gene pool and releases

[Paul Cherubini]

Pat Foley wrote:

> Every time we see some general claim that there is no
> scientific basis for worry about nonlocal butterfly releases we should 
> recognize these claims for what they are: 

> 1) optimistic guesses,
> 2) doubtful,  based on evidence from humans and other 
       mammalian species well studied medically
> 3) plausible only because no major disasters have occurred so far.

Pat, what are your specific worries about the potential harm of shipping 
Monarchs or Painted Ladies randomly anywhere within the USA?  What 
reasonable theoretical and/or empirical evidence can you provide to support 
these worries? 

GENETIC WORRIES:

1. Are you worried about the potential to alter the gene pool of Monarchs
and Painted Ladies? If so, five genetic studies involving monarchs and 
two involving Painted Ladies have revealed no clear differences among 
samples tested within the USA.  Monarchs and Painted Ladies are 
both low Fst butterfly species.

In the past you have stated the following concern about Fst: "It does not
deal with all the details and does not identify and reveal the uniqueness of the all
the small populations...much of the future of a lineage lies in rarish events 
in small populations." 

Your concern could be reasonable if there was evidence that small, reproductively
isolated populations of Monarchs and Painted Ladies exist within the USA. 
But the many genetic studies have found no clear evidence that any
reproductively isolated populations of these two species exist within the USA. 

Now lets assume the worst - that all these genetic studies to date have failed
to detect significant differences of some kind like disease resistance to a
certain parasite or complex of unstudied pathogens. Then what are the
potential theoretical consequences? 

Population geneticist Bruce Walsh has explained the potential 
theoretical consequences in the following way:

"for a gene to spread that is opposed by selection (all those bad
genes the no-release folks are worried about), it must be pumped into the
population (via migration) at a rate which exceeds that at which it is
removed.  For example, if the gene as a 5% reduction in fitness, one must
pump in migrants equal to 5% of the entire population each generation 
just to keep the gene in place, much less cause it to spread."

"suppose the worst case: that the western monarch
indeed harbors a killer strain absent in the eastern population.  
Western monarchs would also have to have evolved defensive
genes to counter this parasite, and these would be cospread 
with the parasite, minimizing the fitness effects.   Such genes 
are highly liked to be single gene (as opposed to polygenic) 
and hence readily transmitted along with the parasite."

Since wild Monarch and Painted Lady populations number in the tens 
to hundreds of millions and commercial breeders release only hundreds 
of thousands, there is no reasonable theoretical evidence here that these 
releases pose any potential of altering the disease resistance of the
wild populations.

As far as empirical evidence is concerned, for the past 100+ years we
have seen both monarchs and painted ladies thrive despite continual
human assisted movement across the USA via planes, trains, trucks, 
automobiles and ships as well as huge changes in the abundance and 
prevalence of their caterpillar host plants. 

DISEASE EPIDEMIC WORRIES:

Your concern has been: 

> there is not enough evidence to speak very securely about the geographic 
> distribution of infectious diseases in butterflies and how critical is isolation
> to avoid endemic(enzootic if you must) and epidemic outbreak dangers?

Despite 45 years of rearing tens of thousands of caterpillars collected 
in the wild, no one has found any devastating parasite or pathogen of monarchs 
or painted ladies. Breeders can confidently collect thousands of wild
caterpillars and expect less than a 2% loss due to any factor other than
tachinid flies or hymenopteran parasitoids (the latter are rare in monarchs)

There are no geographically or reproductively isolated populations of
monarchs or painted ladies in the USA.

Breeders are logistically and financially unable to ship out substantial
numbers of heavily diseased adult monarchs or painted ladies because 
such individuals are too weak to fly, survive overnight shipping or mate
and lay eggs if released. (Customers do not pay for imperfect butterflies).

20% of all breeders produce 80% of all the monarchs and painted ladies
shipped for release. The largest monarch breeder has samples of their adults 
inspected and certified free of known parasites and pathogens by an insect 
pathologist.

In sum, I am unaware of any reasonable theoretical and/or empirical
evidence that would suggest random nonlocal butterfly releases of
Painted Ladies or Monarchs within the USA pose anything more than
a negligible risk of causing a disease epidemic.

Paul Cherubini, Placerville, Calif.

 
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