Biology Reference
In-Depth Information
but gene identities must be estimated from RFLP patterns. RFLP data also can be
analyzed as changes in base pairs if the assumption is made that each change in
restriction pattern is caused by a change in a single base pair.
13.6.5 Sequencing
Computer programs are used to analyze DNA sequence data to determine the
best alignment (
Doolittle 1990, Gribskov and Devereux 1991, Gibson and Muse
2002, Mount 2004
). The identity of two sequences is compared on the percent-
age of shared bases. Deletions and insertions (indels) are usually scored as a sin-
gle change regardless of length (
Hoelzel and Bancroft 1992
). As with proteins or
RFLP data, nucleotide diversity, genetic distance, and interpopulation diversity
can be estimated (
Hoelzel and Bancroft 1992
). Also see Chapter 12 for details on
DNA sequence analysis methods.
13.7 Case Studies in Molecular Ecology and Population Biology
An extensive and growing literature published in a variety of journals and topics
makes it impossible to provide a comprehensive overview of the effect that
molecular methods are having on theoretical and applied insect ecology. Thus,
some “case studies” are presented to illustrate applications of different molecu-
lar tools and their statistical methods.
13.7.1 Genetic Variability in the Fall Armyworm: Incipient Species or
Multiple Species?
The fall armyworm,
Spodoptera frugiperda
, is a polyphagous lepidopteran “spe-
cies” that attacks over 60 plants, particularly corn and rice (but also Bermuda
grass, soybean, peanut, cotton, and alfalfa). It is found throughout the Western
Hemisphere but, because it does not diapause, must colonize northern states
in the United States and in Canada by migrating from overwintering sites in
Florida and Texas (
Nagoshi and Meagher 2008, Nagoshi et al. 2009
). Its range
also extends south into Argentina and Brazil (
Nagoshi et al. 2007
). The “fall
armyworm” has exhibited anomalous differences in tolerance to pesticides
and other life-history traits that are important in pest-management practices.
It appears that it is, in fact, undergoing “incipient speciation” (
Pashley 1986
).
However, the genetics of the fall armyworm may be complex because
Nagoshi
et al. (2007)
reported that the “corn strain” might consist of subgroups.
The undetected presence of cryptic species has practical significance for pest-
management programs.
Pashley (1986)
showed there are two “species,” each
associated with different host plants in the southern United States; one is asso-
ciated with rice (and Bermuda grass) and the other with corn (and cotton and
