In the mite genus Bryobia many species reproduce strictly asexually' This is a rare phenomenon in th

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Wolbachia and Cardinium in Bryobia
mites Distribution and effects in sexual and
asexual species
Vera I.D. Ros Johannes A.J. Breeuwer
Evolutionary Biology, Institute for Biodiversity
and Ecosystem Dynamics (IBED), University of
Amsterdam
Introduction In the mite genus Bryobia many
species reproduce strictly asexually. This is a
rare phenomenon in the animal kingdom, where
asexuality often concerns single lineages among
sexual relatives. Asexuals are generally
considered evolutionary dead-ends that do not
radiate. The asexuality in at least two Bryobia
species is caused by the endosymbiotic bacteria
Wolbachia (Weeks and Breeuwer, 2001). Wolbachia
are widespread in arthropods, and manipulate host
reproduction in various ways, including
feminization, cytoplasmic incompatibility, male
killing, and parthenogenesis (reproductive
parasites).
Bryobia praetiosa adult female feeding on grass
Bryobia sarothamni adult female and male on broom
Evolution history of asexuality and occurrence of
reproductive parasites Is there a single origin
of asexuality (do asexuals form a monophyletic
clade)? Do asexuals radiate? Are all asexuals
infected with Wolbachia? Are other reproductive
parasites present? Are these bacteria found in
sexuals as well?
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• Results
• Asexuality
• Asexual species do not form a monophyletic
  clade
• This indicates either multiple origins or a
  single
• origin with reversals to sexuality.
• Reproductive parasites
• All asexuals are infected with Wolbachia
• Wolbachia is also found in a sexual species
• A second reproductive parasite, Cardinium, is
  co-
• infecting a sexual and an asexual species

Phylogenetic tree of mites inferred from 28S rDNA
sequences, ML analysis. Numbers on branches are
bootstrap values (1000 replicates gt50). Colours
indicate sampled host plant (see legend).
Reproductive mode (A asexual Ssexual),
Wolbachia infection (red ovals) and Cardinium
infection (blue ovals) are shown. Blank ovals
indicate absence of infection.
Host plant
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Effects and interactions of Wolbachia and
Cardinium in a sexual Bryobia species Do both
bacteria cause CI? What is the effect in double
infected individuals? Can both bacteria rescue
each others effects?

• Results
• Single effects
• Wolbachia causes no CI (a)
• Cardinium has a strong CI effect (b)

Wolbachia and Cardinium were found co-infecting
B. sarothamni, a sexual species. Populations of
this species were found polymorphic for both
infections, including double infected, single
infected (Cardinium or Wolbachia), and uninfected
individuals. Wolbachia and Cardinium are known
to cause cytoplasmic incompatibility (CI) in
sexual hosts. Their interactions however have
rarely been studied. We performed crossing
experiments to look for CI effects, using
naturally uninfected, single and double infected
isofemale lines.
Wolbachia no CI
Cardinium strong CI
a
b
U x U
U x U
U x W
U x C
W x U
C x U
W x W
C x C
unhatched eggs
0
10
20
0
10
20
30
40
50
60
70
Expectations were based on single effect results
(a and b)
obs
exp
c
W x C
C x W
U x WC
d
Cytoplasmic Incompatibility (CI) The final
result of CI is an increase in number of infected
females in the population. Bacteria modify the
sperm in males, resulting in failure of crossings
between uninfected (U) females and infected (I)
males due to paternal chromosome elimination. In
haplodiploids (including mites) this results in
reduced egg-hatching.
Wolbachia-Cardinium interactions
W x WC
C x WC
WC x U
WC x W
e
WC x C
WC x WC
0
10
20
30
40
50
60
70
80

• Interactions
• Wolbachia can not rescue Cardinium CI (c)
• Double infected Wolbachia and Cardinium do not
  cause CI (d)
• Double infected individuals can not rescue
  Cardinium CI (e)
• possible explanations
• - interference within double infected
  individuals
• - double and single individuals harbour
  different Cardinium strains,
• leading to bidirectional CI

Other species than for which Weeks and Breeuwer
(2001) showed a strict association between
Wolbachia and parthenogenesis. Weeks, A.R. and
Breeuwer, J.A.J. 2001. Wolbachia-induced
parthenogenesis in a genus of phytophagous mites.
Proc. R. Soc. Lond. Ser. B Biol. Sci. 268
2245-2251.
vidros_at_science.uva.nl