Re: Genetic Diversity

Michael.Chamberland (23274MJC@MSU.EDU)
Fri, 27 Dec 96 09:28 EST

> From: "Mellard, David" <dam7@atsdha1.em.cdc.gov>
>
> Just a reminder that the seeds produced have a great deal of genetic
> diversity in them, whether the seeds come from plants grown from seed or
> from vegetatively produced plants. The diversity results from dominant and
> recessive genes that are found in the same plant and the wonderful shuffling

A plant's genome contains a great deal of genetic information regardless of
the method of propagation. But this is not the same as genetic diversity.

> of the chromosome (and hence genes) as gametes are produced. Not to
> mention jumping genes between chromosomes.

The phenomenon of "jumping genes" has been documented in corn, but has it
been observed in CP?

> I'm reminded of the story of the 30 British starlings that were released in
> New York (I think in the 1930's). They're now a pest and are found all over
> the United States, much to the consternation of our American blue bird. The
> genetic diversity of those 30 starlings was enough to ensure the survival of

As has been pointed out in other posts, there is a difference between the
desirable reintroduction of organisms to their original habitat, and the
introduction of exotic (non-native) organisms to a new habitat. In this
case the starlings were introduced to a habitat lacking their natural
preditors and pathogens. The birds were able to exploit this "free" habitat
without utilizing many of the genetic adaptions which they had needed in the
more competitive natural habitat. If starlings had been wiped out in Europe,
and 30 were reintroduced to their original habitat, I should think they would
have experienced a greater bottleneck effect, since they'd be facing all the
preditors and pathogens which have adapted to prey on starlings. Also, in
the starling example, we do not know what degree of genetic diversity was
present in the original sample of birds (or how often other starlings may have
been brought in). Starlings do not propagate "vegetatively", and since they
were likely brought in from the wild and not from a captive breeding program
(where inbreeding is a concern), I imagine that the genetic diversity present
in the original sample was quite high.

Fortunately, exotic introduction "successes" like the starlings, cheat grass,
purple loostrife, salt cedar, and water hyacinth in the US. are rare. But
the rarity doesn't diminish the disasterous impact of those introductions
which succeeded. We cannot expect conservation reintroductions to be
comperable to these exotic invasions. Nor can we count on the "invasion
factor" to work for us, if we should decide to introduce a rare plant into
a new "exotic" habitat, and expect it to proliferate.

We must rely on tested conservation methods and sound management to conserve
species. We must not expect conservation of species to arise as a "byproduct"
of hobby collection or hypothetical "Jurassic Park" technologies, etc.
Conservation is a complex pursuit, and a new science. There is still much to
be learned, and we are running out of time, with little funds. I would
encourage those who are interested in conservation to do some reading and
investigation on the matter. This should prove more valuable than
hypothetical arguments about how conservation MIGHT be derived from tangential
activities.

> the species in the US. My impression is that the diversity within a plant
> is much greater than the diversity within a bird.

This I do not follow at all. Do you mean that plants have a higher chromosome
number than birds? This may often be the case, but not always, and anyway is
not related to genetic diversity.

Michael Chamberland