Truly Random Mating and Selfing Rate - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 164

How does increasing the selfi ng rate compare to designating the species
as experiencing no selfi ng except that brought about by true random
mating? To examine this question, four trials were conducted with similar
initial input conditions in general agreement with Input File 1 (including 20
founders). First we will discuss three of the trials (c, r, and s), in which the
20 founders were in two central horizontal lines of 10 with closest spacing.
All initial conditions for these trials were identical except the following:
Population c had a selfi ng rate = 0; random mating = true (self-compatible,
but selfi ng occurring randomly in proportion to the number of eligible
mates).
Population r had a selfi ng rate = 0.05.
Population s had a selfi ng rate = 0.1.
These three populations do not differ extensively across 15 generations
with regard to population growth rate, loss of observed heterozygosity,
increase in F, or unique alleles retained, although population s appears to
be losing observed heterozygosity and increasing in F at slightly higher
rates ( Figs. 11.3 and 11.4) .
Earlier we showed that increasing the spacing between founders can
increase population growth rate, F, loss of observed heterozygosity, and
unique allele retention in self-incompatible species with 0 selfi ng. Are
similar effects observed when spacing between founders increases and when
selfi ng is allowed at a rate proportional to true random mating with eligible
mates? In Figs. 11.3 and 11.4, populations c (discussed in the preceding
paragraph) and q are identical in having 20 founders in two horizontal lines,
but whereas in c the founders have closest spacing, for population q there
are 13 spaces between individuals. Note fi rst that if a hypothetical trial is
run with identical conditions to population q for which input dictates that
selfi ng rate = 0 and random mating = false (completely self-incompatible),
no offspring are produced since pollen dispersal distance is a maximum of
5 units (data not shown). Since no founder is within mating range of other
founders and selfi ng is prohibited, such a hypothetical population would
not produce any offspring and would disappear after the initial round of
attempted matings. However, when random mating is set to true, then
because selfi ng will occur at a rate proportional to the number of available
mates, selfi ng will always occur exclusively in the fi rst two generations,
with a mixture of selfi ngs and outcrossings occurring as the population
grows and more individuals are dispersed within pollination distance of
one another. Eventually, at later phases of expansion, the proportion of
selfi ng should decrease substantially since many mates will be available to
most individuals. These patterns can be clearly seen in Figs. 11.3 and 11.4
(compare trials c and q).