Biology Reference
In-Depth Information
Chapters 6-8. Each varies in the time required, ease of execution, cost, and level
of genetic variability that can be detected (
Table 13.1
).
DNA-based methods provide a way to examine DNA directly. Which DNA-
based technique should be used in a particular project depends on the goals and
the level of DNA variation in the species of interest (
Moritz et al. 1987, Mitton
1994, Roderick 1996, Loxdale and Luschai 1998
). When attempting to resolve
problems involving species not analyzed previously by that specific molecular
method, it is difficult to predict whether a particular DNA sequence or tech-
nique will be informative. This is because different insect groups differ in the
amount and type of genetic variability they contain. Thus, molecular ecology
remains a developing field that is still refining the molecular tools used and the
statistical methods utilized for data analysis.
13.5.1 Allele-Specific PCR
Allele-specific PCR is rapid, easy, and appropriate for many population biol-
ogy or ecology studies (
Erlich 1989, Arnheim et al. 1990
, see Chapter 8). Allele-
specific PCR requires DNA sequence data so that primers can be developed and
synthesized (see Chapter 8), although some “universal” primers for ribosomal
and mt DNA can be used on many species (
Table 13.1
).
Ecologists have long wanted to know who is eating whom in the environment.
Allele-specific PCR has been used to evaluate the diets of predators (
Agusti et al.
1999, Zaidi et al. 1999, Hoogendorn and Heimpel 2001
). Persistence time of prey
DNA in the gut, size of target DNA sequences, as well as the abundance (single
copy vs. multiple copy genes) of prey DNA in predator guts vary by species and by
temperature (which affects the digestion rate). This application of allele-specific
PCR must be developed for each predator-prey system, making validation of gut
analyses time consuming (for more on this topic, see Section 13.7.2.3).
A variation of allele-specific PCR, Long or high-fidelity PCR, was described in
Chapter 8. Because two DNA polymerases are used (one of which has the ability to
proofread and correct errors in incorporation), high-fidelity PCR allows microbial
DNA to be detected even when it is mixed with insect or plant DNA. High-fidelity
PCR is especially useful when monitoring arthropod vectors of disease agents. High-
fidelity PCR can detect very low titers of microbial symbionts such as
Wolbachia
or
of plant pathogens within insects (
Jeyaprakash and Hoy 2000, Hoy et al. 2001
).
13.5.2 Allozymes (Protein Electrophoresis)
Allozymes have been used to analyze mating systems (random versus assorta-
tive mating), inbreeding, genetic drift, hybridization, effective population size,
