Biology Reference
In-Depth Information
large samples of flies from different geographic regions to confirm that the dif-
ferences detected in the preliminary screening hold up when larger samples of,
potentially more-diverse, flies are sampled. The task of identifying appropriate
genetic markers has engaged a number of researchers and considerable funds.
Early attempts to discriminate between different geographic populations of
the Medfly used RAPD-PCR markers (
Haymer and McInnis 1994
), enzyme elec-
trophoresis (
Malacrida et al. 1996
), and compared RAPD-PCR and enzyme elec-
trophoresis data (
(Baruffi et al. 1995
). As expected, RAPD-PCR revealed larger
amounts of genetic variation than enzyme electrophoresis data (
(Baruffi et al.
1995
). The complete mitochondrial genome of the Medfly was sequenced, and
different populations were found to exhibit genetic differences that are poten-
tially useful for developing diagnostic tools (
Spanos et al. 2000
).
A PCR-RFLP method used by
He and Haymer (1999)
compared variation in
intron sequences of the
glucose-6-phosphate dehydrogenase
gene among
different Medfly populations. Five alleles of this locus were found in 26 pop-
ulations of
C. capitata
and two restriction enzymes were used in successive
digestions of the PCR products to document genotypes and allele frequencies.
This approach involved amplifying intron sequences from individuals from vari-
ous populations by using primers designed from cDNA sequences in GenBank.
PCR products were cloned and sequenced, and allelic variants and restriction-site
changes were identified. The restriction-site data allowed
He and Haymer (1999)
to develop a diagnostic test that did not require sequencing the PCR products.
The data were analyzed using principal coordinate analysis and
Analysis of
MOlecular VAriation
(AMOVA) to quantify the distribution of genetic diversity
in a hierarchical manner. For some of the invasive sites, populations that “are
probably acting as sources of origin” were identified (
He and Haymer 1999
).
Five alleles tended to be associated with populations from different geographic
regions: A1 was most common and found in all populations surveyed, so was
not informative. A2 and A3 were widespread in samples from Greece, but only
one allele tended to be prevalent in other samples (A2 was prevalent in sam-
ples from Guatemala, Peru, Florida, and southern California; A3 was prevalent in
samples from Argentina). Hawaiian populations showed substantial frequencies
of A4, but A4 was rare in other populations.
He and Haymer (1999)
concluded “the invasive population from northern
California appears similar to populations from Argentina and Costa Rica. From
southern California, three of the infestations (1992-1994) are clustered with pop-
ulations from Guatemala, suggesting, “that Guatemala is a possible source of
