Biology Reference
In-Depth Information
horizontally versus vertically are greater when the founders are placed at
the lowest left corner of the preserve ( Fig. 9.3) . Although when founders
are placed at the lower left corner (l and L), observed heterozygosity drops
more rapidly for horizontal founder placement (l), F values for that trial
and for the comparable trial in which founders were placed diagonally (L)
are more or less the same (Fig. 9.4A). This suggests that the rate of increase
in inbreeding is the same between the two trials. The more rapid decline
in observed heterozygosity for horizontal founders placed at the corner
is thus likely due to more rapid loss of unique alleles, which is shown to
be the case in Fig. 9.4B. These results indicate that when edge effects are a
factor under the given conditions, populations developing from founders
that are more widely spaced and diagonally placed extending into the
preserve, rather than placed horizontal to a border, will lose unique alleles
and estimated and observed heterozygosity at lower rates. Note that such
diagonal founders placed at a corner have internal individuals that are at
greater distances from a border.
In contrast, when founders are placed centrally in a preserve where
edge effects are eliminated, the rate of observed heterozygosity loss is
slightly greater for diagonal founders (Fig. 9.3). F is also higher for diagonal
founders than for central horizontal founders (Fig. 9.4A) and this is likely
due to increased inbreeding for diagonal founder populations: unique
allele loss is almost identical for populations founded in either geometry
(Fig. 9.4B).
Apparently, the greater distance between individuals and between the
ends of the diagonal lines compared to the horizontal lines of founders
induces more inbreeding for the former under the current conditions (e.g.,
level of dispersal). These results suggest that even slight changes in spacing
can alter trajectories of population genetics parameters.
What if the same number of founders are placed in even more
arrangements? Figures 9.5 and 9.6 show changes in population growth
and different population genetics parameters over generations for
NEWGARDEN trial populations, all of which started with 20 founders
from the same source population. Each trial has identical input conditions
except that the founders, although always placed centrally in the preserve
and with closest spacing, were placed in different geometric patterns at the
outset (v = two lines of 10 founders each; e = one long line of 20 founders;
f = two lines of 10 founders each placed perpendicularly in a cross; or g =
20 founders placed to form a hollow square). All initial input parameters
were otherwise identical to the “basic input fi le” outlined earlier except
that there were 30 loci, each with 100 unique alleles of equal frequency =
0.1, and the trials here continued only for 16 generations.
Figure 9.5A shows that three of these populations grew more or less
at the same rate, although population e, with founders placed in one long
Search WWH ::




Custom Search