Biology Reference
In-Depth Information
seems that the tick and the symbiont have not coevolved, but the bacteria are
vertically transmitted from females to their progeny and are transmitted trans-
stadially.
Pistone et al. (2012)
suggest, “The high prevalence of
M. mitochondrii
in wild-collected adult females of
I. ricinus
seems to suggest a beneficial role
…
.
However, the decrease in the number of bacteria in laboratory-reared ticks,
without visible effects on the biology of the hosts, suggests the presence of the
symbionts, if beneficial, is facultative, at least in laboratory conditions.”
Antlions (Myrmeleontidae) suck out the body fluid after first paralyzing their
prey with a toxin produced by salivary gland secretions produced by bacteria
located in the salivary glands. The paralyzing toxin produced by these bacterial
endosymbionts is a homolog of GroEL, a heat-shock protein that functions as
a molecular chaperone in
E. coli
(
Yoshida et al. 2001
). In the antlion, the GroEL
protein may act on receptors in prey insects to induce paralysis. The antlion
symbionts perhaps evolved this nonchaperone function to establish a mutually
beneficial antlion-bacterium relationship.
Yoshida et al. (2001)
speculated that
insecticidal proteins may be produced by other endosymbionts to help addi-
tional fluid-feeding predatory insects.
4.12.2
Wolbachia
and
Cardinium
Wolbachia
, a genus of
α
-proteobacteria, commonly are found in arthropods
(
Werren et al. 1995, Rigaud and Rousset 1996, O'Neill et al. 1997, Jeyaprakash
and Hoy 2000
).
Wolbachia
are intracellular gram-negative rods that cannot be
cultured easily outside their hosts.
Wolbachia
infection rates range from
≈
17 to
76% of all arthropod species (
Werren et all 1995, Jeyaprakash and Hoy 2000
).
Wolbachia
also have been found in crustaceans (
Rigaud 1999
) and nematodes
(
Bandi et al. 1999, Bazzocchi et al. 2000
). An understanding of their physiologi-
cal and phenotypic effects on their hosts is still being developed. The phylogeny
of
Wolbachia
in nematodes is congruent with the phylogeny of their hosts, sug-
gesting they share a long coevolutionary history. Treatment with the antibiotic
tetracycline inhibits normal reproduction and development of filarial nematodes
that harbor
Wolbachia
, suggesting that
Wolbachia
are necessary to the nema-
tode (
Langworthy et al. 2000
). That is not true for arthropods, where it seems a
great deal of horizontal transfer has occurred.
Wolbachia
have been implicated as both the cause of alterations in sex ratio
(resulting in thelytoky and male killing), to be discussed further in the Chapter
10 on sex determination, and
cytoplasmic incompatibility
in arthropods. Some
Wolbachia
improve fertility or vigor, whereas others seem to decrease these
traits in their hosts. The molecular mechanism(s) by which reproductive incom-
patibility are induced by
Wolbachia
are hypothesized to be due to
Wolbachia
's
