Biology Reference
In-Depth Information
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O O O OOOO OO O O OO O O O O O O O OOO OO O OO O O O OOOO OOO OO OO OO O OOOOOO OOOOOOO
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GENERATION
GENERATION
Fig. 15.7 Levels of F 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.
negative because of heterozygote excess (outbreeding) in a cohort. Once
the populations begin to grow in earnest, F for individual cohorts increases
and approaches a plateau. The relative changes in F among the trial cohorts
across generations refl ect the relative rankings for average F values for the
populations as a whole ( Fig. 15.3) . Again, F increases to a higher value with
increased population subdivision (graph A), likely due to both increased
inbreeding (fewer local mates available) and Wahlund effects. When
Wahlund effects are pronounced because of extreme subdivision (here
there is little or no initial mixing among the four corner subpopulations),
the apparent increased inbreeding may be somewhat of an artifact of such
subdivision. In other words, while some increased inbreeding may be
occurring in the lowercase populations (graph A) compared to the parallel
uppercase populations (graph B) due to founder subdivision in the former,
individual cohorts for each subpopulation in graph A may have F values
close to those for the non-subdivided founder populations of graph B, but
subdivision yields greater F values due to Wahlund effects. Aspects of this
possibility will be examined in more detail below.
 
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