Biology Reference
In-Depth Information
10.11.3
Rickettsia
Neochrysocharis formosa
(Hymenoptera: Eulophidae) is an important natural
enemy of leafminers. It has both thelytokous and arrhenotokous strains, with thely-
toky induced by
Rickettsia
. The mechanism of producing diploid females (thelytoky)
was found to be due to the fact that meiotic cells during female-gamete formation
undergo only a single equational division, followed by the expulsion of a single
polar body. This means that meiotic recombination does not occur and diploidy is
maintained by an apomictic cloning mechanism that differs from the mechanism of
thelytoky-induction by
Wolbachia
(
Adachi-Hagimori et al. 2008
).
10.11.4
Wolbachia
These rickettsia-like bacteria are one of the most commonly described cyto-
plasmically inherited microorganisms in arthropods.
Wolbachia
are discussed
in Chapter 4 with regard to their ability to induce cytoplasmic incompatibility
when populations with and without the same
Wolbachia
strain mate.
Wolbachia
are gram-negative rods that cannot be cultured easily outside their hosts and
they are widespread, with 17-76% of all arthropod species containing them
(
Werren et al. 1995, Werren 1997, Jeyaprakash and Hoy 2000
). Knowledge of
the evolution and physiological and phenotypic effects of
Wolbachia
on most
of their hosts remains limited; only a few of the thousands of insects that contain
Wolbachia
have been studied to determine the phenotype (if any) produced by
the symbiont (
Rigaud 1999
). One of their effects in arthropods is to alter sex ratio
(
Rigaud and Rousset 1996, O'Neill et al. 1997, Bourtzis and O'Neill 1998, Cook
and Butcher 1999, Stouthamer et al. 1999, Stevens et al. 2001, Vavre et al. 2001
).
In addition to infecting insects,
Wolbachia
infect isopods (Crustacea), includ-
ing
Armadillidium album
,
Ligia oceanica
,
Armadillidium nasatum
,
Porcellionides
pruinosus
,
Chaetophiloscia elongata
, and
Spaeroma rugicauda
(
Rigaud and
Rousset 1996
). Some
Wolbachia
-infected isopods produce female-biased broods
because the
Wolbachia
change genetic males (homogametic ZZ individuals)
into functional “females.” These ZZ individuals are chromosomally male, but
phenotypically appear and function
as females. “Daughters” of infected moth-
ers produce all-female or highly female-biased progeny, resulting in isopod lin-
eages that are chromosomally males (ZZ) but are functional females (
Rigaud
and Rousset 1996
). There is speculation that some
Wolbachia
genes have been
transferred to the isopod nuclear genome. If the “females” are cured of their
Wolbachia
with antibiotics, their progeny are all males (ZZ).
Wolbachia
can cause thelytoky, male killing, and female mortality (
Rousset
and Raymond 1991, Stouthamer and Werren 1993, Bandi et al. 1999, Majerus
