Parthenogenesis Associated with Wolbachia - Insect Symbiosis - page 183

TABLE 15.1A (CONTINUED)
Cases of Parthenogenetic Reproduction in Which Evidence Exists for Wolbachia
Involvement

Taxon h a w p c a Ref.

B. rubrioculus ? ? + f ? eeks and Breeuwer, 2001

B. neopraetisosa ? ? + f ? eeks and Breeuwer, 2001

Bryobia sp. x ? + + f + eeks and Breeuwer, 2001

Note: The evidence is classiÝed as males following heat treatment (h), males following antibiotic treatment (a), and
molecular evidence for Wolbachia presence (w). In addition, information is given if the parthenogenetic forms are found
in populations where parthenogenesis is Ýxed in the population or if it occurs mixed with sexual reproduction (p) and if
the males and females are capable of successful copulations (c). + = Evidence exists, ? = information not available, f =
parthenogenesis Ýxed in population, m = parthenogenesis and sexual reproduction occur in populations.

a Copulations are successful (+) or not (Ï).
b Mating and sperm transfer take place, but no successful fertilization of eggs
c Mating of males of parthenogenetic lines is successful with closely related sexual females, but not with parthenogenetic
females.

parthenogenesis in six species within the phytophagous mite genus Bryobia . Through antibiotic
treatment they showed that in two of those species, B. praetiosa and an unidentiÝed species, the
Wolbachia infection was strictly associated with parthenogenesis.
We expect the incidence of PI- Wolbachia among species to be much higher than reported so
far. In particular, low infection frequencies with PI- Wolbachia have most likely been underestimated.
Low frequencies of infection with PI- Wolbachia in Ýeld populations have only been found in
Trichogramma sp. (Stouthamer, 1997). This may simply be a consequence of the way populations
are sampled. In general, laboratory colonies of species are initiated by pooling large numbers of
Ýeld-collected individuals. In this way, low levels of parthenogenesis are easily overlooked because
partially parthenogenetic populations cannot be distinguished from sexual populations; in both
cases, the colony consists of both males and females. Trichogramma sp. stands out because the
Ýeld populations have been sampled by establishing isofemale lines from wasps emerging from
Ýeld-collected host eggs. All-female isofemale lines (= infected lines) are easily detected using this
protocol (Pinto et al., 1991).

CYTOGENETICS: PARTHENOGENESIS NOT ONLY THROUGH
GAMETE DUPLICATION

Cytogenetic processes involving diploidization can be divided into meiotic and postmeiotic mod-
iÝcations (Stouthamer, 1997). A review of parthenogenesis in insects shows that most belong to
the Ýrst group (Suomalainen et al., 1987). In most species, the meiosis is entirely suppressed and
the division has a mitotic character. The process of diploidization in parasitoid wasps due to
Wolbachia infection, however, seems to be mostly a postmeiotic modiÝcation. Stouthamer and
Kazmer (1994) described in detail the restoration of diploidy for several infected Trichogramma
species. They showed that the meiosis was the same for infected and uninfected eggs. At Ýrst, in
both infected and uninfected eggs, the haploid number of chromosomes is doubled in the prophase
of the Ýrst mitotic division. In the normal anaphase, each haploid set of chromosomes is pulled to
a different pole. In infected eggs, however, the two haploid sets of chromosomes do not separate
during the anaphase and result in a single nucleus containing the two identical sets of haploid
chromosomes. The following mitotic divisions are the same in infected and uninfected eggs. An