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

[Paul Cherubini]

On Feb 15, 2013, at 2:40 PM, Foley, Patrick wrote:

> It does appear that present North American Monarchs
> show little genetic variation over space (Brower & Bryce 1991).

There have been several newer genetic studies that
all failed to find genetic differences between eastern
and western monarchs.

> 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).

That's all irrevalent because fall migrants from coast
to coast enter reproductive diapause in the late summer
and migrate to overwintering sites where butterflies
from widely varying geographic locations randomly
mate with one another multiple times hence destroying
any slight geographically based population structure 
that may have occurred over the summer

> If Eames is right (or Darwin for that matter), then
> isolated Monarch populations have the potential
> to evolve away from the mass migration strategy.

Irrevalent because there is no such thing as a
temperate zone monarch population anywhere in the World
that fails to enter reproductive diapause and migrate

> Carol Chaffee is presently researching Monarch population
> genetics for her PhD. This research should help work
> out how differentiated migratory and nonmigratory
> populations are.

We already know the Winnipeg, Point Pelee and Houston
monarch populations Carol is studying are diapausal
and migratory and we already know the Miami population
is non-diapausal and non-migratory because it's located
at only 25 degrees N latitude.
 
> 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.

It's not a genetically based migration strategy because
there is no population structure in monarchs in North 
America north of about 27-28 degrees N latitude
and all of those monarchs are migratory.  It's a 
physiologically based migration; i.e. only diapausers
are interested in seeking out a refrigerator like 
overwintering climate.

> 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.

You and Chip Taylor have not provided evidence that
millions of milkweeds and thousands of acres of
forest trees in Mexico will NOT still be available
to support a population of millions of migration
eastern monarchs 50-100 years from now.  Nor 
evidence that the during the past 75 years of 
global warming the migratory and overwintering 
behavior of monarchs changed. So your beliefs that the
eastern monarch migration is "vulnerable" or
"fragile" or "on the brink of extinction" (Chips
belief)" due to climate change or changes
in land use are not science based.

Paul Cherubini