Biology Reference
In-Depth Information
10.8.2
Distorter
in Mosquitoes
Meiotic drive has been described in the mosquitoes
Aedes aegypti
and
Culex
quinquefasciatus
. In both species, a Y-linked gene results in excess males
(
Wood and Newton 1991
). Excess males are produced because X chromosomes
are broken during meiosis in males and thus fewer X than Y chromosomes are
transmitted in the sperm, leading to the production of fewer female embryos.
The
Distorter
gene (
D
) is linked closely to the sex locus
m/M
and causes chro-
mosome breakage. Additional genes are involved, and sensitivity to
Distorter
is controlled by
m
, the female-determining locus. In some strains, sensitiv-
ity is influenced by a second sex-linked gene
t
. Yet another sex-linked gene
A
enhances the effect of
Distorter
.
Distorter
has been found in mosquito popu-
lations from Africa, America, Australia, and Sri Lanka, but resistance to it is
widespread.
10.8.3 Female-Biased Sex Ratios in Stalk-Eyed Flies
Extreme female-biased sex ratios are found in two stalk-eyed fly species,
Cyrtodiopsis dalmanni
and
Cyrtodiopsis whitei
(Diopsidae), due to a meiotic-
drive element on the X chromosome (
Presgraves et al. 1997
). Eyestalks are more
exaggerated in males than in females (
Wilkinson et al. 1998
) and females pre-
fer to mate with males with a long eye span. The long stalks appear to indicate
to the female that the male either lacks meiotic-drive elements or can suppress
meiotic drive, thereby increasing the female's fitness by avoiding a biased sex
ratio in her progeny (
Wilkinson and Reillo 1994
). Apparently, there are both
autosomal- and Y-linked polymorphisms for resistance to meiotic drive.
10.8.4 Meiotic Drive as a Pest-Management Tool?
Meiotic drive operates as an evolutionary force that can cause an increase in
the population frequency of the allele or chromosome that is favored in trans-
mission, even if it confers a disadvantage on its carriers. It has been proposed
that meiotic drive might be used to introduce new genes (such as cold-sensitive
lethal genes, insecticide-susceptibility genes, or behavior-altering genes that
would reduce the negative effects of mosquitoes on humans) into natural pop-
ulations as a method to achieve control of these important vectors of disease
(
Wood and Newton 1991
). However, much remains to be learned about the sta-
bility of meiotic-drive mechanisms and the conditions under which they might
function in pest-management programs. The fact that resistances can develop
to suppress meiotic drive could limit the effectiveness of meiotic drive in pest-
management programs.
