Conclusions and Discussion - Genetic Diversity in Establishing Plant Populations: Founder Number and Geometry - page 323

There are numerous other reasons for alleles to be rare at founding.
For example, a set of founders may comprise propagules arriving from
a diverse array of genetically differentiated source populations, with
contributions from some populations being relatively uncommon. Consider
200 founders that come primarily from one tight-knit cluster of individuals
in a source subpopulation or inbred group, with a few other individuals
arriving from a more diverse array of adjacent subpopulations. In new-
planting or restoration schemes, seed is often primarily collected at one or
a few locations, with occasional seed collected at more distant locations.
Geographically separated accessions for restoration plantings may be mixed
in an attempt to mimic a “panmictic” population, but the representation
of some collections may become greatly diminished because of differing
collection-storage protocols or environmental suitability differences
among accessions. When newly establishing populations are founded by
individuals from different source populations, an allele common in one of
those source populations may have a much lower frequency among the
colonizers, especially if their numbers are relatively small.
Some newly founded populations might arise, at least in part, from
seed or standing seedlings-saplings. Dormant seed banks, or established
but not reproductive seedling-sapling banks, may be quite complex in
composition genetically, with allele frequencies from different episodes of
gene input varying greatly. Some alleles may be rare among the dormant
individuals released.
Mutation
Rare alleles are also constantly arising in plant populations via mutation.
New mutations may be more likely to persist in establishing small, isolated
populations, since they are disproportionately represented at higher
frequencies compared to their occurrence in an infi nite population, and
thus they are more likely to randomly drift to higher frequencies. In many
of the previous NEWGARDEN trials, when founders numbered 172, a
signifi cant proportion of the founding unique alleles are at low frequencies
(i.e., frequency in source population = 0.01, and they are thus present only
once or a few times among the founders), similar to a new mutant allele.
Still, many such rare alleles are preserved as the population develops. These
results suggest that when low-frequency alleles or new mutations occur
among the founders under conditions that would not appear to be extreme
and where strong negative selection is not initially involved, many of them
may be preserved to interact in future evolutionary processes.
Most plants are likely mosaics of different mutant cell lineages
(Klekowski 1988). Imagine 100,000 functionally active loci-genes per cell
genome. Further, imagine that the apical meristem cells that continuously