re: genetic diversity

Wayne Forrester (forrestr@mendel.Berkeley.EDU)
Thu, 12 Dec 1996 17:21:11 -0800 (PST)

I feel the term diversity is being used in different ways in this
discussion. On the one hand, preserving a species is preserving
diversity, because if that species is lost it is one less species present
on the planet. On the other hand, there can be innumerable variation
within a species. Some of this variation is clearly evident, for example
in different color expression in leave. Much of the variation is not
visible, and would only be detected by examining the DNA of the plants.
Whether this second type of genetic diversity is important, who can say.
In conservative terms, one would like to preserve as much diversity as
possible because it may well be very important. Clearly, preserving the
first, visible, form of diversity is desirable. We like seeing the
different forms of plants.
It is not possible to preserve the diversity of most species
(possible exceptions for plants with very small populations and very
limited numbers of sites, but even here the genetic diversity could be
fairly large) without large numbers. One could have two plants with large
numbers of genetic differences, but that still would only be two plants.
To really preserve the range of diversity found in the wild, one would
have to cultivate, and maintain, at least one example of each genetically
different plant. Strictly speaking, the full range of these differences
cannot be detected without determining the complete DNA sequence of each
plant, which of course is not possible. To be conservative, one would
want to preserve a very large number of plants, from as many different
habitats and sites as possible, assuming that these would represent
variants of a species. This just is not possible without culturing large
numbers of plants.
Hybrids, whether or not they are naturally occuring, do not
contribute to conserving a species. Sure, they preserve part of the
genetic makeup of that species, but the species is lost if its DNA is
only represented in hybrids.
Finally, how many species in culture now are derived from only a
few or a single wild collected parent? How many of us grow large numbers
of representatives of any single species? My feeling is that the number
of people growing more than a few, or in many cases more than a single
plant, of a particular species is probably very small. And many of those
with multiple representatives of a particular species generated all those
plants from a single, or at most a few parents. This just does not
represent much diversity.
Just more of my thoughts on this apparently very controversial topic.
Wayne Forrester