there is
clear and strong evidence to the contrary then the name should be
changed in field guides. If the established name were P. whateverus
joanae instead, then I would just as strongly be in support of
keeping that name. And perhaps we never will get crystal clear
evidence that it is one or the other (nature is a lot more
wonderfully messy than we try to make it). In that case we might as
well be spared the confusion of a name change every time someone
publishes a study with another line of evidence. I have detailed this
interpretation of P. joanae, and the reasoning behind it, in a book
chapter that I have in press in the symposium volume from the
International Butterfly Congress that was held in Colorado in 1998.
However, the supporting information is all published.

5. What about subspecies - are they useless? I don't have a problem
with the idea of naming geographically discrete and diagnosable
populations as subspecies. In fact I have done it with P. machaon
pikei, though I only did so after I showed that at least 75% of
specimens could be identified without knowing where they came from.
On the other hand, I think that there are an awful lot of subspecies
names out there that are useless - that is to say that most of the
specimens cannot be reliably identified without the locality. I would
challenge anyone who wants to name a subspecies to show that their
name is not useless in this sense.

Enough for now - I have miles to go before I sleep tonight.

    Felix

Felix Sperling
Associate Professor - Insect Systematics
Department of Biological Sciences
cw405 Biological Sciences Centre
University of Alberta
Edmonton, Alberta  T6G 2E9  Canada

fax:   780-492-9234
phone: 780-492-3991
email: felix.sperling at ualberta.ca
http://www.biology.ualberta.ca/sperling/sperling.html

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