Biology Reference
In-Depth Information
13
Wolbachia pipientis
:
Impotent by Association
Stephen L. Dobson
CONTENTS
Reproductive Parasites............................................................................199
Evolution of
Wolbachia
Wolbachia
Description and Early Applied Suppression Strategies ..............................................202
Wolbachia
Incrimination ................................................................................................................204
Wolbachia
Morphology and Interaction with Host Cells..............................................................205
Wolbachia
Effect on Host Population Size ...................................................................................206
Applied Strategies Employing
Infections ....................................................................206
Wolbachia
EVOLUTION OF
WOLBACHIA
REPRODUCTIVE PARASITES
Two evolutionary trajectories are commonly recognized for obligate bacterial symbionts that are
vertically inherited. As the success of vertically inherited infections depends on host Ýtness, bacterial
variants with an increasingly benign or beneÝcial relationship with their host have a selective
advantage, resulting in a trend toward commensalism or mutualism, respectively (Ewald, 1987;
Fine, 1975). Examples of mutualistic
Wolbachia
infections occur in nematodes (Hoerauf
et al.,
1999; Langworthy
et al., 2000) and a wasp (Dedeine
et al., 2001). However, additional
Wolbachia
infections have followed an alternative evolutionary trajectory of reproductive parasitism.
Reproductive parasitism can evolve when the bacterial infection is inherited exclusively
through a single sex of the host population. Thus, direct selective pressure on the symbiont occurs
only through the sex that is responsible for transmission. Multiple examples of reproductive
parasitism can be observed in infections of obligate intracellular
Wolbachia
bacteria. As
Wolba-
chia
is maternally transmitted to embryos via female-host cytoplasm, males are an evolutionary
dead end for
infections, and there is no direct selection for beneÝcial symbiosis in
infected males. On the contrary, examples occur in which
Wolbachia
infections decrease male
Ýtness. Cytoplasmic incompatibility (CI) (Hoffmann and Turelli, 1997), male killing (Hurst
Wolbachia
et al.,
1999), parthenogenesis (Stouthamer
et al., 1993), and feminization (Rousset
et al., 1992) all
provide examples of
symbioses in which infected female reproductive success is
increased at the expense of infected male hosts.
The
Wolbachia
reproductive manipulations of parthenogenesis and feminization act to increase
infection frequency by escalating the number of daughters produced by infected females. Parthe-
nogenesis-inducing
Wolbachia
infections are predicted to spread in a bisexual population if par-
thenogenic females produce more infected daughters (Stouthamer
Wolbachia
et al., 2001). With nearly perfect
maternal transmission of infections, parthenogenesis-inducing
Wolbachia
infections can spread to
