---------- Forwarded message ----------
Date: 12 Apr 96 10:23:37 EDT
From: Jack, Sobel <SOBELJ at DCCMC.MHS.CompuServe.COM>
To: rob at pinetree.org
Subject: Re: genetic diversity
Response to message below from: joshua at intrinsa.com (Joshua Levy)
Subject: genetic diversity
Date: Thu, 11 Apr 1996 19:10:25 -0700
Your argument regarding genetic diversity being recreated has limited
validity for a number of reasons, but perhaps most importantly, even if
true, your conclusion with respect to loss of genetic diversity from
captive breeding programs therefore being moot, would still be wrong for
the following reason. Genetic diversity does not only include single
point mutations or alleles for single genes for that matter, it also
includes suites or collections of genes. In many cases, particularly
with respect to fish, these suites of genes have co-evolved with one
another over many generations and may be well-tailored to each other and
to specific local environmental conditions to enhance survival. Even if
all the individual genetic mutations are conserved, or as you suggest
recreated, reassembling them in the same combinations would require
considerble luck and many generations, if it ever occurred. Thousands or
millions of years later, you might end up back at the same point, but
most likely, you'd end up somewhere different. In the mean time, taxa
could be lost or greatly compromised. This is relevant not only to
captive breeding programs, but also to the release of both captive bred
individuals and stock transfers into native populations where they may
interbreed and break up locally adapted genetic assemblages. Due to
their genetic make-up and stock structure, this is particularly important
for salmonids, on which considerable work has been done and for which
there is considerable evidence.
Jack Sobel
Senior Scientist, Ecosystem Protection
Center For Marine Conservation
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I have heard this, but I have also heard the opposite: that genetic
diversity is almost always re-created. That argument went like this:
Genetic mutations are not random: certain mutations happen over and
over again, because that particular DNA change is easier to trigger.
Coversely, other DNA changes are much harder to trigger. Therefore,
if a mutation (say: A -> A') has happened once, it will likely happen
again. So even if all the A' fish die, more will mutate. (Obviously,
we're talking about whole populations of fish, over a period of years or
longer.)
I do not have the biology background to argue this point, but perhaps
someone
else does? This point is relatively important for captive breeding
programs.
If it were true, then the discussions about maintaining genetic diversity
would be moot. If the fish survived, the genetic diversity could be
largely
regenerated.
Joshua Levy <joshua at intrinsa.com>