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provide an estimate of generational
N
e
(
Figure 8.1
A).
56
If this holds true
(currently being tested by R. Waples, personal communication), one
should aim for larger sample sizes than the current data set (e.g.
50 per
subpopulation) in order to make sure that all potential cohorts making up
a generation are sampled. If this does not hold true, extensive data
collection will be needed to obtain an estimate of generational
N
e
(i.e.
using the formula
N
e
z
T
˜
t
)
65
as one will need estimates of
T
and the
N
t
's.
An estimate of
T
for
Ascaris
will likely require experiments in pigs by
either monitoring infections from a cohort of eggs over years or using
different aged pastures (i.e. eggs left standing 1 year, 2 years, etc.) to
estimate infection efficiencies of different egg ages. For now, it must
suffice to say that
T
is likely
9 years as this is the current knowledge of
egg longevity in the environment.
12
Because parasite breeders within
a given breeding year (
N
t
) are separated among hosts,
N
t
is function of the
effective number of breeders within each host (
N
b
) of the subpopulation
and the proportional offspring contributions of each
N
b
(
Figure 8.1
B).
13
I
refer readers to Criscione and Blouin
13
for a detailed description of
a model for subdivided parasite breeders that can be used to estimate
N
t
frommeasures of the
N
b
's. Here I draw attention to the fact that the single-
sample estimators can be used to estimate the
N
b
of a given host. One
simply would collect and genotype eggs/larvae from an individual
person. Moreover, the
N
b
values themselves may be of epidemiological
use especially if one does not have a means to directly count adult
parasites in a person (e.g. schistosome parasites).
13
If
N
b
estimates
correlate to actual intensities of infection (a relationship that still warrants
testing), then
N
b
estimates could provide a more accurate depiction of
infection intensities among hosts compared to other surrogate methods
such as eggs per gram of feces.
N
b
estimates could also be important in
helping determine the role an individual host has in contributing to
a parasite's subpopulation
N
e
(or
N
t
in the case of
Ascaris
).
13
In this chapter, I have illustrated the feasibility of using of single-
sample estimators in estimating generational
N
e
estimates for subpopu-
lations (households) of
A. lumbricoides
. In order to illustrate different
concepts and applications that one could use with
N
e
estimates, I have
made several assumptions and extrapolations with these data. Nonethe-
less, these estimates have shed additional light on the population and
thus epidemiological dynamics of
Ascaris
in Jiri. Overall, the household
N
e
estimates were low (~100) and it appears that they were stable over
time even with chemotherapy treatment (though a more formal test is
needed). Comparison of metapopulation
N
e
(
N
eT
) between the island
model and the single-sample estimators further elucidated transmis-
sion patterns in that subpopulations appear to be contributing fairly
equally to overall dispersal of
Ascaris
across the metapopulation. Thus,
among-subpopulation dynamics were relatively stable such that this
<
6
e