Biology Reference
In-Depth Information
population biology such as transmission, population growth, or selected
traits) asks the same questions as asked in the field of conservation
genetics. Is there just one species or are there cryptic evolutionary units, is
the species fragmented into subpopulations, was the fragmentation the
result of human perturbation, is the population declining, what facilitates
connectivity/gene flow among subpopulations, what was the source of
invasion (outbreak) for an exotic species (emerging pathogen), what loci
are of adaptive significance? The key difference between epidemiology
and conservation is the end goal. Epidemiologists try to eliminate or
reduce populations of parasites/pathogens. In contrast, conservationists
strive to maintain or increase population sizes and continuity of endan-
gered species. Population genetic applications are now integral in con-
servation because it is well recognized that low genetic diversity, small
effective population sizes, and population fragmentation (all three of
which can be measured via genetic methods) can increase the chance of
population extinction.
1,2
Because conservation geneticists are interested in
these factors to prevent extinction, then it seems logical that epidemiol-
ogists could use similar data to help reduce or eradicate parasites/path-
ogens. Indeed, because of the parallel questions between the fields, much
of the population genetics theory, methods, and reasoning that are used in
conservation genetics could be applied to genetic epidemiology. For
instance, it is recognized that low genetic diversity can reduce evolu-
tionary potential (i.e. the ability of populations to evolve to cope with
environmental change).
1,3
Chemotherapy control programs are a major
environmental change for parasites. Given that drug resistance has
evolved among several helminths,
4,5
it seems reasonable that reducing
genetic diversity, via a reduction in effective population size (discussed
below), should be an imperative epidemiological goal to help prevent
drug-resistant evolution.
In this chapter, I discuss three pertinent applications of population
genetics (all of which have been utilized in conservation biology) to
further our understanding of
Ascaris
epidemiology in fine scale
geographic studies. First, I focus on whether sympatric populations of
Ascaris
in humans and pigs constitute separate populations in order to
ascertain if there is cross-transmission between human and pig hosts.
Second, I discuss the use of landscape genetics to identify foci of trans-
mission and epidemiologically relevant variables correlated to substruc-
ture of parasite populations. These first two topics correspond to a series
of recently proposed hierarchical questions aimed at addressing local
scale population genetics in metazoan parasites.
6
Thus, I refer readers
to Gorton and colleagues
6
for a more general discussion of these topics
in metazoan parasites. Also, these sections are not intended to be
a comprehensive summary of the
Ascaris
population genetics literature
as this was recently reviewed by Peng and Criscione.
7
The third section
