Biology Reference
In-Depth Information
The polygyne form of the red fire ant in the United States, first
reported in the 1970s, appears to lack many of the alleles present in South
American populations (Ross et al. 1993). In particular, loss of variability
at the locus involved in sex determination results in a preponderance of
diploid, homozygous, sterile males at the expense of haploid, fertile males
(Ross et al. 1996). Multiple queens are produced in each nest, and many
of these queens migrate to other nests. As a result, in North American
polygyne populations, the number of egg-laying queens per nest is much
higher than in South American populations. These queens tend to be
unrelated to each other and to worker ants of the nest in which they are
reproducing. Together with the lack of intercolony aggression, these ants
are thus able to maintain a very high density of interconnected nests
(Holway et al. 2002).
The Mediterranean fruit fly (
Ceratitis capitata
) is another insect for
which worldwide spread can be correlated with patterns of loss of genetic
variability (Gasparich et al. 1997). Mitochondrial DNA analysis showed
that greatest variability occurred in sub-Saharan Africa, where eight hap-
lotypes were found in the DNA section examined. In the Mediterranean
region of Europe, where the fly appeared in the early 1800s, two of these
haplotypes were found. Most New World populations showed one, or
occasionally two, haplotypes.The predominant, and often only, haplotype
differed in eastern South America, the Andean region of South America,
and Central America, suggesting at least three independent colonizations
from the Old World. In Australia and Hawaii, only one haplotype was
found.
Recent appearances of the Mediterranean fruit fly in California and
southern Florida have created controversy about whether reappearances
were separate invasions or simply recovery of populations from levels that
were continually present, but undetectable. In southern California, in six
outbreak years between 1975 and 1994, most localities showed popula-
tions fixed for one haplotype. In 1992, however, an additional haplotype
appeared in both central and southern California.Thus, it appears that at
least two colonization events occurred in California but that the recur-
ring outbreaks in southern California might be occurring from small res-
ident populations. In Florida, on the other hand, the haplotypes that
appeared in 1962-63 were different from those in 1984, 1990, and 1994.
In addition, the haplotype that appeared in 1984 differed from that in
1990, but it reappeared in 1994.Thus, outbreaks in Florida may be due to
independent colonizations.
