Government views Monarch Butterfly Releases as a threat to Western Milkweeds

[Paul Cherubini]

Pat wrote:

> The contribution of this year's releases to the target gene pool will presumably
> continue to influence next year's population. And so on. If the location-unique
> alleles are presently selectively neutral (this is not to say neutral forever),
> they will on average then build up in the target population to the point where they
> would be noticeable. In fact until the source and target populations are
> homogeneous (for _neutral_ alleles only!). The cumulative homogenizing effects of
> even a small amount of migration on otherwise separated populations is astonishing.
> Some models require only one migrant per generation to bring about long-term
> homogeneity (Crow and Kimura 1970, p 269, Maruyama 1977 ch 11).

Pat, I guess I should have made clear that I was interested in a
reasonable MATHEMATICAL model that demonstrates the validity of Dr. 
Karen Oberhauser's concerns; i.e. that a modest amount of human assisted 
shipping of Maine monarchs to Minnesota (or vice versa) in late summer 
has a slight chance of disrupting the genetic structure of the recipient 
monarch population and could make it difficult for a researcher to study that
structure.

Bruce Walsh explained the value of mathematical modeling last year:
"The concern about [interstate] transfers have never been stated in terms of
explicit models with parameters and assumptions that we can examine/debate. 
Clearly, I'm sure some of my numbers may be too high or too low, but we can
examine the consequences of those changes to see if they have a real impact. 
In other works, we can do hypothesis testing." 

Pat, since I don't have a math based model from you at the moment to
examine and debate, I would like to ask you to expand on your statement
"The contribution of this year's releases to the target gene pool will presumably
 continue to influence next year's population. And so on."  What I don't
understand is how can Maine to Minnesota and vice versa transfers possibly
influence next year's genetic structure in those states given 
what we already know about monarch population genetics:

1. The same authors (Eanes & Koehn 1978) that found monarchs become
slightly genetically differentiated (based on electrophoretic markers)
in late summer in the northern states from (presumably)  
either local adaptation or non-adaptive genetic drift, also found the
fall migratory population has the same gene frequencies throughout the
area from the Rockies to the Atlantic coast.  "Western" monarchs were
not analyzed at the time of this 1978 study, but a subsequent 
electrophoretic study has found they have the same gene frequencies as well.

2. At the overwintering sites in Mexico, "the mating is random
and the population can be characterized as panmictic" (O.R.Taylor, 2001)

3. In the spring, "Males move north in good numbers along with
the ovipositing females. Mating occurs en route and females reaching
the end of their life have usually mated more than four times" 
(O.R.Taylor, 2001)

Best regards,

Paul Cherubini

 
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