is an endosymbiotic bacteria that lives as a reproductive parasite in a large
fraction of insect species worldwide. In order to be passed on to future generations, the infection
must be present in the eggs of the mother, since it lives in the cytoplasm of the cells of the
reproductive system, but most of the cytoplasm is removed from the sperm cells during
thus, the infection is only inherited via the mother. This means that it is most
to be present in females, and for the offspring of a pairing of insects to
be mostly or all female as well. To this end, the parasitic bacterium has various methods of
subterfuge which can be used to hijack the reproductive systems of its host.
One such host of
, a parasitic wasp that is dependent on
certain flies for its lifecycle.
females, in order to lay their eggs, must find a pupating fly
to act as a host: once located, the females will drill a hole through the puparium wall, and inject
venom into it to kill the larva inside. They then proceed to lay their eggs on the surface of the fly
pupa, which then hatch and consume it for food as they grow, pupate, and metamorphosize
inside the pupal casing, and finally emerge.
reproduces through a haplo-diplo mating system, where an unfertilized female
will lay haploid offspring, which will result in males, and where a fertilized female will lay
diploid offspring, rearing more females.
, however, interferes with this normal cycle
by four main mechanisms of disruption: feminization, male killing, parthenogenesis, and
cytoplasmic incompatibility (CI). In CI, the sperm of infected males and uninfected females, or
of females infected with a different strain of
, are rendered incompatible with one
another due to
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failure of fertilization, and thus in all-male broods; in contrast, in parthenogenesis, unfertilized
females will develop diploid eggs which in turn form all-female broods from unfertilized eggs.
Male killing is the result of successful copulation, whereby
-infected haploid eggs are
killed by the infection itself, leaving only diploid eggs in the brood, and thus resulting in an all-
female, but much smaller than normal, filial generation; this presumably serves the purpose of
reserving all the available resources for the diploid female offspring, thus increasing their chance
of surviving and passing on the infection, by eliminating those known not to pass on the
infection. Finally, in feminization, the
will override the normal masculine
development of the haploid males, and instead force them to become haploid females and
pseudo-females, which are often infertile. (Werren, 2003)
From the patterns of offspring formation thus described, this experiment was conceived
with two main goals in mind: the fir
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