Papilio joanae

Sat Jan 27 12:14:35 EST 2001

Felix and others,

I am agnostic about the status of Papilio joanae. I have two vague points
about mtDNA, hoping they will be made more precise by someone expert in
their use in this case.

mtDNA seems to introgress pretty readily, moving from one species to
another if any hybridization occurs. Introgressive hybridization (Edgar
Anderson first studied it in plants) seems faster for mtDNA than nuclear
DNA for most eukaryotes. Is this true for papilionids?

Ignoring introgression, mtDNA evolves at very different rates in
different organisms. By evolution here I mean mutation and substitution
of DNA bases. As far as I know, and this is very limited, the best study
in Drosophila suggests that mtDNA evolves more quickly in mtDNA than
nuclear DNA, but this is not always true. What is true in swallowtails?

The answers to these questions may help to clear up the amount of
separate evolution P. joanae has done from its relatives.

Patrick Foley
patfoley at csus.edu

Felix Sperling wrote:

> 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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