Butterfly releases

Mark Berman bugman at bugs.org
Thu Sep 23 20:37:41 EDT 1999


I suppose I need to respond, here. Not because I really like arguing about
these things, but more because I feel my contentions were misunderstood. And
I think there is much confusion in the scientific and non-scientific
communities about what Natural Selection really is (it took me long enough
to understand it!) The recent controversy taking place in the Kansas schools
demonstrates this more dramatically than anything here.

>  Jacob Groth <jgroth at ns.net> wrote in message
news:199909231746.KAA17570 at eagle.sac.verio.net...
>  Mark wrote:
>>      "Assuming these are potentially interbreeding individuals
>>      and there's is a recurring - even small - introduction (i.e.
>>      school releases), then this might effect the gene pool and
>>      alter the "wild-type." And there seems to be a serious
>>      likelihood of this if, all of a sudden, there are an extra 200
>>      lab reared individuals from a festive "mass release."  I
>>      surely don't mean sound alarmist about the whole thing... it
>>      hardly rises to that level. But I do think that's the real issue
>>      here, and not unexpected data in July counts."
>  It seems that many of you, as shown the above statement,
>  have completely disregarded the laws of natural selection
>  Here are some statements by Dr. J.B. Keiper, Dept. of
>  Biology Sciences at Kent State University from
>  BioScience Vol. 46, no. 8 (pg. 562) to help illustrate:
>     "In all of humankind's efforts to eliminate insect species
>     with poisons and pathogens, not one has been totally
>     eradicated.  This is a salute to the unfailing effectiveness
>     of natural selection... If an interpopulation transferee is
>     placed in a region where its adaptations are poorly suited
>     to the biotic and abiotic conditions present, natural
>     selection would act against those offspring produced by
>     the alien individual.  Thus, directional selection
>     will  eventually eliminate those genes present in
>     submarginal individuals."
>  --------------------
>  In other words, natural selection will automatically
>  eliminate the "bad genes" and promote the "good
>  genes."  If there is a genetic weakness with the butterflies
>  being released, why would you worry about them "taking
>  over the genetic population?"  If they were "weak genes,"
>  they would be eliminated only after a few short
>  generations causing know impact to the population
>  whatsoever.

hmmmm.... a harsh, but either unresponsive, or uneducated, response. The
"laws" of Natural Selection (more appropriately called the "Theory of
Natural Selection" - natural "laws" are more firmly established than this
is) are simply a set of assumptions which, when met, allow us to predict the
outcomes of phenotypic (or, expressed genetic) patterns in populations.
There are no real "laws" in any natural system. We just agree upon certain
conventions to help us understand the world better.

If you read *carefully* my post (please), you will not see the terms "weak,"
"bad," or "poorly suited to the biotic and abiotic conditions ." I also did
not say that the butterflies being released would "take over the genetic
population." I said they might alter the wild-type.

Natural Selection is not directed. Nor is it benevolent. It doesn't care if
genes are weak or bad. Some characteristics are more or less suited for a
particular environment, and, if they are more suited, an individual
possessing them is more likely to have offspring who share those
characteristics. If, in the meantime, the environment changes, the offspring
might be out of luck. Then those characteristics are less likely to get
passed on to future generations.

This is very different, I think, from what you suggested I said.

The problem here is that lab-reared individuals might be better or worse
suited for a particular environment than the local wild-type. If they happen
to be poorly suited... end of story. Consider this passage from Anne
Kilmer's recent post (9-23-99):

      My granddaughter's second grade class released their Painted Ladies in
      November, in Maryland ...

Obviously, those individuals were not well suited for the environment into
which they were released. Not to mention there probably was no one there to
breed with! Dead genes.

But... suppose the released animals have a selective, or perhaps more
importantly, a reproductive advantage over the native wild-types. And
suppose they also have a preference for a different host plant. Can you see
a problem here?

I understand that I am basing this scenario on a set of assumptions, but
welcome to the world of theoretical ecology. The assumptions I'm suggesting
are plausible, perhaps even possible. And the repeated, or large-scale
releases we're considering here certainly might test any hypothetical

Just like the theory of Natural Selection!

Example: No one expected Africanized Honey Bees to be transformed into
Killer Bees in the Americas. And this would not have been a problem except
that the male Africanized bees seem to have a reproductive advantage over
the European bees (in this case, the wild-type). Now they are a major public
health, economic, and perhaps (though it's really not up to us to judge) an
ecological problem.

>  IT IS GOOD TO MIX THE GENE POOL!  Mixing can only strengthen a species.
This is why breeders have to
>  occassionally mix their gene pool:  to bring in more "good genes."  It is
strange to hear many of you who
>  understand natural selection, but somehow "forget about it" when it comes
to transfers.

You are correct that "it is good to mix the gene pool." A diverse gene pool
gives a population more "options" when dealing with environmental

You are also correct that this usually requires immigration of "fresh" genes
into the population. This is one of the assumptions addressed in the Theory
of Natural Selection (though, for predictive purposes, Natural Selection
assumes NO immigration or emigration). That is why it's not recommended to
breed with your cousins. (Okay, flippant.... sorry) But it is a common
problem with captive-bred populations. That is why breeders mix their gene
pool. They are introducing genes present in the wild-type which have been
"filtered out" of their isolated populations.

In cases where a natural species or a portion of a natural species becomes
isolated from immigration, it usually either changes or dies out. This is
one way new species are formed. It is also one way extinctions occur. We can
assume this is not a problem for the wild-type butterflies in this
discussion. In other words, we can assume we have a healthy natural
population in this case.

The problem with your objections, Jacob, is the notion of "good" and "bad"
genes. To be fair, I understand you put them in quotes because you are using
the terms loosely. But it is important to consider that what is good for the
individual might not be good for the ecosystem. Introductions of aggressive
exotic plants into a wetland may very much favor all the individuals in the
introduced species, yet choke out much of the native life in the wetland. So
when we try to evaluate the relative costs and benefits of our "tinkering"
with the ecosystem, it should be an objective evaluation.

When a breeder introduces new genes **into** a captive gene pool, where
there is a controlled environment, and no *random* immigration, different
assumptions apply. This is clearly NOT Natural Selection. It is
significantly different (conceptually and statistically) from introducing
lab-reared genes into a natural population where the non-directional forces
of Natural Selection rule.

It is very different.


I apologize for the length of this post, but Natural Selection is a very
challenging concept around which many misconceptions abound. Darwin was a
brilliant theorist.

Thank you for your time (those of you still here!)

BUGMAN Educational Entoprises

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