Re: Re: Genetic diversity (long)

dave evans (T442119@RUTADMIN.RUTGERS.EDU)
Thu, 12 Dec 96 18:56 EST

> From: Wayne Forrester <forrestr@MENDEL.BERKELEY.EDU>
>
> >> this is a significant contribution to diversity.
> >
> >Why not?
> >
> Because the numbers are too small. The frequency of spontaneous mutation
> is very low, and even with mutagen treatment, which I donUt think is
> desirable in this context, it is still low. Thus, to have significantly
> contribute to maintaining genetic diversity, one needs very large numbers
> of plants, in this case.

No, large #'s are not needed, they may help some though. Someone,
by placing a species and only a small sample of individauls, in
cultivation, you will end up with a population of plants that
are, on average, more different than the orginal larger
population they came from. The key here is *more different*
than other populations (in cultivation or not) while more alike
to each other. There is no point to try and save individual
wild populations =--> Once the land is gone there is no way to
replant said population. Even if you did put it in another wild
location, many would die in the new place and you would still
get the same selectiveness (not choosing for the same traits but
just as effective.) as when taking the plants home. I was never
saying that by growing these plants, we're saving them from us.
Where did that idea coming from? Anyway, even if all, say,
S.flava did all die in the wild and there was still room to
replant some, we very well could replace many populations with
homegrown plants from many growers. These plants would not have
the seemly endless diversity but they would still have a lot of
diversity. And that would be enough to start then out again.
That's something people seem to be missing here. Even a very
small poplution can become very different from other populations
within only several generations.

Only when something kills off the larger, more genetically uniform
individuals will diversity show itself. Only then will one popultion
become different from another. It works just as well in cultivation
as it does in the wild. Of course, if you never kill a single plant,
you'll manage to keep them exactly the same as they were in the wild
but even those wild populations will have changed as lighting and water
level change or some new pest comes in. There is nothing "bad"
about losing wild characteristics, since they keep changing anyway.
What, are the roots gonna stop being able to dig their way into
"wild" soil? ;)

> >This goes true for all mutations, also for those occurring in nature.
>
> Yes, but nature deals in large numbers over long periods of time. Thus,
> deleterious mutations are generally selected against, and neutral
> mutations may be permitted.

Yes, but only by removing large numbers of those neutrals does
selection work.

> We agree here, except that I donUt feel that cultivation contributes
> significantly to species diversity. The numbers of individuals cultivated
> are just too small.

I must disagree with the numbers scheme. Of course, they is more
diversity in most wild species. However, I do not think the numbers
are too small to maintain some wild-viable plants in cultivation,
even if that wasn't my point. A good idea for that would be not to
destroy the Wilds in the first place.

> Part of our disagreement here is in the definition of diversity. While it
> iss true that a hybrid represents greater genetic diversity than one of
> its parents, because it contains genetic material from parents from at
> least two different species, it is not useful in terms of conservation of
> species.

Well, completely unnatural hybrids, yes. But several Nepenthes
and Sarracenia show us very well that natural hybrids sometimes
turn out to be a very good source of diversity and new populations
and subspecies and species.

And do species conserve themselves? I rather think they are changing
all the time as well as going extinct. So now, if we have protected
and saved all the land of, say, S.oreophila and it goes extinct all
on it's own within a couple hundred years. What do we do then? Kill
off all our plants of it since it has been selected out by nature?
Won't keeping it alive a grave error? These questions are half in
jest, here, but lets hear some answers on this one.

> Because it only takes a single person to destroy a site, I am
> very concerned about proposals to make detailed information on
> rare plant locations to anyone with a computer.

Here I argee 100%!

Dave Evans