Population Genetics Edge Effects - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 110

the same except that the source population had 10 loci each with two alleles
of equal frequency (compare Fig. 8.16, graphs A versus B, respectively).
These patterns support the notion that there is more localized inbreeding in
populations established further from a border, as was discussed for results
concerning F values in Fig. 8.15. Further, these similar rates of change, no
matter which loci panel was used, refl ect the earlier noted fi nding that
values of F through generations change in a similar fashion for trials with
founders at different distances from the preserve border, with little apparent
difference due to alleles available across loci (Fig. 8.15), at least under the
conditions explored here.
The same cannot be said for loss of unique alleles. Figure 8.17 shows
that when more unique alleles are available per locus, there is increasing
loss of alleles due to drift and dispersal of unique alleles beyond the border
of the preserve. As was shown earlier (Fig. 8.12) , no unique alleles were
lost regardless of placement of founders or consequent rates of population
growth when each source population locus had only two unique alleles with
each allele at equal frequency of 0.5 (the trial populations represented by
lowercase letters). In these trials, when drawing 20 founders, there were
40 draws of alleles for each locus, and since alleles were at high frequency,
chances were high that each unique allele would be represented by multiple
copies among the founders. Figure 8.17B demonstrates that 100% of the
alleles were preserved for all trials with only two unique alleles of equal
frequency per locus. In contrast, when each source population locus has
100 unique alleles at low frequency, when drawing 20 founders (40 allelic
draws), it is likely that most alleles selected will be represented only once.
If every allele drawn for the 2 loci of each of the 20 founders were unique
for each of the 30 source loci, this would give a maximum of 1,200 unique
alleles among those founders. The mean number of unique alleles drawn
for founders approaches 1,000 (Fig. 8.17A); thus, on average, approximately
200 alleles were duplicates, the rest being singletons.
In the former situation with 10 loci each with only two unique alleles,
a particular individual may fail to pass a unique allele on to the next
generation for many reasons, for example:
1. The allele is not passed in any of that individual's seeds resulting from
crosses.
2. Its offspring carrying the lost allele are not chosen (randomly) to
survive among “co-competitors” on the same grid point.
3. An individual is not randomly chosen to participate in any mating as
a pollen donor.
4. The offspring of a particular mating are dispersed out of the preserve
and thus “die”.