Population Genetics Edge Effects - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 103

Does founder placement relative to borders affect the number of unique
alleles retained in a population? In Fig. 8.3 we showed that as founders are
placed at greater distances from the border, the populations they generate
grow more rapidly. We then explored the consequences for heterozygosity
and F. Are there differences in the degree to which unique alleles are retained
as these populations develop at different rates? Populations that grow
more slowly might be subject to greater loss of alleles via drift. Recall that
the source population had 10 loci, each with two unique alleles of equal
frequency = 0.5 (see the basic input trial code given above). This means that,
in the source population, there was a total of 20 unique alleles available for
distribution among the randomly selected founders.
Figure 8.12 shows that there was no effect on unique allele retention
when the founders were placed at different distances from the lower
left border of the preserve. Even though these populations grew at quite
different rates, and with varying degrees of risk of loss of unique alleles
outside the border, all populations retained the original 20 alleles present in
their founders through all generations. Note that, if we consider only one of
these loci, there are two alleles of equal frequency in the source population.
Since each founder carries two alleles for this locus, that means that, in the
generation of the initial population of 20 founders, there are 40 draws of
alleles from the source population pool of the two alleles of equal frequency
at that locus. Thus, the chances are very high that multiple copies of each

40

30

20

222222222222222222222 333333333333333333333 444444444444444444444 555555555555555555555

10

0

0 7 14 21

GENERATION

Fig. 8.12 Mean number of unique alleles retained in each population for the trials 2, 3, 4, and
5 populations generated using NEWGARDEN as described earlier (30 runs per trial). Each
“point” is occupied by all four letters, meaning that for each generation of each trial population,
20 unique alleles were present (starting with generation 0, i.e., among the founders). All
populations began with two horizontal rows of 10 founders each, the founders being placed
at different distances from the border (trial 2 = founders placed at lower left corner (0,0); trial
3 = founders placed 10 units from the corner; trial 4 = 40 units; and trial 5 = 2,560 units from
the border).