Biology Reference
In-Depth Information
Table 12.3: Applications of Selected Molecular Methods to Systematics Problems.
Research
problem
a
Isozymes
RFLPs
RAPD-PCR
Microsatellite
single-locus
Multilocus
fingerprints
DNA/RNA
sequencing
Genome
sequencing
Gene evolution
M
M
I
M
I
A
I
Relatedness
M
M
M
A
M
$
I
Hybridization
A
A
A
M
I
$
I
Species
boundaries
A
A
A
M
I
A
$
Phylogeny
0-5 mya
A
A
I
M
I
A
$
50-500 mya
M
M
I
I
I
A
A
500-3500 mya
I
I
I
I
I
A
A
Modified from
Hillis et al. (1996)
and
Trautwein et al. (2012).
a
I, inappropriate use of the technique; M, marginally appropriate or appropriate under limited circumstances; $, appropriate
but probably not cost-effective; A, appropriate and effective method.
gel systems), polyacrylamide, agarose, and cellulose acetate gels as substrates
(
Hames and Rickwood 1981
). Each has specific advantages and disadvantages
(
Moritz and Hillis 1990
). However, isozyme or allozyme data are useful for esti-
mating the evolution of only a portion of the genome: those genes coding for
enzymes that have a different charge and size. The data also are most useful
for analyzing relatively closely related taxa. Unfortunately, allozyme variation in
some insects, such as aphids and Hymenoptera, is low and other molecular tech-
niques are required.
An example of allozyme analysis illustrates an economically important appli-
cation of the technique. Twenty-four populations consisting of three subspecies
of
Culicoides variipennis
(Diptera: Ceratopogonidae) from different geographic
regions were examined for genetic differences (
Tabachnick 1992
). Twenty-one
loci were examined among the 24 populations of this vector of bluetongue
virus, a disease that causes losses of US$125 million annually to the U.S. livestock
industry. The results were analyzed with a stepwise discriminant analysis and are
consistent with the conclusion that there are three North American subspecies;
the three subspecies appear to be sufficiently different to be considered species.
Furthermore, geographic variation in bluetongue disease epidemiology is cor-
related with the distributions of the three subspecies. These, and subsequent,
data support the hypothesis that one subspecies is more effective as a vector
of the virus (
Tabachnick 1996, Holbrook et al. 2000
). The results had implica-
tions for pest-management programs and had significant economic impacts. The
areas inhabited by the two (nonvector) subspecies could be considered virus-free
regions and animals raised in such areas would not have to undergo extensive
