Biology Reference
In-Depth Information
sorghum). The two occur sympatrically in the United States, exhibit a high level
of reproductive isolation, are physiologically adapted to their different host
plants, and the physiological differences are genetically based (
Pashley 1988
).
These populations have undergone a series of molecular analyses to investigate
their status. As you will note, the sophistication of the molecular methods and
the statistical analysis methodology used increases through time.
Allozyme and RFLP analysis of mitochondrial (mt) DNA indicated the two
types could be distinguished and that there is a near absence of gene flow
(
Pashley 1989
).
Lu et al. (1992)
reported there were RFLP differences in genomic
DNA in the two types after analyzing six colonies with 22 different markers.
Lu et al. (1994)
also found that repeated DNA sequences (microsatellites) in the
two populations differed.
The extent to which the sympatric populations of rice and corn strains of
S. frugiperda
interbreed is problematic (
Pashley 1986, Pashley et al. 2004
). Some
data suggest there is a unidirectional behavioral barrier to interstrain mating,
but other data do not support this (see review by
McMichael and Prowell 1999
).
To answer whether these populations interbreed, several molecular markers
were used because allozymes, mtDNA and nuclear DNA markers did not pro-
vide sufficient resolving power to discriminate between the alternative hypoth-
eses of low frequencies of hybridization vs. expected genetic overlap between
two closely related populations. AFLP-PCR was evaluated to determine whether
this tool might uncover unique genetic markers in each of the two populations,
which would allow hybridization to be detected. AFLP genotyping or finger-
printing is thought to be a useful tool for assessing genetic diversity, relatedness,
population structure and phylogenetic relationships (
Mueller and Wolfenbarger
1999
).
Mueller and Wolfenbarger (1999)
noted that AFLPs can be more reliable
than RAPD markers, and can be easier to use than RFLPs and microsatellites.
McMichael and Prowell (1999)
used ten AFLP markers to compare the two
populations of
S. frugiperda
. The AFLP data identified two populations that
matched up with the majority of individuals from one or the other of the host-
associated strains, as defined by habitat and mtDNA. Unfortunately, not all indi-
viduals could be assigned to the “rice” or “corn” populations. To date, “no pair
of markers shows complete congruence with each other or host of origin. In
other words, allozyme or mtDNA genotypes characterizing 1 strain can occur in
individuals collected on the other strain's host. Individuals on a single host can
contain an allozyme genotype characteristic of 1 strain but a mtDNA genotype
of the other” (
McMichael and Prowell 1999
). These results cannot discriminate
between the alternative hypotheses: sharing of alleles because the variability in
