[Leps-l] [leps-talk] Monarch Armageddon

[Foley, Patrick]

Now we are talking, Paul!

It does appear that present North American Monarchs show little genetic variation over space (Brower & Bryce 1991). The earlier work of Walter Eanes (~1978) seemed to show that before migration there was little population differentiation, but during the summer some geographic genotypic variation arose (presumably due to local natural selection). This variation disappeared after the annual Spring matings in the south. If Eames is right (or Darwin for that matter), then isolated Monarch populations have the potential to evolve away from the mass migration strategy. Such evolutionary differentiation has not yet appeared in the populations I have heard about (again see Brower & Bryce 1991). But it surely can given enough time.

Carol Chaffee is presently researching Monarch population genetics for her PhD. I do not think her work is published yet, but she has a talk on youtube, that repeats much of what we all know, but does show the scope of her research. This research should help work out how differentiated migratory and nonmigratory populations are.

Monarchs are weedy, widespread butterflies who are not in any danger of extinction. Paul and I and everybody agree on this. We disagree about the rate at which climate and other changes will effect the genetically based migration strategy of Monarchs. This is an empirical problem, and I hope over time, evolutionary genetics research on Monarchs will tell us what we want to know. In the mean time, I think a little caution about Monarch migration invulnerability is warranted. Paul does not feel this way. I can live with that.


Patrick Foley
bees, fleas, flowers, disease
patfoley at csus.edu
________________________________________
From: leps-l-bounces at mailman.yale.edu [leps-l-bounces at mailman.yale.edu] on behalf of Paul Cherubini [monarch at saber.net]
Sent: Friday, February 15, 2013 1:11 PM
To: Leps List
Subject: Re: [Leps-l] [leps-talk] Monarch Armageddon

On Feb 15, 2013, at 11:25 AM, Foley, Patrick wrote:

> Paul, Of course there are short-distance migrating
> Monarchs. Many California monarchs migrate
> short distances

Yes many California monarchs migrate short distances
in the fall, but they are physiologically capable of
migrating the same very long 2,000 miles from
Canada to central Mexico as the eastern monarchs are.
And that's because eastern and western fall
migrant monarchs are the same physiologically; i.e.
the dates of onset of diapause and migration and the
length of time (2-3 months) that the migratory instinct
is active are the same (at similar latitudes).

> Monarch migration strategies do not depend on latitude.
> Latitude simply correlates with climate features.

No, latitude has a major influence on monarch physiology;
e.g. at high latitudes (e.g. 49 degrees N)  summer
monarchs to enter diapause and start migrating in
early August vs early September at 35 degrees N
latitude.

> Migration strategies depend on overall energy balance,
> dangers of migration, corridors that are phenologically
> appropriate etc.

As I have already explained, even though western
and eastern monarchs breed in hugely varied
landscapes (deserts to high mountains) they
are physiologically the same (at similar latitudes),
hence their migration behaviors are the same.

> Natural selection on migration strategies will change
> with climate change and Mexican and US land use
> policy changes. The rate of these changes is arguable,
> and so is the danger to the Eastern migration.

It is indisputable that millions of milkweed plants
and therefore monarchs will continue to exist for
many, many decades to come in the same regions
of the USA and Canada as they do now despite
minor climate changes and moderate land use changes.

Therefore it is highly questionable whether or not
Dr. Chip Taylor has a legitimate scientific basis for
telling the public and reporters that just because there
will be less - but still millions - of wild milkweed plants
growing in the decades to come the monarch migration
could be on the "brink of collapse":
http://monarchwatch.org/blog/2008/04/butterfly-on-the-brink/
http://www.youtube.com/watch?v=MdtDcKg-x8w

> I am arguing that the Eastern migration strategy is not
> so secure as you claim, especially in the light of so
> many butterfly species and many Monarchs choosing
> a different migration strategy.

You and Chip Taylor have not provided evidence that
millions of milkweeds and thousands of forest trees in
Mexico will NOT still be available to support a population of
millions of migratory eastern monarchs 50 - 100 years
from now.

> Do you think ongoing climate changes will not change
> the Appalachians or Mexican highlands?

The climate changes since 1895 have been minor (a 1-2
degree rise in temperature) so they are likely to be minor
for the next 100 years as well given that the rate of temperature
rise between 1895-2012 has been relatively linear (and flat
worldwide since 1999)

So these changes should have only minor impacts, both
positive and negative.  Example: Despite some global
warming since 1977-78, the years the Mexican overwintering
sites were first mapped, the altitude where the monarchs
cluster has not changed, nor have California overwintering
clusters moved northward up the coast since they were first
mapped in the 1930's - 1950's.

Paul Cherubini
El Dorado, Calif.








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