MAES & Monarch subspeciation

[Ron Gatrelle]

----- Original Message -----
From: "Jean-Michel MAES" <jmmaes at ibw.com.ni>
To: <leps-l at lists.yale.edu>
Sent: Friday, October 13, 2000 10:52 PM
Subject: migration


> A little bit far of the discussed point... So many topics about monarch
and
> monarch populations...
>
> I understand that monarch (Danaus plexippus) have migrations from Mexico
to
> Canada and back or from Canada to Mexico and back. Why do they migrate ?
>
> In Nicaragua we have also Danaus plexippus, another population or
subspecies
> if i am not wrong. Why do they not migrate ?
>
> Sincerely,
>
> Jean-Michel MAES
> MUSEO ENTOMOLOGICO
> AP 527
> LEON
> NICARAGUA
> tel 505-3116586
> jmmaes at ibw.com.ni
> -----
>From Ron,
    Now this question I like. A whole lot. I recently heard Brower Jr. give
a talk at Wake Forest U. which in part touched on plexippus subspeciation --
yes or no. He seemed to be undecided. Brower was correct in pointing out the
subtle but consistent differences in the phenotype of western and eastern
monarchs. I am on the yes side. Which is why I do not favor release of
monarchs "just anywhere." (More on release in another egram.)
    On the subspecific level discernments and delineations are made in a
very different way than at the species level. Species are determined by
certain set criteria because they are definitive plateaus in the
evolutionary process. Subspecies are steps between these plateaus. As such
they are often very subjective. Far too many subspecies have been described
on just their phenotype (what they look like). Evolutionary direction should
be the primary factor in subspecific determination. Thus a phenosyncronic
subspecies(see Gatrelle, 2000 The Taxonomic Report 2:2)  while looking
almost like a sister subspecies is actually very different because of its
evolutional direction. This may be evidenced in host toxicity/acceptance
between subspecies, differing univoltine seasonality (spring vs. fall),
migratory vs. non migratory, and other ecological or biological (not-yet
genetically detectable) factors.
    I don't think that the plexippus populations south of Mexico "stay put"
just because they went too far south and didn't have the bus fare to get
back north. Since migration is known to be the result of photo period, the
less radical sun shift nearer the equator may keep the migrations from being
triggered. Or, these populations could have entirely lost the migratory
impulse. OR MOST LIKELY, looking at the origins, and worldwide range, of the
genus Danaus, the non migratory south of Mexico population is what the
northern migratory "subspecies" arose from (peri-Pleistocene?). Monarchs
don't just migrate for the heck of it. Something triggered this.
    Hypothesis: During the Illinoian and Wisconsin ice glaciations the push
and retreat of cold/warm climates gave opportunity for the migratory
"subspecies" to arise. Those which did not migrate died. Those which did
lived. Anthocharis midea in the southeast US will still remain in pupal
diapause for years even though the event that caused this wet/dry season
response has long since vanished.
    D. plexippus' range is North, Central, and South America, West Indies,
Cocos Island, Philippines, Australia, Sulawesi, Moluccas, New Guinea, and
occasional migrations to western Europe (DeVries, 1987). (Strange range for
an endangered species.)
Ron Gatrelle