Conclusions and Discussion - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 333

alleles, all of very similar frequency), for which there is no difference between
trial types o and r at Generation 1 only. This generally greater variation in
expected heterozygosity values is likely due, in part, to the greater variance
in loss of copies of different higher-frequency alleles at a locus. In the sense
that some authors use the term expected heterozygosity as interchangeable with
gene diversity , the results given in Table 3 demonstrate that the population
conditions losing low-frequency unique alleles at a higher rate will also
commonly yield greater standard deviation of the mean gene diversity across
replicate trials. Further, these fi ndings imply that founder placements that
induce greater losses of either lower-frequency unique alleles or copies of
alleles at higher frequencies will produce a greater range of random changes
of the probabilities of occurrence of particular multilocus allele combinations
across repeated identical trials or founding events.
The NEWGARDEN comparative trials presented in this topic
demonstrate that alterations in unique allele frequencies dependent solely
on differing spationumeric processes are not unusual. Such processes bring
about not only loss of unique alleles from populations, but also alterations
of frequencies of alleles that may affect the population-level frequency of
certain interacting gene combinations. Founding trial conditions leading
to greater losses of low-frequency alleles in NEWGARDEN analyses result
in greater variance in frequencies of more common alleles from replicate to
replicate under that set of establishment conditions. The potential for certain
genotypes to arise will vary between comparative populations differing
in rates of allele loss, and thus the pathways available for populations to
move about on gene-combination adaptive landscapes may vary between
populations solely because of different spationumeric establishment
histories. Two populations may come to differ in fi tness-related multilocus
alternate allele combination frequencies as a direct random result of allele
combinatorial histories driven by differing founding geometry, even if
all other initial conditions have been held constant. Directional selection
becomes less effective since allele frequencies, including alleles of lower
fi tness, become more subject to chance fl uctuations. Such idiosyncratic
changes in adaptive landscapes between populations may contribute to
Templeton's model (see Templeton 1999 and references) of differentiation
via transilience. Note that in the example above we have used only three
interacting loci: this issue becomes more complex as more interacting loci
become involved.
Thus, with regard to population evolutionary dynamics and population
genetics conservation processes, spationumeric effects not only affect loss
of rare population-unique alleles, but also can alter to various degrees the
likelihood that certain portions of the entire potential multilocus universe
of allelic combinations existing in the founding generation will be available
for evolutionary exploration as populations grow. For a species, there may