Truly Random Mating and Selfing Rate - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 161

often likely to occur, for example, at low population growth rates, under
subdivision, or early in the development of a population. While choosing
this option may not produce Hardy-Weinberg equilibrium populations that
are contingent on an essentially infi nite population size, such a scenario
may refl ect what occurs for species with mixed mating capabilities early in
the founding process: when few neighboring mates are available and with
a delayed self-mating mechanism, the proportion of matings produced via
selfi ng should increase. As numerous potential mates establish around an
individual, selfi ng becomes less common.
Another effect of increasing the frequency of selfi ng for newly founded
populations is that population growth rate can increase. Offspring dispersed
beyond the pollination distance range are doomed to reproductive failure,
unless they can produce at least some offspring via selfi ng.
Figures 11.1 and 11.2 compare population development parameters
for populations with the same number of founders placed in different
geometries while demonstrating the effect of setting selfi ng rate to 0
and setting random mating to true (self-compatible) versus false (self-
incompatible). These populations are similar to populations examined in
earlier chapters, being bisexual annuals with 30 loci, each with 100 unique
alleles of equal frequency. Offspring production is a mean of 2, with a
Poisson distribution of production across individuals. Offspring and
microgamete dispersal distance maximum is 5 units. All populations are
initiated with 20 founders.
As shown earlier, placing the founders in separate groups towards
the corners of the preserve can increase population growth rate, loss of
heterozygosity (Fig. 11.1), F values, and unique alleles retained (Fig. 11.2).
However, prohibiting (populations v and b) or permitting selfi ng at a rate
proportional to all eligible mates (true Hardy-Weinberg mating, trials c and
k) does not seem to substantially affect population growth. If self-mating is
allowed, there is some loss of observed heterozygosity and increase in F values
(Fig. 11.1B and Fig. 11.2A, respectively). The differences in rates between non-
selfi ng and Hardy-Weinberg selfi ng appear to be higher early on, most likely
because there are proportionally fewer mates at early phase of population
growth, which increases the relative rate of selfi ngs. Eventually, the rates of
change appear to become more equal as more mates become available. While
population subdivision increases the proportion of unique alleles retained
(Fig. 11.2B), that loss of unique alleles is least for completely self-incompatible
species (b versus k, v versus c), this difference increasing to approximately
7.1% when the founders are placed in two lines. These results suggest that,
compared to self-incompatible species, species with mixed mating systems
will experience an increased loss of heterozygosity, increase in F, and increased
loss of unique alleles in early phases of population establishment when low
numbers of founders are involved under the given conditions.