Truly Random Mating and Selfing Rate - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 160

11

CHAPTER

Truly Random Mating and
Selfing Rate

Mating systems range from species that are obligately outcrossing (e.g.,
dioecious or completely self-incompatible species) to species with mixed
mating systems, to obligate selfers. In numerous species, mechanisms that
facilitate selfi ng within a fl ower are delayed, thus providing a back-up
method for reproduction if outcrossing fails (e.g., when pollinators are
not suffi cient). For some of those species, selfi ng can be rare and occurs at
increased rates only when outcrossing fails (e.g., Lloyd and Schoen 1992;
Harder and Barrett 2006). The proportion of offspring produced via selfi ng
versus outcrossing thus varies considerably across and within species.
For NEWGARDEN-simulated populations, the proportion of self-
matings can generally be controlled with the Selfi ng Rate statements. All
of the previous examples used the following input statements:

<Selfi ng_Rate value =“0.0”/>
<RandomMating value=“false”/>

The fi rst statement dictates that, in determining a mate for a particular
cross, self-matings are not included in the list of choices. So all previous
trials represent obligately self-incompatible species.
The second statement is provided to more exactly match the Hardy-
Weinberg criteria for equilibrium populations. Note that completely self-
incompatible populations cannot be in exact Hardy-Weinberg equilibrium,
which can be achieved only via true random mating: selfi ng is as likely as
mating with any other individual in a population. For true Hardy-Weinberg
equilibrium to be established, a species must have a level of compatibility
on average equal to that for any other potential mating. This latter option
can be chosen for a NEWGARDEN trial by setting selfi ng rate to 0, and the
RandomMating value to true. If the latter options are chosen, this has the
effect that, for the mating of a given individual, selfi ng is added to the list
of eligible mates, and the frequency of self-matings depends on the total
number of eligible mates (the mate is chosen at random from the eligibles).
This can have the effect that selfi ng is relatively promoted when there are
few eligible mates in the grid around an individual, these being conditions