Biology Reference
In-Depth Information
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GENERATION
GENERATION
Fig. 15.6
Levels of observed heterozygosity in successive new cohorts for trials modeling
establishment of the dioecious shrub
Lindera benzoin
. 172 founders were placed either in
squares of 43 at each corner with no founder closer than 80 grid units from a border (A,
lowercase letters), or in a single central square in the preserve (B, uppercase letters). In every
trial, there were 4 grid points between all adjacent founders. The different trials are compared
to basic trial M, in which 25% of offspring are dispersed to, and 25% of pollen comes from,
each of the four dispersal distance frames (see
Table 15.1
).
To summarize, comparative trials
differ as follows:
In trials N and n, more offspring are dispersed more closely to the maternal plant; 25% pollen
from each frame.
In trials O and o, 25% of an individual's offspring are dispersed to each frame; more pollen
comes from nearer the maternal plant.
In trials P and p, 25% of an individual's offspring are dispersed to each frame; more pollen
comes from a greater distance from the maternal plant.
For complete details on the trials, see text and Table 15.1.
and then heterozygosity of cohorts increases and remains steady at levels
approaching those of the founders for several generations. By age 20 for all
trials, heterozygosity of successive cohorts declines, following the pattern
seen for the population as a whole (
Fig. 15.2).
A signifi cant portion of the
decline in heterozygosity seen for the entire population is accounted for by
the slightly more rapid decline in heterozygosity for the cohorts (e.g., at age
68, o has a cohort observed heterozygosity of around 0.89, but a population
observed heterozygosity greater than 0.9). The more rapid decline in cohort
heterozygosity for trials with founders in four separate squares (graph A)
versus founders in one large square (graph B) is most likely due to more
localized inbreeding in the former.
Levels of F for cohorts in these trials are depicted in
Fig. 15.7.
For all
trials, the initial cohort has an F value of 0, since the initial founders are
“taken” from a source population at Hardy-Weinberg equilibrium, and no
new cohorts are created until founders achieve the designated generation
at which reproduction commences (age 8). Values of F can sometimes be
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